W3006  Fall '98     Physiology       Problem Set #  7   Digestive system

1. Sometimes. They'll be 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. Their half-life is about 5-10 minutes.
2. Never. Liver secretes bile. Enzymes produced by pancreas and intestinal epithelium.
3. A. F This describes small intestine.
B. F Chief cells secrete pepsinogen. Parietal cells secrete HCl and IF.
C. F They enter the lymphatic vessels.
D. T
E. Some bile is excreted, most is reabsorbed to enter the liver for re-use.
F. T  (bilirubin)
G. F ...into maltose.
H. F  First lipase acts to break them down into monoglycerides + fatty acids.

4. A. x    B. y    C. y   D. y   E. y
5. a, b,c,e
6. a, b, e
7. When food is in the stomach, large amounts of acid (H+) are moved from the blood to the lumen of the stomach, leaving the blood slightly more alkaline than usual.  When the stomach contents gradually dribble into the intestines, the H+ is reabsorbed from there into the blood.
8. Bile emulsifies fats, 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 intestinal wall dissolved in the micelles, so if bile is absent other fat-soluble substances would remain in the globules and never make it to the micelles and intestinal epithelium.  Without bile, Vitamin K would not be absorbed.  Bleeding is normally prevented because clots form to close small breaks in blood vessels.  This requires prothrombin conversion to thrombin, which converts fibrinogen to fibrin to form a clot.  With less Vitamin K absorbed, less will be available for prothrombin synthesis and fewer fibrin clots will form, and more bleeding will occur through the walls of broken vessels.  (The info you needed was in 1st and last statements.)
9. a. Although pepsin in the stomach can begin protein digestion, most digestion occurs in the small intestine, so this wouldn't be affected.  b. Absorption of Vitamin B12 in the intestine is dependent on Intrinsic Factor which is produced by the stomach, so withouth the stomach B12 won't be absorbed.  c. The stomach stores food for several hours, gradually opening the sphincter that allows it to move into the small intestine.   If the stomach is removed and food moves directly into the small intestine, the sudden load of glucose in the small intestine will be more rapidly absorbed, and blood glucose will be higher than usual.
10. Eating period.  Lipoprotein lipase is found in the blood vessels and breaks down triglycerides, both those that have been ingested and those brought from the liver, all 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.