17.11: Organs with Secondary Endocrine Functions
By the end of this section, you will be able to:
- Identify the organs with a secondary endocrine function, the hormone they produce, and its effects
In your study of anatomy and physiology, you have already encountered a few of the many organs of the body that have secondary endocrine functions. Here, you will learn about the hormone-producing activities of the heart, gastrointestinal tract, kidneys, skeleton, adipose tissue, skin, and thymus.
Heart
When the body experiences an increase in blood volume or pressure, the cells of the heart’s atrial wall stretch. In response, specialized cells in the wall of the atria produce and secrete the peptide hormone atrial natriuretic peptide (ANP) . ANP signals the kidneys to reduce sodium reabsorption, thereby decreasing the amount of water reabsorbed from the urine filtrate and reducing blood volume. Other actions of ANP include the inhibition of renin secretion, thus inhibition of the renin-angiotensin-aldosterone system (RAAS) and vasodilation.
Gastrointestinal Tract
The endocrine cells of the GI tract are located in the mucosa of the stomach and small intestine. Some of these hormones are secreted in response to eating a meal and aid in digestion. An example of a hormone secreted by the stomach cells is gastrin, a peptide hormone secreted in response to stomach distention that stimulates the release of hydrochloric acid. Secretin is a peptide hormone secreted by the small intestine as acidic chyme (partially digested food and fluid) moves from the stomach. It stimulates the release of bicarbonate from the pancreas, which buffers the acidic chyme, and inhibits the further secretion of hydrochloric acid by the stomach. Cholecystokinin (CCK) is another peptide hormone released from the small intestine. It promotes the secretion of pancreatic enzymes and the release of bile from the gallbladder, both of which facilitate digestion. Other hormones produced by the intestinal cells aid in glucose metabolism, such as by stimulating the pancreatic beta cells to secrete insulin, reducing glucagon secretion from the alpha cells, or enhancing cellular sensitivity to insulin.
Kidneys
The kidneys participate in several complex endocrine pathways and produce certain hormones. A decline in blood flow to the kidneys stimulates them to release the enzyme renin, triggering the renin-angiotensin-aldosterone (RAAS) system, and stimulating the reabsorption of sodium and water. The reabsorption increases blood flow and blood pressure. The kidneys also play a role in regulating blood calcium levels through the production of calcitriol from vitamin D 3 , which is released in response to the secretion of parathyroid hormone (PTH). In addition, the kidneys produce the hormone erythropoietin (EPO) in response to low oxygen levels. EPO stimulates the production of red blood cells (erythrocytes) in the bone marrow, thereby increasing oxygen delivery to tissues. You may have heard of EPO as a performance-enhancing drug (in a synthetic form).
Skeleton
Although bone has long been recognized as a target for hormones, only recently have researchers recognized that the skeleton itself produces at least two hormones. Fibroblast growth factor 23 (FGF23) is produced by bone cells in response to increased blood levels of vitamin D 3 or phosphate. It triggers the kidneys to inhibit the formation of calcitriol from vitamin D 3 and to increase phosphorus excretion. Osteocalcin, produced by osteoblasts, stimulates the pancreatic beta cells to increase insulin production. It also acts on peripheral tissues to increase their sensitivity to insulin and their utilization of glucose.
Adipose Tissue
Adipose tissue produces and secretes several hormones involved in lipid metabolism and storage. One important example is leptin , a protein manufactured by adipose cells that circulates in amounts directly proportional to levels of body fat. Leptin is released in response to food consumption and acts by binding to brain neurons involved in energy intake and expenditure. Binding of leptin produces a feeling of satiety after a meal, thereby reducing appetite. It also appears that the binding of leptin to brain receptors triggers the sympathetic nervous system to regulate bone metabolism, increasing deposition of cortical bone. Adiponectin—another hormone synthesized by adipose cells—appears to reduce cellular insulin resistance and to protect blood vessels from inflammation and atherosclerosis. Its levels are lower in people who are obese, and rise following weight loss.
Skin
The skin functions as an endocrine organ in the production of the inactive form of vitamin D 3 , cholecalciferol. When cholesterol present in the epidermis is exposed to ultraviolet radiation, it is converted to cholecalciferol, which then enters the blood. In the liver, cholecalciferol is converted to an intermediate that travels to the kidneys and is further converted to calcitriol, the active form of vitamin D 3 . Vitamin D is important in a variety of physiological processes, including intestinal calcium absorption and immune system function. In some studies, low levels of vitamin D have been associated with increased risks of cancer, severe asthma, and multiple sclerosis. Vitamin D deficiency in children causes rickets, and in adults, osteomalacia—both of which are characterized by bone deterioration.
Thymus
The thymus is an organ of the immune system that is larger and more active during infancy and early childhood, and begins to atrophy as we age. Its endocrine function is the production of a group of hormones called thymosins that contribute to the development and differentiation of T lymphocytes, which are immune cells. Although the role of thymosins is not yet well understood, it is clear that they contribute to the immune response. Thymosins have been found in tissues other than the thymus and have a wide variety of functions, so the thymosins cannot be strictly categorized as thymic hormones.
Liver
The liver is responsible for secreting at least four important hormones or hormone precursors: insulin-like growth factor (somatomedin), angiotensinogen, thrombopoietin, and hepcidin. Insulin-like growth factor-1 is the immediate stimulus for growth in the body, especially of the bones. Angiotensinogen is the precursor to angiotensin, mentioned earlier, which increases blood pressure. Thrombopoietin stimulates the production of the blood’s platelets. Hepcidins block the release of iron from cells in the body, helping to regulate iron homeostasis in our body fluids. The major hormones of these other organs are summarized in Table \(\PageIndex{1}\).
| Organ | Major hormones | Effects |
|---|---|---|
| Heart | Atrial natriuretic peptide (ANP) | Reduces blood volume, blood pressure, and Na + concentration |
| Gastrointestinal tract | Gastrin, secretin, and cholecystokinin | Aid digestion of food and buffering of stomach acids |
| Gastrointestinal tract | Glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1) | Stimulate beta cells of the pancreas to release insulin |
| Kidneys | Renin | Stimulates release of aldosterone |
| Kidneys | Calcitriol | Aids in the absorption of Ca 2 + |
| Kidneys | Erythropoietin | Triggers the formation of red blood cells in the bone marrow |
| Skeleton | FGF23 | Inhibits production of calcitriol and increases phosphate excretion |
| Skeleton | Osteocalcin | Increases insulin production |
| Adipose tissue | Leptin | Promotes satiety signals in the brain |
| Adipose tissue | Adiponectin | Reduces insulin resistance |
| Skin | Cholecalciferol | Modified to form vitamin D |
| Thymus (and other organs) | Thymosins | Among other things, aids in the development of T lymphocytes of the immune system |
| Liver | Insulin-like growth factor-1 | Stimulates bodily growth |
| Liver | Angiotensinogen | Raises blood pressure |
| Liver | Thrombopoietin | Causes increase in platelets |
| Liver | Hepcidin | Blocks release of iron into body fluids |


11.11: Essay Questions
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51 .
Explain how cultural factors can shape the experience of emerging adulthood, particularly in the process of identity formation. Consider the differences between individualistic and collectivistic cultures, as well as the impact of globalization on cultural values and identity exploration. Provide examples to illustrate how culture can influence the challenges and opportunities faced during this period.
52 .
Discuss how socioeconomic status (SES) and cultural context influence physical health during young adulthood. Consider how factors such as access to resources, social support, and health-related beliefs may shape an individual’s ability to maintain healthy habits. Reflect on the potential long-term consequences of these influences on an individual’s health as they transition from early to later adulthood.
53 .
Sleep and stress management are two critical factors for maintaining physical and mental health during early adulthood. In your essay, discuss how sleep habits and stress management techniques during young adulthood influence long-term health outcomes. Reflect on both the immediate and lasting effects of poor sleep and chronic stress, and propose strategies for improving these areas of health as young adults transition to later adulthood.
54 .
 In this essay, examine how social and cultural factors, such as community acceptance, family support, and media portrayals, influence this process.  Consider how individuals navigate these challenges and how the acceptance or rejection they encounter shapes their overall well-being and identity formation.
55 .
In early adulthood, cognitive development extends beyond Piaget’s formal operational stage, evolving into postformal thought. This type of thinking allows for flexibility, practicality, and an understanding that life’s problems often have multiple solutions. Reflect on your own experiences during early adulthood (or the period you are currently navigating). Provide an example of when you used flexible thinking, practical problem-solving, and multiple solutions thinking. Explain how each type of thinking helped you make decisions or navigate challenges in your life.
56 .
Reflect on the challenges and opportunities young adults face in preparing for work and career. How do societal, economic, and personal factors influence career decisions, and how might these factors affect the success or satisfaction in the chosen career? Provide examples from your own experiences or observations.
57 .
Discuss the role of formal and informal educational opportunities in early adulthood. How do these learning experiences impact personal growth and career advancement? Provide specific examples of how formal education (such as college) or informal education (such as internships or volunteering) has shaped your personal or professional development.


1.4.2: Geographical Zones
Natural systems of climate, vegetation, and soil change substantially as one travels from the equator to the pole due largely to the latitudinal variation in energy input to the earth system. The early Greek scholar Aristotle was the first to divide the Earth into zones based on climate. His "torrid zone", thought to be too hot for human habitation, lay between 23.5 o N and 23.5 o S. Aristotle thought that the "temperate zones" between 23.5 o N - 66.5 o N and 23.5 o S - 66.5 o S were the only livable zones. From the arctic (66.5 N) and and antarctic circles (66.5 S) to the the poles (90 N and S) were the uninhabitable "frigid zones".
Geographers continue to use latitudinal variation of climate characteristics as a way of dividing the Earth into fairly homogeneous geographical zones. These zones are:
Equatorial: 10
o
N - 10
o
S
Tropical: 10
o
N - 25
o
N and 10
o
S - 25
o
S
Subtropical: 25
o
N - 35
o
N and 25
o
S - 35
o
S
Midlatitude: 35
o
N - 55
o
N and 35
o
S - 55
o
S
Subarctic: 55
o
N - 60
o
N
Subantarctic: 55
o
S - 60
o
S
Arctic: 60
o
N - 75
o
N
Antarctic: 60
o
S - 75
o
S
North Polar: 75
o
N - 90
o
N
South Polar: 75
o
S - 90
o
S
The equatorial zone is characterized by warm temperatures and nearly uniform day length throughout the year. The boundary of the tropical zone lies close to the Tropic of Cancer (23.5 o N) and Capricorn (23.5 o S), the latitudinal limit where the Sun is directly over head at noon at different times of the year. The subtropical zone includes Aristotle's home of Greece, and seasonal changes in temperature become more pronounced. The temperate midlatitude zone is noted for is variable weather conditions. Large annual swings in temperature are characteristic of the subarctic and subantarctic zone where extensive areas of cold air form during winter and milder conditions prevail during summer. The coldest zones are the Arctic and Antarctic, where the Sun never rises above the horizon for several months at a time. Much of the light that does reach the surface is reflected off the light colored surfaces of the North (sea ice) and South (mostly glacial ice) poles. The coldest zones are the North and South Polar. Like the Arctic and Antarctic Zones, the Sun never rises above the horizon for many months of the year. The coldest temperatures are near the South Pole, far from any moderating influence of an ocean and the little light that does make it to the surface is reflected from glacier ice.


5.1: Primer on Quantum Theory
Part 1: Particles and waves
Q1. What is a particle?
A particle is a discrete unit of matter having the attributes of mass , momentum (and thus kinetic energy ) and optionally of electric charge .
Q2. What is a wave?
A wave is a periodic variation of some quantity as a function of location or time. For example, the wave motion of a vibrating guitar string is defined by the displacement of the string from its center as a function of distance along the string. A sound wave consists of variations in the pressure with location.
A wave is characterized by its wavelength \( λ\) (lambda) and frequency \(\nu\ ) (nu), which are connected by the relation
\[ \lmabda =\dfrac{u}{\nu}
in which u is the velocity of propagation of the disturbance in the medium.
The velocity of sound in the air is 330 m s –1 . What is the wavelength of A440 on the piano keyboard?
Solution
\[ \lambda =\dfrac{330\, m S^{-1}}{440 \,s^{-1}} = 0.75\,m\]
Two other attributes of waves are the amplitude (the height of the wave crests with respect to the base line) and the phase , which measures the position of a crest with respect to some fixed point. The square of the amplitude gives the intensity of the wave: the energy transmitted per unit time).
A unique property of waves is their ability to combine constructively or destructively, depending on the relative phases of the combining waves.
Q3. What is light?
Phrasing the question in this way reflects the deterministic mode of Western thought which assumes that something cannot "be" two quite different things at the same time. The short response to this question is that all we know about light (or anything else, for that matter) are the results of experiments, and that some kinds of experiments show that light behaves like particles , and that other experiments reveal light to have the properties of waves .
Q4. What is the wave theory of light?
In the early 19th century, the English scientist Thomas Young carried out the famous two-slit experiment which demonstrated that a beam of light, when split into two beams and then recombined, will show interference effects that can only be explained by assuming that light is a wavelike disturbance. By 1820, Augustin Fresnel had put this theory on a sound mathematical basis, but the exact nature of the waves remained unclear until the 1860's when James Clerk Maxwell developed his electromagnetic theory .
From the laws of electromagnetic induction that were discovered in the period 1820-1830 by Hans Christien Oersted and Michael Faraday, it was known that a moving electric charge gives rise to a magnetic field, and that a changing magnetic field can induce electric charges to move. Maxwell showed theoretically that when an electric charge is accelerated (by being made to oscillate within a piece of wire, for example), electrical energy will be lost, and an equivalent amount of energy is radiated into space, spreading out as a series of waves extending in all directions.
What is "waving" in electromagnetic radiation? According to Maxwell, it is the strengths of the electric and magnetic fields as they travel through space. The two fields are oriented at right angles to each other and to the direction of travel.
As the electric field changes, it induces a magnetic field, which then induces a new electric field, etc., allowing the wave to propagate itself through space
These waves consist of periodic variations in the electrostatic and electromagnetic field strengths. These variations occur at right angles to each other. Each electrostatic component of the wave induces a magnetic component, which then creates a new electrostatic component, so that the wave, once formed, continues to propagate through space, essentially feeding on itself. In one of the most brilliant mathematical developments in the history of science, Maxwell expounded a detailed theory, and even showed that these waves should travel at about 3E8 m s –1 , a value which experimental observations had shown corresponded to the speed of light. In 1887, the German physicist Heinrich Hertz demonstrated that an oscillating electric charge (in what was in essence the world's first radio transmitting antenna) actually does produce electromagnetic radiation just as Maxwell had predicted, and that these waves behave exactly like light.
It is now understood that light is electromagnetic radiation that falls within a range of wavelengths that can be perceived by the eye. The entire electromagnetic spectrum runs from radio waves at the long-wavelength end, through heat, light, X-rays, and to gamma radiation.
Part 2: Quantum theory of light
Q5. How did the quantum theory of light come about?
It did not arise from any attempt to explain the behavior of light itself; by 1890 it was generally accepted that the electromagnetic theory could explain all of the properties of light that were then known.
Certain aspects of the interaction between light and matter that were observed during the next decade proved rather troublesome, however. The relation between the temperature of an object and the peak wavelength emitted by it was established empirically by Wilhelm Wien in 1893. This put on a quantitative basis what everyone knows: the hotter the object, the "bluer" the light it emits.
Q6. What is black body radiation?
All objects above the temperature of absolute zero emit electromagnetic radiation consisting of a broad range of wavelengths described by a distribution curve whose peak wavelength l at absolute temperature T for a "perfect radiator" known as a black body is given by Wien's law.
\[ \lambda_{peak} (cm) = 0.0029\,m\,K\]
At ordinary temperatures this radiation is entirely in the infrared region of the spectrum, but as the temperature rises above about 1000K, more energy is emitted in the visible wavelength region and the object begins to glow, first with red light, and then shifting toward the blue as the temperature is increased.
This type of radiation has two important characteristics. First, the spectrum is a continuous one, meaning that all wavelengths are emitted, although with intensities that vary smoothly with wavelength. The other curious property of black body radiation is that it is independent of the composition of the object; all that is important is the temperature.
Q7. How did black body radiation lead to quantum physics?
Black body radiation, like all electromagnetic radiation, must originate from oscillations of electric charges which in this case were assumed to be the electrons within the atoms of an object acting somewhat as miniature Hertzian oscillators. It was presumed that since all wavelengths seemed to be present in the continuous spectrum of a glowing body, these tiny oscillators could send or receive any portion of their total energy. However, all attempts to predict the actual shape of the emission spectrum of a glowing object on the basis of classical physical theory proved futile.
In 1900, the great German physicist Max Planck (who earlier in the same year had worked out an empirical formula giving the detailed shape of the black body emission spectrum) showed that the shape of the observed spectrum could be exactly predicted if the energies emitted or absorbed by each oscillator were restricted to integral values of hν, where ν ("nu") is the frequency and h is a constant 6.626E–34 J s which we now know as Planck's Constant . The allowable energies of each oscillator are quantized, but the emission spectrum of the body remains continuous because of differences in frequency among the uncountable numbers of oscillators it contains.This modification of classical theory, the first use of the quantum concept, was as unprecedented as it was simple, and it set the stage for the development of modern quantum physics.
Q8. What is the photoelectric effect?
Shortly after J.J. Thompson's experiments led to the identification of the elementary charged particles we now know as electrons, it was discovered that the illumination of a metallic surface by light can cause electrons to be emitted from the surface. This phenomenon, the photoelectric effect, is studied by illuminating one of two metal plates in an evacuated tube.
The kinetic energy of the photoelectrons causes them to move to the opposite electrode, thus completing the circuit and producing a measurable current. However, if an opposing potential (the retarding potential ) is imposed between the two plates, the kinetic energy can be reduced to zero so that the electron current is stopped. By observing the value of the retarding potential V r , the kinetic energy of the photoelectrons can be calculated from the electron charge e , its mass m and the frequency of the incident light:
These two diagrams are taken from a web page by Joseph Alward of the University of the Pacific.
The plot at the right shows how the kinetic energy of the photoelectrons falls to zero at the critical wavelength corresponding to frequency f 0 .
Q9. What peculiarity of the photoelectric effect led to the photon?
Although the number of electrons ejected from the metal surface per second depends on the intensity of the light, as expected, the kinetic energies of these electrons (as determined by measuring the retarding potential needed to stop them) does not, and this was definitely not expected. Just as a more intense physical disturbance will produce higher energy waves on the surface of the ocean, it was supposed that a more intense light beam would confer greater energy on the photoelectrons. But what was found, to everyone's surprise, is that the photoelectron energy is controlled by the wavelength of the light, and that there is a critical wavelength below which no photoelectrons are emitted at all.
Albert Einstein quickly saw that if the kinetic energy of the photoelectrons depends on the wavelength of the light, then so must its energy. Further, if Planck was correct in supposing that energy must be exchanged in packets restricted to certain values, then light must similarly be organized into energy packets. But a light ray consists of electric and magnetic fields that spread out in a uniform, continuous manner; how can a continuously-varying wave front exchange energy in discrete amounts? Einstein's answer was that the energy contained in each packet of the light must be concentrated into a tiny region of the wave front. This is tantamount to saying that light has the nature of a quantized particle whose energy is given by the product of Planck's constant and the frequency:
Einstein's publication of this explanation in 1905 led to the rapid acceptance of Planck's idea of energy quantization, which had not previously attracted much support from the physics community of the time. It is interesting to note, however, that this did not make Planck happy at all. Planck, ever the conservative, had been reluctant to accept that his own quantized-energy hypothesis was much more than an artifice to explain black-body radiation; to extend it to light seemed an absurdity that would negate the well-established electromagnetic theory and would set science back to the time before Maxwell.
Q10. Where does relativity come in?
Einstein's special theory of relativity arose from his attempt to understand why the laws of physics that describe the current induced in a fixed conductor when a magnet moves past it are not formulated in the same way as the ones that describe the magnetic field produced by a moving conductor. The details of this development are not relevant to our immediate purpose, but some of the conclusions that this line of thinking led to very definitely are. Einstein showed that the velocity of light, unlike that of a material body, has the same value no matter what velocity the observer has. Further, the mass of any material object, which had previously been regarded as an absolute, is itself a function of the velocity of the body relative to that of the observer (hence "relativity"), the relation being given by
in which m o is the rest mass of the particle, v is its velocity with respect to the observer, and c is the velocity of light.
According to this formula, the mass of an object increases without limit as the velocity approaches that of light. Where does the increased mass come from? Einstein's answer was that the increased mass is that of the kinetic energy of the object; that is, energy itself has mass, so that mass and energy are equivalent according to the famous formula
The only particle that can move at the velocity of light is the photon itself, due to its zero rest mass.
Q11. Can the mass-less photon have momentum?
Although the photon has no rest mass, its energy, given by , confers upon it an effective mass of
and a momentum of
Q12. If waves can be particles, can particles be waves?
In 1924, the French physicist Louis de Broglie proposed (in his doctoral thesis) that just as light possesses particle-like properties, so should particles of matter exhibit a wave-like character. Within two years this hypothesis had been confirmed experimentally by observing the diffraction (a wave interference effect) produced by a beam of electrons as they were scattered by the row of atoms at the surface of a metal.
deBroglie showed that the wavelength of a particle is inversely proportional to its momentum:
Notice that the wavelength of a stationary particle is infinitely large, while that of a particle of large mass approaches zero. For most practical purposes, the only particle of interest to chemistry that is sufficiently small to exhibit wavelike behavior is the electron (mass 9.11E31 kg).
Q13. Exactly what is it that is "waving"?
We pointed out earlier that a wave is a change that varies with location in a periodic, repeating way. What kind of a change do the crests and hollows of a "matter wave" trace out? The answer is that the wave represents the value of a quantity whose square is a measure of the probability of finding the particle in that particular location. In other words, what is "waving" is the value of a mathematical probability function .
Q14. What is the uncertainty principle?
In 1927, Werner Heisenberg proposed that certain pairs of properties of a particle cannot simultaneously have exact values. In particular, the position and the momentum of a particle have associated with them uncertainties x and p given by
As with the de Broglie particle wavelength, this has practical consequences only for electrons and other particles of very small mass. It is very important to understand that these "uncertainties" are not merely limitations related to experimental error or observational technique, but instead they express an underlying fact that Nature does not allow a particle to possess definite values of position and momentum at the same time. This principle (which would be better described by the term "indeterminacy" than "uncertainty") has been thoroughly verified and has far-reaching practical consequences which extend to chemical bonding and molecular structure.
Q15. Is the uncertainty principle consistent with particle waves?
Yes; either one really implies the other. Consider the following two limiting cases: · A particle whose velocity is known to within a very small uncertainty will have a sharply-defined energy (because its kinetic energy is known) which can be represented by a probability wave having a single, sharply-defined frequency. A "monochromatic" wave of this kind must extend infinitely in space:
But if the peaks of the wave represent locations at which the particle is most likely to manifest itself, we are forced to the conclusion that it can "be" virtually anywhere, since the number of such peaks is infinite! Now think of the opposite extreme: a particle whose location is closely known. Such a particle would be described by a short wave train having only a single peak, the smaller the uncertainty in position, the more narrow the peak.
To help you see how waveforms of different wavelength combine, two such combinations are shown below:
It is apparent that as more waves of different frequency are mixed, the regions in which they add constructively diminish in extent. The extreme case would be a wave train in which destructive interference occurs at all locations except one, resulting in a single pulse:
Is such a wave possible, and if so, what is its wavelength? Such a wave is possible, but only as the sum (interference) of other waves whose wavelengths are all slightly different. Each component wave possesses its own energy (momentum), and adds that value to the range of momenta carried by the particle, thus increasing the uncertainty δ p . In the extreme case of a quantum particle whose location is known exactly, the probability wavelet would have zero width which could be achieved only by combining waves of all wavelengths-- an infinite number of wavelengths, and thus an infinite range of momentum dp and thus kinetic energy.
Q16. Are they particles or are they waves?
Suppose we direct a beam of photons (or electrons; the experiment works with both) toward a piece of metal having a narrow opening. On the other side there are two more openings, or slits. Finally the particles impinge on a photographic plate or some other recording device. Taking into account their wavelike character, we would expect the probability waves to produce an interference pattern of the kind that is well known for sound and light waves, and this is exactly what is observed; the plate records a series of alternating dark and light bands, thus demonstrating beyond doubt that electrons and light have the character of waves.
Now let us reduce the intensity of the light so that only one photon at a time passes through the apparatus (it is experimentally possible to count single photons, so this is a practical experiment). Each photon passes through the first slit, and then through one or the other of the second set of slits, eventually striking the photographic film where it creates a tiny dot. If we develop the film after a sufficient number of photons have passed through, we find the very same interference pattern we obtained previously.
There is something strange here. Each photon, acting as a particle, must pass through one or the other of the pair of slits, so we would expect to get only two groups of spots on the film, each opposite one of the two slits. Instead, it appears that the each particle, on passing through one slit, "knows" about the other, and adjusts its final trajectory so as to build up a wavelike interference pattern.
It gets even stranger: suppose that we set up a detector to determine which slit a photon is heading for, and then block off the other slit with a shutter. We find that the photon sails straight through the open slit and onto the film without trying to create any kind of an interference pattern. Apparently, any attempt to observe the photon as a discrete particle causes it to behave like one.
The only conclusion possible is that quantum particles have no well defined paths; each photon (or electron) seems to have an infinity of paths which thread their way through space, seeking out and collecting information about all possible routes, and then adjusting its behavior so that its final trajectory, when combined with that of others, produces the same overall effect that we would see from a train of waves of wavelength λ= h/mv.
Part 3: Electrons in atoms
Q17. What are line spectra?
We have already seen that a glowing body (or actually, any body whose temperature is above absolute zero) emits and absorbs radiation of all wavelength in a continuous spectrum . In striking contrast is the spectrum of light produced when certain substances are volatilized in a flame, or when an electric discharge is passed through a tube containing gaseous atoms of an element. The light emitted by such sources consists entirely of discrete wavelengths. This kind of emission is known as a discrete spectrum or line spectrum (the "lines" that appear on photographic images of the spectrum are really images of the slit through which the light passes before being dispersed by the prism in the spectrograph).
Every element has its own line spectrum which serves as a sensitive and useful tool for detecting the presence and relative abundance of the element, not only in terrestrial samples but also in stars. (As a matter of fact, the element helium was discovered in the sun, through its line spectrum, before it had been found on Earth.) In some elements, most of the energy in the visible part of the emission spectrum is concentrated into just a few lines, giving their light characteristic colors: yellow-orange for sodium, blue-green for mercury (these are commonly seen in street lights) and orange for neon.
Line spectra were well known early in the 19th century, and were widely used for the analysis of ores and metals. The German spectroscopist R.W. Bunsen, now famous for his gas burner, was then best known for discovering two new elements, rubidium and cesium, from the line spectrum he obtained from samples of mineral spring waters.
Q18. How are line spectra organized?
Until 1885, line spectra were little more than "fingerprints" of the elements; extremely useful in themselves, but incapable of revealing any more than the identify of the individual atoms from which they arise. In that year a Swiss school teacher named Johann Balmer published a formula that related the wavelengths of the four known lines in the emission spectrum of hydrogen in a simple way. Balmer's formula was not based on theory; it was probably a case of cut-and-try, but it worked: he was able to predict the wavelength of a fifth, yet-to-be discovered emission line of hydrogen, and as spectroscopic and astronomical techniques improved (the only way of observing highly excited hydrogen atoms at the time was to observe the solar spectrum during an eclipse), a total of 35 lines were discovered, all having wavelengths given by the formula which we write in the modern manner as
in which m = 2 and R is a constant (the Rydberg constant , after the Swedish spectroscopist) whose value is 1.09678E7 m –1 . The variable n is an integer whose values 1, 2, etc. give the wavelengths of the different lines.
It was soon discovered that by replacing m with integers other than 2, other series of hydrogen lines could be accounted for. These series, which span the wavelength region from the ultraviolet through infrared, are named after their discoverers.
|
name of series |
when discovered |
value of m |
| Lyman | 1906-14 |
1 |
| Balmer | 1885 |
2 |
| Paschen | 1908 |
3 |
| Brackett | 1922 |
4 |
| Pfund | 1924 |
5 |
Attempts to adapt Balmer's formula to describe the spectra of atoms other than hydrogen generally failed, although certain lines of some of the spectra seemed to fit this same scheme, with the same value of R .
Q19. How large can n be?
There is no limit; values in the hundreds have been observed, although doing so is very difficult because of the increasingly close spacing of successive levels as n becomes large. Atoms excited to very high values of n are said to be in Rydberg states .
Q20. Why do line spectra become continuous at short wavelengths?
As n becomes larger, the spacing between neighboring levels diminishes and the discrete lines merge into a continuum . This can mean only one thing: the energy levels converge as n approaches infinity. This convergence limit corresponds to the energy required to completely remove the electron from the atom; it is the ionization energy .
At energies in excess of this, the electron is no longer bound to the rest of the atom, which is now of course a positive ion. But an unbound system is not quantized; the kinetic energy of the ion and electron can now have any value in excess of the ionization energy. When such an ion and electron pair recombine to form a new atom, the light emitted will have a wavelength that falls in the continuum region of the spectrum. Spectroscopic observation of the convergence limit is an important method of measuring the ionization energies of atoms.
Q21. What were the problems with the planetary model of the atom?
Rutherford's demonstration that the mass and the positive charge of the atom is mostly concentrated in a very tiny region called the nucleus, forced the question of just how the electrons are disposed outside the nucleus. By analogy with the solar system, a planetary model was suggested: if the electrons were orbiting the nucleus, there would be a centrifugal force that could oppose the electrostatic attraction and thus keep the electrons from falling into the nucleus. This of course is similar to the way in which the centrifugal force produced by an orbiting planet exactly balances the force due to its gravitational attraction to the sun.
The planetary model suffers from one fatal weakness: electrons, unlike planets, are electrically charged. An electric charge revolving in an orbit is continually undergoing a change of direction, that is, acceleration. It has been well known since the time of Hertz that an accelerating electric charge radiates energy. We would therefore expect all atoms to act as miniature radio stations. Even worse, conservation of energy requires that any energy that is radiated must be at the expense of the kinetic energy of the orbital motion of the electron. Thus the electron would slow down, reducing the centrifugal force and allowing the electron to spiral closer and closer to the nucleus, eventually falling into it. In short, no atom that operates according to the planetary model would last long enough for us to talk about it.
As if this were not enough, the planetary model was totally unable to explain any of the observed properties of atoms, including their line spectra.
Q22. How did Bohr's theory save the planetary model... for a while?
Niels Bohr was born in the same year (1885) that Balmer published his formula for the line spectrum of hydrogen. Beginning in 1913, the brilliant Danish physicist published a series of papers that would ultimately derive Balmer's formula from first principles.
Bohr's first task was to explain why the orbiting electron does not radiate energy as it moves around the nucleus. This energy loss, if it were to occur at all, would do so gradually and smoothly. But Planck had shown that black body radiation could only be explained if energy changes were limited to jumps instead of gradual changes. If this were a universal characteristic of energy- that is, if all energy changes were quantized, then very small changes in energy would be impossible, so that the electron would in effect be "locked in" to its orbit.
From this, Bohr went on to propose that there are certain stable orbits in which the electron can exist without radiating and thus without falling into a "death spiral". This supposition was a daring one at the time because it was inconsistent with classical physics, and the theory which would eventually lend it support would not come along until the work of de Broglie and Heisenberg more than ten years later.
Since Planck's quanta came in multiples of h , Bohr restricted his allowed orbits to those in which the product of the radius r and the momentum of the electron mv (which has the same units as h , J–s ) are integral multiples of h:
2π rmv = nh ( n = 1,2,3, . .)
Each orbit corresponds to a different energy, with the electron normally occupying the one having the lowest energy, which would be the innermost orbit of the hydrogen atom.
Taking the lead from Einstein's explanation of the photoelectric effect, Bohr assumed that each spectral line emitted by an atom that has been excited by absorption of energy from an electrical discharge or a flame represents a change in energy given by Δ E = hn = hc /λ, the energy lost when the electron falls from a higher orbit (value of n ) into a lower one.
Finally, as a crowning triumph, Bohr derived an expression giving the radius of the nth orbit for the electron in hydrogen as
Substitution of the observed values of the electron mass and electron charge into this equation yielded a value of 0.529E10 m for the radius of the first orbit, a value that corresponds to the radius of the hydrogen atom obtained experimentally from the kinetic theory of gases. Bohr was also able to derive a formula giving the value of the Rydberg constant, and thus in effect predict the entire emission spectrum of the hydrogen atom.
Q23. What were the main problems with Bohr's theory?
There were two kinds of difficulties. First, there was the practical limitation that it only works for atoms that have one electron-- that is, for H, He + , Li 2 + , etc. The second problem was that Bohr was unable to provide any theoretical justification for his assumption that electrons in orbits described by the preceding equation would not lose energy by radiation. This reflects the fundamental underlying difficulty: because de Broglie's picture of matter waves would not come until a decade later, Bohr had to regard the electron as a classical particle traversing a definite orbital path.
Q24. How did the wave picture of the electron save Bohr's theory?
Once it became apparent that the electron must have a wavelike character, things began to fall into place. The possible states of an electron confined to a fixed space are in many ways analogous to the allowed states of a vibrating guitar string. These states are described as standing waves that must possess integral numbers of nodes. The states of vibration of the string are described by a series of integral numbers n = 1,2,... which we call the fundamental, first overtone, second overtone, etc. The energy of vibration is proportional to n 2 . Each mode of vibration contains one more complete wave than the one below it.
In exactly the same way, the mathematical function that defines the probability of finding the electron at any given location within a confined space possesses n peaks and corresponds to states in which the energy is proportional to n 2 .
The electron in a hydrogen atom is bound to the nucleus by its spherically symmetrical electrostatic charge, and should therefore exhibit a similar kind of wave behavior. This is most easily visualized in a two-dimensional cross section that corresponds to the conventional electron orbit. But if the particle picture is replaced by de Broglie's probability wave, this wave must follow a circular path, and- most important of all- its wavelength (and consequently its energy) is restricted to integral multiples n = 1,2,.. of the circumference 2π r = n λ.
for otherwise the wave would collapse owing to self-interference. That is, the energy of the electron must be quantized; what Bohr had taken as a daring but arbitrary assumption was now seen as a fundamental requirement. Indeed the above equation can be derived very simply by combining Bohr's quantum condition 2π r mv = nh with the expression mv = h /λ for the deBroglie wavelength of a particle.
Viewing the electron as a standing-wave pattern also explains its failure to lose energy by radiating. Classical theory predicts that an accelerating electric charge will act as a radio transmitter; an electron traveling around a circular wire would certainly act in this way, and so would one rotating in an orbit around the nucleus. In a standing wave, however, the charge is distributed over space in a regular and unchanging way; there is no motion of the charge itself, and thus no radiation.
Q25. What is an orbital?
Because the classical view of an electron as a localizable particle is now seen to be untenable, so is the concept of a definite trajectory, or "orbit". Instead, we now use the word orbital to describe the state of existence of an electron. An orbital is really no more than a mathematical function describing the standing wave that gives the probability of the electron manifesting itself at any given location in space. More commonly (and loosely) we use the word to describe the region of space in which an electron is likely to be found. Each kind of orbital is characterized by a set of quantum numbers n, l , and m These relate, respectively, to the average distance of the electron from the nucleus, to the shape of the orbital, and to its orientation in space.
Q26. If the electron cannot be localized, can it be moving?
In its lowest state in the hydrogen atom (in which l =0) the electron has zero angular momentum, so electrons in s orbitals are not in motion. In orbitals for which l >0 the electron does have an effective angular momentum, and since the electron also has a definite rest mass m e = 9.11E31 kg, it must possess an effective velocity. Its value can be estimated from the Uncertainty Principle; if the volume in which the electron is confined is about 10 –10 m, then the uncertainty in its momentum is at least h /(10 10 ) = 6.6E–24 kg m s –1 , which implies a velocity of around 10 7 m s –1 , or almost one-tenth the velocity of light.
The stronger the electrostatic force of attraction by the nucleus, the faster the effective electron velocity. In fact, the innermost electrons of the heavier elements have effective velocities so high that relativistic effects set in; that is, the effective mass of the electron significantly exceeds its rest mass. This has direct chemical effects; it is the cause, for example, of the low melting point of metallic mercury and of the color of gold.
Q27. Why does the electron not fall into the nucleus?
The negatively-charged electron is attracted to the positive charge of the nucleus. What prevents it from falling in? This question can be answered in various ways at various levels. All start with the statement that the electron, being a quantum particle, has a dual character and cannot be treated solely by the laws of Newtonian mechanics.
We saw above that in its wavelike guise, the electron exists as a standing wave which must circle the nucleus at a sufficient distance to allow at least one wavelength to fit on its circumference. This means that the smaller the radius of the circle, the shorter must be the wavelength of the electron, and thus the higher the energy. Thus it ends up "costing" the electron energy if it gets too close to the nucleus. The normal orbital radius represents the balance between the electrostatic force trying to pull the electron in, and what we might call the "confinement energy" that opposes the electrostatic energy. This confinement energy can be related to both the particle and wave character of the electron.
If the electron as a particle were to approach the nucleus, the uncertainty in its position would become so small (owing to the very small volume of space close to the nucleus) that the momentum, and therefore the energy, would have to become very large. The electron would, in effect, be "kicked out" of the nuclear region by the confinement energy.
The standing-wave patterns of an electron in a box can be calculated quite easily. For a spherical enclosure of diameter d , the energy is given by
in which n = 1,2,3. etc.
Q28. What is electron spin?
Each electron in an atom has associated with it a magnetic field whose direction is quantized; there are only two possible values that point in opposite directions. We usually refer to these as "up" and "down", but the actual directions are parallel and antiparallel to the local magnetic field associated with the orbital motion of the electron.
The term spin implies that this magnetic moment is produced by the electron charge as the electron rotates about its own axis. Although this conveys a vivid mental picture of the source of the magnetism, the electron is not an extended body and its rotation is meaningless. Electron spin has no classical counterpart and no simple explanation; the magnetic moment is a consequence of relativistic shifts in local space and time due to the high effective velocity of the electron in the atom. This effect was predicted theoretically by P.A.M. Dirac in 1928.


11.24: Reading- Shorelines
There are a lot of different geologic features associated with shorelines. Let’s take a moment to look at some of the most common features.
Beaches
A beach is a landform along the coast of an ocean or sea. It usually consists of loose particles, which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones. The particles comprising a beach are occasionally biological in origin, such as mollusc shells or coralline algae.
Beaches typically occur in areas along the coast where wave or current action deposits and reworks sediments.
Beach may refer to:
- small systems where rock material moves onshore, offshore, or alongshore by the forces of waves and currents; or
- geological units of considerable size.
The former are described in detail below; the larger geological units are discussed elsewhere under bars.
There are several conspicuous parts to a beach that relate to the processes that form and shape it.
- Swash zone: is alternately covered and exposed by wave run-up.
- Beach face: sloping section below berm that is exposed to the swash of the waves.
- Wrack line: the highest reach of the daily tide where organic and inorganic debris is deposited by wave action.
- Berm: Nearly horizontal portion that stays dry except during extremely high tides and storms. May have sand dunes.
The part mostly above water (depending upon tide), and more or less actively influenced by the waves at some point in the tide, is termed the beach berm. The berm is the deposit of material comprising the active shoreline. The berm has a crest (top) and a face—the latter being the slope leading down towards the water from the crest. At the very bottom of the face, there may be a trough, and further seaward one or more long shore bars: slightly raised, underwater embankments formed where the waves first start to break.
The sand deposit may extend well inland from the berm crest, where there may be evidence of one or more older crests (the storm beach) resulting from very large storm waves and beyond the influence of the normal waves. At some point the influence of the waves (even storm waves) on the material comprising the beach stops, and if the particles are small enough (sand size or smaller), winds shape the feature. Where wind is the force distributing the grains inland, the deposit behind the beach becomes a dune.
These geomorphic features compose what is called the beach profile. The beach profile changes seasonally due to the change in wave energy experienced during summer and winter months. In temperate areas where summer is characterised by calmer seas and longer periods between breaking wave crests, the beach profile is higher in summer. The gentle wave action during this season tends to transport sediment up the beach towards the berm where it is deposited and remains while the water recedes. Onshore winds carry it further inland forming and enhancing dunes.
Conversely, the beach profile is lower in the storm season (winter in temperate areas) due to the increased wave energy, and the shorter periods between breaking wave crests. Higher energy waves breaking in quick succession tend to mobilise sediment from the shallows, keeping it in suspension where it is prone to be carried along the beach by longshore currents, or carried out to sea to form longshore bars, especially if the longshore current meets an outflow from a river or flooding stream. The removal of sediment from the beach berm and dune thus decreases the beach profile.
Cliffs
A cliffed coast, also called an abrasion coast, is a form of coast where the action of marine waves has formed steep cliffs that may or may not be precipitous.
In coastal areas in which the land surface dips at a relatively steep angle below the water table, the continuous action of marine waves on the coastline, known as abrasion, may create a steep declivity known as a cliff, the slope angle of which depends on a variety of factors including the jointing, bedding and hardness of the materials making up the cliff as well as the erosional processes themselves. [1] The slope is constantly being eroded. The waves attacking the cliff-foot form a wave-cut notch by constant abrasion action producing an overhang. This overhang grows in size as the cliff is undercut, until it collapses under its own weight. The loose debris that has broken off is gradually carried away from the area in front of the cliff by the action of the sea. As the coastal cliffs collapse, the shoreline recedes inland. The speed at which this happens depends, in particular, on the strength of the surf, the height of the cliff, the frequency of storm surges and the hardness of the bedrock. Thus, the Mecklenburg coast in Germany recedes by about 25 centimetres per year, whereas the chalk cliffs of southern England retreat by just ½ a centimetre each year. A cliffed coast is made of a loose bedrock material, such as at the Red Cliff on the German island of Sylt, but can also occur in hard rock like the red sandstone cliffs on Heligoland. There are, however, differences between the former and the latter regarding some peculiarities of the coast line.
Deltas
Deltas form when a river carrying sediment reaches either (1) a body of standing water, such as a lake, ocean, or reservoir, (2) another river that cannot remove the sediment quickly enough to stop delta formation, or (3) an inland region where the water spreads out and deposits sediments.
The tidal currents also cannot be too strong, as sediment would wash out into the water body faster than the river deposits it. Of course, the river must carry enough sediment to layer into deltas over time. The river’s velocity decreases rapidly, causing it to deposit the majority, if not all, of its load. This alluvium builds up to form the river delta. When the flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity, which diminishes the ability of the flow to transport sediment. As a result, sediment drops out of the flow and deposits. Over time, this single channel builds a deltaic lobe (such as the bird’s-foot of the Mississippi or Ural river deltas), pushing its mouth into the standing water. As the deltaic lobe advances, the gradient of the river channel becomes lower because the river channel is longer but has the same change in elevation (see slope).
As the slope of the river channel decreases, it becomes unstable for two reasons. First, gravity makes the water flow in the most direct course down slope. If the river breaches its natural levees (i.e., during a flood), it spills out onto a new course with a shorter route to the ocean, thereby obtaining a more stable steeper slope. [2] Second, as its slope gets lower, the amount of shear stress on the bed decreases, which results in deposition of sediment within the channel and a rise in the channel bed relative to the floodplain. This makes it easier for the river to breach its levees and cut a new channel that enters the body of standing water at a steeper slope. Often when the channel does this, some of its flow remains in the abandoned channel. When these channel-switching events occur, a mature delta develops a distributary network.
Another way these distributary networks form is from deposition of mouth bars (mid-channel sand and/or gravel bars at the mouth of a river). When this mid-channel bar is deposited at the mouth of a river, the flow is routed around it. This results in additional deposition on the upstream end of the mouth-bar, which splits the river into two distributary channels. A good example of the result of this process is the Wax Lake Delta in Louisiana.
In both of these cases, depositional processes force redistribution of deposition from areas of high deposition to areas of low deposition. This results in the smoothing of the planform (or map-view) shape of the delta as the channels move across its surface and deposit sediment. Because the sediment is laid down in this fashion, the shape of these deltas approximates a fan. The more often the flow changes course, the shape develops as closer to an ideal fan, because more rapid changes in channel position results in more uniform deposition of sediment on the delta front. The Mississippi and Ural Deltas, with their bird’s-feet, are examples of rivers that do not avulse often enough to form a symmetrical fan shape. Alluvial fan deltas, as seen by their name, avulse frequently and more closely approximate an ideal fan shape.
 Reefs may be up to 261 feet (80 m) below the surface. While the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae, there are also reefs that result from geologic processes—deposition of sand, wave erosion planing down rock outcrops, and other natural processes.
One useful definition distinguishes reefs from mounds as follows. Both are considered to be varieties of organosedimentary buildups: sedimentary features, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor. Reefs are held up by a macroscopic skeletal framework. Coral reefs are an excellent example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. By contrast, mounds lack a macroscopic skeletal framework. Mounds are built by microorganisms or by organisms that don’t grow a skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria. Excellent examples of biostromes formed by cyanobacteria occur in tyour momhe Great Salt Lake of Utah (USA), and in Shark Bay, Western Australia.
Cyanobacteria do not have skeletons and individuals are microscopic. Cyanobacteria encourage the precipitation or accumulation of calcium carbonate and can produce distinct sediment bodies in composition that have relief on the seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today (stromatolites are microbial mounds with a laminated internal structure). Bryozoans and crinoids, common contributors to marine sediments during the Mississippian (for example), produced a very different kind of mound. Bryozoans are small and the skeletons of crinoids disintegrate. However, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief.
The Proterozoic Belt Supergroup contains evidence of possible microbial mat and dome structures similar to stromatolite reef complexes. [3]
Geologic reef structures
Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth’s history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.
Corals, including some major extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of the red algae Rhodophyta, and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha, an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa have been important interstitial organisms, living between the framework builders. The corals which build reefs today, the Scleractinia, arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals (as well as many other groups), and became increasingly important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of the scleractinian corals, whose skeletons are aragonite. However, there are some unusual examples of well-preserved aragonitic rugose corals in the late Permian. In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of the rugosan corals (which disappeared in the late Permian).
Barrier Islands
Barrier islands are coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend uninterrupted for over a hundred kilometers, excepting the tidal inlets that separate the islands, the longest and widest being Padre Island of Texas. [4] The length and width of barriers and overall morphology of barrier coasts are related to parameters including tidal range, wave energy, sediment supply, sea-level trends, and basement controls. [5]
Chains of barrier islands can be found along approximately thirteen percent of the world’s coastlines. [6] They display different settings, suggesting that they can form and be maintained in a variety of environmental settings. Numerous theories have been given to explain their formation.
Constituent parts
Barrier islands are made of several different elements:
- Lower shoreface. The shoreface is the part of the barrier where the ocean meets the shore of the island. The barrier island body itself separates the shoreface from the backshore and lagoon/tidal flat area. Characteristics common to the lower shoreface are fine sands with mud and possibly silt. Further out into the ocean the sediment becomes finer. The effect from the waves at this point is weak because of the depth. Bioturbation is common and many fossils can be found here.
- Middle shoreface. The middle shore face is located in the upper shoreface. The middle shoreface is strongly influenced by wave action because of its depth. Closer to shore the grain size will be medium size sands with shell pieces common. Since wave action is heavier, bioturbation is not likely.
- Upper shoreface. The upper shore face is constantly effected by wave action. This results in development of herringbone sedimentary structures because of the constant differing flow of waves. Grain size is larger sands.
- Foreshore. The foreshore is the area on land between high and low tide. Like the upper shoreface, it is constantly affected by wave action. Cross bedding and lamination are present and coarser sands are present because of the high energy present by the crashing of the waves. The sand is also very well sorted.
- Backshore. The backshore is always above the highest water level point. The berm is also found here which marks the boundary between the foreshore and backshore. Wind is the important factor here, not water. During strong storms high waves and wind can deliver and erode sediment from the backshore.
- Dunes. The dunes are typical of a barrier island, located at the top of the backshore. See Coastal Dunes for more information. The dunes will display characteristics of typical eolian wind blown dunes. The difference here is that dunes on a barrier island typically contain coastal vegetation roots and marine bioturbation.
- Lagoon and tidal flats. The lagoon and tidal flat area is located behind the dune and backshore area. Here the water is still and this allows for fine silts, sands, and mud to settle out. Lagoons can become host to an anaerobic environment. This will allow high amounts of organic rich mud to form. Vegetation is also common.
- Whittow, John (1984). Dictionary of Physical Geography . London: Penguin, 1984, p. 97. See also Herbert Louis and Klaus Fischer: Allgemeine Geomorphologie , de Gruyter, 4th ed., Berlin 1979, pp. 532–537 ↵
- Slingerland, R. and N. D. Smith (1998), "Necessary conditions for a meandering-river avulsion," Geology (Boulder), 26, 435–438. ↵
- Jürgen Schieber, Possible indicators of microbial mat deposits in shales and sandstones: examples from the Mid-Proterozoic Belt Supergroup, Montana, U.S.A. , Sedimentary Geology, 120 (1998) pp. 105–124 ↵
- Garrison, J.R., Jr., Williams, J., Potter Miller, S., Weber, E.T., II, McMechan, G., and Zeng, X., 2010, "Ground-penetrating radar study of North Padre Island; Implications for barrier island interval architecture, model for growth of progradational microtidal barrier islands, and Gulf of Mexico sea-level cyclicity:" Journal of Sedimentary Research, v. 80, p. 303–319. ↵
- Davis Jr., Richard A.; Fitzgerald, Duncan M. (2004), Beaches and Coasts , United Kingdom: Blackwell Publishing, p. 144. ↵
- Smith, Q.H.T., Heap, A.D., and Nichol, S.L., 2010, "Origin and formation of an estuarine barrier island, Tapora Island, New Zealand:" Journal of Coastal Research, v. 26, p. 292–300. ↵
Contributors and Attributions
- Revision, adaptation, and original content. Authored by : Kimberly Schulte and Lumen Learning. Provided by : Lumen Learning. License : CC BY-SA: Attribution-ShareAlike
- Beach. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Beach . License : CC BY-SA: Attribution-ShareAlike
- Cliffed coast. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Cliffed_coast . License : CC BY-SA: Attribution-ShareAlike
- River delta. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/River_delta . License : CC BY-SA: Attribution-ShareAlike
- Reef. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Reef . License : CC BY-SA: Attribution-ShareAlike
- Barrier island. Provided by : Wikipedia. Located at : https://en.Wikipedia.org/wiki/Barrier_island . License : CC BY-SA: Attribution-ShareAlike


2.3: Success During Class- Effective Note-Taking
Learning Objectives
At the end of this section, the learner will:
- Recognize effective note-taking strategies.
- Select a method of note-taking from various examples.
- Formulate a plan to improve listening skills.
Effective Note Taking
The first step in being able to review is to take notes when you are originally learning the information. Students who do not take notes in class in the first place will not be able to recall all of the information covered in order to best review. Different systems work best for different people. Experiment in different ways to find the most success.
Taking notes during lectures is a skill, just like riding a bike. It is challenging to listen to someone speak and then make a note about what they said, while at the same time continuing to listen to their next thought.
Attending class and taking the notes is important primarily because the professor may be presenting information that is not presented in the text. It should also be seen as a structured opportunity to engage with the material that will further aid recall when needed. By attending class, students can also get clues as to what professor perceives as important material that will aid in test preparation.
Tips for Taking Notes During Lecture
- Arrive early and find a good seat- front and center are best for being able to see and hear information.
- Accept responsibility as a listener with a positive attitude; listening is a choice.
- Don’t try and write everything down the instructor talks about; distinguish the most important topics and ideas only.
- Use abbreviations and don’t worry about writing in complete sentences, correct spelling, or punctuation.
- Leave space to add information later.
- Monitor your concentration throughout the class period and continually refocus.
Key Information in Lectures
NONVERBAL CUES
As the lecturer, live or video, presents the material, there are two types of key information cues to be aware of. A speaker will often have unique facial and body nonverbal cues that alert you to several things, as you learn to “read” your professor:
- Stances or movements that alert you to when he/she will shift to a different topic or subtopic.
- Other cues that alert you to when the information is of special significance (including verbal cues, below).
VERBAL CUES
-
Pay attention to when the speaker uses any of the transition cues used in reading comprehension.
- Some instructors will give you cues to let you know something is important. If you hear or see one of these cues, it’s something you should write down. This might include an instructor saying, “this is important,” or “this will be covered on the exam.” If you notice an instructor giving multiple examples, repeating information or spending a lot of time with one idea, these may be cues. Writing on the board or presenting a handout or visual information may also be a cue.
- Many speakers also announce when they are adding information or changing topics in various other ways.
Review
The most important aspect of reviewing your lecture notes is when your review takes place in relation to when your notes were taken. For maximum efficiency and retention of memory, it’s best to review within 20 minutes of when the lecture ends. Ideally, if you can avoid taking back-to-back classes without 30 minutes in between, you could have adequate review time and give your brain a break. Reviewing shortly after the lecture will allow you to best highlight or underline main points as well as fill in any missing portions of your notes. Students who take lecture notes on a Monday and then review them for the first time a week later often have challenges recalling information that help make the notes coherent.
If you wish to go “above and beyond,” you may consider discussing your notes in a study group with your classmates, which can give you a different perspective on main points and deepen your understanding of the material. You may also want to make flashcards for yourself with vocabulary terms, formulas, important dates, people, places, etc. Online flash cards are another option. Students can make them for free and test themselves online or on their phone.
The Big Picture
Keep in mind that students who know what their instructor is going to lecture on before the lecture are at an advantage. Why? Because the more they understand about what the instructor will be talking about, the easier it is to take notes. How? Take a look at the syllabus before the lecture. It won’t take much time but it can make a world of difference. You will also be more prepared and be able to see important connections if you read your assigned reading before the lecture. It’s not easy to do, but students that do it will be rewarded. Refer back to Chapter 3.2.
Note-Taking Methods: What Is Right for You?
Types of Note-Taking Methods
Outline Method
The Outline Method provides a running list of statements that capture the main ideas and supporting ideas for the main points. The highest level of main idea is justified on the left, followed by the next level of supporting ideas that are right indented, followed by the next level of supporting ideas that are further indented, etc. The statements you write down at each level could be key phrases or could utilize the Sentence Method of note taking (see below). It is key for students who utilize the Outline Method to avoid getting so immersed in the “proper” number method for outlining that they lose sight of the information; use a simple numbering or bulleted method. This method is ideal for note taking while reading or listening to a lecturer with a highly structured presentation style.
Cornell Method (sometimes called Split Page Method)
The Cornell Method is a well-known note-taking method that not only encourages documentation of information but also builds in critical thinking and self-testing methods for future review of the material.
- The Cornell Method requires that students set aside a “cue column” on the left side of the paper that is about 2 1⁄2 inches of the left side of the paper. Notes are taken on the right side of the paper using whatever methods students choose to utilize. After class, a summary of the lecture is written to ensure a review of the material and main points to be considered and expressed. In the cue column, students are encouraged to develop questions regarding the adjacent notes. Consider Bloom’s Taxonomy as you develop questions to ensure that you are not only developing knowledge and comprehension questions, but also including higher-level questions that you might anticipate on an exam. Later, this format can be used for self-testing. Cover up the answer on the right side of the page, and then ask yourself to answer the question on the left side. Check your answer and determine where you have holes in your knowledge to help focus further review. If you search Google for Cornell Note Taking , you can find Web sites that will generate the Cornell paper format for you to print, though drawing a line on notebook paper works perfectly fine.
Text-Class Integration Method (sometimes also called Split Page Method)
For this method, students split their notebook paper in half with a line in the middle. On the left side, students take notes from their course reading, and on the right side, they take notes in class for the corresponding text material. This method allows for easy integration of material from both sources.
Mapping Method
The Mapping Method represents the lecture in a visual or graphic format. It helps to utilize 11 ̋ 17 ̋ inch paper or 8 1⁄2 ̋ 11 ̋ inch paper in landscape profile. Students should start with documenting the main idea and placing that in the center of the paper. Then additional ideas feed off of that center point in a hierarchical manner. It allows students to see quickly the main point and relationships to follow. Typically, it is better if students stick with brief statements—one or two words—that capture the ideas. Mapping Methods are also useful to summarize notes taken in another method.
Sentence Method (sometimes also called the Paragraph Method)
This is a simple method in which students write down a main point, fact, or topic, each on separate lines, numbering as they go. It is a useful technique when a lecture is somewhat organized and material is presented at a fast pace. However, relationships may be lost without reorganization of notes at a later time.
Combined Method
You may start with a particular method described above. However, as you become more skilled in your note taking abilities, you may begin combining methodologies to suit the type of information that is being presented. For instance, you may start off the session using the Sentence Method but then use the Mapping Method as you see a pattern emerge in a new concept that is conducive to mapping. You may opt to use the Outline Method in your Political Science course, because the faculty member presents a very organized lecture and use the Text-Class Integration Method in your Math class so that you can see parallel steps between examples from the textbook and the class. The key is to try out some of the different methods and use what works for you.
*Should I use my laptop for note-taking?
Many students use laptop computers for taking notes. It is noteworthy that many students report missing information. You may find that you try to type everything you hear because you can type faster than you can write. In addition, you may be distracted with formatting issues or even other activities that you can opt to do with your laptop. Whichever method you choose to do, remember that the most important part of note-taking may very well be the act of reviewing your notes after.
Activity 3.3 – Improving Your Listening Skills
Improving Your Listening Skills
Watch the TED talk below:
Video: 5 Ways to Listen Better, Julian Treasure at TED Global 2011
Write a one-page (250-300 words) reflection summary covering these questions:
- What are the three types of listening the speaker discusses?
- How and why have we been “losing our ability to listen,” as the speaker suggests?
- What are some of the tools we can use to listen better?
- How you can use the information on non-verbal and listening skills to enhance both your ability to pay attention to lectures and to take better notes on them?


25.6: Physiology of Urine Formation
By the end of this section, you will be able to:
- Describe the hydrostatic and colloid osmotic forces that favor and oppose filtration
- Describe glomerular filtration rate (GFR), state the average value of GFR, and explain how clearance rate can be used to measure GFR
- Predict specific factors that will increase or decrease GFR
- State the percent of the filtrate that is normally reabsorbed and explain why the process of reabsorption is so important
- Calculate daily urine production
- List common symptoms of kidney failure
Having reviewed the anatomy and microanatomy of the urinary system, now is the time to focus on the physiology. You will discover that different parts of the nephron utilize specific processes to produce urine: filtration, reabsorption, and secretion. You will learn how each of these processes works and where they occur along the nephron and collecting ducts. The physiologic goal is to modify the composition of the plasma and, in doing so, produce the waste product urine.
Failure of the renal anatomy and/or physiology can lead suddenly or gradually to renal failure. In this event, a number of symptoms, signs, or laboratory findings point to the diagnosis (Table \(\PageIndex{1}\)).
| Weakness |
| Lethargy |
| Shortness of breath |
| Widespread edema |
| Anemia |
| Metabolic acidosis |
| Metabolic alkalosis |
| Heart arrhythmias |
| Uremia (high urea level in the blood) |
| Loss of appetite |
| Fatigue |
| Excessive urination |
| Oliguria (too little urine output) |
Glomerular Filtration Rate (GFR)
The volume of filtrate formed by both kidneys per minute is termed the glomerular filtration rate (GFR) . The heart pumps about 5 L blood per min under resting conditions. Approximately 20 percent or one liter enters the kidneys to be filtered. On average, this liter results in the production of about 125 mL/min filtrate produced in males (range of 90 to 140 mL/min) and 105 mL/min filtrate produced in females (range of 80 to 125 mL/min). This amount equates to a volume of about 180 L/day in males and 150 L/day in females. Ninety-nine percent of this filtrate is returned to the circulation by reabsorption so that only about 1–2 liters of urine are produced per day (Table \(\PageIndex{2}\)).
| Flow per minute (mL) | Calculation | |
|---|---|---|
| Renal blood flow | 1050 |
Cardiac output is about 5000 mL/minute, of which 21 percent flows through the kidney.
5000*0.21 = 1050 mL blood/min |
| Renal plasma flow | 578 |
Renal plasma flow equals the blood flow per minute times the hematocrit. If a person has a hematocrit of 45, then the renal plasma flow is 55 percent.
1050*0.55 = 578 mL plasma/min |
| Glomerular filtration rate | 110 |
The GFR is the amount of plasma entering Bowman’s capsule per minute. It is the renal plasma flow times the fraction that enters the renal capsule (19 percent).
578*0.19 = 110 mL filtrate/min |
| Urine | 1296 ml/day |
The filtrate not recovered by the kidney is the urine that will be eliminated. It is the GFR times the fraction of the filtrate that is not reabsorbed (0.8 percent).
110*.008 = 0.9 mL urine /min Multiply urine/min times 60 minutes times 24 hours to get daily urine production. 0.9*60*24 = 1296 mL/day urine |
GFR is influenced by the hydrostatic pressure and colloid osmotic pressure on either side of the capillary membrane of the glomerulus. Recall that filtration occurs as pressure forces fluid and solutes through a semipermeable barrier with the solute movement constrained by particle size. Hydrostatic pressure is the pressure produced by a fluid against a surface. If you have a fluid on both sides of a barrier, both fluids exert a pressure in opposing directions. Net fluid movement will be in the direction of the lower pressure. Osmosis is the movement of solvent (water) across a membrane that is impermeable to a solute in the solution. This creates a pressure, osmotic pressure, which will exist until the solute concentration is the same on both sides of a semipermeable membrane. As long as the concentration differs, water will move. Glomerular filtration occurs when glomerular hydrostatic pressure exceeds the luminal hydrostatic pressure of Bowman’s capsule. There is also an opposing force, the osmotic pressure, which is typically higher in the glomerular capillary.
To understand why this is so, look more closely at the microenvironment on either side of the filtration membrane. You will find osmotic pressure exerted by the solutes inside the lumen of the capillary as well as inside of Bowman’s capsule. Since the filtration membrane limits the size of particles crossing the membrane, the osmotic pressure inside the glomerular capillary is higher than the osmotic pressure in Bowman’s capsule. Recall that cells and the medium-to-large proteins cannot pass between the podocyte processes or through the fenestrations of the capillary endothelial cells. This means that red and white blood cells, platelets, albumins, and other proteins too large to pass through the filter remain in the capillary, creating an average colloid osmotic pressure of 30 mm Hg within the capillary. The absence of proteins in Bowman’s space (the lumen within Bowman’s capsule) results in an osmotic pressure near zero. Thus, the only pressure moving fluid across the capillary wall into the lumen of Bowman’s space is hydrostatic pressure. Hydrostatic (fluid) pressure is sufficient to push water through the membrane despite the osmotic pressure working against it. The sum of all of the influences, both osmotic and hydrostatic, results in a net filtration pressure (NFP) of about 10 mm Hg (Figure \(\PageIndex{1}\)).
A proper concentration of solutes in the blood is important in maintaining osmotic pressure both in the glomerulus and systemically. There are disorders in which too much protein passes through the filtration slits into the kidney filtrate. This excess protein in the filtrate leads to a deficiency of circulating plasma proteins. In turn, the presence of protein in the urine increases its osmolarity; this holds more water in the filtrate and results in an increase in urine volume. Because there is less circulating protein, principally albumin, the osmotic pressure of the blood falls. Less osmotic pressure pulling water into the capillaries tips the balance towards hydrostatic pressure, which tends to push it out of the capillaries. The net effect is that water is lost from the circulation to interstitial tissues and cells. This “plumps up” the tissues and cells, a condition termed systemic edema .
Net Filtration Pressure (NFP)
NFP determines filtration rates through the kidney. It is determined as follows:
\[NFP = Glomerular\;blood\;hydrostatic\;pressure\;(GBHP)-[capsular\;hydrostatic\;pressure\;(CHP)+blood\;colloid\;osmotic\;pressure\;(BCOP)] = 10\;mm\;Hg \]
That is:
\[NFP = GBHP-[CHP+BCOP] = 10\;mm\;Hg \]
Or:
\[NFP = 55-[15+30] = 10\;mm\;Hg \]
As you can see, there is a low net pressure across the filtration membrane. Intuitively, you should realize that minor changes in osmolarity of the blood or changes in capillary blood pressure result in major changes in the amount of filtrate formed at any given point in time. The kidney is able to cope with a wide range of blood pressures. In large part, this is due to the autoregulatory nature of smooth muscle. When you stretch it, it contracts. Thus, when blood pressure goes up, smooth muscle in the afferent capillaries contracts to limit any increase in blood flow and filtration rate. When blood pressure drops, the same capillaries relax to maintain blood flow and filtration rate. The net result is a relatively steady flow of blood into the glomerulus and a relatively steady filtration rate in spite of significant systemic blood pressure changes. Mean arterial blood pressure is calculated by adding 1/3 of the difference between the systolic and diastolic pressures to the diastolic pressure. Therefore, if the blood pressure is 110/80, the difference between systolic and diastolic pressure is 30. One third of this is 10, and when you add this to the diastolic pressure of 80, you arrive at a calculated mean arterial pressure of 90 mm Hg. Therefore, if you use mean arterial pressure for the GBHP in the formula for calculating NFP, you can determine that as long as mean arterial pressure is above approximately 60 mm Hg, the pressure will be adequate to maintain glomerular filtration. Blood pressures below this level will impair renal function and cause systemic disorders that are severe enough to threaten survival. This condition is called shock.
Determination of the GFR is one of the tools used to assess the kidney’s excretory function. This is more than just an academic exercise. Since many drugs are excreted in the urine, a decline in renal function can lead to toxic accumulations. Additionally, administration of appropriate drug dosages for those drugs primarily excreted by the kidney requires an accurate assessment of GFR. GFR can be estimated closely by intravenous administration of inulin . Inulin is a plant polysaccharide that is neither reabsorbed nor secreted by the kidney. Its appearance in the urine is directly proportional to the rate at which it is filtered by the renal corpuscle. However, since measuring inulin clearance is cumbersome in the clinical setting, most often, the GFR is estimated by measuring naturally occurring creatinine, a protein-derived molecule produced by muscle metabolism that is not reabsorbed and only slightly secreted by the nephron.