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Interpret, from function notation, an action or several actions to be taken on a known function, \(f\), in order to sketch the transformed function.
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Sketch transformations from \(9\) familiar functions.
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Write the equation of a function associated with descriptive transformations such as shifting left, right, up, or down, reflecting, stretching, and compressing of its parent function.
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3.1: Transformations of f(x)
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In this section, you will practice manipulating a given graph, according to the corresponding function notation. We’ll use the function f for demonstration throughout this section. But any graph will do!
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3.2: Transformations of Common Graphs
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The transformation of graphs, using common functions, will be a skill that will bring insight to graphing functions quickly and painlessly. Anticipating how a graph of a function will look, and transforming old graphs to new graphs, is a skill we will explore in this section. Mastering this skill will give you a leg up on understanding analytic geometry, a key component to calculus.


6.5: Daily Life in Western Europe and the Byzantine Empires
Most of the population of the Byzantine Empire live in small villages, living at a subsistence level, and selling what rare surplus they had. Byzantium, like its Western European counterpart, was fundamentally rural.
In Western Europe, dependent farmers lived on the lands of aristocrats and gave over much of their surplus to their landlords. But in many villages, the majority of farmers might live on their own land and even enjoy a form of self-government. Overall, free and independent farmers enjoyed greater freedom than had their Roman counterparts. Some slavery existed—especially in zones of conflict like the Mediterranean.
The nobles of Western Europe were generally part of a warrior aristocracy. They often outfitted and equipped themselves based on the wealth of their lands. Nobles would often not live on their lands but follow the royal court, which would itself travel from place to place rather than having a fixed location. Battle may have been frequent, but until Charlemagne, the scale of battle was often small, with armies numbering a few hundred at most.
Gender roles in the Frankish kingdom—like those of the Roman Empire that came before it—reflected a patriarchal society. The Christian religion generally taught that wives were to submit to their husbands, and the men who wrote much of the religious texts often thought of women in terms of weakness. An early Christian writer wrote that women “are the devil’s gateway…you are the first deserter of the divine law…you destroyed so easily God’s image, man…” 4 Both Roman and Germanic law placed women in subordination to their fathers and then, when married, to their husbands.
That said, women did enjoy certain rights. Although legally inferior to men in Roman Law (practiced in the Byzantine Empire and often among those peoples who were subjects of the Germanic aristocracies), a wife maintained the right to any property she brought into a marriage. Women often played a strong economic role in peasant life. Similar to their aristocratic counterparts, peasant women often managed the household even if men performed tasks such as plowing and the like.
The Church gave women a fair degree of autonomy in certain circumstances. We often read of women choosing to become nuns and take vows of celibacy against the desires of their families. If they framed their choices in terms of Christian devotion, these women could often count on institutional support in their life choices. Although monasticism was usually limited to noblewomen, women who became nuns often had access to education. Certain noblewomen who became abbesses could even become powerful political actors in their own right, such as Gertrude of Nivelles (c. 621 – 659), abbess of the monastery of Nivelles in what is today Belgium.
4 Tertullian, On the Apparel of Women, 1:1


19.1: Unit 3 Overview and Objectives
Overview
Now that you have passed “Go!” and have been traveling along your journey, in this unit you will make some changes and then “Keep Going!”
Learning Objectives
At the end of unit, you will be able to:
- Discuss how body composition influences wellness
- Identify current body composition recommendations
- Re-assess fitness level, body mass index (BMI), and waist circumference
- Evaluate the progress of your fitness program and make the necessary adjustments
- Define body composition terminology such as overweight, obese, underweight, fat-free mass, essential fat, and nonessential fat
- Determine recommended energy requirements and own current energy intake
- Explain the physiological function of essential nutrients
- Outline current nutrition guidelines for healthy adults and for individuals with special dietary needs, and how to maintain a lifetime healthy diet
- Articulate the importance of portion size and food labels on a well-balanced diet
- Compare the nutritional characteristics and affordability of various foods and how you can use this information to implement a personal nutrition plan to promote wellness
- Describe the basic anatomy and physiology of the musculoskeletal system and how it is affected by exercise
- Define muscular strength and muscular endurance and describe the benefits of each
- Apply the FITT dimensions to the development of a muscular fitness program and select safe and effective muscular strength/endurance exercises for major muscle groups to accomplish your goals
CC licensed content, Shared previously
- Lifetime Fitness and Wellness. Provided by : Extended Learning Institute of Northern Virginia Community College. Located at : https://eli.nvcc.edu/ . License : CC BY: Attribution


20.6: Circulatory Pathways
By the end of this section, you will be able to:
- Identify the vessels through which blood travels within the pulmonary circuit, beginning from the right ventricle of the heart and ending at the left atrium
- Create a flow chart showing the major systemic arteries through which blood travels from the aorta and its major branches, to the most significant arteries feeding into the right and left upper and lower limbs
- Create a flow chart showing the major systemic veins through which blood travels from the feet to the right atrium of the heart
Virtually every cell, tissue, organ, and system in the body is impacted by the circulatory system. This includes the generalized and more specialized functions of transport of materials, capillary exchange, maintaining health by transporting white blood cells and various immunoglobulins (antibodies), hemostasis, regulation of body temperature, and helping to maintain acid-base balance. In addition to these shared functions, many systems enjoy a unique relationship with the circulatory system. Figure \(\PageIndex{1}\) summarizes these relationships.
As you learn about the vessels of the systemic and pulmonary circuits, notice that many arteries and veins share the same names, parallel one another throughout the body, and are very similar on the right and left sides of the body. These pairs of vessels will be traced through only one side of the body. Where differences occur in branching patterns or when vessels are singular, this will be indicated. For example, you will find a pair of femoral arteries and a pair of femoral veins, with one vessel on each side of the body. In contrast, some vessels closer to the midline of the body, such as the aorta, are unique. Moreover, some superficial veins, such as the great saphenous vein in the femoral region, have no arterial counterpart. Another phenomenon that can make the study of vessels challenging is that names of vessels can change with location. Like a street that changes name as it passes through an intersection, an artery or vein can change names as it passes an anatomical landmark. For example, the left subclavian artery becomes the axillary artery as it passes through the body wall and into the axillary region, and then becomes the brachial artery as it flows from the axillary region into the upper arm (or brachium). You will also find examples of anastomoses where two blood vessels that previously branched reconnect. Anastomoses are especially common in veins, where they help maintain blood flow even when one vessel is blocked or narrowed, although there are some important ones in the arteries supplying the brain.
As you read about circular pathways, notice that there is an occasional, very large artery referred to as a trunk , a term indicating that the vessel gives rise to several smaller arteries. For example, the celiac trunk gives rise to the left gastric, common hepatic, and splenic arteries.
As you study this section, imagine you are on a “Voyage of Discovery” similar to Lewis and Clark’s expedition in 1804–1806, which followed rivers and streams through unfamiliar territory, seeking a water route from the Atlantic to the Pacific Ocean. You might envision being inside a miniature boat, exploring the various branches of the circulatory system. This simple approach has proven effective for many students in mastering these major circulatory patterns. Another approach that works well for many students is to create simple line drawings similar to the ones provided, labeling each of the major vessels. It is beyond the scope of this text to name every vessel in the body. However, we will attempt to discuss the major pathways for blood and acquaint you with the major named arteries and veins in the body. Also, please keep in mind that individual variations in circulation patterns are not uncommon.
Interactive Link
Visit this site for a brief summary of the arteries.
Pulmonary Circulation
Recall that blood returning from the systemic circuit enters the right atrium (Figure \(\PageIndex{2}\) ) via the superior and inferior venae cavae and the coronary sinus, which drains the blood supply of the heart muscle. These vessels will be described more fully later in this section. This blood is relatively low in oxygen and relatively high in carbon dioxide, since much of the oxygen has been extracted for use by the tissues and the waste gas carbon dioxide was picked up to be transported to the lungs for elimination. From the right atrium, blood moves into the right ventricle, which pumps it to the lungs for gas exchange. This system of vessels is referred to as the pulmonary circuit .
The single vessel exiting the right ventricle is the pulmonary trunk . At the base of the pulmonary trunk is the pulmonary semilunar valve, which prevents backflow of blood into the right ventricle during ventricular diastole. As the pulmonary trunk reaches the superior surface of the heart, it curves posteriorly and rapidly bifurcates (divides) into two branches, a left and a right pulmonary artery . To prevent confusion between these vessels, it is important to refer to the vessel exiting the heart as the pulmonary trunk, rather than also calling it a pulmonary artery. The pulmonary arteries in turn branch many times within the lung, forming a series of smaller arteries and arterioles that eventually lead to the pulmonary capillaries. The pulmonary capillaries surround lung structures known as alveoli that are the sites of oxygen and carbon dioxide exchange.
Once gas exchange is completed, oxygenated blood flows from the pulmonary capillaries into a series of pulmonary venules that eventually lead to a series of larger pulmonary veins . Four pulmonary veins, two on the left and two on the right, return blood to the left atrium. At this point, the pulmonary circuit is complete. Table \(\PageIndex{1}\ defines the major arteries and veins of the pulmonary circuit discussed in the text.
| Vessel | Description |
|---|---|
| Pulmonary trunk | Single large vessel exiting the right ventricle that divides to form the right and left pulmonary arteries |
| Pulmonary arteries | Left and right vessels that form from the pulmonary trunk and lead to smaller arterioles and eventually to the pulmonary capillaries |
| Pulmonary veins | Two sets of paired vessels—one pair on each side—that are formed from the small venules, leading away from the pulmonary capillaries to flow into the left atrium |
Overview of Systemic Arteries
Blood relatively high in oxygen concentration is returned from the pulmonary circuit to the left atrium via the four pulmonary veins. From the left atrium, blood moves into the left ventricle, which pumps blood into the aorta. The aorta and its branches—the systemic arteries—send blood to virtually every organ of the body (Figure \(\PageIndex{3}\)).
The Aorta
The aorta is the largest artery in the body (Figure \(\PageIndex{4}\)). It arises from the left ventricle and eventually descends to the abdominal region, where it bifurcates at the level of the fourth lumbar vertebra into the two common iliac arteries. The aorta consists of the ascending aorta, the aortic arch, and the descending aorta, which passes through the diaphragm and a landmark that divides into the superior thoracic and inferior abdominal components. Arteries originating from the aorta ultimately distribute blood to virtually all tissues of the body. At the base of the aorta is the aortic semilunar valve that prevents backflow of blood into the left ventricle while the heart is relaxing. After exiting the heart, the ascending aorta moves in a superior direction for approximately 5 cm and ends at the sternal angle. Following this ascent, it reverses direction, forming a graceful arc to the left, called the aortic arch . The aortic arch descends toward the inferior portions of the body and ends at the level of the intervertebral disk between the fourth and fifth thoracic vertebrae. Beyond this point, the descending aorta continues close to the bodies of the vertebrae and passes through an opening in the diaphragm known as the aortic hiatus . Superior to the diaphragm, the aorta is called the thoracic aorta , and inferior to the diaphragm, it is called the abdominal aorta . The abdominal aorta terminates when it bifurcates into the two common iliac arteries at the level of the fourth lumbar vertebra. See Figure \(\PageIndex{4}\) for an illustration of the ascending aorta, the aortic arch, and the initial segment of the descending aorta plus major branches; Table \(\PageIndex{2}\) summarizes the structures of the aorta.
| Vessel | Description |
|---|---|
| Aorta | Largest artery in the body, originating from the left ventricle and descending to the abdominal region, where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body |
| Ascending aorta | Initial portion of the aorta, rising superiorly from the left ventricle for a distance of approximately 5 cm |
| Aortic arch | Graceful arc to the left that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae |
| Descending aorta | Portion of the aorta that continues inferiorly past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta |
| Thoracic aorta | Portion of the descending aorta superior to the aortic hiatus |
| Abdominal aorta | Portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries |
Coronary Circulation
The first vessels that branch from the ascending aorta are the paired coronary arteries (see Figure \(\PageIndex{4}\)), which arise from two of the three sinuses in the ascending aorta just superior to the aortic semilunar valve. These sinuses contain the aortic baroreceptors and chemoreceptors critical to maintain cardiac function. The left coronary artery arises from the left posterior aortic sinus. The right coronary artery arises from the anterior aortic sinus. Normally, the right posterior aortic sinus does not give rise to a vessel.
The coronary arteries encircle the heart, forming a ring-like structure that divides into the next level of branches that supplies blood to the heart tissues. (Seek additional content for more detail on cardiac circulation.)
Aortic Arch Branches
There are three major branches of the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian (literally “under the clavicle”) artery. As you would expect based upon proximity to the heart, each of these vessels is classified as an elastic artery.
The brachiocephalic artery is located only on the right side of the body; there is no corresponding artery on the left. The brachiocephalic artery branches into the right subclavian artery and the right common carotid artery. The left subclavian and left common carotid arteries arise independently from the aortic arch but otherwise follow a similar pattern and distribution to the corresponding arteries on the right side (see Figure \(\PageIndex{2}\)).
Each subclavian artery supplies blood to the arms, chest, shoulders, back, and central nervous system. It then gives rise to three major branches: the internal thoracic artery, the vertebral artery, and the thyrocervical artery. The internal thoracic artery , or mammary artery, supplies blood to the thymus, the pericardium of the heart, and the anterior chest wall. The vertebral artery passes through the vertebral foramen in the cervical vertebrae and then through the foramen magnum into the cranial cavity to supply blood to the brain and spinal cord. The paired vertebral arteries join together to form the large basilar artery at the base of the medulla oblongata. This is an example of an anastomosis. The subclavian artery also gives rise to the thyrocervical artery that provides blood to the thyroid, the cervical region of the neck, and the upper back and shoulder.
The common carotid artery divides into internal and external carotid arteries. The right common carotid artery arises from the brachiocephalic artery and the left common carotid artery arises directly from the aortic arch. The external carotid artery supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx. These branches include the lingual, facial, occipital, maxillary, and superficial temporal arteries. The internal carotid artery initially forms an expansion known as the carotid sinus, containing the carotid baroreceptors and chemoreceptors. Like their counterparts in the aortic sinuses, the information provided by these receptors is critical to maintaining cardiovascular homeostasis (see Figure \(\PageIndex{2}\)).
The internal carotid arteries along with the vertebral arteries are the two primary suppliers of blood to the human brain. Given the central role and vital importance of the brain to life, it is critical that blood supply to this organ remains uninterrupted. Recall that blood flow to the brain is remarkably constant, with approximately 20 percent of blood flow directed to this organ at any given time. When blood flow is interrupted, even for just a few seconds, a transient ischemic attack (TIA) , or mini-stroke, may occur, resulting in loss of consciousness or temporary loss of neurological function. In some cases, the damage may be permanent. Loss of blood flow for longer periods, typically between 3 and 4 minutes, will likely produce irreversible brain damage or a stroke, also called a cerebrovascular accident (CVA) .  Both the carotid and vertebral arteries branch once they enter the cranial cavity, and some of these branches form a structure known as the arterial circle (or circle of Willis ), an anastomosis that is remarkably like a traffic circle that sends off branches (in this case, arterial branches to the brain). As a rule, branches to the anterior portion of the cerebrum are normally fed by the internal carotid arteries; the remainder of the brain receives blood flow from branches associated with the vertebral arteries.
The internal carotid artery continues through the carotid canal of the temporal bone and enters the base of the brain through the carotid foramen where it gives rise to several branches (Figure \(\PageIndex{5}\) and Figure \(\PageIndex{6}\)). One of these branches is the anterior cerebral artery that supplies blood to the frontal lobe of the cerebrum. Another branch, the middle cerebral artery , supplies blood to the temporal and parietal lobes, which are the most common sites of CVAs. The ophthalmic artery , the third major branch, provides blood to the eyes.
The right and left anterior cerebral arteries join together to form an anastomosis called the anterior communicating artery . The initial segments of the anterior cerebral arteries and the anterior communicating artery form the anterior portion of the arterial circle. The posterior portion of the arterial circle is formed by a left and a right posterior communicating artery that branches from the posterior cerebral artery , which arises from the basilar artery. It provides blood to the posterior portion of the cerebrum and brain stem. The basilar artery is an anastomosis that begins at the junction of the two vertebral arteries and sends branches to the cerebellum and brain stem. It flows into the posterior cerebral arteries. Table \(\PageIndex{3}\) summarizes the aortic arch branches, including the major branches supplying the brain.
| Vessel | Description |
|---|---|
| Brachiocephalic artery | Single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region |
| Subclavian artery | The right subclavian artery arises from the brachiocephalic artery while the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system |
| Internal thoracic artery | Also called the mammary artery; arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and anterior chest wall |
| Vertebral artery | Arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord |
| Thyrocervical artery | Arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder |
| Common carotid artery | The right common carotid artery arises from the brachiocephalic artery and the left common carotid artery arises from the aortic arch; each gives rise to the external and internal carotid arteries; supplies the respective sides of the head and neck |
| External carotid artery | Arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx |
| Internal carotid artery | Arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with the branches of the vertebral artery, forming the arterial circle; supplies blood to the brain |
| Arterial circle or circle of Willis | An anastomosis located at the base of the brain that ensures continual blood supply; formed from the branches of the internal carotid and vertebral arteries; supplies blood to the brain |
| Anterior cerebral artery | Arises from the internal carotid artery; supplies blood to the frontal lobe of the cerebrum |
| Middle cerebral artery | Another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum |
| Ophthalmic artery | Branch of the internal carotid artery; supplies blood to the eyes |
| Anterior communicating artery | An anastomosis of the right and left internal carotid arteries; supplies blood to the brain |
| Posterior communicating artery | Branches of the posterior cerebral artery that form part of the posterior portion of the arterial circle; supplies blood to the brain |
| Posterior cerebral artery | Branch of the basilar artery that forms a portion of the posterior segment of the arterial circle of Willis; supplies blood to the posterior portion of the cerebrum and brain stem |
| Basilar artery | Formed from the fusion of the two vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries; the main blood supply to the brain stem |
Thoracic Aorta and Major Branches
The thoracic aorta begins at the level of vertebra T5 and continues through to the diaphragm at the level of T12, initially traveling within the mediastinum to the left of the vertebral column. As it passes through the thoracic region, the thoracic aorta gives rise to several branches, which are collectively referred to as visceral branches and parietal branches (Figure \(\PageIndex{7}\)). Those branches that supply blood primarily to visceral organs are known as the visceral branches and include the bronchial arteries, pericardial arteries, esophageal arteries, and the mediastinal arteries, each named after the tissues it supplies. Each bronchial artery (typically two on the left and one on the right) supplies systemic blood to the lungs and visceral pleura, in addition to the blood pumped to the lungs for oxygenation via the pulmonary circuit. The bronchial arteries follow the same path as the respiratory branches, beginning with the bronchi and ending with the bronchioles. There is considerable, but not total, intermingling of the systemic and pulmonary blood at anastomoses in the smaller branches of the lungs. This may sound incongruous—that is, the mixing of systemic arterial blood high in oxygen with the pulmonary arterial blood lower in oxygen—but the systemic vessels also deliver nutrients to the lung tissue just as they do elsewhere in the body. The mixed blood drains into typical pulmonary veins, whereas the bronchial artery branches remain separate and drain into bronchial veins described later. Each pericardial artery supplies blood to the pericardium, the esophageal artery provides blood to the esophagus, and the mediastinal artery provides blood to the mediastinum. The remaining thoracic aorta branches are collectively referred to as parietal branches or somatic branches, and include the intercostal and superior phrenic arteries. Each intercostal artery provides blood to the muscles of the thoracic cavity and vertebral column. The superior phrenic artery provides blood to the superior surface of the diaphragm. Table \(\PageIndex{4}\) lists the arteries of the thoracic region.
| Vessel | Description |
|---|---|
| Visceral branches | A group of arterial branches of the thoracic aorta; supplies blood to the viscera (i.e., organs) of the thorax |
| Bronchial artery | Systemic branch from the aorta that provides oxygenated blood to the lungs; this blood supply is in addition to the pulmonary circuit that brings blood for oxygenation |
| Pericardial artery | Branch of the thoracic aorta; supplies blood to the pericardium |
| Esophageal artery | Branch of the thoracic aorta; supplies blood to the esophagus |
| Mediastinal artery | Branch of the thoracic aorta; supplies blood to the mediastinum |
| Parietal branches | Also called somatic branches, a group of arterial branches of the thoracic aorta; include those that supply blood to the thoracic wall, vertebral column, and the superior surface of the diaphragm |
| Intercostal artery | Branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column |
| Superior phrenic artery | Branch of the thoracic aorta; supplies blood to the superior surface of the diaphragm |
Abdominal Aorta and Major Branches
After crossing through the diaphragm at the aortic hiatus, the thoracic aorta is called the abdominal aorta (see Figure \(\PageIndex{7}\)). This vessel remains to the left of the vertebral column and is embedded in adipose tissue behind the peritoneal cavity. It formally ends at approximately the level of vertebra L4, where it bifurcates to form the common iliac arteries. Before this division, the abdominal aorta gives rise to several important branches. A single celiac trunk (artery) emerges and divides into the left gastric artery to supply blood to the stomach and esophagus, the splenic artery to supply blood to the spleen, and the common hepatic artery , which in turn gives rise to the hepatic artery proper to supply blood to the liver, the right gastric artery to supply blood to the stomach, the cystic artery to supply blood to the gall bladder, and several branches, one to supply blood to the duodenum and another to supply blood to the pancreas. Two additional single vessels arise from the abdominal aorta. These are the superior and inferior mesenteric arteries. The superior mesenteric artery arises approximately 2.5 cm after the celiac trunk and branches into several major vessels that supply blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine. The inferior mesenteric artery supplies blood to the distal segment of the large intestine, including the rectum. It arises approximately 5 cm superior to the common iliac arteries.
In addition to these single branches, the abdominal aorta gives rise to several significant paired arteries along the way. These include the inferior phrenic arteries, the adrenal arteries, the renal arteries, the gonadal arteries, and the lumbar arteries. Each inferior phrenic artery is a counterpart of a superior phrenic artery and supplies blood to the inferior surface of the diaphragm. The adrenal artery supplies blood to the adrenal (suprarenal) glands and arises near the superior mesenteric artery. Each renal artery branches approximately 2.5 cm inferior to the superior mesenteric arteries and supplies a kidney. The right renal artery is longer than the left since the aorta lies to the left of the vertebral column and the vessel must travel a greater distance to reach its target. Renal arteries branch repeatedly to supply blood to the kidneys. Each gonadal artery supplies blood to the gonads, or reproductive organs, and is also described as either an ovarian artery or a testicular artery (internal spermatic), depending upon the sex of the individual. An ovarian artery supplies blood to an ovary, uterine (Fallopian) tube, and the uterus, and is located within the suspensory ligament of the uterus. It is considerably shorter than a testicular artery , which ultimately travels outside the body cavity to the testes, forming one component of the spermatic cord. The gonadal arteries arise inferior to the renal arteries and are generally retroperitoneal. The ovarian artery continues to the uterus where it forms an anastomosis with the uterine artery that supplies blood to the uterus. Both the uterine arteries and vaginal arteries, which distribute blood to the vagina, are branches of the internal iliac artery. The four paired lumbar arteries are the counterparts of the intercostal arteries and supply blood to the lumbar region, the abdominal wall, and the spinal cord. In some instances, a fifth pair of lumbar arteries emerges from the median sacral artery.
The aorta divides at approximately the level of vertebra L4 into a left and a right common iliac artery but continues as a small vessel, the median sacral artery , into the sacrum. The common iliac arteries provide blood to the pelvic region and ultimately to the lower limbs. They split into external and internal iliac arteries approximately at the level of the lumbar-sacral articulation. Each internal iliac artery sends branches to the urinary bladder, the walls of the pelvis, the external genitalia, and the medial portion of the femoral region. In females, they also provide blood to the uterus and vagina. The much larger external iliac artery supplies blood to each of the lower limbs. Figure \(\PageIndex{8}\) shows the distribution of the major branches of the aorta into the thoracic and abdominal regions. Figure \(\PageIndex{9}\) shows the distribution of the major branches of the common iliac arteries. Table \(\PageIndex{5}\) summarizes the major branches of the abdominal aorta.
| Vessel | Description |
|---|---|
| Celiac trunk | Also called the celiac artery; a major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder |
| Left gastric artery | Branch of the celiac trunk; supplies blood to the stomach |
| Splenic artery | Branch of the celiac trunk; supplies blood to the spleen |
| Common hepatic artery | Branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery |
| Hepatic artery proper | Branch of the common hepatic artery; supplies systemic blood to the liver |
| Right gastric artery | Branch of the common hepatic artery; supplies blood to the stomach |
| Cystic artery | Branch of the common hepatic artery; supplies blood to the gall bladder |
| Superior mesenteric artery | Branch of the abdominal aorta; supplies blood to the small intestine (duodenum, jejunum, and ileum), the pancreas, and a majority of the large intestine |
| Inferior mesenteric artery | Branch of the abdominal aorta; supplies blood to the distal segment of the large intestine and rectum |
| Inferior phrenic arteries | Branches of the abdominal aorta; supply blood to the inferior surface of the diaphragm |
| Adrenal artery | Branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands |
| Renal artery | Branch of the abdominal aorta; supplies each kidney |
| Gonadal artery | Branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending upon the sex of the individual |
| Ovarian artery | Branch of the abdominal aorta; supplies blood to ovary, uterine (Fallopian) tube, and uterus |
| Testicular artery | Branch of the abdominal aorta; ultimately travels outside the body cavity to the testes and forms one component of the spermatic cord |
| Lumbar arteries | Branches of the abdominal aorta; supply blood to the lumbar region, the abdominal wall, and spinal cord |
| Common iliac artery | Branch of the aorta that leads to the internal and external iliac arteries |
| Median sacral artery | Continuation of the aorta into the sacrum |
| Internal iliac artery | Branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provides blood to the uterus and vagina |
| External iliac artery | Branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs |
Arteries Serving the Upper Limbs
As the subclavian artery exits the thorax into the axillary region, it is renamed the axillary artery . Although it does branch and supply blood to the region near the head of the humerus (via the humeral circumflex arteries), the majority of the vessel continues into the upper arm, or brachium, and becomes the brachial artery (Figure \(\PageIndex{10}\)). The brachial artery supplies blood to much of the brachial region and divides at the elbow into several smaller branches, including the deep brachial arteries, which provide blood to the posterior surface of the arm, and the ulnar collateral arteries, which supply blood to the region of the elbow. As the brachial artery approaches the coronoid fossa, it bifurcates into the radial and ulnar arteries, which continue into the forearm, or antebrachium. The radial artery and ulnar artery parallel their namesake bones, giving off smaller branches until they reach the wrist, or carpal region. At this level, they fuse to form the superficial and deep palmar arches that supply blood to the hand, as well as the digital arteries that supply blood to the digits. Figure \(\PageIndex{11}\) shows the distribution of systemic arteries from the heart into the upper limb. Table \(\PageIndex{6}\) summarizes the arteries serving the upper limbs.
| Vessel | Description |
|---|---|
| Axillary artery | Continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery |
| Brachial artery | Continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa |
| Radial artery | Formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region |
| Ulnar artery | Formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region |
| Palmar arches (superficial and deep) | Formed from anastomosis of the radial and ulnar arteries; supply blood to the hand and digital arteries |
| Digital arteries | Formed from the superficial and deep palmar arches; supply blood to the digits |
Arteries Serving the Lower Limbs
The external iliac artery exits the body cavity and enters the femoral region of the lower leg (Figure \(\PageIndex{12}\)). As it passes through the body wall, it is renamed the femoral artery . It gives off several smaller branches as well as the lateral deep femoral artery that in turn gives rise to a lateral circumflex artery . These arteries supply blood to the deep muscles of the thigh as well as ventral and lateral regions of the integument. The femoral artery also gives rise to the genicular artery , which provides blood to the region of the knee. As the femoral artery passes posterior to the knee near the popliteal fossa, it is called the popliteal artery. The popliteal artery branches into the anterior and posterior tibial arteries.
The anterior tibial artery is located between the tibia and fibula, and supplies blood to the muscles and integument of the anterior tibial region. Upon reaching the tarsal region, it becomes the dorsalis pedis artery , which branches repeatedly and provides blood to the tarsal and dorsal regions of the foot. The posterior tibial artery provides blood to the muscles and integument on the posterior surface of the tibial region. The fibular or peroneal artery branches from the posterior tibial artery. It bifurcates and becomes the medial plantar artery and lateral plantar artery , providing blood to the plantar surfaces. There is an anastomosis with the dorsalis pedis artery, and the medial and lateral plantar arteries form two arches called the dorsal arch (also called the arcuate arch) and the plantar arch , which provide blood to the remainder of the foot and toes. Figure \(\PageIndex{13}\) shows the distribution of the major systemic arteries in the lower limb. Table \(\PageIndex{7}\) summarizes the major systemic arteries discussed in the text.
| Vessel | Description |
|---|---|
| Femoral artery | Continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee |
| Deep femoral artery | Branch of the femoral artery; gives rise to the lateral circumflex arteries |
| Lateral circumflex artery | Branch of the deep femoral artery; supplies blood to the deep muscles of the thigh and the ventral and lateral regions of the integument |
| Genicular artery | Branch of the femoral artery; supplies blood to the region of the knee |
| Popliteal artery | Continuation of the femoral artery posterior to the knee; branches into the anterior and posterior tibial arteries |
| Anterior tibial artery | Branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery |
| Dorsalis pedis artery | Forms from the anterior tibial artery; branches repeatedly to supply blood to the tarsal and dorsal regions of the foot |
| Posterior tibial artery | Branches from the popliteal artery and gives rise to the fibular or peroneal artery; supplies blood to the posterior tibial region |
| Medial plantar artery | Arises from the bifurcation of the posterior tibial arteries; supplies blood to the medial plantar surfaces of the foot |
| Lateral plantar artery | Arises from the bifurcation of the posterior tibial arteries; supplies blood to the lateral plantar surfaces of the foot |
| Dorsal or arcuate arch | Formed from the anastomosis of the dorsalis pedis artery and the medial and plantar arteries; branches supply the distal portions of the foot and digits |
| Plantar arch | Formed from the anastomosis of the dorsalis pedis artery and the medial and plantar arteries; branches supply the distal portions of the foot and digits |
Overview of Systemic Veins
Systemic veins return blood to the right atrium. Since the blood has already passed through the systemic capillaries, it will be relatively low in oxygen concentration. In many cases, there will be veins draining organs and regions of the body with the same name as the arteries that supplied these regions and the two often parallel one another. This is often described as a “complementary” pattern. However, there is a great deal more variability in the venous circulation than normally occurs in the arteries. For the sake of brevity and clarity, this text will discuss only the most commonly encountered patterns. However, keep this variation in mind when you move from the classroom to clinical practice.
In both the neck and limb regions, there are often both superficial and deeper levels of veins. The deeper veins generally correspond to the complementary arteries. The superficial veins do not normally have direct arterial counterparts, but in addition to returning blood, they also make contributions to the maintenance of body temperature. When the ambient temperature is warm, more blood is diverted to the superficial veins where heat can be more easily dissipated to the environment. In colder weather, there is more constriction of the superficial veins and blood is diverted deeper where the body can retain more of the heat.
The “Voyage of Discovery” analogy and stick drawings mentioned earlier remain valid techniques for the study of systemic veins, but veins present a more difficult challenge because there are numerous anastomoses and multiple branches. It is like following a river with many tributaries and channels, several of which interconnect. Tracing blood flow through arteries follows the current in the direction of blood flow, so that we move from the heart through the large arteries and into the smaller arteries to the capillaries. From the capillaries, we move into the smallest veins and follow the direction of blood flow into larger veins and back to the heart. Figure \(\PageIndex{14}\) outlines the path of the major systemic veins.
Interactive Link
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The right atrium receives all of the systemic venous return. Most of the blood flows into either the superior vena cava or inferior vena cava. If you draw an imaginary line at the level of the diaphragm, systemic venous circulation from above that line will generally flow into the superior vena cava; this includes blood from the head, neck, chest, shoulders, and upper limbs. The exception to this is that most venous blood flow from the coronary veins flows directly into the coronary sinus and from there directly into the right atrium. Beneath the diaphragm, systemic venous flow enters the inferior vena cava, that is, blood from the abdominal and pelvic regions and the lower limbs.
The Superior Vena Cava
The superior vena cava drains most of the body superior to the diaphragm (Figure \(\PageIndex{15}\)). On both the left and right sides, the subclavian vein forms when the axillary vein passes through the body wall from the axillary region. It fuses with the external and internal jugular veins from the head and neck to form the brachiocephalic vein . Each vertebral vein also flows into the brachiocephalic vein close to this fusion. These veins arise from the base of the brain and the cervical region of the spinal cord, and flow largely through the intervertebral foramina in the cervical vertebrae. They are the counterparts of the vertebral arteries. Each internal thoracic vein , also known as an internal mammary vein, drains the anterior surface of the chest wall and flows into the brachiocephalic vein.
The remainder of the blood supply from the thorax drains into the azygos vein. Each intercostal vein drains muscles of the thoracic wall, each esophageal vein delivers blood from the inferior portions of the esophagus, each bronchial vein drains the systemic circulation from the lungs, and several smaller veins drain the mediastinal region. Bronchial veins carry approximately 13 percent of the blood that flows into the bronchial arteries; the remainder intermingles with the pulmonary circulation and returns to the heart via the pulmonary veins. These veins flow into the azygos vein , and with the smaller hemiazygos vein (hemi- = “half”) on the left of the vertebral column, drain blood from the thoracic region. The hemiazygos vein does not drain directly into the superior vena cava but enters the brachiocephalic vein via the superior intercostal vein.
The azygos vein passes through the diaphragm from the thoracic cavity on the right side of the vertebral column and begins in the lumbar region of the thoracic cavity. It flows into the superior vena cava at approximately the level of T2, making a significant contribution to the flow of blood. It combines with the two large left and right brachiocephalic veins to form the superior vena cava.
Table \(\PageIndex{8}\) summarizes the veins of the thoracic region that flow into the superior vena cava.
| Vessel | Description |
|---|---|
| Superior vena cava | Large systemic vein; drains blood from most areas superior to the diaphragm; empties into the right atrium |
| Subclavian vein | Located deep in the thoracic cavity; formed by the axillary vein as it enters the thoracic cavity from the axillary region; drains the axillary and smaller local veins near the scapular region and leads to the brachiocephalic vein |
| Brachiocephalic veins | Pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins flow into it; drain the upper thoracic region and lead to the superior vena cava |
| Vertebral vein | Arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery |
| Internal thoracic veins | Also called internal mammary veins; drain the anterior surface of the chest wall and lead to the brachiocephalic vein |
| Intercostal vein | Drains the muscles of the thoracic wall and leads to the azygos vein |
| Esophageal vein | Drains the inferior portions of the esophagus and leads to the azygos vein |
| Bronchial vein | Drains the systemic circulation from the lungs and leads to the azygos vein |
| Azygos vein | Originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region, and leads to the superior vena cava |
| Hemiazygos vein | Smaller vein complementary to the azygos vein; drains the esophageal veins from the esophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein |
Veins of the Head and Neck
Blood from the brain and the superficial facial vein flow into each internal jugular vein (Figure \(\PageIndex{16}\)). Blood from the more superficial portions of the head, scalp, and cranial regions, including the temporal vein and maxillary vein , flow into each external jugular vein . Although the external and internal jugular veins are separate vessels, there are anastomoses between them close to the thoracic region. Blood from the external jugular vein empties into the subclavian vein. Table \(\PageIndex{9}\) summarizes the major veins of the head and neck.
| Vessel | Description |
|---|---|
| Internal jugular vein | Parallel to the common carotid artery, which is more or less its counterpart, and passes through the jugular foramen and canal; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein |
| Temporal vein | Drains blood from the temporal region and flows into the external jugular vein |
| Maxillary vein | Drains blood from the maxillary region and flows into the external jugular vein |
| External jugular vein | Drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein |
Venous Drainage of the Brain
Circulation to the brain is both critical and complex (see Figure \(\PageIndex{16}\)). Many smaller veins of the brain stem and the superficial veins of the cerebrum lead to larger vessels referred to as intracranial sinuses. These include the superior and inferior sagittal sinuses, straight sinus, cavernous sinuses, left and right sinuses, the petrosal sinuses, and the occipital sinuses. Ultimately, sinuses will lead back to either the inferior jugular vein or vertebral vein.
Most of the veins on the superior surface of the cerebrum flow into the largest of the sinuses, the superior sagittal sinus . It is located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri and, at first glance in images or models, can be mistaken for the subarachnoid space. Most reabsorption of cerebrospinal fluid occurs via the chorionic villi (arachnoid granulations) into the superior sagittal sinus. Blood from most of the smaller vessels originating from the inferior cerebral veins flows into the great cerebral vein and into the straight sinus . Other cerebral veins and those from the eye socket flow into the cavernous sinus , which flows into the petrosal sinus and then into the internal jugular vein. The occipital sinus , sagittal sinus, and straight sinuses all flow into the left and right transverse sinuses near the lambdoid suture. The transverse sinuses in turn flow into the sigmoid sinuses that pass through the jugular foramen and into the internal jugular vein. The internal jugular vein flows parallel to the common carotid artery and is more or less its counterpart. It empties into the brachiocephalic vein. The veins draining the cervical vertebrae and the posterior surface of the skull, including some blood from the occipital sinus, flow into the vertebral veins. These parallel the vertebral arteries and travel through the transverse foramina of the cervical vertebrae. The vertebral veins also flow into the brachiocephalic veins. Table \(\PageIndex{10}\) summarizes the major veins of the brain.
| Vessel | Description |
|---|---|
| Superior sagittal sinus | Enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein |
| Great cerebral vein | Receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus |
| Straight sinus | Enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and leads to the left or right transverse sinus |
| Cavernous sinus | Enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus |
| Petrosal sinus | Enlarged vein that receives blood from the cavernous sinus and leads into the internal jugular veins |
| Occipital sinus | Enlarged vein that drains the occipital region near the falx cerebelli and leads to the left and right transverse sinuses, and also the vertebral veins |
| Transverse sinuses | Pair of enlarged veins near the lambdoid suture that drains the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses |
| Sigmoid sinuses | Enlarged vein that receives blood from the transverse sinuses and leads through the jugular foramen to the internal jugular vein |
Veins Draining the Upper Limbs
The digital veins in the fingers come together in the hand to form the palmar venous arches (Figure \(\PageIndex{17}\)). From here, the veins come together to form the radial vein, the ulnar vein, and the median antebrachial vein. The radial vein and the ulnar vein parallel the bones of the forearm and join together at the antebrachium to form the brachial vein , a deep vein that flows into the axillary vein in the brachium.
The median antebrachial vein parallels the ulnar vein, is more medial in location, and joins the basilic vein in the forearm. As the basilic vein reaches the antecubital region, it gives off a branch called the median cubital vein that crosses at an angle to join the cephalic vein. The median cubital vein is the most common site for drawing venous blood in humans. The basilic vein continues through the arm medially and superficially to the axillary vein.
The cephalic vein begins in the antebrachium and drains blood from the superficial surface of the arm into the axillary vein. It is extremely superficial and easily seen along the surface of the biceps brachii muscle in individuals with good muscle tone and in those without excessive subcutaneous adipose tissue in the arms.
The subscapular vein drains blood from the subscapular region and joins the cephalic vein to form the axillary vein . As it passes through the body wall and enters the thorax, the axillary vein becomes the subclavian vein.
Many of the larger veins of the thoracic and abdominal region and upper limb are further represented in the flow chart in Figure \(\PageIndex{18}\). Table \(\PageIndex{11}\) summarizes the veins of the upper limbs.
| Vessel | Description |
|---|---|
| Digital veins | Drain the digits and lead to the palmar arches of the hand and dorsal venous arch of the foot |
| Palmar venous arches | Drain the hand and digits, and lead to the radial vein, ulnar veins, and the median antebrachial vein |
| Radial vein | Vein that parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein |
| Ulnar vein | Vein that parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein |
| Brachial vein | Deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein |
| Median antebrachial vein | Vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches; leads to the basilic vein |
| Basilic vein | Superficial vein of the arm that arises from the median antebrachial vein, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein |
| Median cubital vein | Superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site from which to draw blood |
| Cephalic vein | Superficial vessel in the upper arm; leads to the axillary vein |
| Subscapular vein | Drains blood from the subscapular region and leads to the axillary vein |
| Axillary vein | The major vein in the axillary region; drains the upper limb and becomes the subclavian vein |
The Inferior Vena Cava
Other than the small amount of blood drained by the azygos and hemiazygos veins, most of the blood inferior to the diaphragm drains into the inferior vena cava before it is returned to the heart (see Figure 20.36). Lying just beneath the parietal peritoneum in the abdominal cavity, the inferior vena cava parallels the abdominal aorta, where it can receive blood from abdominal veins. The lumbar portions of the abdominal wall and spinal cord are drained by a series of lumbar veins , usually four on each side. The ascending lumbar veins drain into either the azygos vein on the right or the hemiazygos vein on the left, and return to the superior vena cava. The remaining lumbar veins drain directly into the inferior vena cava.
Blood supply from the kidneys flows into each renal vein , normally the largest veins entering the inferior vena cava. A number of other, smaller veins empty into the left renal vein. Each adrenal vein drains the adrenal or suprarenal glands located immediately superior to the kidneys. The right adrenal vein enters the inferior vena cava directly, whereas the left adrenal vein enters the left renal vein.
From the male reproductive organs, each testicular vein flows from the scrotum, forming a portion of the spermatic cord. Each ovarian vein drains an ovary in females. Each of these veins is generically called a gonadal vein . The right gonadal vein empties directly into the inferior vena cava, and the left gonadal vein empties into the left renal vein.
Each side of the diaphragm drains into a phrenic vein ; the right phrenic vein empties directly into the inferior vena cava, whereas the left phrenic vein empties into the left renal vein. Blood supply from the liver drains into each hepatic vein and directly into the inferior vena cava. Since the inferior vena cava lies primarily to the right of the vertebral column and aorta, the left renal vein is longer, as are the left phrenic, adrenal, and gonadal veins. The longer length of the left renal vein makes the left kidney the primary target of surgeons removing this organ for donation. Figure \(\PageIndex{19}\) provides a flow chart of the veins flowing into the inferior vena cava. Table \(\PageIndex{12}\) summarizes the major veins of the abdominal region.
| Vessel | Description |
|---|---|
| Inferior vena cava | Large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium |
| Lumbar veins | Series of veins that drain the lumbar portion of the abdominal wall and spinal cord; the ascending lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; the remaining lumbar veins drain directly into the inferior vena cava |
| Renal vein | Largest vein entering the inferior vena cava; drains the kidneys and flows into the inferior vena cava |
| Adrenal vein | Drains the adrenal or suprarenal; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein |
| Testicular vein | Drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein |
| Ovarian vein | Drains the ovary; the right ovarian vein empties directly into the inferior vena cava and the left ovarian vein empties into the left renal vein |
| Gonadal vein | Generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual |
| Phrenic vein | Drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein empties into the left renal vein |
| Hepatic vein | Drains systemic blood from the liver and flows into the inferior vena cava |
Veins Draining the Lower Limbs
The superior surface of the foot drains into the digital veins, and the inferior surface drains into the plantar veins , which flow into a complex series of anastomoses in the feet and ankles, including the dorsal venous arch and the plantar venous arch (Figure \(\PageIndex{20}\)). From the dorsal venous arch, blood supply drains into the anterior and posterior tibial veins. The anterior tibial vein drains the area near the tibialis anterior muscle and combines with the posterior tibial vein and the fibular vein to form the popliteal vein. The posterior tibial vein drains the posterior surface of the tibia and joins the popliteal vein. The fibular vein drains the muscles and integument in proximity to the fibula and also joins the popliteal vein. The small saphenous vein located on the lateral surface of the leg drains blood from the superficial regions of the lower leg and foot, and flows into to the popliteal vein . As the popliteal vein passes behind the knee in the popliteal region, it becomes the femoral vein. It is palpable in patients without excessive adipose tissue.
Close to the body wall, the great saphenous vein, the deep femoral vein, and the femoral circumflex vein drain into the femoral vein. The great saphenous vein is a prominent surface vessel located on the medial surface of the leg and thigh that collects blood from the superficial portions of these areas. The deep femoral vein , as the name suggests, drains blood from the deeper portions of the thigh. The femoral circumflex vein forms a loop around the femur just inferior to the trochanters and drains blood from the areas in proximity to the head and neck of the femur.
As the femoral vein penetrates the body wall from the femoral portion of the upper limb, it becomes the external iliac vein , a large vein that drains blood from the leg to the common iliac vein. The pelvic organs and integument drain into the internal iliac vein , which forms from several smaller veins in the region, including the umbilical veins that run on either side of the bladder. The external and internal iliac veins combine near the inferior portion of the sacroiliac joint to form the common iliac vein. In addition to blood supply from the external and internal iliac veins, the middle sacral vein drains the sacral region into the common iliac vein . Similar to the common iliac arteries, the common iliac veins come together at the level of L5 to form the inferior vena cava.
Figure \(\PageIndex{21}\) is a flow chart of veins flowing into the lower limb. Table \(\PageIndex{13}\) summarizes the major veins of the lower limbs.
| Vessel | Description |
|---|---|
| Plantar veins | Drain the foot and flow into the plantar venous arch |
| Dorsal venous arch | Drains blood from digital veins and vessels on the superior surface of the foot |
| Plantar venous arch | Formed from the plantar veins; flows into the anterior and posterior tibial veins through anastomoses |
| Anterior tibial vein | Formed from the dorsal venous arch; drains the area near the tibialis anterior muscle and flows into the popliteal vein |
| Posterior tibial vein | Formed from the dorsal venous arch; drains the area near the posterior surface of the tibia and flows into the popliteal vein |
| Fibular vein | Drains the muscles and integument near the fibula and flows into the popliteal vein |
| Small saphenous vein | Located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and flows into the popliteal vein |
| Popliteal vein | Drains the region behind the knee and forms from the fusion of the fibular, anterior, and posterior tibial veins; flows into the femoral vein |
| Great saphenous vein | Prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and flows into the femoral vein |
| Deep femoral vein | Drains blood from the deeper portions of the thigh and flows into the femoral vein |
| Femoral circumflex vein | Forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; flows into the femoral vein |
| Femoral vein | Drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall |
| External iliac vein | Formed when the femoral vein passes into the body cavity; drains the legs and flows into the common iliac vein |
| Internal iliac vein | Drains the pelvic organs and integument; formed from several smaller veins in the region; flows into the common iliac vein |
| Middle sacral vein | Drains the sacral region and flows into the left common iliac vein |
| Common iliac vein | Flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; formed from the union of the external and internal iliac veins near the inferior portion of the sacroiliac joint |
Hepatic Portal System
The liver is a complex biochemical processing plant. It packages nutrients absorbed by the digestive system; produces plasma proteins, clotting factors, and bile; and disposes of worn-out cell components and waste products. Instead of entering the circulation directly, absorbed nutrients and certain wastes (for example, materials produced by the spleen) travel to the liver for processing. They do so via the hepatic portal system (Figure \(\PageIndex{22}\)). Portal systems begin and end in capillaries. In this case, the initial capillaries from the stomach, small intestine, large intestine, and spleen lead to the hepatic portal vein and end in specialized capillaries within the liver, the hepatic sinusoids. You saw the only other portal system with the hypothalamic-hypophyseal portal vessel in the endocrine chapter.
The hepatic portal system consists of the hepatic portal vein and the veins that drain into it. The hepatic portal vein itself is relatively short, beginning at the level of L2 with the confluence of the superior mesenteric and splenic veins. It also receives branches from the inferior mesenteric vein, plus the splenic veins and all their tributaries. The superior mesenteric vein receives blood from the small intestine, two-thirds of the large intestine, and the stomach. The inferior mesenteric vein drains the distal third of the large intestine, including the descending colon, the sigmoid colon, and the rectum. The splenic vein is formed from branches from the spleen, pancreas, and portions of the stomach, and the inferior mesenteric vein. After its formation, the hepatic portal vein also receives branches from the gastric veins of the stomach and cystic veins from the gall bladder. The hepatic portal vein delivers materials from these digestive and circulatory organs directly to the liver for processing.
Because of the hepatic portal system, the liver receives its blood supply from two different sources: from normal systemic circulation via the hepatic artery and from the hepatic portal vein. The liver processes the blood from the portal system to remove certain wastes and excess nutrients, which are stored for later use. This processed blood, as well as the systemic blood that came from the hepatic artery, exits the liver via the right, left, and middle hepatic veins, and flows into the inferior vena cava. Overall systemic blood composition remains relatively stable, since the liver is able to metabolize the absorbed digestive components.


5.2: Skin Structures Made of Keratin
Claws, Nails and Hoofs
Reptiles, birds and mammals all have nails or claws on the ends of their toes. They protect the end of the toe and may be used for grasping, grooming, digging or in defense. They are continually worn away and grow continuously from a growth layer at their base (see diagram 5.2).
Diagram 5.2 - A carnivore’s claw. Wikipedia
Hoofs are found in sheep, cows, horses etc. otherwise known as ungulate mammals . These are animals that have lost toes in the process of evolution and walk on the “nails” of the remaining toes. The hoof is a cylinder of horny material that surrounds and protects the tip of the toe (see diagram 5.3).
Diagram 5.3 - A horse’s hoof
Horns And Antlers
True horns are made of keratin and are found in sheep, goats and cattle. They are never branched and, once grown, are never shed. They consist of a core of bone arising in the dermis of the skin and are fused with the skull. The horn itself forms as a hollow cone-shaped sheath around the bone (see diagram 5.4).
Diagram 5.4 - A horn
The antlers of male deer have quite a different structure. They are not formed in the epidermis and do not consist of keratin but are entirely of bone. They are shed each year and are often branched, especially in older animals. When growing they are covered in skin called velvet that forms the bone. Later the velvet is shed to leave the bony antler. The velvet is often removed artificially to be sold in Asia as a traditional medicine (see diagram 5.5).
Diagram 5.5 - A deer antler
Other animals have projections on their heads that are not true horns either. The horns on the head of giraffes are made of bone covered with skin and hair, and the ‘horn’ of a rhinoceros is made of modified and fused hair-like structures.
Hair
Hair is also made of keratin and develops in the epidermis. It covers the body of most mammals where it acts as an insulator and helps to regulate the temperature of the body (see below). The colour in hairs is formed from the same pigment, melanin that colours the skin. Coat colour may help camouflage animals and sometimes acts to attract the opposite sex.
Diagram 5.6 - A hair
Hairs lie in a follicle and grow from a root that is well supplied with blood vessels. The hair itself consists of layers of dead keratin - containing cells and usually lies at a slant in the skin. A small bundle of smooth muscle fibres (the hair erector muscle ) is attached to the side of each hair and when this contracts the hair stands on end. This increases the insulating power of the coat and is also used by some animals to make them seem larger when confronted by a foe or a competitor(see diagram 5.6).
The whiskers of cats and the spines of hedgehogs are examples of special types of hairs.
Feathers
The lightness and stiffness of keratin is also a key to bird flight. In the form of feathers it provides the large airfoils necessary for flapping and gliding flight. In another form, the light fluffy down feathers,also made of keratin, are some of the best natural insulators known. This superior insulation is necessary to help maintain the high body temperatures of birds.
Diagram 5.7 - A Contour Feather
Countour feathers are large feathers that cover the body, wings and tail. They have an expanded vane that provides the smooth, continuous surface that is required for effective flight. This surface is formed by barbs that extend out from the central shaft. If you look carefully at a feather you can see that on either side of each barb are thousands of barbules that lock together by a complex system of hooks and notches. if this arrangement becomes disrupted, the bird uses its beak to draw the barbs and barbules together again in an action known as preening (see diagram 5.7).
Diagram 5.8 - A Down Feather
Diagram 5.9 - A Pin Feather
Down feathers are the only feathers covering a chick and form the main insulation layer under the contour feathers of the adult. They have no shaft but consist of a spray of simple, slender branches (see diagram 5.8).
Pin feathers have a slender hair-like shaft often with a tiny tuft of barbs on the end. They are found between the other feathers and help tell a bird how its feathers are lying (see diagram 5.9).


4.3: Reference Frame Changes and Relative Motion
Everything up to this point assumes that we are using a fixed, previously agreed upon reference frame . Basically, this is just an origin and a set of axes along which to measure our coordinates.
There are, however, a number of situations in physics that call for the use of different reference frames, and, more importantly, that require us to convert various physical quantities from one reference frame to another. For instance, imagine you are on a boat on a river, rowing downstream. You are moving with a certain velocity relative to the water around you, but the water itself is flowing with a different velocity relative to the shore, and your actual velocity relative to the shore is the sum of those two quantities. Ships generally have to do this kind of calculation all the time, as do airplanes: the “airspeed” is the speed of a plane relative to the air around it, but that air is usually moving at a substantial speed relative to the earth.
 One of them, say A, is “at rest” relative to the earth, and the other one is “at rest” relative to something else—which means, really, moving along with that something else. (For instance, a reference frame at rest “relative to the river” would be a frame that’s moving along with the river water, like a piece of driftwood that you could measure your progress relative to.)
In any case, graphically, this will look as in Figure \(\PageIndex{1}\), which we have drawn for the two-dimensional case:
Figure \(\PageIndex{1}\): Position vectors and coordinates of a point P in two different reference frames, A and B.
In the reference frame A, the point P has position coordinates \((x_{AP} , y_{AP})\). Likewise, in the reference frame B, its coordinates are \((x_{BP} , y_{BP})\). As you can see, the notation chosen is such that every coordinate in A will have an “A” as a first subscript, while the second subscript indicates the object to which it refers, and similarly for coordinates in B.
The coordinates \((x_{AB}, y_{AB})\) are special: they are the coordinates, in the reference frame A, of the origin of reference frame B. This is enough to fully locate the frame B in A, as long as the frames are not rotated relative to each other.
The thin colored lines I have drawn along the axes in Figure \(\PageIndex{1}\) are intended to make it clear that the following equations hold:
\[ \begin{array}{l}
{x_{A P}=x_{A B}+x_{B P}} \\
{x_{A P}=x_{A B}+x_{B P}}
\end{array} \label{eq:14} \]
Although the figure is drawn for the easy case where all these quantities are positive, you should be able to convince yourself that Eqs. (\ref{eq:14}) hold also when one or more of the coordinates have negative values.
All these coordinates are also the components of the respective position vectors, shown in the figure and color-coded by reference frame (so, for instance, \(\vec r_{AP}\) is the position vector of P in the frame A), so the equations (\ref{eq:14}) can be written more compactly as the single vector equation
\[ \vec r_{AP} = \vec r_{AB} + \vec r_{BP} \label{eq:15} .\]
From all this you can see how to add vectors: algebraically, you just add their components separately, as in Eqs. (\ref{eq:14}); graphically, you draw them so the tip of one vector coincides with the tail of the other (we call this “tip-to-tail”), and then draw the sum vector from the tail of the first one to the tip of the other one.
Of course, I showed you already how to subtract vectors with Figure 1.2.3 : again, algebraically, you just subtract the corresponding coordinates, whereas graphically you draw them with a common origin, and then draw the vector from the tip of the vector you are subtracting to the tip of the other one. If you read the previous paragraph again, you can see that Figure 1.2.3 can equally well be used to show that \(\Delta \vec r = \vec r_f - \vec r_i\), as to show that \(\vec r_f = \vec r_i + \Delta \vec r\).
In a similar way, you can see graphically from Figure \(\PageIndex{1}\) (or algebraically from Equation (\ref{eq:15})) that the position vector of P in the frame B is given by \(\vec r_{BP} = \vec r_{AP} − \vec r_{AB}\). The last term in this expression can be written in a different way, as follows. If I follow the convention I have introduced above, the quantity \(x_{BA}\) (with the order of the subscripts reversed) would be the \(x\) coordinate of the origin of frame A in frame B, and algebraically that would be equal to \(−x_{AB}\), and similarly \(y_{BA} = −y_{AB}\). Hence the vector equality \(\vec r_{AB} = −\vec r_{BA}\) holds. Then,
\[ \vec{r}_{B P}=\vec{r}_{A P}-\vec{r}_{A B}=\vec{r}_{A P}+\vec{r}_{B A} \label{eq:16}. \]
This is, in a way, the “inverse” of Equation (\ref{eq:15}): it tells us how to get the position of P in the frame B if we know its position in the frame A.
Let's show next how all this extends to displacements and velocities. Suppose the point P indicates the position of a particle at the time \(t\). Over a time interval \(\Delta t\), both the position of the particle and the relative position of the two reference frames may change. We can add yet another subscript, \(i\) or \(f\), (for initial and final) to the coordinates, and write, for example,
\[ \begin{array}{l}
{x_{A P, i}=x_{A B, i}+x_{B P, i}} \\
{x_{A P, f}=x_{A B, f}+x_{B P, f}}
\end{array} \label{eq:17} \]
Subtracting these equations gives us the corresponding displacements:
\[ \Delta x_{A P}=\Delta x_{A B}+\Delta x_{B P} \label{eq:18} .\]
Dividing Equation (\ref{eq:18}) by \(\Delta t\) we get the average velocities\(^1\), and then taking the limit \(\Delta t \rightarrow 0\) we get the instantaneous velocities. This applies in the same way to the \(y\) coordinates, and the result is the vector equation
\[ \vec{v}_{A P}=\vec{v}_{B P}+\vec{v}_{A B} \label{eq:19} .\]
We have rearranged the terms on the right-hand side to (hopefully) make it easier to visualize what’s going on. In words: the velocity of the particle P relative to (or measured in ) frame A is equal to the (vector) sum of the velocity of the particle as measured in frame B, plus the velocity of frame B relative to frame A.
The result (\ref{eq:19}) is just what we would have expected from the examples mentioned at the beginning of this section, like rowing in a river or an airplane flying in the wind. For instance, for the airplane \(\vec v_{BP}\) could be its “airspeed” (only it has to be a vector, so it would be more like its “airvelocity”: that is, its velocity relative to the air around it), and \(\vec v_{AB}\) would be the velocity of the air relative to the earth (the wind velocity, at the location of the airplane). In other words, A represents the earth frame of reference and B the air, or wind, frame of reference. Then, \(\vec v_{AP}\) would be the “true” velocity of the airplane relative to the earth. You can see how it would be important to add these quantities as vectors, in general, by considering what happens when you fly in a cross wind, or try to row across a river, as in Figure \(\PageIndex{2}\) below.
Figure \(\PageIndex{2}\): Rowing across a river. If you head “straight across” the river (with velocity vector \(\vec v_{Rb}\) in the moving frame of the river, which is flowing with velocity \(\vec v_{ER}\) in the frame of the earth), your actual velocity relative to the shore will be the vector \(\vec v_{Eb}\). This is an instance of Equation (\ref{eq:19}), with frame A being E (the earth), frame B being R (the river), and “b” (for “boat”) standing for the point P we are tracking.
As you can see from this couple of examples, Equation (\ref{eq:19}) is often useful as it is written, but sometimes the information we have is given to us in a different way: for instance, we could be given the velocity of the object in frame A \((\vec v_{AP})\), and the velocity of frame B as seen in frame A \((\vec v_{AB})\), and told to calculate the velocity of the object as seen in frame B. This can be easily accomplished if we note that the vector \(\vec v_{AB}\) is equal to \(-\vec v_{BA}\); that is to say, the velocity of frame B as seen from frame A is just the opposite of the velocity of frame A as seen from frame B. Hence, Equation (\ref{eq:19}) can be rewritten as
\[ \vec{v}_{A P}=\vec{v}_{B P}-\vec{v}_{B A} \label{eq:20} .\]
For most of the next few chapters we are going to be considering only motion in one dimension, and so we will write Equation (\ref{eq:19}) (or (\ref{eq:20})) without the vector symbols, and it will be understood that \(v\) refers to the component of the vector \(\vec v\) along the coordinate axis of interest.
A quantity that will be particularly important later on is the relative velocity of two objects, which we could label 1 and 2. The velocity of object 2 relative to object 1 is, by definition, the velocity which an observer moving along with 1 would measure for object 2. So it is just a simple frame change: let the earth frame be frame E and the frame moving with object 1 be frame 1, then the velocity we want is \(v_{12}\) (“velocity of object 2 in frame 1”). If we make the change A \(\rightarrow\) 1, B \(\rightarrow\) E, and P \(\rightarrow\) 2 in Equation (\ref{eq:20}), we get
\[ v_{12}=v_{E 2}-v_{E 1} \label{eq:21} .\]
In other words, the velocity of 2 relative to 1 is just the velocity of 2 minus the velocity of 1. This is again a familiar effect: if you are driving down the highway at 50 miles per hour, and the car in front of you is driving at 55, then its velocity relative to you is 5 mph, which is the rate at which it is moving away from you (in the forward direction, assumed to be the positive one).
It is important to realize that all these velocities are real velocities, each in its own reference frame. Something may be said to be truly moving at some velocity in one reference frame, and just as truly moving with a different velocity in a different reference frame. I will have a lot more to say about this in the next chapter, but in the meantime you can reflect on the fact that, if a car moving at 55 mph collides with another one moving at 50 mph in the same direction, the damage will be basically the same as if the first car had been moving at 5 mph and the second one had been at rest. For practical purposes, where you are concerned, another car’s velocity relative to yours is that car’s “real” velocity.
Resources
A good app for practicing how to add vectors (and how to break them up into components, magnitude and direction, etc.) may be found here: https://phet.colorado.edu/en/simulation/vector-addition .
Perhaps the most dramatic demonstration of how Equation (\ref{eq:19}) works in the real world is in this episode of Mythbusters : https://www.youtube.com/watch?v=BLuI118nhzc . (If this link does not work, do a search for “Mythbusters cancel momentum.”) They shoot a ball from the bed of a truck, with a velocity (relative to the truck) of 60 mph backwards, while the truck is moving forward at 60 mph. I think the result is worth watching.
A very old, but also very good, educational video about different frames of reference is this one: https://www.youtube.com/watch?v=sS17fCom0Ns . You should try to watch at least part of it. Many things will be relevant to later parts of the course, including projectile motion.
\(^1\) We have made a very natural assumption, that the time interval \(\Delta t\) is the same for observers tracking the particle’s motion in frames A and B, respectively (where each observer is understood to be moving along with his or her frame). This, however, turns out to be not true when any of the velocities involved is close to the speed of light, and so the simple addition of velocities formula (\ref{eq:19}) does not hold in Einstein’s relativity theory.


24.1: Characteristics of Fungi
Skills to Develop
- List the characteristics of fungi
- Describe the composition of the mycelium
- Describe the mode of nutrition of fungi
- Explain sexual and asexual reproduction in fungi
Although humans have used yeasts and mushrooms since prehistoric times, until recently, the biology of fungi was poorly understood. Up until the mid-20th century, many scientists classified fungi as plants. Fungi, like plants, arose mostly sessile and seemingly rooted in place. They possess a stem-like structure similar to plants, as well as having a root-like fungal mycelium in the soil. In addition, their mode of nutrition was poorly understood. Progress in the field of fungal biology was the result of mycology : the scientific study of fungi. Based on fossil evidence, fungi appeared in the pre-Cambrian era, about 450 million years ago. Molecular biology analysis of the fungal genome demonstrates that fungi are more closely related to animals than plants. They are a polyphyletic group of organisms that share characteristics, rather than sharing a single common ancestor.
Career Connection: Mycologist
Mycologists are biologists who study fungi. Mycology is a branch of microbiology, and many mycologists start their careers with a degree in microbiology. To become a mycologist, a bachelor's degree in a biological science (preferably majoring in microbiology) and a master's degree in mycology are minimally necessary. Mycologists can specialize in taxonomy and fungal genomics, molecular and cellular biology, plant pathology, biotechnology, or biochemistry. Some medical microbiologists concentrate on the study of infectious diseases caused by fungi (mycoses). Mycologists collaborate with zoologists and plant pathologists to identify and control difficult fungal infections, such as the devastating chestnut blight, the mysterious decline in frog populations in many areas of the world, or the deadly epidemic called white nose syndrome, which is decimating bats in the Eastern United States.
Government agencies hire mycologists as research scientists and technicians to monitor the health of crops, national parks, and national forests. Mycologists are also employed in the private sector by companies that develop chemical and biological control products or new agricultural products, and by companies that provide disease control services. Because of the key role played by fungi in the fermentation of alcohol and the preparation of many important foods, scientists with a good understanding of fungal physiology routinely work in the food technology industry. Oenology, the science of wine making, relies not only on the knowledge of grape varietals and soil composition, but also on a solid understanding of the characteristics of the wild yeasts that thrive in different wine-making regions. It is possible to purchase yeast strains isolated from specific grape-growing regions. The great French chemist and microbiologist, Louis Pasteur, made many of his essential discoveries working on the humble brewer’s yeast, thus discovering the process of fermentation.
Cell Structure and Function
Fungi are eukaryotes, and as such, have a complex cellular organization. As eukaryotes, fungal cells contain a membrane-bound nucleus. The DNA in the nucleus is wrapped around histone proteins, as is observed in other eukaryotic cells. A few types of fungi have structures comparable to bacterial plasmids (loops of DNA); however, the horizontal transfer of genetic information from one mature bacterium to another rarely occurs in fungi. Fungal cells also contain mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus.
Unlike plant cells, fungal cells do not have chloroplasts or chlorophyll. Many fungi display bright colors arising from other cellular pigments, ranging from red to green to black. The poisonous Amanita muscaria (fly agaric) is recognizable by its bright red cap with white patches (Figure \(\PageIndex{1}\)). Pigments in fungi are associated with the cell wall and play a protective role against ultraviolet radiation. Some fungal pigments are toxic.
Like plant cells, fungal cells have a thick cell wall. The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans. Chitin, also found in the exoskeleton of insects, gives structural strength to the cell walls of fungi. The wall protects the cell from desiccation and predators. Fungi have plasma membranes similar to other eukaryotes, except that the structure is stabilized by ergosterol: a steroid molecule that replaces the cholesterol found in animal cell membranes. Most members of the kingdom Fungi are nonmotile. Flagella are produced only by the gametes in the primitive Phylum Chytridiomycota.
Growth
The vegetative body of a fungus is a unicellular or multicellular thallus . Dimorphic fungi can change from the unicellular to multicellular state depending on environmental conditions. Unicellular fungi are generally referred to as yeasts . Saccharomyces cerevisiae (baker’s yeast) and Candida species (the agents of thrush, a common fungal infection) are examples of unicellular fungi (Figure \(\PageIndex{2}\)).
Most fungi are multicellular organisms. They display two distinct morphological stages: the vegetative and reproductive. The vegetative stage consists of a tangle of slender thread-like structures called hyphae (singular, hypha ), whereas the reproductive stage can be more conspicuous. The mass of hyphae is a mycelium (Figure \(\PageIndex{3}\)). It can grow on a surface, in soil or decaying material, in a liquid, or even on living tissue. Although individual hyphae must be observed under a microscope, the mycelium of a fungus can be very large, with some species truly being “the fungus humongous.” The giant Armillaria solidipes (honey mushroom) is considered the largest organism on Earth, spreading across more than 2,000 acres of underground soil in eastern Oregon; it is estimated to be at least 2,400 years old.
Most fungal hyphae are divided into separate cells by endwalls called septa (singular, septum ) (Figure \(\PageIndex{4}\)). In most phyla of fungi, tiny holes in the septa allow for the rapid flow of nutrients and small molecules from cell to cell along the hypha. They are described as perforated septa. The hyphae in bread molds (which belong to the Phylum Zygomycota) are not separated by septa. Instead, they are formed by large cells containing many nuclei, an arrangement described as coenocytic hyphae (Figure 24.1.4).
Fungi thrive in environments that are moist and slightly acidic, and can grow with or without light. They vary in their oxygen requirement. Most fungi are obligate aerobes , requiring oxygen to survive. Other species, such as the Chytridiomycota that reside in the rumen of cattle, are are obligate anaerobes , in that they only use anaerobic respiration because oxygen will disrupt their metabolism or kill them. Yeasts are intermediate, being faculative anaerobes . This means that they grow best in the presence of oxygen using aerobic respiration, but can survive using anaerobic respiration when oxygen is not available. The alcohol produced from yeast fermentation is used in wine and beer production.
Nutrition
Like animals, fungi are heterotrophs; they use complex organic compounds as a source of carbon, rather than fix carbon dioxide from the atmosphere as do some bacteria and most plants. In addition, fungi do not fix nitrogen from the atmosphere. Like animals, they must obtain it from their diet. However, unlike most animals, which ingest food and then digest it internally in specialized organs, fungi perform these steps in the reverse order; digestion precedes ingestion. First, exoenzymes are transported out of the hyphae, where they process nutrients in the environment. Then, the smaller molecules produced by this external digestion are absorbed through the large surface area of the mycelium. As with animal cells, the polysaccharide of storage is glycogen, rather than starch, as found in plants.
Fungi are mostly saprobes (saprophyte is an equivalent term): organisms that derive nutrients from decaying organic matter. They obtain their nutrients from dead or decomposing organic matter: mainly plant material. Fungal exoenzymes are able to break down insoluble polysaccharides, such as the cellulose and lignin of dead wood, into readily absorbable glucose molecules. The carbon, nitrogen, and other elements are thus released into the environment. Because of their varied metabolic pathways, fungi fulfill an important ecological role and are being investigated as potential tools in bioremediation. For example, some species of fungi can be used to break down diesel oil and polycyclic aromatic hydrocarbons (PAHs). Other species take up heavy metals, such as cadmium and lead.
Some fungi are parasitic, infecting either plants or animals. Smut and Dutch elm disease affect plants, whereas athlete’s foot and candidiasis (thrush) are medically important fungal infections in humans. In environments poor in nitrogen, some fungi resort to predation of nematodes (small non-segmented roundworms). Species of Arthrobotrys fungi have a number of mechanisms to trap nematodes. One mechanism involves constricting rings within the network of hyphae. The rings swell when they touch the nematode, gripping it in a tight hold. The fungus penetrates the tissue of the worm by extending specialized hyphae called haustoria . Many parasitic fungi possess haustoria, as these structures penetrate the tissues of the host, release digestive enzymes within the host's body, and absorb the digested nutrients.
Reproduction
Fungi reproduce sexually and/or asexually. Perfect fungi reproduce both sexually and asexually, while the so-called imperfect fungi reproduce only asexually (by mitosis).
In both sexual and asexual reproduction, fungi produce spores that disperse from the parent organism by either floating on the wind or hitching a ride on an animal. Fungal spores are smaller and lighter than plant seeds. The giant puffball mushroom bursts open and releases trillions of spores. The huge number of spores released increases the likelihood of landing in an environment that will support growth (Figure \(\PageIndex{5}\)).
Asexual Reproduction
Fungi reproduce asexually by fragmentation, budding, or producing spores. Fragments of hyphae can grow new colonies. Somatic cells in yeast form buds. During budding (a type of cytokinesis), a bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell (Figure \(\PageIndex{6}\)).
The most common mode of asexual reproduction is through the formation of asexual spores, which are produced by one parent only (through mitosis) and are genetically identical to that parent (Figure \(\PageIndex{7}\)). Spores allow fungi to expand their distribution and colonize new environments. They may be released from the parent thallus either outside or within a special reproductive sac called a sporangium .
There are many types of asexual spores. Conidiospores are unicellular or multicellular spores that are released directly from the tip or side of the hypha. Other asexual spores originate in the fragmentation of a hypha to form single cells that are released as spores; some of these have a thick wall surrounding the fragment. Yet others bud off the vegetative parent cell. Sporangiospores are produced in a sporangium (Figure \(\PageIndex{8}\)).
Sexual Reproduction
Sexual reproduction introduces genetic variation into a population of fungi. In fungi, sexual reproduction often occurs in response to adverse environmental conditions. During sexual reproduction, two mating types are produced. When both mating types are present in the same mycelium, it is called homothallic , or self-fertile. Heterothallic mycelia require two different, but compatible, mycelia to reproduce sexually.
Although there are many variations in fungal sexual reproduction, all include the following three stages (Figure \(\PageIndex{7}\)). First, during plasmogamy (literally, “marriage or union of cytoplasm”), two haploid cells fuse, leading to a dikaryotic stage where two haploid nuclei coexist in a single cell. During karyogamy (“nuclear marriage”), the haploid nuclei fuse to form a diploid zygote nucleus. Finally, meiosis takes place in the gametangia (singular, gametangium) organs, in which gametes of different mating types are generated. At this stage, spores are disseminated into the environment.
Link to Learning
Review the characteristics of fungi by visiting this interactive site from Wisconsin-online.
Summary
Fungi are eukaryotic organisms that appeared on land more than 450 million years ago. They are heterotrophs and contain neither photosynthetic pigments such as chlorophyll, nor organelles such as chloroplasts. Because fungi feed on decaying and dead matter, they are saprobes. Fungi are important decomposers that release essential elements into the environment. External enzymes digest nutrients that are absorbed by the body of the fungus, which is called a thallus. A thick cell wall made of chitin surrounds the cell. Fungi can be unicellular as yeasts, or develop a network of filaments called a mycelium, which is often described as mold. Most species multiply by asexual and sexual reproductive cycles and display an alternation of generations. Another group of fungi do not have a sexual cycle. Sexual reproduction involves plasmogamy (the fusion of the cytoplasm), followed by karyogamy (the fusion of nuclei). Meiosis regenerates haploid individuals, resulting in haploid spores.
Glossary
- coenocytic hypha
- single hypha that lacks septa and contains many nuclei
- faculative anaerobes
- organisms that can perform both aerobic and anaerobic respiration and can survive in oxygen-rich and oxygen-poor environment
- haustoria
- modified hyphae on many parasitic fungi that penetrate the tissues of their hosts, release digestive enzymes, and/or absorb nutrients from the host
- heterothallic
- describes when only one mating type is present in an individual mycelium
- homothallic
- describes when both mating types are present in mycelium
- hypha
- fungal filament composed of one or more cells
- karyogamy
- fusion of nuclei
- mycelium
- mass of fungal hyphae
- mycology
- scientific study of fungi
- obligate aerobes
- organisms, such as humans, that must perform aerobic respiration to survive
- obligate anaerobes
- organisms that only perform anaerobic respiration and often cannot survive in the presence of oxygen
- plasmogamy
- fusion of cytoplasm
- saprobe
- organism that derives nutrients from decaying organic matter; also saprophyte
- septa
- cell wall division between hyphae
- sporangium
- reproductive sac that contains spores
- thallus
- vegetative body of a fungus
- yeast
- general term used to describe unicellular fungi