Comparative Animal Physiology

I taught Comparative Animal Physiology (Biology 334) at the University of Puget Sound in the fall of 2002. A course overview and logistical details are included in the official course syllabus. Also available here is a post-course reflection on aspects of the course that could be improved next time.

Answer keys are now available for in-class exam #1, take-home exam #1, in-class exam #2, and the final exam.

Fun Animal Questions asked by Biology 334B students....

Q. Why does hyperkalemia (high potassium levels in the blood) cause cardiac arrhythmias? (11-27-02)

A. Hyperkalemia changes the resting membrane potential of the cardiac cells (to the extent that cardiac cells are ever at rest). Since the cell membrane is permeable to potassium, most of the "excess" extracellular potassium diffuses into the cell, depolarizing the membrane somewhat. Following an action potential, the voltage-gated sodium channels are normally "reset" so that they may open again during the next action potential. However, this resetting process is voltage-dependent. UPS neurobiologist Sue Hannaford suggests that the more-depolarized-than-normal membrane potential interferes with the resetting process such that the sodium channels remain inactivated for a long time after each action potential, leading to a slow and irregular heartbeat.

Q. When a heat shock protein binds to a protein that has unfolded due to heat stress, does the unfolded protein regain function? (11-6-02)

A. Not while the heat shock protein is bound, no. However, by stabilizing the unfolded protein and preventing it from "getting into trouble," the heat shock protein increases the likelihood that the unfolded protein will refold properly once the temperature drops to normal levels (M.E. Feder, "Ecological and evolutionary physiology of stress proteins and the stress response: the Drosophila melanogaster model," in Animals and Temperature [1996], edited by I.A. Johnston and A.F. Bennett).

Q. Are any hormones known to cause fast-twitch muscle fibers to become slow-twitch fibers or vice versa? (11-4-02)

A. Yes. According to Baldwin & Haddad (2001), thyroid hormone exerts a strong influence on muscle fiber type. Hypothyroidism leads to an increase in the fraction of fibers expressing type I (slow-twitch) myosin, whereas hyperthyroidism causes an increase in the proportion of type II (fast-twitch) fibers.

Q. Do dogs have blood glucose levels similar to humans? In other words, is Figure 9.9 of our text a reasonable depiction of glucose reabsorption in humans as well as dogs? (10-16-02)

A. Dogs and humans have similar blood glucose levels (~5 mM). Figure 9.9 is confusing because it uses units of mg/ml, whereas most blood glucose measurements are given in units of mM (mmol/l) or mg/dl.

Q. Do we yawn because we aren't getting enough oxygen? Do animals other than humans yawn? (10-4-02)

A. According to a post to madsci.org, many different animals display yawning behavior. Apparently, it is not fully understood why yawning occurs, but post author Benjamin Walker does offer an intriguing explanation.

Q. Since frogs depend on their skin for gas exchange when underwater, is cutaneous circulation more extensive in aquatic frogs than in terrestrial frogs? (9-27-02)

A. Yes and no. According to Ed DeGrauw, "Highly specialized aquatic frogs have greater capillary density in the skin than your average frog, but the most xeric [moisture-deprived] forms also have very high capillary densities confined to the region of the ventral thighs and pelvic region." This "pelvic patch" is used to absorb water from the ground.

Q. Can the pooling of blood in the legs lead to the development of varicose veins? (9-23-02)

A. Yes, it can. In healthy individuals, venous valves and pressure from the leg muscles ensures that blood flows from the legs back to the heart. However, if the valves fail, blood lingers in the legs longer than it should, causing the veins to swell.

Q. Can a Q10 be as high as, say, 5? (9-11-02)

A. Yes. In their book Biochemical Adaption, Hochachka & Somero note that some chemical reactions are extraordinarily temperature-sensitive because temperature affects both the enzyme's affinity for its substrate (Km) and its activity at a given substrate concentration. As temperature falls, they say, "The combined effects of reduced substrate binding ... and reduced kinetic energy for driving the reaction over its activation enthalpy 'barrier' can lead to Q10 values greater than 10 at physiological substrate concentrations."

Q. What happens if an animal doesn't get enough protein? (9-9-02)

A. If an immature animal is chronically deprived of protein, its growth will be stunted, since it won't be able to synthesize the proteins that cells need to grow and divide. If a (juvenile or adult) animal's intake is not sufficient to sustain its current body size, it will literally digest its tissues (mainly muscle, the body's biggest reserve of protein) in order to free up some amino acids for maintenance and repair. The fertility of females may also be compromised by inadequate protein intake.

Since animals can synthesize some amino acids from scratch but not others, what is most important is their intake of the "essential" amino acids rather than their total protein intake per se. According to Eckert & Randall's Animal Physiology text, "The rate of growth of chickens at one time was limited by too small a proportion of one essential amino acid in the grain diet they were provided. Supplementing the diet with this amino acid allowed full utilization of the other amino acids present in the feed, greatly increasing the rate of protein synthesis and hence the rate of poultry growth and egg laying."

Q. Do different feedback control loops have different error signal thresholds? In other words, are small error signals ignored by some control loops but not others? (9-6-02)

A. Yes. A recent article about fluid balance in humans (Shirreffs & Maughan, Exerc Sport Sci Rev 28: 27-32, 2000) provides a good example: "A rise of 2-3% in plasma osmolality is sufficient to evoke a profound sensation of thirst coupled with an increase in the circulating concentration of vasopressin. The mechanisms that respond to changes in intravascular volume and pressure seem to be less sensitive than those that monitor plasma osmolality; hypovolemic thirst is evident only after a 10% decrease in blood volume."