17.1: The Romanesque Period
The Romanesque Period
Romanesque art was affected by shifting political powers following the Carolingian period and mobility during the Crusades.
Summarize the economics and politics of the Romanesque Period
Key Points
- The invasion of England by William Duke of Normandy in 1066 led to the construction of castles and churches to reinforce the Norman presence. Several significant churches built at this time were founded as seats of temporal and religious power or places of coronation and burial.
- The Crusades (1095–1270) brought about extensive migration and resultant spread of ideas and trade skills.
- The continual movement of people, rulers, nobles, bishops, abbots, craftsmen and peasants was an important factor in creating homogenous building methods and a recognizable Romanesque style , despite regional differences.
- The period saw Europe grow steadily more prosperous, and art of the highest quality was no longer confined to the royal court and a small circle of monasteries. Lay artists became increasingly valuable, and this category included most masons, goldsmiths, and painters by the end of the period.
Key Terms
- lay : Not belonging to the clergy, but associated with them.
- Crusade : One of a series of ostensibly religious campaigns by Christian forces from the 11th to the 13th century, mostly to capture the Holy Land from the Muslims who occupied it.
- feudalism : A social system based on personal ownership of resources and fealty between a suzerain (lord) and a vassal (subject). Defining characteristics are direct ownership of resources, personal loyalty, and a hierarchical social structure reinforced by religion.
The Source of Inspiration
Romanesque architecture was the first distinctive style to spread across Europe after the collapse of the Roman Empire. Despite the misconception of 19 th century art historians that Romanesque architecture was a continuation of Roman styles, Roman brick and stone building techniques were lost in most parts of Europe. In the northern countries Roman style and methods were only adopted for official buildings, and in Scandinavia they were unknown. The exception was several great Constantinian basilicas that continued to stand in Rome as an inspiration to later builders. However, these did not inspire the Emperor Charlemagne’s Palatine Chapel in Aachen, Germany, built around the year AD 800. Instead, the greatest building of the Dark Ages in Europe was the artistic child of the octagonal Byzantine Basilica of San Vitale in Ravenna, built in the sixth century.
A New European Empire
Charlemagne was crowned by the Pope in St. Peter’s Basilica on Christmas Day in 800 CE, with an aim of reestablishing the old Roman Empire. Charlemagne’s political successors continued to rule much of Europe, leading to the gradual emergence of the separate political states that were eventually welded into nations by allegiance or defeat. In the process, the Kingdom of Germany gave rise to the Holy Roman Empire. The invasion of England by William Duke of Normandy, in 1066 saw the building of castles and churches that reinforced the Norman presence. Several significant churches built at this time were founded by rulers as seats of temporal and religious power or as places of coronation and burial. These include the Abbaye-Saint-Denis and Westminster Abbey (where little of the Norman church now remains).
The remaining architectural structures of the Roman Empire were falling into decay and much of its technology was lost. At the same time, however, the building of masonry domes and carving of decorative architectural details continued unabated, though the style had greatly evolved since the fall of Rome in the enduring Byzantine Empire. The domed churches of Constantinople and Eastern Europe had a substantial influence on the architecture of certain towns, particularly through trade and the Crusades. The most notable example is St Mark’s Basilica, Venice , but there are many lesser known examples such as the church of Saint Front, Périgueux and Angoulême Cathedral .
Feudalism and Warfare
Much of Europe was affected by feudalism, in which peasants held tenure from local rulers over the land they farmed in exchange for military service. As a result, they could be called on for local spats as well as to follow their lord across Europe to the Crusades.
The Crusades (1095–1270) brought about substantial migration and resultant spread of ideas and trade skills, particularly the building of fortifications and the metalworking for the provision of arms, which was also applied to the fitting and decoration of buildings. The continual movement of people, rulers, nobles, bishops, abbots, craftsmen, and peasants was an important factor in creating homogeneous building methods and a recognizable Romanesque style, despite regional differences.
Life became less secure after the Carolingian period, resulting in castles built at strategic points. Many were constructed as strongholds of the Normans, descendants of the Vikings who invaded northern France in 911. Political struggles also resulted in the fortification of towns by rebuilding and strengthening walls that remained from the Roman period. One of the most notable surviving fortifications is that of the city of Carcassonne. The enclosure of towns resulted in a style of tall, narrow townhouse with limited living space . These often surrounded communal courtyards, as at San Gimignano in Tuscany.
Growing Prosperity
As Europe grew steadily more prosperous during this period, art of the highest quality was no longer confined to the royal court and a small circle of monasteries as in the Carolingian and Ottonian periods. Monasteries remained important, especially those of the new Cistercian , Cluniac , and Carthusian orders that spread across Europe. City churches, including those on pilgrimage routes and many in small towns and villages, were elaborately decorated. Indeed, these have often survived when cathedrals and city churches have been rebuilt, while Romanesque royal palaces have not. The lay artist, Nicholas of Verdun, became a valued figure known across the continent. Most masons and goldsmiths were now lay professionals rather than monastic clergy, and lay painters like Master Hugo were the majority by the end of the period. The iconography of their church work was likely determined in consultation with clerical advisers.
Romanesque Art
Romanesque art refers to the art of Europe from the late 10th century to the rise of the Gothic style in the 13th century.
Evaluate Romanesque architecture, sculpture, and painting
Key Points
- The Romanesque style was the first to spread across the whole of Catholic Europe and thus the first pan-European style since Imperial Roman Architecture.
- Combining features of Roman and Byzantine buildings and other local traditions, Romanesque architecture exhibits massive quality, thick walls, round arches , sturdy piers , groin vaults , large towers, and symmetrical plans.
- The art of the period was characterized by a vigorous style in both painting and sculpture.
- Colors, which we can now see in their original brightness only in stained glass and well-preserved manuscripts, tended to be very striking.
- The tympanums of important church portals were carved with monumental schemes, often depicting iconography from Byzantine painting.
Key Terms
- groin vault : The intersection at right angles of two barrel vaults.
- tympanum : A triangular space between the sides of a pediment; the space within an arch and above a lintel or a subordinate arch, spanning the opening below the arch.
- pier : In architecture, an upright support for a structure or superstructure such as an arch or bridge.
Romanesque art refers to the art of Europe from the late 10 th century to the rise of the Gothic style in the 13 th century or later, depending on region. The term “Romanesque” was invented by 19 th century art historians to refer specifically to architecture of the time period, which retained many basic features of Roman architectural style—most notably semi-circular arches—but retained distinctive regional characteristics. In Southern France, Spain, and Italy, there was architectural continuity with the Late Antique period, but the Romanesque style was the first style to spread across the whole of Catholic Europe and thus the first pan-European style since Imperial Roman Architecture. Romanesque art was also influenced by Byzantine art, especially in painting, and by the anti-classical energy of the decoration of the Insular art of the British Isles. From these elements was forged a highly innovative and coherent style.
Architecture
Combining features of Roman and Byzantine buildings along with other local traditions, Romanesque architecture is distinguished by massive quality, thick walls, round arches, sturdy piers, groin vaults, large towers, and decorative arcades . Each building has clearly defined forms and a symmetrical plan, resulting in a much simpler appearance than the Gothic buildings that would follow. The style can be identified across Europe, despite regional characteristics and materials.
Painting
Aside from architecture, the art of the period was characterized by a vigorous style in both painting and sculpture. In churches, painting continued to follow Byzantine iconographic models. Christ in Majesty, the Last Judgement and scenes from the Life of Christ remained among the most common depictions. In illuminated manuscripts , the most lavishly decorated examples of the period included bibles or psalters . As new scenes were depicted, more originality developed. They used intensely saturated primary colors , which now exist in their original brightness only in stained glass and well-preserved manuscripts. Stained glass first came to wide use during this period, although there are few surviving examples.
Pictorial compositions usually had little depth as they were limited to the narrow spaces of historiated initials, column capitals , and church tympanums. The tension between a tight frame and a composition that sometimes escapes its designated space is a recurrent theme in Romanesque art. Figures often varied in size in relation to their importance, and landscape backgrounds were absent or closer to abstract decorations than realism , as in the trees in the “Morgan Leaf.” Human forms were often elongated and contorted to fit the shape provided and at times appeared to be floating in space. These figures focused on linear details with emphasis on drapery folds and hair.
Sculpture
Sculpture also exhibited a vigorous style, evident in the carved capitals of columns, which often depicted complete scenes consisting of several figures. Precious objects sculpted in metal, enamel , and ivory , such as reliquaries , also had high status in this period. While the large wooden crucifix and statues of the enthroned Madonna were German innovations at the start of the period, the high relief carvings of architectural elements are most evocative of this style.
In a significant innovation, the tympanums of important church portals were carved with monumental schemes, again depicting Christ in Majesty or the Last Judgement but treated with more freedom than in painted versions. These portal sculptures were meant to both intimidate and educate the viewer . As there were no equivalent Byzantine models, Romanesque sculptors felt free to expand in their treatment of tympanums.
- Curation and Revision. Provided by : Boundless.com. License : CC BY-SA: Attribution-ShareAlike
- San Gimignano. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:San_Gimignano.JPG. License : CC BY-SA: Attribution-ShareAlike
- Pu00e9rigueux 3. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:P%C3%A9rigueux_3.JPG. License : Public Domain: No Known Copyright
- Europe 1142. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Europe_1142.jpg. License : Public Domain: No Known Copyright
- Romanesque architecture. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Romanesque_architecture%23Portals. License : CC BY-SA: Attribution-ShareAlike
- Romanesque art. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Romanesque_art. License : CC BY-SA: Attribution-ShareAlike
- Crusade. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/Crusade. License : CC BY-SA: Attribution-ShareAlike
- feudalism. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/feudalism. License : CC BY-SA: Attribution-ShareAlike
- lay. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/lay. License : CC BY-SA: Attribution-ShareAlike
- Portal moissac. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Portal_moissac.jpg. License : CC BY-SA: Attribution-ShareAlike
- MorganLeafVerso. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:MorganLeafVerso.jpg. License : Public Domain: No Known Copyright
- Maria Lach 02. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/File:Maria_Lach_02.jpg. License : CC BY-SA: Attribution-ShareAlike
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- Romanesque architecture. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/Romanesque_architecture. License : CC BY-SA: Attribution-ShareAlike
- groin vault. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/groin%20vault. License : CC BY-SA: Attribution-ShareAlike
- Boundless. Provided by : Boundless Learning. Located at : www.boundless.com//biology/definition/tympanum. License : CC BY-SA: Attribution-ShareAlike
- pier. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/pier. License : CC BY-SA: Attribution-ShareAlike


10.6: Sage Exercises
Build every subgroup of the alternating group on 5 symbols, \(A_5\text{,}\) and check that each is not a normal subgroup (except for the two trivial cases). This command might take a couple seconds to run. Compare this with the time needed to run the
.is_simple()
method and realize that there is a significant amount of theory and cleverness brought to bear in speeding up commands like this. (It is possible that your Sage installation lacks
GAP
's “Table of Marks” library and you will be unable to compute the list of subgroups.)
Consider the quotient group of the group of symmetries of an \(8\)-gon, formed with the cyclic subgroup of order \(4\) generated by a quarter-turn. Use the
coset_product
function to determine the Cayley table for this quotient group. Use the number of each coset, as produced by the
.cosets()
method as names for the elements of the quotient group. You will need to build the table “by hand” as there is no easy way to have Sage's Cayley table command do this one for you. You can build a table in the Sage Notebook pop-up editor (shift-click on a blue line) or you might read the documentation of the
html.table()
method.
Consider the cyclic subgroup of order \(4\) in the symmetries of an \(8\)-gon. Verify that the subgroup is normal by first building the raw left and right cosets (without using the
.cosets()
method) and then checking their equality in Sage, all with a single command that employs sorting with the
sorted()
command.
Again, use the same cyclic subgroup of order \(4\) in the group of symmetries of an \(8\)-gon. Check that the subgroup is normal by using part (2) of Theorem \(10.3\). Construct a one-line command that does the complete check and returns
True
. Maybe sort the elements of the subgroup
S
first, then slowly build up the necessary lists, commands, and conditions in steps. Notice that this check does not require ever building the cosets.
Repeat the demonstration from the previous subsection that for the symmetries of a tetrahedron, a cyclic subgroup of order \(3\) results in an undefined coset multiplication. Above, the default setting for the
.cosets()
method builds right cosets — but in this problem, work instead with left cosets. You need to choose two cosets to multiply, and then demonstrate two choices for representatives that lead to different results for the product of the cosets.
Construct some dihedral groups of order \(2n\) (i.e. symmetries of an \(n\)-gon, \(D_{n}\) in the text,
DihedralGroup(n)
in Sage). Maybe all of them for \(3\leq n \leq 100\text{.}\) For each dihedral group, construct a list of the orders of each of the normal subgroups (so use
.normal_subgroups()
). You may need to wait ten or twenty seconds for this to finish - be patient. Observe enough examples to hypothesize a pattern to your observations, check your hypothesis against each of your examples and then state your hypothesis clearly.
Can you predict how many normal subgroups there are in the dihedral group \(D_{470448}\) without using Sage to build all the normal subgroups? Can you describe all of the normal subgroups of a dihedral group in a way that would let us predict all of the normal subgroups of \(D_{470448}\) without using Sage?


1.17: Endocrine System
- Apply the rules of medical language to build, analyze, spell, pronounce, abbreviate, and define terms as they relate to the endocrine system
- Identify meanings of key word components of the endocrine system
- Categorize diagnostic, therapeutic, procedural or anatomic terms related to the endocrine system
- Use terms related to the endocrine system
- Use terms related to the diseases and disorders of the endocrine system
Endocrine System Word Parts
Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Endocrine System.
Introduction to Endocrine System
You may never have thought of it this way, but when you send a text message to two friends to meet you for dinner at six, you’re sending digital signals that (you hope) will affect their behavior—even though they are some distance away. Similarly, certain cells send chemical signals to other cells in the body that influence their behavior. This long-distance intercellular communication, coordination, and control is critical to maintain equilibrium (homeostasis). This intercellular activity is the fundamental function of the endocrine system.
Watch this video:
Media 17.1 Endocrine System, Part 1 – Glands & Hormones: Crash Course A&P #23 [Online video]. Copyright 2015 by CrashCourse .
Endocrine System Medical Terms
Anatomy (Structure) of the Endocrine System
The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of the endocrine gland is to secrete hormones directly into the surrounding fluid. The surrounding fluid (interstitial fluid) and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands (see Figure 17.2). Some of these glands have both endocrine and non-endocrine functions. For example, the pancreas contains cells that function in digestion as well as cells that secrete the endocrine hormones like insulin and glucagon, which regulate blood glucose levels. The hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, skin, female ovaries, and male testes are other organs that contain cells with endocrine function. Moreover, fat (adipose) tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.
The ductless endocrine glands are not to be confused with the body’s exocrine system , whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine.
Anatomy Labeling Activity
Physiology (Function) of the Endocrine System
Endocrine Signaling
The endocrine system uses one method of communication called chemical signaling. These chemical signals are sent by the endocrine organs. The endocrine organs secrete chemicals—called hormones —into the fluid outside of the tissue cells (extracellular fluid). Hormones are then transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, creating a particular response. For example, the hormones released when you are presented with a dangerous or a frightening situation, called the fight-or-flight response, occurs through the release of hormones from the adrenal gland, epinephrine and norepinephrine—within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones.
In addition, endocrine signaling is typically less specific than neural (nerve) signaling. The same hormone may also play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin generates uterine contractions in women who are in labor. This hormone is also important in generating the milk release reflex during breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in both males and females.
Generally, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining equilibrium (homeostasis), and in controlling reproduction (see Table 17.1). So how does the fight-or-flight response, that was mentioned earlier, happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones, epinephrine and norepinephrine. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments, when necessary .
| Characteristic | Endocrine System | Nervous System |
|---|---|---|
| Signaling mechanism(s) | Chemical | Chemical/electrical |
| Primary chemical signal | Hormones | Neurotransmitters |
| Distance traveled | Long or short | Always short |
| Response time | Fast or slow | Always fast |
| Environment targeted | Internal | Internal and external |
Hormones
Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. Once the hormone binds to the receptor, a chain of events is initiated that leads to the target cell’s response. Hormones play a critical role in the regulation of physiological processes because of the target cell responses they regulate. These responses contribute to human reproduction, growth and development of body tissues, metabolism, fluid, and electrolyte balance, sleep, and many other body functions. The major hormones of the human body and their effects are identified in Table 17.2 .
| Endocrine Gland | Associated Hormones | Chemical Class | Effect |
|---|---|---|---|
| Pituitary (anterior) | Growth hormone (GH) | Protein | Promotes growth of body tissues |
| Pituitary (anterior) | Prolactin (PRL) | Peptide | Promotes milk production |
| Pituitary (anterior) | Thyroid-stimulating hormone (TSH) | Glycoprotein | Stimulates thyroid hormone release |
| Pituitary (anterior) | Adrenocorticotropic hormone (ACTH) | Peptide | Stimulates hormone release by adrenal cortex |
| Pituitary (anterior) | Follicle-stimulating hormone (FSH) | Glycoprotein | Stimulates gamete production |
| Pituitary (anterior) | Luteinizing hormone (LH) | Glycoprotein | Stimulates androgen production by gonads |
| Pituitary (posterior) | Antidiuretic hormone (ADH) | Peptide | Stimulates water reabsorption by kidneys |
| Pituitary (posterior) | Oxytocin | Peptide | Stimulates uterine contractions during childbirth |
| Thyroid | Thyroxine (T 4 ), triiodothyronine (T 3 ) | Amine | Stimulate basal metabolic rate |
| Thyroid | Calcitonin | Peptide | Reduces blood Ca 2 + levels |
| Parathyroid | Parathyroid hormone (PTH) | Peptide | Increases blood Ca 2 + levels |
| Adrenal (cortex) | Aldosterone | Steroid | Increases blood Na + levels |
| Adrenal (cortex) | Cortisol, corticosterone, cortisone | Steroid | Increase blood glucose levels |
| Adrenal (medulla) | Epinephrine, norepinephrine | Amine | Stimulate fight-or-flight response |
| Pineal | Melatonin | Amine | Regulates sleep cycles |
| Pancreas | Insulin | Protein | Reduces blood glucose levels |
| Pancreas | Glucagon | Protein | Increases blood glucose levels |
| Testes | Testosterone | Steroid | Stimulates development of male secondary sex characteristics and sperm production |
| Ovaries | Estrogens and progesterone | Steroid | Stimulate development of female secondary sex characteristics and prepare the body for childbirth |
Types of Hormones
The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids. These chemical groups affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its function .
Amine Hormones
Hormones derived from the modification of amino acids are referred to as amine hormones. Amine hormones are synthesized from the amino acids tryptophan or tyrosine. An example of a hormone derived from tryptophan is melatonin, which is secreted by the pineal gland and helps regulate circadian rhythm.
Peptide and Protein Hormones
Whereas the amine hormones are derived from a single amino acid, peptide and protein hormones consist of multiple amino acids that link to form an amino acid chain. Examples of peptide hormones include antidiuretic hormone (ADH), a pituitary hormone important in fluid balance. Some examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH). FSH helps stimulate the maturation of eggs in the ovaries and sperm in the testes.
Steroid Hormones
The primary hormones derived from lipids are steroids. Steroid hormones are derived from the lipid cholesterol. For example, the reproductive hormones testosterone and the estrogens—which are produced by the gonads (testes and ovaries)—are steroid hormones. The adrenal glands produce the steroid hormone aldosterone, which is involved in osmoregulation, and cortisol, which plays a role in metabolism.
Like cholesterol, steroid hormones are not soluble in water (they are hydrophobic). Because blood is water-based, lipid-derived hormones must travel to their target cell bound to a transport protein .
Pathways of Hormone Action
The message a hormone sends is received by a hormone receptor , a protein located either inside the cell or within the cell membrane. The receptor will process the message by initiating other signaling events or cellular mechanisms that result in the target cell’s response. Hormone receptors recognize molecules with specific shapes and side groups, and respond only to those hormones that are recognized. The same type of receptor may be located on cells in different body tissues, and trigger somewhat different responses. Thus, the response triggered by a hormone depends not only on the hormone, but also on the target cell.
Once the target cell receives the hormone signal, it can respond in a variety of ways. The response may include the stimulation of protein synthesis, activation or deactivation of enzymes, alteration in the permeability of the cell membrane, altered rates of mitosis and cell growth, and stimulation of the secretion of products. Moreover, a single hormone may be capable of inducing different responses in a given cell .
Factors Affecting Target Cell Response
You will recall that target cells must have receptors specific to a given hormone if that hormone is to trigger a response. But several other factors influence the target cell response. For example, the presence of a significant level of a hormone circulating in the bloodstream can cause its target cells to decrease their number of receptors for that hormone. This process is called downregulation , and it allows cells to become less reactive to the excessive hormone levels. When the level of a hormone is chronically reduced, target cells engage in upregulation to increase their number of receptors. This process allows cells to be more sensitive to the hormone that is present. Cells can also alter the sensitivity of the receptors themselves to various hormones.
Two or more hormones can interact to affect the response of cells in a variety of ways. The three most common types of interaction are as follows:
- The permissive effect, in which the presence of one hormone enables another hormone to act. For example, thyroid hormones have complex permissive relationships with certain reproductive hormones. A dietary deficiency of iodine, a component of thyroid hormones, can therefore affect reproductive system development and functioning.
- The synergistic effect, in which two hormones with similar effects produce an amplified response. In some cases, two hormones are required for an adequate response. For example, two different reproductive hormones—FSH from the pituitary gland and estrogens from the ovaries—are required for the maturation of female ova (egg cells).
- The antagonistic effect, in which two hormones have opposing effects. A familiar example is the effect of two pancreatic hormones, insulin and glucagon. Insulin increases the liver’s storage of glucose as glycogen, decreasing blood glucose, whereas glucagon stimulates the breakdown of glycogen stores, increasing blood glucose .
Concept Check
- Describe how a hormone receptor functions and reacts to messages received.
Regulation of Hormone Secretion
To prevent abnormal hormone levels and a potential disease state, hormone levels must be tightly controlled. The body maintains this control by balancing hormone production and degradation. Feedback loops govern the initiation and maintenance of most hormone secretion in response to various stimuli.
Role of Feedback Loops
The contribution of feedback loops to homeostasis will only be briefly reviewed here. Positive feedback loops are characterized by the release of additional hormone in response to an original hormone release. The release of oxytocin during childbirth is a positive feedback loop. The initial release of oxytocin begins to signal the uterine muscles to contract, which pushes the fetus toward the cervix, causing it to stretch. This, in turn, signals the pituitary gland to release more oxytocin, causing labor contractions to intensify. The release of oxytocin decreases after the birth of the child.
The more common method of hormone regulation is the negative feedback loop. Negative feedback is characterized by the inhibition of further secretion of a hormone in response to adequate levels of that hormone. This allows blood levels of the hormone to be regulated within a narrow range. An example of a negative feedback loop is the release of glucocorticoid hormones from the adrenal glands, as directed by the hypothalamus and pituitary gland. As glucocorticoid concentrations in the blood rise, the hypothalamus and pituitary gland reduce their signaling to the adrenal glands to prevent additional glucocorticoid secretion (see Figure 17.3 ) .
Anterior Pituitary Gland
Recall that the posterior pituitary does not synthesize hormones, but merely stores them. In contrast, the anterior pituitary does manufacture hormones. However, the secretion of hormones from the anterior pituitary is regulated by two classes of hormones. These hormones—secreted by the hypothalamus—are the releasing hormones that stimulate the secretion of hormones from the anterior pituitary and the inhibiting hormones that inhibit secretion.
Hypothalamic hormones are secreted by neurons, but enter the anterior pituitary through blood vessels.
The anterior pituitary produces seven hormones. These are the growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), beta endorphin, and prolactin. Of the hormones of the anterior pituitary, TSH, ACTH, FSH, and LH are collectively referred to as tropic hormones (trope- = “turning”) because they turn on or off the function of other endocrine glands.
Growth Hormone
The endocrine system regulates the growth of the human body, protein synthesis, and cellular replication. A major hormone involved in this process is growth hormone (GH) , also called somatotropin—a protein hormone produced and secreted by the anterior pituitary gland. Its primary function is anabolic; it promotes protein synthesis and tissue building through direct and indirect mechanisms.
A glucose-sparing effect occurs when GH stimulates lipolysis, or the breakdown of adipose tissue, releasing fatty acids into the blood. As a result, many tissues switch from glucose to fatty acids as their main energy source, which means that less glucose is taken up from the bloodstream.
GH also initiates the diabetogenic effect in which GH stimulates the liver to break down glycogen to glucose, which is then deposited into the blood. The name “diabetogenic” is derived from the similarity in elevated blood glucose levels observed between individuals with untreated diabetes mellitus and individuals experiencing GH excess. Blood glucose levels rise as the result of a combination of glucose-sparing and diabetogenic effects.
Dysfunction of the endocrine system’s control of growth can result in several disorders. For example, gigantism is a disorder in children that is caused by the secretion of abnormally large amounts of GH, resulting in excessive growth. A similar condition in adults is acromegaly , a disorder that results in the growth of bones in the face, hands, and feet in response to excessive levels of GH in individuals who have stopped growing. Abnormally low levels of GH in children can cause growth impairment—a disorder called pituitary dwarfism (also known as growth hormone deficiency) .
Posterior Pituitary Gland
The posterior pituitary is actually an extension of the neurons of the nuclei of the hypothalamus. The cell bodies of these regions rest in the hypothalamus.
The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH. These hormones travel along the axons into storage sites in the axon terminals of the posterior pituitary. In response to signals from the same hypothalamic neurons, the hormones are released from the axon terminals into the bloodstream.
Oxytocin
When fetal development is complete, the peptide-derived hormone oxytocin (tocia- = “childbirth”) stimulates uterine contractions and dilation of the cervix. Throughout most of pregnancy, oxytocin hormone receptors are not expressed at high levels in the uterus. Toward the end of pregnancy, the synthesis of oxytocin receptors in the uterus increases, and the smooth muscle cells of the uterus become more sensitive to its effects. Oxytocin is continually released throughout childbirth through a positive feedback mechanism. As noted earlier, oxytocin prompts uterine contractions that push the fetal head toward the cervix. In response, cervical stretching stimulates additional oxytocin to be synthesized by the hypothalamus and released from the pituitary. This increases the intensity and effectiveness of uterine contractions and prompts additional dilation of the cervix. The feedback loop continues until birth.
Although the mother’s high blood levels of oxytocin begin to decrease immediately following birth, oxytocin continues to play a role in maternal and newborn health. First, oxytocin is necessary for the milk ejection reflex (commonly referred to as “let-down”) in breastfeeding women. As the newborn begins suckling, sensory receptors in the nipples transmit signals to the hypothalamus. In response, oxytocin is secreted and released into the bloodstream. Within seconds, cells in the mother’s milk ducts contract, ejecting milk into the infant’s mouth. Secondly, in both males and females, oxytocin is thought to contribute to parent–newborn bonding, known as attachment. Oxytocin is also thought to be involved in feelings of love and closeness, as well as in the sexual response .
Antidiuretic Hormone (ADH)
The solute concentration of the blood, or blood osmolarity, may change in response to the consumption of certain foods and fluids, as well as in response to disease, injury, medications, or other factors. Blood osmolarity is constantly monitored by osmoreceptors —specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.
In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors signal the posterior pituitary to release antidiuretic hormone (ADH) . The target cells of ADH are located in the tubular cells of the kidneys. Its effect is to increase epithelial permeability to water, allowing increased water reabsorption. The more water reabsorbed from the filtrate, the greater the amount of water that is returned to the blood and the less that is excreted in the urine. A greater concentration of water results in a reduced concentration of solutes. ADH is also known as vasopressin because, in very high concentrations, it causes constriction of blood vessels, which increases blood pressure by increasing peripheral resistance. The release of ADH is controlled by a negative feedback loop. As blood osmolarity decreases, the hypothalamic osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the urine filtrate.
Interestingly, drugs can affect the secretion of ADH. For example, alcohol consumption inhibits the release of ADH, resulting in increased urine production that can eventually lead to dehydration and a hangover. A disease called diabetes insipidus is characterized by chronic underproduction of ADH that causes chronic dehydration. Because little ADH is produced and secreted, not enough water is reabsorbed by the kidneys. Although patients feel thirsty, and increase their fluid consumption, this doesn’t effectively decrease the solute concentration in their blood because ADH levels are not high enough to trigger water reabsorption in the kidneys. Electrolyte imbalances can occur in severe cases of diabetes insipidus .
Thyroid-Stimulating Hormone
The activity of the thyroid gland is regulated by thyroid-stimulating hormone (TSH) , also called thyrotropin. TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. As discussed shortly, it triggers the secretion of thyroid hormones by the thyroid gland. In a classic negative feedback loop, elevated levels of thyroid hormones in the bloodstream then trigger a drop in production of TRH and subsequently TSH .
Adrenocorticotropic Hormone
The adrenocorticotropic hormone (ACTH) , also called corticotropin, stimulates the adrenal cortex (the more superficial “bark” of the adrenal glands) to secrete corticosteroid hormones such as cortisol. The release of ACTH is regulated by the corticotropin-releasing hormone (CRH) from the hypothalamus in response to normal physiologic rhythms. A variety of stressors can also influence its release, and the role of ACTH in the stress response is discussed later in this chapter .
Follicle-Stimulating Hormone and Luteinizing Hormone
The endocrine glands secrete a variety of hormones that control the development and regulation of the reproductive system (these glands include the anterior pituitary, the adrenal cortex, and the gonads—the testes in males and the ovaries in females). Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in both male and female adolescents. Puberty is initiated by gonadotropin-releasing hormone (GnRH), a hormone produced and secreted by the hypothalamus. GnRH stimulates the anterior pituitary to secrete gonadotropins —hormones that regulate the function of the gonads. The levels of GnRH are regulated through a negative feedback loop; high levels of reproductive hormones inhibit the release of GnRH. Throughout life, gonadotropins regulate reproductive function and, in the case of women, the onset and cessation of reproductive capacity.
The gonadotropins include two glycoprotein hormones: follicle-stimulating hormone (FSH) stimulates the production and maturation of sex cells, or gametes, including ova in women and sperm in men. FSH also promotes follicular growth; these follicles then release estrogens in the female ovaries. Luteinizing hormone (LH) triggers ovulation in women, as well as the production of estrogens and progesterone by the ovaries. LH stimulates production of testosterone by the male testes .
Prolactin
As its name implies, prolactin (PRL) promotes lactation (milk production) in women. During pregnancy, it contributes to development of the mammary glands, and after birth, it stimulates the mammary glands to produce breast milk. However, the effects of prolactin depend heavily upon the permissive effects of estrogens, progesterone, and other hormones. And as noted earlier, the let-down of milk occurs in response to stimulation from oxytocin.
In a non-pregnant woman, prolactin secretion is inhibited by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine, and is released from neurons in the hypothalamus. Only during pregnancy do prolactin levels rise in response to prolactin-releasing hormone (PRH) from the hypothalamus .
Intermediate Pituitary: Melanocyte-Stimulating Hormone
The cells in the zone between the pituitary lobes secrete a hormone known as melanocyte-stimulating hormone (MSH) that is formed by cleavage of the pro-opiomelanocortin (POMC) precursor protein. Local production of MSH in the skin is responsible for melanin production in response to UV light exposure. The role of MSH made by the pituitary is more complicated. For instance, people with lighter skin generally have the same amount of MSH as people with darker skin. Nevertheless, this hormone is capable of darkening of the skin by inducing melanin production in the skin’s melanocytes. Women also show increased MSH production during pregnancy; in combination with estrogens, it can lead to darker skin pigmentation, especially the skin of the areolas and labia minora. Table 17.3 is a summary of the pituitary hormones and their principal effects .
| IMAGE OF GLANDS | HORMONES | |||
|
|
Posterior Pituitary Hormones | |||
| Releasing hormone (hypothalamus) | Pituitary Hormone | Target | Effects | |
| ADH | Stores ADH | Kidneys, sweat glands, circulatory system | Water balance | |
| – | OT | Female reproductive system | Triggers uterine contractions during childbirth | |
|
|
Anterior Pituitary Hormones | |||
| Releasing hormone (hypothalamus) | Pituitary Hormone | Target | Effects | |
| GnRH | LH | Reproductive system | Stimulates production of sex hormones by gonads | |
| GnRH | FSH | Reproductive system | stimulates production of sperm and eggs | |
| TRH | TSH | Thyroid gland | Stimulates the release of thyroid hormone (TH), TH regulates metabolism | |
| PRH (inhibited by PIH) | PRL | Mammary glands | Promotes milk production | |
| GHRH (inhibited by GHIH) | GH | Liver, bone, muscles | Induces targets to produce insulin-like growth factors (IGF). IGFs stimulate body growth and higher metabolic rate. | |
| CRH | ACTH | Adrenal glands | Induces targets to produce glucocorticoids, which regulate metabolism and stress response |
Pineal Gland
A tiny endocrine gland whose functions are not entirely clear. The pinealocyte cells that make up the pineal gland are known to produce and secrete the amine hormone melatonin , which is derived from serotonin.
The secretion of melatonin varies according to the level of light received from the environment. When photons of light stimulate the retinas of the eyes, a nerve impulse is sent to a region of the hypothalamus which is important in regulating biological rhythms. When blood levels of melatonin fall they promote wakefulness. In contrast, as light levels decline—such as during the evening—melatonin production increases, boosting blood levels and causing drowsiness.
Watch this video:
Media 17.2 2-Minute Neuroscience: Melatonin [Youtube]. Copyright 2020 by Neuroscientifically Challenged .
What should you avoid doing in the middle of your sleep cycle that would lower melatonin?
The secretion of melatonin may influence the body’s circadian rhythms, the dark-light fluctuations that affect not only sleepiness and wakefulness, but also appetite and body temperature. Interestingly, children have higher melatonin levels than adults, which may prevent the release of gonadotropins from the anterior pituitary, thereby inhibiting the onset of puberty. Finally, an antioxidant role of melatonin is the subject of current research.
Jet lag occurs when a person travels across several time zones and feels sleepy during the day or wakeful at night. Traveling across multiple time zones significantly disturbs the light-dark cycle regulated by melatonin. It can take up to several days for melatonin synthesis to adjust to the light-dark patterns in the new environment, resulting in jet lag. Some air travelers take melatonin supplements to induce sleep .
Thyroid Gland
A butterfly-shaped organ, the thyroid gland is located anterior to the trachea, just inferior to the larynx (see Figure 17.5 ). The medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of the thyroid lobes are embedded with parathyroid glands, primarily on their posterior surfaces.
Regulation of TH Synthesis
The release of T 3 and T 4 from the thyroid gland is regulated by thyroid-stimulating hormone (TSH). Low blood levels of T 3 and T 4 stimulate the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, which triggers secretion of TSH from the anterior pituitary. In turn, TSH stimulates the thyroid gland to secrete T 3 and T 4 . The levels of TRH, TSH, T 3 , and T 4 are regulated by a negative feedback system in which increasing levels of T 3 and T 4 decrease the production and secretion of TSH. The thyroid hormones, T 3 and T 4 , are often referred to as metabolic hormones because their levels influence the body’s basal metabolic rate, the amount of energy used by the body at rest.
The thyroid gland also secretes a hormone called calcitonin. Calcitonin is released in response to a rise in blood calcium levels .
Parathyroid Gland
The parathyroid glands are tiny, round structures usually found embedded in the posterior surface of the thyroid gland. A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. The primary functional cells of the parathyroid glands are the chief cells. These epithelial cells produce and secrete the parathyroid hormone (PTH) , the major hormone involved in the regulation of blood calcium levels .
Adrenal Gland
The adrenal glands are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule (see Figure 17.6). The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. They are served by several arteries branching off the aorta, including the suprarenal and renal arteries. Blood flows to each adrenal gland at the adrenal cortex and then drains into the adrenal medulla. Adrenal hormones are released into the circulation via the left and right suprarenal veins.
The adrenal cortex , as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. The HPA axis involves the stimulation of hormone release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. ACTH then stimulates the adrenal cortex to produce the hormone cortisol. This pathway will be discussed in more detail below.
The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons. It is really an extension of the autonomic nervous system, which regulates homeostasis in the body. The medulla is stimulated to secrete the amine hormones epinephrine and norepinephrine.
One of the major functions of the adrenal gland is to respond to stress. Stress can be either physical or psychological or both. Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school.
The body responds in different ways to short-term stress and long-term stress following a pattern known as the general adaptation syndrome (GAS) . Stage one of GAS is called the alarm reaction . This is short-term stress, the fight-or-flight response, mediated by the hormones epinephrine and norepinephrine from the adrenal medulla via the SAM pathway. Their function is to prepare the body for extreme physical exertion. Once this stress is relieved, the body quickly returns to normal. The section on the adrenal medulla covers this response in more detail.
If the stress is not soon relieved, the body adapts to the stress in the second stage called the stage of resistance . If a person is starving for example, the body may send signals to the gastrointestinal tract to maximize the absorption of nutrients from food.
If the stress continues for a longer term however, the body responds with symptoms quite different than the fight-or-flight response. During the stage of exhaustion , individuals may begin to suffer depression, the suppression of their immune response, severe fatigue, or even a fatal heart attack. These symptoms are mediated by the hormones of the adrenal cortex, especially cortisol, released as a result of signals from the HPA axis.
Adrenal hormones also have several non–stress-related functions, including the increase of blood sodium and glucose levels, which will be described in detail below .
Adrenal Cortex
The adrenal cortex consists of multiple layers of lipid-storing cells that occur in three structurally distinct regions. Each of these regions produces different hormones.
Watch this video:
Media 17.3 Endocrine System, Part 2 – Hormone Cascades: Crash Course A&P #24 [Online video]. Copyright 2015 by CrashCourse .
Concept Check
- Which hormone produced by the adrenal glands is responsible for the mobilization of energy stores?
The Adrenal Cortex
Aldosterone is important in the regulation of the concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is released in response to elevated blood K + , low blood Na + , low blood pressure, or low blood volume. In response, aldosterone increases the excretion of K + and the retention of Na + , which in turn increases blood volume and blood pressure. Its secretion is prompted when CRH from the hypothalamus triggers ACTH release from the anterior pituitary.Aldosterone is also a key component of the renin-angiotensin-aldosterone system (RAAS) in which specialized cells of the kidneys secrete the enzyme renin in response to low blood volume or low blood pressure. Renin then catalyzes the conversion of the blood protein angiotensinogen, produced by the liver, to the hormone angiotensin I. Angiotensin I is converted in the lungs to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II has three major functions:
- Initiating vasoconstriction of the arterioles, decreasing blood flow
- Stimulating kidney tubules to reabsorb NaCl and water, increasing blood volume
- Signaling the adrenal cortex to secrete aldosterone, the effects of which further contribute to fluid retention, restoring blood pressure and blood volume
For individuals with hypertension, or high blood pressure, drugs are available that block the production of angiotensin II. These drugs, known as ACE inhibitors, block the ACE enzyme from converting angiotensin I to angiotensin II, thus mitigating the latter’s ability to increase blood pressure.
Glucocorticoid
The glucocorticoid hormones play a role in glucose metabolism. The most important of these is cortisol , some of which the liver converts to cortisone. A glucocorticoid produced in much smaller amounts is corticosterone. In response to long-term stressors, the hypothalamus secretes CRH, which in turn triggers the release of ACTH by the anterior pituitary. ACTH triggers the release of the glucocorticoids. Their overall effect is to inhibit tissue building while stimulating the breakdown of stored nutrients to maintain adequate fuel supplies. In conditions of long-term stress, for example, cortisol promotes the catabolism of glycogen to glucose, the catabolism of stored triglycerides into fatty acids and glycerol, and the catabolism of muscle proteins into amino acids. These raw materials can then be used to synthesize additional glucose and ketones for use as body fuels. The hippocampus, which is part of the temporal lobe of the cerebral cortex and important in memory formation, is highly sensitive to stress levels because of its many glucocorticoid receptors.
You are probably familiar with prescription and over-the-counter medications containing glucocorticoids, such as cortisone injections into inflamed joints, prednisone tablets and steroid-based inhalers used to manage severe asthma, and hydrocortisone creams applied to relieve itchy skin rashes. These drugs reflect another role of cortisol—the downregulation of the immune system, which inhibits the inflammatory response.
Androgens
The deepest region of the adrenal cortex produces small amounts of a class of steroid sex hormones called androgens. During puberty and most of adulthood, androgens are produced in the gonads. The androgens produced in the zona reticularis supplement the gonadal androgens. They are produced in response to ACTH from the anteri or pituitary and are converted in the tissues to testosterone or estrogens. In adult women, they may contribute to the sex drive, but their function in adult men is not well understood. In post-menopausal women, as the functions of the ovaries decline, the main source of estrogens becomes the androgens produced by the zona reticularis .
Adrenal Medulla
As noted earlier, the adrenal cortex releases glucocorticoids in response to long-term stress such as severe illness. In contrast, the adrenal medulla releases its hormones in response to acute, short-term stress mediated by the sympathetic nervous system (SNS).The medullary tissue is composed of unique postganglionic SNS neurons called chromaffin cells, which are large and irregularly shaped, and produce the neurotransmitters epinephrine (also called adrenaline) and norepinephrine (or noradrenaline). Epinephrine is produced in greater quantities—approximately a 4 to 1 ratio with norepinephrine—and is the more powerful hormone. Because the chromaffin cells release epinephrine and norepinephrine into the systemic circulation, where they travel widely and exert effects on distant cells, they are considered hormones. Derived from the amino acid tyrosine, they are chemically classified as catecholamines.
The secretion of medullary epinephrine and norepinephrine is controlled by a neural pathway that originates from the hypothalamus in response to danger or stress. Both epinephrine and norepinephrine signal the liver and skeletal muscle cells to convert glycogen into glucose, resulting in increased blood glucose levels. These hormones increase the heart rate, pulse, and blood pressure to prepare the body to fight the perceived threat or flee from it. In addition, the pathway dilates the airways, raising blood oxygen levels. It also prompts vasodilation, further increasing the oxygenation of important organs such as the lungs, brain, heart, and skeletal muscle. At the same time, it triggers vasoconstriction to blood vessels serving less essential organs such as the gastrointestinal tract, kidneys, and skin, and downregulates some components of the immune system. Other effects include a dry mouth, loss of appetite, pupil dilation, and a loss of peripheral vision .
Pancreas
The pancreas is a long, slender organ, most of which is located posterior to the bottom half of the stomach (see Figure 17.7). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its pancreatic islets —clusters of cells formerly known as the islets of Langerhans—secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).
Cells and Secretions of the Pancreatic Islets
The pancreatic islets each contain four varieties of cells:
- The alpha cell produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.
- The beta cell produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.
- The delta cell accounts for four percent of the islet cells and secretes the peptide hormone somatostatin. Recall that somatostatin is also released by the hypothalamus (as GHIH), and the stomach and intestines also secrete it. An inhibiting hormone, pancreatic somatostatin inhibits the release of both glucagon and insulin.
- The PP cell accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.
Regulation of Blood Glucose Levels by Insulin and Glucagon
Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels .
Gonadal Glands
The male testes and female ovaries—which produce the sex cells (sperm and ova) and secrete the gonadal hormones. The roles of the gonadotropins released from the anterior pituitary (FSH and LH) were discussed earlier.
The primary hormone produced by the male testes is testosterone , a steroid hormone important in the development of the male reproductive system, the maturation of sperm cells, and the development of male secondary sex characteristics such as a deepened voice, body hair, and increased muscle mass. Interestingly, testosterone is also produced in the female ovaries, but at a much reduced level. In addition, the testes produce the peptide hormone inhibin , which inhibits the secretion of FSH from the anterior pituitary gland. FSH stimulates spermatogenesis.
The primary hormones produced by the ovaries are estrogens , which include estradiol, estriol, and estrone. Estrogens play an important role in a larger number of physiological processes, including the development of the female reproductive system, regulation of the menstrual cycle, the development of female secondary sex characteristics such as increased adipose tissue and the development of breast tissue, and the maintenance of pregnancy. Another significant ovarian hormone is progesterone , which contributes to regulation of the menstrual cycle and is important in preparing the body for pregnancy as well as maintaining pregnancy. In addition, the granulosa cells of the ovarian follicles produce inhibin, which—as in males—inhibits the secretion of FSH. During the initial stages of pregnancy, an organ called the placenta develops within the uterus. The placenta supplies oxygen and nutrients to the fetus, excretes waste products, and produces and secretes estrogens and progesterone. The placenta produces human chorionic gonadotropin (hCG) as well. The hCG hormone promotes progesterone synthesis and reduces the mother’s immune function to protect the fetus from immune rejection. It also secretes human placental lactogen (hPL), which plays a role in preparing the breasts for lactation, and relaxin, which is thought to help soften and widen the pubic symphysis in preparation for childbirth .
Common Endocrine System Abbreviations
Concept Check
- Do you recall the term which describes high level of glucose in the blood?
- Do you recall the neurotransmitter responsible for assisting the response to danger or stress?
- Suggest what may happen if the adrenal cortex failed to secrete its hormones.
Diseases and Disorders
Acromegaly
- A disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet.
Addison’s disease
A rare disorder that causes low blood glucose levels and low blood sodium levels. The signs and symptoms of Addison’s disease are vague and are typical of other disorders as well, making diagnosis difficult. They may include general weakness, abdominal pain, weight loss, nausea, vomiting, sweating, and cravings for salty food (Betts, et al., 2021).
Cushing’s disease
A disorder characterized by high blood glucose levels and the accumulation of lipid deposits on the face and neck. It is caused by hypersecretion of cortisol. The most common source of Cushing’s disease is a pituitary tumor that secretes cortisol or ACTH in abnormally high amounts (Betts, et al., 2021).
Gigantism
- A disorder in children caused when abnormally high levels of GH prompt excessive growth in the body (Betts, et al., 2021).
Hirsutism
Hirsutism is a symptom of an excessive production of androgens causing hair growth in women where they typically do not have hair growth. While some medications may cause the increased androgen production it can also be linked to endocrine disorders such as Polycystic Ovary Syndrome (PCOS), Cushing syndrome and tumors in the ovaries or adrenal glands (Mayo Clinic Staff, 2020).
Hyperthyroidism
A condition marked by high levels of thyroid hormones that results in weight loss, profuse sweating, and increased heart rate (Betts, et al., 2021).
Hypothyroidism
A condition marked by low levels of thyroid hormones that results in weight gain, cold sensitivity, and reduced mental activity (Betts, et al., 2021).
Graves Disease
A condition marked by a disorder of the thyroid gland, resulting in hyperthyroidism (Betts, et al., 2021).
Diabetes Insipidus
A condition caused by a lack of or hyposecretion of the antidiuretic hormone (ADH). The condition can also be caused by the failure of the kidneys to respond to ADH (Betts, et al., 2021).
Diabetes (Mellitus)
A condition marked by a disorder of the pancreas, resulting in high levels of glucose in the blood (Betts, et al., 2021).
Medical Terms in Context
Medical Specialties and Procedures Related to the Endocrine System
Endocrinology is a specialization in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists—medical doctors who specialize in this field—are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes. Endocrine surgeons treat endocrine disease through the removal of the affected endocrine gland or tissue. Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones. In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases (Betts, et al., 2021).
- A thyroid specialist is an endocrinologist whose sub specialty is focused on the treatment and disorders of the thyroid gland such as hypothyroidism (too low secretion) and hyperthyroidism (too high secretion).
- A diabetes specialist is an endocrinologist whose sub specialty is focused on the treatment of diabetic conditions.
Procedures
Thyroid Scan
This procedure is designed to check the status of the thyroid. In a thyroid scan, a radioactive compound is given and localized in the thyroid gland (Giorgi & Cherney, 2018). To learn more about a thyroid scan visit HealthLine: Thyroid Scan.
Radioactive iodine uptake
Thyroid function evaluated by injecting radioactive iodine and then measuring how much is removed from the blood by the thyroid (MedlinePlus, 2020). To learn more about a radioactive iodine update test visit Medline Plus: Radioactive Iodine Uptake.
Blood Serum Testing
Blood testing to determine the concentration and the presence of various endocrine hormones in the blood. These tests include the following levels: calcium, cortisol, electrolytes, FSH, GH, glucose, insulin, parathyroid hormones, T3, T4, testosterone, and TSH. All of these can be evaluated with blood serum tests (Betts, et al., 2021).
Endocrine Surgical Procedures
Most of the surgeries and procedures performed with the endocrine system involve removal of a gland or an incision into the gland. Once an endocrine gland is surgically removed, due to a tumor or enlargement, hormone replacement treatment is required. Medication is required to artificially or synthetically replace the hormone produced by the gland and the function it regulates (Betts, et al., 2021).
Test Yourself
-
Query \(\PageIndex{7}
References
[CrashCourse]. (2015, June 22). Endocrine system, part 1 – glands & hormones: Crash course A&P #23 [Video]. YouTube. https://www.youtube.com/watch?v=eWHH9je2zG4
[CrashCourse]. (2015, June 29). Endocrine system, part 2 – hormone cascade: Crash course A&P #24 [Video]. YouTube. https://www.youtube.com/watch?v=eWHH9je2zG4
Giorgi, A., & Cherney, K. (2018). Thyroid scan . Healthline. https://www.healthline.com/health/thyroid-scan
MedlinePlus. (2020). Radioactive iodine uptake . US National Library of Medicine. https://medlineplus.gov/ency/article/003689.htm
Shurkin, J.N.(2013, August 2). Trouble sleeping? Go camping: Artificial light sources can negatively affect circadian rhythms, scientists say . Scientific American. https://www.scientificamerican.com/article/trouble-sleeping-go-campi/
Neuroscientifically Challenged. (2020, May 16). 2-Minute Neuroscience: M elatonin [Video]. YouTube. https://www.youtube.com/watch?v=SpaBMgZG9XQ
Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts, et al. and is used under a a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .


1: Essentials of Geography
Geography touches every aspect of our lives. At its simplest, geography is concerned with where something is at, why it's there, and how it relates to things around it. Geography influences where we live, affects our economic prosperity, has dictated the outcome of significant historical events, and shapes our local, regional, and global relationships with each other. This textbook focuses on physical geography and can answer many questions that you might have about the natural world and how it relates to your life. Ever wondered why present-day volcanoes occur on the west coast of the United States but not on the east coast? Why tornadoes seem to be unique to the United States? Why palm trees are found in Florida and pine trees in Maine? Where to go for a break from cold winter weather, or to escape a hot summer day? Physical geography can answer these questions, and more.
In this chapter you'll be introduced to the discipline of geography and what it means to study the Earth from a geographic perspective. You will become familiar with the array of tools geographers possess to investigate the Earth system. We'll conclude by looking at how geographers are well suited to address issues related to current trends in environmental change.
By the end of the chapter you should be able to:
- Explain why geographers describe their discipline as a spatial science and uniquely qualified to tackle issues related to environmental change.
- Construct a diagram showing how hypotheses are developed and become theories in physical geography.
-
Compare and contrast qualitative and quantitative map data.
Explain what a map projection is. - Choose the appropriate type and scale of map for its intended purpose.
- Use latitude and longitude to determine location.
- Explain how a global positioning system works.
- List and give examples of remote sensing techniques.
- Differentiate between standard time and daylight saving time.
- Explain how a GIS is used to solve problems in physical geography.
- Explain how models are used in physical geography.
- Calculate the mean and range to describe a set of data.


4.1: The Integumentary System
What do you think when you look at your skin in the mirror? Do you think about covering it with makeup, adding a tattoo, or maybe a body piercing? Or do you think about the fact that the skin belongs to one of the body’s most essential and dynamic systems: the integumentary system? The integumentary system refers to the skin and its accessory structures, and it is responsible for much more than simply lending to your outward appearance. In the adult human body, the skin makes up about 16 percent of body weight and covers an area of 1.5 to 2 m 2 . In fact, the skin and accessory structures are the largest organ system in the human body. As such, the skin protects your inner organs and it is in need of daily care and protection to maintain its health. This chapter will introduce the structure and functions of the integumentary system, as well as some of the diseases, disorders, and injuries that can affect this system.
Layers of the Skin
-
The Epidermis
- Stratum Basale
- Stratum Spinosum
- Stratum Granulosum
- Stratum Lucidum
- Stratum Corneum
-
Dermis
- Papillary Layer
- Reticular Layer
- Hypodermis
- Pigmentation
Although you may not typically think of the skin as an organ, it is in fact made of tissues that work together as a single structure to perform unique and critical functions. The skin and its accessory structures make up the integumentary system , which provides the body with overall protection. The skin is made of multiple layers of cells and tissues, which are held to underlying structures by connective tissue (Figure 4.2). The deeper layer of skin is well vascularized (has numerous blood vessels). It also has numerous sensory, and autonomic and sympathetic nerve fibers ensuring communication to and from the brain.
The skin consists of two main layers and a closely associated layer.
The Epidermis
The epidermis is composed of keratinized, stratified squamous epithelium. It is made of four or five layers of epithelial cells, depending on its location in the body. It does not have any blood vessels within it (i.e., it is avascular). Skin that has four layers of cells is referred to as “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin can be classified as thin skin. “Thick skin” is found only on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum (Figure 4.3).
The cells in all of the layers except the stratum basale are called keratinocytes. A keratinocyte is a cell that manufactures and stores the protein keratin. Keratin is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from the deeper layers (Figure 4.4).
Stratum Basale
The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane. A finger-like projection, or fold, known as the dermal papilla (plural = dermal papillae) is found in the superficial portion of the dermis. Dermal papillae increase the strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made (Figure 4.5).
The stratum basale is a single layer of cells primarily made of basal cells. A basal cell is a cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis. All of the keratinocytes are produced from this single layer of cells, which are constantly going through mitosis to produce new cells. As new cells are formed, the existing cells are pushed superficially away from the stratum basale. Two other cell types are found dispersed among the basal cells in the stratum basale. The first is a Merkel cell , which functions as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially abundant on the surfaces of the hands and feet. The second is a melanocyte , a cell that produces the pigment melanin. Melanin gives hair and skin its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.
In a growing fetus, fingerprints form where the cells of the stratum basale meet the papillae of the underlying dermal layer (papillary layer), resulting in the formation of the ridges on your fingers that you recognize as fingerprints. Fingerprints are unique to each individual and are used for forensic analyses because the patterns do not change with the growth and aging processes.
Stratum Spinosum
As the name suggests, the stratum spinosum is spiny in appearance due to the protruding cell processes that join the cells via a structure called a desmosome . The desmosomes interlock with each other and strengthen the bond between the cells. It is interesting to note that the “spiny” nature of this layer is an artifact of the staining process. Unstained epidermis samples do not exhibit this characteristic appearance. The stratum spinosum is composed of eight to 10 layers of keratinocytes, formed as a result of cell division in the stratum basale (Figure 4.6). Interspersed among the keratinocytes of this layer is a type of dendritic cell called the Langerhans cell , which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.
Stratum Granulosum
The stratum granulosum has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum. The cells (three to five layers deep) become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, and keratohyalin , which accumulates as lamellar granules within the cells (see Figure 4.5). These two proteins make up the bulk of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and cell membranes that will form the stratum lucidum, the stratum corneum, and the accessory structures of hair and nails.
Stratum Lucidum
The stratum lucidum is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is found only in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (see Figure 4.5). These cells are densely packed with eleiden , a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.e., lucid) appearance and provides a barrier to water.
Stratum Corneum
The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment (see Figure 4.5). The increased keratinization (also called cornification) of the cells in this layer gives it its name. There are usually 15 to 30 layers of cells in the stratum corneum. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum (or stratum lucidum in the case of the palms and soles of feet). The entire layer is replaced during a period of about 4 weeks. Cosmetic procedures, such as microdermabrasion, help remove some of the dry, upper layer and aim to keep the skin looking “fresh” and healthy.
Dermis
The dermis might be considered the “core” of the integumentary system (derma- = “skin”), as distinct from the epidermis (epi- = “upon” or “over”) and hypodermis (hypo- = “below”). It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts (Figure 4.7).
Papillary Layer
The papillary layer is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae (see Figure 4.7).  In addition, the papillary layer contains phagocytes, defensive cells that help fight bacteria or other infections that have breached the skin. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles.
Reticular Layer
Underlying the papillary layer is the much thicker reticular layer , composed of dense, irregular connective tissue. This layer is well vascularized and has a rich sensory and sympathetic nerve supply. The reticular layer appears reticulated (net-like) due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the skin, enabling movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. In addition, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.
Hypodermis
The hypodermis (also called the subcutaneous layer or superficial fascia) is a layer directly below the dermis and serves to connect the skin to the underlying fascia (fibrous tissue) of the bones and muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.
Everyday Connection: Lipid Storage
The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight under control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes. This stored fat can serve as an energy reserve, insulate the body to prevent heat loss, and act as a cushion to protect underlying structures from trauma.
Where the fat is deposited and accumulates within the hypodermis depends on hormones (testosterone, estrogen, insulin, glucagon, leptin, and others), as well as genetic factors. Fat distribution changes as our bodies mature and age. Men tend to accumulate fat in different areas (neck, arms, lower back, and abdomen) than do women (breasts, hips, thighs, and buttocks). The body mass index (BMI) is often used as a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight (mass) to height. Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit.
In many animals, there is a pattern of storing excess calories as fat to be used in times when food is not readily available. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people. Although periodic accumulation of excess fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now becoming chronic and considered a major health threat. Recent studies indicate that a distressing percentage of our population is overweight and/or clinically obese. Not only is this a problem for the individuals affected, but it also has a severe impact on our healthcare system. Changes in lifestyle, specifically in diet and exercise, are the best ways to control body fat accumulation, especially when it reaches levels that increase the risk of heart disease and diabetes.
Pigmentation
The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome (Figure 4.8).
Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color. Dark-skinned individuals produce more melanin than those with pale skin. Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid, a nutrient necessary for our health and well-being. In contrast, too much melanin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption. Thus, the amount of melanin present in our skin is dependent on a balance between available sunlight and folic acid destruction, and protection from UV radiation and vitamin D production.
It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially. Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.
Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin, and in severe cases, can cause sufficient DNA damage to result in skin cancer. When there is an irregular accumulation of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although most are benign, they should be monitored for changes that might indicate the presence of cancer (Figure 4.9).
Disorders of the Integumentary System
The first thing a clinician sees is the skin, and so the examination of the skin should be part of any thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs. Although neither is fatal, it would be hard to claim that they are benign, at least to the individuals so afflicted.
Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. The defect is primarily due to the inability of melanocytes to produce melanin. Individuals with albinism tend to appear white or very pale due to the lack of melanin in their skin and hair. Recall that melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall. Treatment of this disorder usually involves addressing the symptoms, such as limiting UV light exposure to the skin and eyes. In vitiligo , the melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction. This leads to a loss of color in patches (Figure 4.10). Neither albinism nor vitiligo directly affects the lifespan of an individual.
Other changes in the appearance of skin coloration can be indicative of diseases associated with other body systems. Liver disease or liver cancer can cause the accumulation of bile and the yellow pigment bilirubin, leading to the skin appearing yellow or jaundiced ( jaune is the French word for “yellow”). Tumors of the pituitary gland can result in the secretion of large amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the skin. Similarly, Addison’s disease can stimulate the release of excess amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze color. A sudden drop in oxygenation can affect skin color, causing the skin to initially turn ashen (white). With a prolonged reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the blood, making the skin appear blue, a condition referred to as cyanosis ( kyanos is the Greek word for “blue”). This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart attack. However, in these cases the effect on skin color has nothing do with the skin’s pigmentation.
Contributors and Attributions
- Chapter 5. Authored by : OpenStax College. Provided by : Rice University. Located at : openstaxcollege.org/files/textbook_version/low_res_pdf/13/col11496-lr.pdf. Project : Anatomy & Physiology. License : CC BY: Attribution . License Terms : Download for free at cnx.org/content/col11496/latest/.


1.8.1: What is in the Food You Eat?
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STOP: Choose a Food
STOP! Before you go any further in this chapter, think about something you want to eat today.
Maybe you want to eat a burrito, or a burger, a salad, some soup, or maybe spaghetti?
- Choose something you want to eat.
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Find the nutrition label for the food you chose.
- If the food you chose is something you bought at the grocery store it likely has a food label, or you may be able to view the food label through the grocery stores website. For example, Raley’s grocery store provides images of the product including the food label (check out the Mott's Applesauce label on the Raley's website .
- If you would like to get something from a restaurant you can usually find the food label online by either going to the restaurants website or searching for the item using online databases like CalorieKing , MyFitnessPal, Nutritionvalue.org , or try Food Data Central.
- You might not be able to find the exact food item, do your best to find something close.
- Take a moment to review the Interactive Nutrition Facts Label website to familiarize yourself with the information on the label.
- Keep the nutrition information with you as you read this chapter!
Understanding Food Labels
Food labels are a tool to help us understand more about the foods we choose to eat. By understanding the nutrition of our food we can make better informed choices that contribute to our wellness. Nutrition labels have changed over time based on updated scientific information, new nutrition research, and input from the public. The most recent Food Label requirements were launched in 2016. Interested in seeing how the food label changed in 2016? Check out this comparison of the old and new label.
Ultimately, by having a standard way to show nutrition facts we are able to easily and quickly compare food choices to make informed decisions about the fuel we put into our body. Just like a car needs fuel to run, our bodies need food to provide us with energy.
Try this Nutrition Facts Pre-Test to see how much you already know about nutrition.
Nutrition Facts Pre-Test
Servings
At the top of the food label you should see information about the number of servings and the size of the servings. The data provided on the food label is based on the serving size listed on the label. It is important to first identify how many servings you are consuming. If you are consuming two servings then you will need to multiple the data on the nutrition label by two.
The serving size on a nutrition label is based on the amount of food that is typically eaten at one time and is not a recommendation of how much to eat. Many people found that that servings sizes on the old food labels, prior to 2016, were unrealistic. For example, a 12 ounce can of Coke used to be 1.5 servings and has now been adjusted to being 1 serving.
Your food label: Servings
Evaluate the serving size and number of servings on your food label. How many servings do you eat? Did the serving size surprise you?
Calories
The next item on the food label is the amount of calories in the food. Calories refer to how much energy the food provides. Our bodies need energy (calories) to keep us alive and our organs functioning normally. When we eat and drink, we put energy (calories) into our bodies, and we use that energy in many ways, for example to keep our heart beating, to breathe, to digest food, to move throughout the day, to exercise, or to participate in sports.
Although the term calorie is the term commonly used, it actually refers to a kilocalorie. One (1) kilocalorie is the same as one (1) calorie (upper case C). In technical terms, a kilocalorie is the amount of heat required to raise the temperature of 1 kilogram of water one degree celsius.
When looking at the amount of calories on your food label, it is important to recognize the amount of calories in the food you are eating compared to how many calories you should consume each day. Look at the very bottom of the food label and you should see an asterisk with a statement similar to “2,000 calories a day is used as a general guide for nutrition advice.” Although 2,000 calories is used, the total number of calories you need each day varies depending on a number of factors including your age, sex, height, weight, level of physical activity, and pregnancy or lactation status. The total number of calories you should consume may also be determined by whether would like to lose, maintain, or gain weight affects how many calories should be consumed.
Use the MyPlate Plan to calculate how many calories you should consume each day.
As you look at the calories on your food label compared to your recommended daily caloric intake, be mindful of your energy balance. Energy balance refers to the balance of calories consumed through eating and drinking compared to calories burned through daily activities and physical activity. If we consume more calories (energy) than we use throughout the day, we store that energy for use at a later time as body fat. If we consume less calories (energy) than we use throughout the day, we utilize our stored body fat for energy.
Your Food Label: Calories
Evaluate the calories on your food label. How many calories does it contain? Is this considered a low or high calorie food? How much does this food item contribute to the total amount of calories you should consumer each day?
Use the MyPlate Plan to calculate how many calories you should consume each day and remember, if you are eating more than one serving you need to multiply the number of calories on the food label to see the total amount of calories consumed!
Nutrients
It is now time to learn about what your food is made up of, meaning what are the nutrients provided to your body when you consume the food. Nutrients are commonly divided into two categories, macronutrients and micronutrients. On the food label, the macronutrients are listed first followed by the micronutrients.
- Macronutrients: Carbohydrates, fats, proteins, and water.
- Micronutrients: Vitamins and minerals
When reviewing your food labels, you might notice some variation in the nutrients listed. The label must include total fat, saturated fat, trans fat, cholesterol, sodium, total carbohydrate, dietary fiber, total sugars, added sugars, protein, vitamin D, calcium, iron, and potassium. The label might also include monounsaturated fat, polyunsaturated fat, soluble fiber, insoluble fiber, sugar alcohols, vitamins (biotin, choline, folate, niacin, pantothenic acid, riboflavin, thiamin, and vitamins A, B6, B12, C, E, and K) and minerals (chloride, chromium, copper, iodine, magnesium, manganese, molybdenum, phosphorus, selenium, and zinc).
Some nutrients are essential and some are considered nonessential. Essential nutrients are nutrients that must be consumed through the foods we eat, the body cannot synthesize the nutrients. Nonessential nutrients are nutrients that the body can synthesize, so they do not need to be consumed from food.
Three essential nutrients provide energy (calories), these are fats, carbohydrates, proteins. Alcohol also provides energy (calories), but is not considered an essential nutrient. The other nutrients do not directly provide calories, but they do aid in the production and utilization of energy by the body.
% Daily Value
For each nutrient, you will see the % Daily Value (%DV). This percentage is very helpful for understanding how the food contributes to the recommended total amount you should consume. it is important to note that the % Daily Value does not add up to 100%, it is not telling you the breakdown of the item, but rather how much the food item contributes to what you should consume each day. For example if you notice that the %DV for sodium is 50% this would mean the food you are eating contributes to half of your daily total for sodium. %DV makes it easy for you to compare foods.
An easy way to use %DV is to determine if a serving of the food is high or low in an individual nutrient. As a general guide:
- 5% DV or less of a nutrient per serving is considered low.
- 20% DV or more of a nutrient per serving is considered high.
The %DV for each nutrient is calculated by comparing the nutrient to the Dietary Reference Intakes (DRIs) . The DRIs represent the most current scientific knowledge on nutrient needs of healthy populations. Some DRI’s are listed as a specific amounts, such as number of grams, and others are based on the energy they provide in relation to your entire diet. The Acceptable Macronutrient Distribution Ranges (AMDRs) helps you to determine the amount of fats, proteins, and carbohydrates you should consume based on a percentage of your total calories.
Acceptable Macronutrient Distribution Ranges (AMDRs)
- Carbohydrates: Consume 45-65% of your calories from carbohydrates
- Fats: Consume 20-35% of your calories from fats
- Protein: Consume 10-35% of your calories from protein
Fat (lipids) and Cholesterol
The first nutrients on the food label are fats and cholesterol. Fats are also called lipids. We need both fats and cholesterol, however too much of both can negatively impact health.
We need fats in our diet for many reasons. First, fats provide us with energy.  Fat is considered a high-energy nutrient. Fat also provides us with long term energy storage, so if we do not consume enough energy our body can burn out stored body fat. Our body needs fat for other basic bodily function such as the synthesis of cell membranes, for growth and development, healthy skin and hair, blood clotting, nervous system function, reproduction, immune response, and to absorb important fat-soluble vitamins (vitamins A, D, E, and K). Fats also make food taste really good and help you feel full. Fat is found in foods from both plants and animals.