W3006 '02        Physiology           Answers to Study Questions #7 - Digestion


1. Lipoprotein Liapse is found in the blood vessels and breaks down ingested triglycerides, or tryglycerides from the liver both of which are carried in the form of lipoproteins. Other lipases are found inside the adipose cells, and catalyze the breakdown of stored triglycerides during the denning period.


2.   When food is in the stomach, large amounts of H+ are moved into the lumen of the stomach, with HCO3- moving into the blood, leaving the blood      slightly more alkaline than usual. When the stomach contents dribble into the intestines, the H+ is reabsorbed into the blood.


3. Sometimes. Theyll be found in the blood for a short time after eating a fatty meal, but they are quickly converted to chylomicron remnants and taken up by the liver. (Half life of chylomicrons is about 5-10 minutes).


4. Never. The liver secretes bile slats while the enzymes are produced by the pancreas and the walls of the intestines.


5. False they must be first hydrolyzed by lipase.


6. Bile emulsifies fat, breaking large globules into smaller globules, which can be digested by lipase and then absorbed from the micelles into the intestinal cells. In addition to triglycerides, other fat soluble molecules will also reach the the intestinal walls dissolved in the micelles, so if bile is absent, the fat soluble substances would remain in the globules and never make it into the micelles and intestinal epithelium. Without bile, Vitamin K would not be absorbed. Bleeding is normally prevented because clots form to close to close small breaks in blood vessels. This requires prothrombin thrombin which converts fibrinogen fibrin clot. With less vitamin K absorbed, less will be available for protothrombin synthesis, and fewer fibrin clots will form, and more bleeding will occur through the walls of unclotted broken blood vessels. (The info you needed was the first and last statements).


7. a,b,e



9. The parietal cells in the stomach usually secrete HCl. It will usually not have an effect on the walls of the stomach because mucus is also secreted to coat (and protect)  the cells in the wall of the stomach. The acid is usually prevented from affecting the esophagus because there is a muscular sphincter which separates these compartments. If this sphincter opens, stomach contents can move upwards and burn the esophagus. The acid  is usually prevented from damaging the intestines because the pancreas produces bicarbonate which neutralizes the acid. If there is an increase in stomach acid, this can increase the probability of developing ulcers in the intestines.


10. Parietal cells, which require huge amounts of ATP to pump H+ into the stomach across a concentration gradient of about 2millon to one.


11. None. Pancreatic amylase, secreted into the intestine, is the major enzyme involved in the digestion of polysaccharides. Very little digestion occurs in the mouth anyway, because food is there a very short time.


12. The gall bladder does not bile, it just stores the bile made by the liver. Without the gallbladder, bile can not be stored, but it will still dribble out into the intestines. Even without any bile, lipase can still digest those fat molecules that are on the outside of a fat globule. Digestion will still take place, but not as effectively. Much fat leaves in the feces.


13. a Stomach has a lot of water sloshing around from food and drink, salivary secretions and from gastric secretions.

     b. The parietal cells of the stomach secrete HCl into the lumen, which exits the mouth in vomiting.

     c. When H= leaves the body, the blood compensates for the of acid by shifting the equation to the right. C02+H20H2CO3 H+ +         HCO3-. This helps maintain the homeostatic levels of H+ in the blood. However it uses up more of the C02. The major stimulus           for increased breathing is the CO2 which reaches the medulla oblogonta in the central nervous system. If more C02 is converted to          H2CO3, less CO2 is available in the blood to diffuse into the CSF to stimulate the chemoreceptors that control breathing, and so            breathing rate slows.


14. a. x   b.x    c. y    d. y  e. y   f. y

15.d    16. b   17. a

19.  A. Sometimes.  This is true for muscle and adipose cells, but not for liver cells.   B. Sometimes.  Pepsinogen is always present, but pepsin will be present in significant quantities only when HCl is secreted.


20.   a.      F. This describes the samll intestines

b.           F.  Chief cells secrete pepsinogen. Parietal cells secrete HCl and intrinsic factor 

c.            F. They enter the lymphatic vessels

d.           T

e.            Some bile is excreted, but most is reabsorbed to enter the liver for reuse

f. F. Protein in the stomach is the main stimulus for gastrin secretion.

g.             T. (bilirubin)

h.           F. ..into maltose


21. a

22. a. increases    b. does not affect   c. does not affect   d. increases    e. does not affect


23. Glut 1 -> probably transports into the cells because all cells take in glucose to use as energy.

      Glut-2 -> probably transports glucose out of cells liver and muscle both store glucose as glycogen, but only the liver exports the           glucose from broken down glycogen.


24. (a) pepsin in the stomach usually begins protein digestion, but there is enough protesase/peptidase in the small intestine to do the job.

      (b) absorption vitamin B12 occurs in the small intestine, but requires intrinsic facto, made by the stomach.

(c) The stomach dribbles chyme gradually into the intestines, so absorption is slow. Without the stomach, glucose is more rapidly absorbed.


25. (a) alkalotic

(b) drop in H+ decrease in CO2 less CO2 DIFFUSE ACROSS THE BLOOD BRAIN BARRIER lower signal to medulla oblongata less message to respiratory muscles lower rate of inhalation


drop in H+ lower stimulation of chemoreceptors in carotid artery and aorta lower signal to medulla oblongata less message to respiratory muscles lower rate of inhalation

all because decrease in H+ causes this equation to shift to left H+ + HCO3- H2CO3 H2O + CO2


(c) Alkalotic blood means there was a net loss of H+ compared to HCO3- loss. HCl is secreted into the stomach, HCO3- into the intestines. So the effect of vomiting prevailed


26. The function of lipase is the breakdown of triglycerides into monoglycerides and fatty acids. If there is no lipase, fats are not broken down. Since triglycerides are mostly not absorbed directly, they will exit in the feces and will not be stored in adipose tissue.


27. Like other lipases, this must be breaking down triglycerides, so you'd expect it to be activated in the catabolic/fasted state, when glucagon is high, so it's probably activated by glucagon.

28. skeletal muscles 

29.  We expect fats to be taken into adipose cells during the high-insulin (absorptive) state, so the lipase produced during this time might be breaking down the lipids in lipoproteins, so that they can leave the blood and enter the adipose cells.  This would be Lipase A.   During the postabsorptive state (low insulin) lipase is required to break down triglycerides, so that the fats can contribute to the energy needs of the cell, so this would be Lipase B.

30.  Digestion of lipids is due to lipase, which is still secreted as normal.  Bile helps to disperse the fat, and thereby increase the rate at which lipase can digest the fat.  Instead of getting a burst of bile when fat enters the intestine, there will be small amounts of bile dribbling out of the liver, and so digestion is slower. 

31. Glucagon elevates blood glucose levels by promoting glycogen breakdown.   Glycogen is stored in the muscles too, but this glycogen serves the glucose needs of the muscle itself, and doesn't contribute to blood glucose.

32. A. d. post-absorptive

B. Gycogen (1), Liver (1) glycogen broken down to release glucose to the blood for use by other tissues, esp brain (2). Muscle (1), glycogen broken down to release glucose, used to provide energy for that muscle cell.

C. brain - glucose(1), liver glycogenolysis (2) and gluconeogenesis (2). Other tissues: free fatty acids (1) adipose tissue lipolysis = release ffa's to blood, take up by other tissues (2)

33. A. glycerol . Digestion of fats: lipase cleaves 2 fa's from the tg, producing a mg and 2 fa's. requires emulsification of fat globules, so lipase can reach the bonds of the triglyceride. (3)

Absorption of fats: small micelles with mg and fa's reach microvilli of intestinal epithelial cells, mg and fa's diffuse across membrane to inside of cells, tg's are resynthesized, combined into chylomicrons, and exocytosed to blood. (3)

With olestra, structure of molecule prevents lipase from getting close to the ester bonds in the connecting the fa's to sucrose or the micelles are too large to get near the microvilli to get absorbed (2)

B. These are all fat-soluble. (1). They'll remain in large fatty, undigested fat globules with olestra, so won't get absorbed, just pass out with feces. (2)