Fall 2001 Physiology
1. One kind of male infertility occurs when there are small deletions in the Y chromosome which result in a smaller than usual number of sperm being produced -- not enough to ensure that sperm will reach and fertilize an egg. To treat this, Intracytoplasmic Sperm Injection (ICSI) is used, in which a single sperm is injected directly into the egg in the lab, then the fertilized egg is implanted in the mother. Some have criticized this technique, because the father's genetic defect would be passed on to the offspring, but prospective parents don't care; they just want a kid, and if their son turns out to have the same infertility, he can use the same technique to have his own kids. This month, scientists reported that these microdeletions imply an instability in the Y chromosome, and in some cells, the Y chromosome is so unstable that it is completely lost from the cell. When an XY baby is born to these men using ICSI, the baby may be a genetic mosaic, with most cells having the expected XY, but something like 10% of the cells having no Y chromosome at all.
Explain why babies born by ICSI have a greater than usual chance of having Turner's syndrome. Assume that the offspring is a genetic mosaic, in which some cells are XY and some have no Y. Your explanation should include a description of which are the embryonic cells that must have lacked the Y chromosome for Turner's syndrome to develop (5) AND draw a flowchart that summarizes the factors that are responsible for sexual differentiation at the level of the gonads (4), hormones (4), ducts (8), and external genitals (4) in this individual.
2. A patient, Ms. Terryess enters your office with somewhat mysterious symptoms: She has developed a painful stomach ulcer and has watery diarrhea. You suspect that she has Zollinger-Ellison syndrome, which results from a tumor of gastrin-secreting cells.
A. Her stomach contents are more acidic than usual. Why would this be compatible with the suggestion that she has Zollinger-Ellison? You can use a diagram or flowchart for your answer, provided it is well-labeled. (6)
Gastrin stimulates parietal cells(3) to
secrete HCl (3)into the lumen of the stomach. So a gastrin-secreting tumor
would be expected to produce a more acidic stomach.
B. You ask about her recent bowel movements, and she sounds amazed when she tells you that she noticed that the feces float on the surface of the water in the toilet bowl. You realize that this means that they have a high fat content. What is the mechanism by which an extremely high level of stomach acid leads to a lot of fat leaving the body in the feces? Your answer should include an explanation of what normally happens when gastric acid enters the intestines, and what would be altered if the gastric contents is super acidic. You can use a diagram or flowchart for your answer, provided it is well-labeled. (6 NOTE: I changed the points on this to 9)
H+ in intestine stimulates intestinal
cells to secrete secretin
(1), which stimulates pancreatic duct cells to secrete
HCO3-(2), which neutralizes the acid. The intestinal cells also secrete CCK,
which stimulates the pancreas to secrete lipase(2) into the lumen of the
intestine. If the stomach contents are very acidic, bicarbonate secretions
may not be enough to neutralize the acid, and the pH doesn't rise as much as
needed for optimal activity of the lipase(2). If the lipase doesn't function,
the triglycerides won't be broken down to monoglycerides and free fatty acids,
which is necessary for fat absorption, and if the fats aren't absorbed, they
leave the body in the feces.(2)
3. During finals week, the snack machines have a special discount on Voop!, a purplish drink made from the V. niko herb, which has the unusual ability to disable the valves in the veins.
A. After drinking Voop!, end diastolic volume will a. increase b. decrease(1). Explain why. Your answer should include an explanation of the role of valves and the meaning of end diastolic volume. 2 sentences is enough. (5)
Valves assure one-way flow of blood towards the heart.(2) If valves don't function, less blood flows into the heart, leading to a lower end diastolic volume, which is the volume of blood that fills the heart at relaxation of the cardiac muscles.(2)
B. To compensate for the effect of Voop!-ingestion, alpha and beta-1 receptors are stimulated. Explain where these receptors are and how stimulation of them will help to maintain a constant cardiac output, despite the change in EDV. Use formulas as appropriate. (8)
SV=EDV-ESV(2), so if EDV decreases, as explained above, then SV will decrease.
CO=SV x HR(2), so if SV has decreased
due to valve malfunction, there are two ways to maintain normal CO:
a. Increase SV in some other way, such as using other mechanisms to increase EDV. Vasoconstriction will increase the venous return to the heart, and stimulating alpha-receptors will cause the necessary vasoconstriction.(2)
b. Increase heart rate, which will occur if beta-1 receptors on the heart are stimulated..(2)
4. A pulse of ultrasound can kill the axons of neurons, but doesn't affect blood vessels. You apply ultrasound to the stalk connecting the pituitary gland to the hypothalamus of a rat that has recently been put in a stressful situation. Explain how this treatment will affect her ability to respond to the stress. Your explanation should include the various endocrine changes that occur in stress, and whether they would or wouldn’t be affected by the ultrasound treatment. (15 NOTE: I changed the points for this question to 10 instead of 15)
We discussed several hormones (8 points for any 4) that may increase during stress: cortisol, epinephrine, MSH, beta-endorphin, glucagon, aldosterone, ADH (vasopressin). Insulin may decrease, and GH initially increases, then decreases in the long term. The stalk contains axons of the neuroendocrine cells that have cell bodies in the hypothalamus and terminals in the posterior pituitary, so destroying these axons would eliminate signals getting to the posterior pituitary to allow secretions from there. ADH is the only listed hormone from the posterior pituitary, so only this would be involved.(2) (Note: The hypothalamus sends neurons to other parts of the brain, and to other parts of the body via the spinal cord; these pathways don't go through the pituitary gland.)
5. Compare and contrast B and T cells. (12)
points for any 4)
Where they mature: B - bone marrow T- thymus
Target cells may be: B - bacteria T - cancer cells, viral-infected cells
Antigen receptor: B - membrane-bound antibody T- T-cell receptor
Membrane proteins: B- IgM, MHCII T - TCR, CD8
What's recognized by antigen receptor: B - free antigen T - Ag+MHCI
# of antigen receptor binding sites: B- 2 T - 1
Protect against antigens that are: B- free in solution T - part of cells
Type of immunity: B - humoral T - cell-mediated
How fights infection: B - antibodies neutralize toxin, agglutinate antigens, amplify nonspecific immune responses such as phagocytosis. T - lysis, apoptosis of infected cell
Secretes: B - antibody T - perforin
points for any 2)
Are part of specific immune system
Form memory clls
Stimulated by T helper cells
When stimulated, multiply to produce clone of cells
Are mostly found in the lymphatic system
PTH activates 1-alpha hydroxylase in the kidney, which catalyzes the final step in production of 1,25 Vit D, the active form of Vitamin D(2). This Vit D increases Ca++ absorption from the small intestine.(4) PTH also increases Ca++ reabsorption from the nephron.(2)
If high fiber diet is associated with decreased calcium absorption, it might be because a high fiber content in the intestines moves the contents more rapidly through, which may be too fast for all the calcium to be absorbed before it exits the body in the feces. (4)
(10 points for any two:)
Limitations may include:
studied were much older than the typical reader of SELFLESS magazine;
Although the authors say that there is no association between calcium absorption
and age, they were looking at a very small range of ages (46-54) and it's
possible that fiber doesn't affect calcium absorption of women in their 20's.
Calcium intake was based on self-reports - could be inaccurate because people don't know exactly how much they ate
The decrease in calcium absorption was relatively small (from 38% of ingested calcium to 31%), and it may make more sense for women to slightly increase their calcium intake, rather than decrease their fiber intake.
Even if calcium absorption is decreased by low fat diets, it doesn't follow that we should increase the fat content of our diet, because high fat diets are associated with atherosclerosis.
Sample essays will be posted later.