W3006 Fall 2001 Physiology Problem set #6 - Blood pressure, atherosclerosis, digestion

1. The following appeared in the well known journal (The Annals of Improbable Research): "Scientists found that some people carry a gene that allows them to eat high cholesterol food without increasing their production of low-density lipoproteins (LDL)… One major restaurant chain will soon urge consumers to take the simple blood test that shows whether they carry the gene. Those who do will be eligible for discount coupons for french fries and special high-fat hamburgers."      Suggest a mechanism by which this gene might prevent high blood levels of LDLs.

3. Consider a fatty acid side chain on a triglyceride molecule, which is digested and absorbed and remains in the blood for at least 12 hours. Number the structures, to indicate which the fatty acid will be found in first, which second, and so on, from the time it is ingested through the 12 hours it is in the blood. Use 0 if the fatty acid will not be in that structure at all during this period.

lumen of stomach lumen of small intestine micelle epithelial cell of small intestine chylomicron lacteal lymph node chylomicron remnant VLDL LDL epithelial cell of stomach lumen of large intestine epithelial cell of large intestine

4. The end systolic volume

a. is the volume of blood in the ventricle after it has ejected its blood

b. is the volume of blood in the ventricle after it has filled with blood

c. is always equal to the stroke volume

a. and c. are both correct

b. and c. are both correct

5. Which is greater X or Y

X. Stroke Volume when End Diastolic Volume is 135 ml.

Y. Stroke Volume when End Diastolic Volume is 155ml

6. The protein SR-B1 which was recently found identified as the HDL receptor, is found in high concentrations in the adrenal gland.

In which part of the adrenal gland is it high?

Why is it high there?

7. There are several longitudinal, cross-sectional and cross-cultural studies that support the hypothesis that a low fat diet decreases the risk of heart disease and cancer. But there are other studies that fail to support this idea. Dale Atrens, an Australian psychologist, argues that given the uncertainty in the benefits of a low fat diet, public health messages to adhere to such an unpleasant diet is "irrational and mischievous" and we have " a great deal to lose from subscribing to a fear-riddled and ineffective lifestyle."

Is it likely that the emotional stress caused by giving up steak, french fries and ice cream, cause more heart disease or cancer than the high fat diet would have?

(This hasn’t been researched, so I don’t expect a definitive answer; I expect you to discuss this idea while referring to the specifics from lecture or readings.)

8. Hemorrhage, or loss of blood, stimulates numerous compensatory mechanisms to maintain homeostasis. Hemorrhage causes (an increase)(a decrease) in blood pressure, which (increases)(decreases) the frequency of messages from the arterial baroreceptors. This leads to an increase in messages along the (sympathetic)(parasympathetic) neurons causing a) constriction of (arterioles)(veins)(capillaries) which leads to an increase in arterial blood pressure and b) constriction of (arterioles)(veins)(capillaries) which leads to an increase in end diastolic volume and (increase)(decrease) of cardiac output.

9. This adorable face belongs to the vampire bat, Desmodus rotundus. It hangs around in caves in South America, venturing out at night to land on unsuspecting vertebrates. It swoops down onto a sleeping cow or horse or pig,  makes an incision with its razor-sharp teeth, and as the blood oozes out, it quickly slurps it up. You wouldn't  take your time over dinner, either, if your dinner might wake up any minute. A bat will consume so much of the  delicious red blood -- about 60% of its body weight in 20-30 minutes -- that it can become, as its name implies,  quite rotund and too heavy to fly away. In order to decrease its weight, it urinates as it eats, even before it has digested its meal, in that way getting rid of the fluid it has imbibed, while retaining the protein-rich cells.

A. Vampire bats have heat sensors in their nose. This allows them to find warm living bodies, , but it also helps them find the best place on the animal to take a bite. Why would a heat sensor help them know where to bite? 

B. (Don't worry about this one; it was covered in the intro course so I didn't cover it this semester.)  Scientists recently identified a chemical in the saliva of the vampire bat, and named it Draculin (I am not making this up!) It acts as an inhibitor of Factor X. What's this Draculin good for? Your answer should include an explanation of what Factor X is, the pathway in which it works, and why the bat would want to inhibit it. 

C. Compared to a human, the vampire bat has a very small small intestine, virtually no large intestine, and a proportionally larger stomach. The stomach is shaped like a blind sac, which fills with ingested blood. The vampire bat's stomach has many many more capillaries than a human's. The epithelial cells have much higher Na+/K+ ATPase activity. Explain why the bat's stomach has evolved in this way. How does this adapt it to its unique food-getting behavior? Your answer should include an explanation of what is occurring in the bat's stomach as it fills with blood, and how this differs from what occurs (in general terms) in a human stomach. 

D. A bat ingests 800 times as much Fe/day as a human, but only a tiny fraction of this is absorbed into the bat's blood. If you looked inside the epithelial cells lining the bat digestive tract, you'd expect to see lots of
a. calbindin  b. ferritin  c. transferrin  d. bilirubin  e. hemoglobin  f. myoglobin 

E. Trace an ingested Fe++ backwards, from the bat's mouth to the cow, explaining where it probably was in the past 4 months. Assume the cow is like a human, and that the life of a cow's RBC is 2 months. 

A. Although St. Martin did occasionally run a fever, in general, he did not develop massive infections from having unsterilized stuff stuck directly into his stomach. What prevented the development of infection in the stomach? 

B. St. Martin wasn't always so thrilled with his employer's hobby, and Beaumont noticed that when St. Martin was particularly angry, digestion took much longer. How would you explain this? Your answer should include the specific steps in the pathway that lead from the stressful emotion of anger to a decrease in the rate at which food is digested in the stomach. 

11. Moses was stranded on a mountain top for 40 days and 40 nights without food. What happened to his body's glycogen over that period of time? (Assume normal Homo sapiens, no miracles accepted in your answer.) NOTE: Changes occur in many aspects of the body, but the question asks you to deal only with glycogen stores. Your answer should include glycogen, wherever it may be, and the factors that are responsible for the change. 

12. Is sugar consumption related to heart disease? To answer this question, Yudkin and Roddy asked two groups of patients about their usual intake of food. The results are as follows.

Yudkin and Roddy concluded that sugar is likely to be a cause of heart disease. However there are other conclusions that are compatible with the data. List three reasons why you would be hesitant to accept their conclusion, including possible confounding factors.

13.A sudden increase in the pressure in the carotid sinus leads to ______ sympathetic nerve activity. (increased)(decreased)

14. Multiple choice.

a. placed in the mouth
b. placed in the stomach
c. placed in the small intestine
d. placed in the large intestine
e. injected intravenously

a. glucagon
b. CCK
c. gastrin
d. GIP
e. secretin

a. store iron
b. make fibrinogen
c. store bile
d. activate vitamin D
e. detoxify wastes

a. high LDL
b. low LDL
c. oxidized LDL
d. all of the above
e. none of the above

a. histamine
b. endothelin
c. nitric oxide
d. rise in temperature
e. rise in carbon dioxide

a. always
b. never
c. sometimes

1. An enzyme found in the liver catalyzes the rate determining step in the synthesis of cholesterol. If these people have a particular allele that produces a slow-working enzyme or an enzyme that does not work at all, they’ll produce less cholesterol. This in turn will reduce the down regulation of LDL receptors. The presence of these extra receptors will increase the amount of dietary cholesterol that will be absorbed form the blood.

3. 1 lumen of stomach 2 lumen of small intestine 3 micelle 4 epithelial cell of small intestine 5 chylomicron 6 lacteal 7 lymph node 8 chylomicron remnant 9 VLDL 8 LDL 0 epithelial cell of stomach 0 lumen of large intestine 0 epithelial cell of large intestine

4.a

5. Y. Frank Starling Law -> The greater the heart muscle is stretched, i.e the greater volume of blood that enters, the stronger the contraction, and the greater the volume of blood ejected in one stroke.

6. A. Adrenal cortex. B. Cholesterol is needed there to synthesize steroid hormones such as cortisol. HDL may bring cholesterol to adrenal,

7. For this question, I expected students to include a summary of some of the mechanisms by which stress might increase the risk of heart disease or cancer, but to also consider this quantitatively, that is, the magnitude of the stress that results from steak-avoidance is probably not sufficient to cause the long-term ill effects we discussed.

8. decrease, decreases, sympathetic, arterioles, veins, increase

9. A. Blood is warmed as it passes by the heat-generating tissues in the body's core. Thus an increase in temperature indicates an area where more blood is present, due to a higher density of capillaries, or due to vasodilation, or it indicates an area where blood vessels are closer to the body's surface. 

B. Factor X----> activated Factor X  catalyzes conversion of Prothrombin ---> Thrombin 1which catalyzes conversion of Fibrinogen ---> Fibrin1, which forms the fibrin clot. Inhibition of X means that no fibrin clot will form, which allows blood to flow instead of clotting, allowing the bat the needed time to finish feeding. 

C. The human stomach functions mostly as an organ of storage, with only a little digestion occurring.  The bats stomach is specialized for both digestion and absorption.   
As blood fills the stomach, water must be extracted, so the fluid can be urinated out, so water absorption must occur here, rather than waiting till the large intestine, as occurs in humans.  For water to be absorbed, a concentration gradient is necessary, so that water can move by osmosis.  The high concentration of Na/K pumps indicates that Na is pumped out of the stomach epithelial cells on the basolateral side, creating the concentration gradient of Na+, which will "pull" water out of the stomach lumen.    The abundance of capillaries is similar to what we saw in the villi in the human small intestines, and indicates that absorption  is occurring here.  The large sac expands to hold the blood, and digestion of the meal (mostly protein, but including other nutrients too) occurs here, and  subsequent absorption too.  

D.  b. ferritin

E.  Bat drinks blood with Fe++ in RBC in blood vessel <---- Fe++ was packaged in RBC in association with hemoglobin    within the bone marrow  <----Fe++ reached the bone marrow in blood, carried by transferrin  <----- was secreted into the blood from the liver where it was stored with ferritin after the liver removed it from a previously broken down RBC 

10. A. HCl - hydrochloric acid inhibits bacterial growth

B. brain --> increased sympathetic ns activation and decreased parasympathetic 
a. decreased smooth muscle contractions of digestive tract, so slower mixing of food, digestion, peristals, moving food along 
b. decreased secretion of HCl from parietal cells and decreased pepsinogen secretion , so less pepsin produced, and slower protein digestion
c. increased stimulation of alphareceptors on blood vessels to stomach, so vasoconstriction decreases blood flow to stomach, slows deliver of hormones (gastrin), thus indirectly decreasing HCl and pepsin secretion.  

11. Glycogen is stored in both the liver and in muscle .  In response to low blood glucose, the pancreas  secretes glucagon , which stimulates breakdown of glycogen to glucose, which is released into the blood .    Glucose depletion, and the consequent lower insulin levels, causes muscle glycogen to be broken down into glucose, but this remains within the muscle cell, for its own use. 

12. Possible answers include: could be one group of patients has poorer memory for food intake; sugar is often found in high fat foods (cakes, ice cream), and could be those eating much sugar are also eating much fat; those people eating those cakes and ice cream may also be smoking cigarettes afterwards; sample size is relatively small.

13. decreased. The increase in blood pressure is sensed by the baroreceptor in the carotid sinus, which sends a message to the medulla oblongata to relax arteriolar smooth muscle, and to decrease rate of the heart beat, both of which will lead to a decrease in blood pressure. These effects are dependent on increased parasympathetic activity, and decreased sympathetic activity.

14. A. c  B. d  C. c  D. e. (not downregulated at all)  E. b  F. a