W3006 '02 Physiology Problem Set #7 - Digestive system

1. During the early fall, brown bears up their caloric intake from a previous 5000 kcal/day to 20,000 kcal/day. They then begin a 3-5 month "denning" period, during which they stay in their dens without eating or drinking, maintaining their metabolic rate through metabolism of stored fats. Recent research shows that the lipoprotein lipase activity measured in blood vessels of adipose tissue is different during the eating and denning periods. During which period would you expect it to be higher? Explain why.

2. After eating a meal, food stays in the stomach for a while before moving to the small intestines. During this time, the blood may become temporarily alkaline. Explain why.

3. Sometimes/Always/Never: Chylomicrons are found in the blood.

4. S/A/N: Digestive enzymes are secreted by the liver.

5. T/F: Once bile has acted on triglycerides, they are ready for absorption through the intestinal epithelium.

6. Obstruction of the bile duct leads to an increase in tendency to bleed. Explain why. In addition to what you learned in class you'll need to use some (but not all) of the following information:

Vitamins A,D,E,K are fat-soluble. Vitamin C and the B vitamins are water-soluble.
Excess vitamin A is stored in the liver.
Vitamins A,C,E are antioxidants.
Vitamin C is a cofactor for an enzyme needed for collagen synthesis.
Vitamin K is a cofactor for an enzyme needed for prothrombin synthesis.

7. The defecation reflex is similar to the micturition (urination) reflex. You would expect the defecation reflex to

a. begin when stretch receptors in the rectum are stimulated
b. involve contraction of the rectum
c. involve contraction of the internal anal sphincter
d. involve contraction of the external anal sphincter
e. be overridden in the adult by signals from the brain

8. Which of the following are functions of the liver?

a. activates vitamin D
b. produces clotting factors
c. synthesis of bile
d. synthesis of chylomicron remnants
e. storage of glucose as glycogen
f. synthesis of renin

9. Ulcers are the erosions of the epithelial lining of the digestive tract and are associated with acid. For every 100 people with duodenal ulcers, there will be about 10 with gastric ulcers and one with esophageal ulcer. Explain why this difference in frequency occurs. In your answer, include type of acid, its source, and the factors that increase or decrease the probability that this acid will have an affect on each of the three tissues.

10.Which cells of the stomach would you expect to show the highest levels of oxidative phosphorylation?

11. If the salivary glands are unable to secrete salivary amylase what affect will this have on starch digestion?

12. Even after the gall bladder is removed, a person can still digest fats. Why?

13. a. Just thinking about a final makes you feel like vomiting. After you vomit, you feel dehydrated. Why?
b. You also feel a sharp acidic taste in your mouth. Why?
c. You begin to breathe more slowly. Why?

14. For each of the following statements, circle whichever is greater, x or y. If x=y circle both. No explanation is required.

a. x. molecular weight of pepsinogen
y. molecular weight of pepsin

b. x. amylase activity in the mouth
y. amylase activity in the stomach

c. x. iron that can be stored when cells make a lot of transferrin
y. iron that can be stored when cells make a lot of ferritin

d. x. size of fat globules when bile is present
y. size of fat globules when bile is absent.

e. x. number of chylomicrons formed after drinking orange juice
y. number of chylomicrons formed after eating peanut butter

f. x. pH of Stomach
y. pH of small intestines

15. Glucagon

  1. facilitates entry of glucose into brain tissue
  2. stimulates phosphorylation of glucose to glucose-6-phosphate in the liver
  3. decreases blood glucose levels
  4. increases glycogen phosphorylase activity
  5. is secreted by beta cells of the islets of Langerhans

16. Insulin induces glucose transporters to be inserted into the membrane of

  1. liver cells
  2. muscle cells
  3. brain cells
  4. all of the above
  5. none of the above

17.Amylase is

  1. secreted in the mouth
  2. requires a low pH for activity
  3. is most active after bile acts on its substrate
  4. more than one of the above is true.

19. For each of the following, indicate whether it is ALWAYS, SOMETIMES or NEVER true, and explain your answer.

  1. During the absorptive state, the way insulin affects its target cells is to increase the number of glucose carriers in thier membrane.
  2. Pepsin is present in the lumen of the stomach

20. True/False. If false, correct it to make it true.

  1. The inner lining of the stomach is thrown into folds known as villi
  2. The parietal cells secrete both pepsinogen and HCl
  3. Chylomicrons which have hydrophilic proteins on their surfaces are absorbed directly into the capillaries.
  4. Amino acids are absorbed by secondary active transport by the epithelial cells of the small intestine.
  5. After emulsifying fat, the bile is excreted with the feces.
  6. Acid in the stomach is the primary signal for endocrine secretion of gastrin
  7. A component of the bile is responsible for both the brown color of the feces and the yellow color of the urine
  8. Amylase breaks down starch into glucose.

21. Which of the following secretion(s) is entirely under nervous control and has no hormonal regulatory component?

a. saliva b. gastric c. pancreatic d. liver

22. Fill in the with increase(s), decreases, does not affect.

  1. acid in the duodenum ___________ secretion of secretin
  2. CCK _________ bicarbonate secretion by pancreatic duct cells
  3. Salivary amylase __________ the breakdown of proteins in the mouth.
  4. Vitamin D __________ the absorption of calcium in the small intestines.
  5. Lipase __________ the emulsification of fats.

23. Several different proteins have been identified that all act to transport glucose across cell membranes. Glut-1 is found in membranes of all cells. Glut-2 is found in liver cells, but not in muscle or most other cells. What would you conclude about the direction of glucose transport by these two carriers?

24. The stomach is surgically removed from a person, and the remaining digestive tract sewn together. Briefly explain each of the following:

Compared to a normal individual,

  1. protein digestion is normal,
  2. blood levels of vitamin B12 are much lower
  3. after a meal hyperglycemia (high blood sugar) is more likely to develop.

25. Last week someone ate in we-won’t say- which cafeteria. That evening, she had a sudden attack of both diarrhea and vomiting. Afterwards, she measured her breathing rate, which was a little slower than normal.

  1. Was someone’s blood more likely to be a) acidotic or b) alkalotic
  2. Explain how the this change in pH (in your answer to A.) led to a decrease in breathing rate.
  3. The fact that her blood reached that pH (in your answer to A.) means that she must have lost more ions (a) form vomiting or (b) from diarrhea. Explain your answer.

26. Xenical is a drug that inhibits pancreatic lipase. Explain how this drug might be effective in treating obesity.

27. Adipose cells have an enzyme called hormone-sensitive lipase, which catalyzes the same process as pancreatic lipase and lipoprotein lipase. You would expect this lipase to be activated by (insulin)(Glucagon). Explain.

28. Insulin increases the entry of glucose into (all tissues)(epithelial cells of the neuron)(epithelial cells of the small intestine)(neurons of the cerebral cortex)(skeletal muscle)

29.Two kinds of lipase are produced by adipose cells, A and B.

Lipase A is stimulated by insulin, Lipase B is inhibited by insulin. What kinds of lipase are these likely to be? Why do these cells need two different kinds of lipase? Undre what consitions would each one be used?

30. A fat forty-ish female has her gall bladder removed.

  1. Explain why a) fat can be digested, but b) the rate of digestion is slower.
  2. During the week after surgery, she often has diarrhea. Explain why?

31. Glycogen is found in both the liver and the muscles. Glucagon receptors are fround on the surface of liver cells, but not muscle cells. Explain the relationship between glucagon and glycogen, and why there is this difference in distribution of glucagon receptors.

32. Rumi, a 13th century Persian Sufi poet, celebrates the euphoric and creative feelings engendered by a period of fasting:

There is an unseen sweetness in the stomach's emptiness.
We are lutes.
When the soundbox is filled, no music can come forth.
When the brain and the belly are burning from fasting,
every moment a new song rises out of the fire.
The mists clear,
And a new vitality makes you spring up the steps before you.
Be empty and cry as a reed instrument.
Be empty and write secrets with a reed pen.

But this poem can also be read as a physiological description of the fasting state. The questions below ask you to "translate" Rumi's poem into modern physiological terminology.

A. The poem is about the _______state.

a. pre-absorptive b. pre-pro-absorptive c. absorptive d. post-absorptive e. post-modernist absorptive

B. "An unseen sweetness in the stomach's emptiness": After the digestive tract is emptied of sweetness (glucose), the glucose is "unseen" because it's stored as a different molecule. Explain the molecule in which glucose is stored, the organs in which it's stored, and the eventual use of the stored glucose in each of those organs.

C. "When the brain and the belly are burning from fasting": During fasting, tissues still need to burn fuel for energy. Explain the type of molecule and source of fuel burned for energy a) by the brain and b) by other tissues such as the connective tissue of the "belly".

33. triglyceride:







A. Olestra, a fat-substitute, is made of fatty acids bound to sucrose, instead of bound to _______________________, as they are in triglycerides. Also, a molecule of olestra has many more fatty acid chains, making the molecule much much larger than a triglyceride. Olestra tastes like fat in the mouth, but passes right out the body in the feces without being digested or absorbed. Explain why. Your answer should include an explanation of how normal triglycerides are digested and absorbed, as well as an explanation of why this process cannot occur with olestra.

B. For optimal health, foods containing olestra must be supplemented with vitamins A, D, E, and K. Why? Your answer should include the property that these four vitamins have in common, and why it is considered important to take extra ADEK if olestra is eaten.