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1. Starting with the form of each basic foodstuff ingested (carbohydrate, protein, lipid), trace its breakdown. Include enzymes involved, pH required for optimum action, and end products of the action of each enzyme.
2. In gastrointestinal smooth muscle, what are the interrelationships between the slow waves in membrane potential, action potentials, and contractility? What are the major differences between smooth and striated muscles in excitation, excitation-contraction coupling, and contraction?
3. Describe the primary mechanisms for motility in the esophagus, stomach, small intestine, and large intestine. What is the dependence upon extrinsic and intrinsic neural organization?
(select the appropriate answers; sometimes there is more than one)
4. Exhaustive digestion of starch by pancreatic amylase results in
(a) maltose. (b) glucose. (c) maltotriose. (d) sucrose.
5. Which of the following enzymes are secreted as inactive proenzymes?
(a) Enterokinase (enteropeptidase) (b) Chymotrypsin (c) Lipase (d) Pepsin
6. Trypsin
(a) is an exopeptidase.
(b) is produced by the action of trypsin on trypsinogen.
(c) converts prolipase to lipase.
(d) is produced by the action of enterokinase on trypsinogen.
7. Gastrointestinal smooth muscle cells
(a) are each directly innervated.
(b) are functionally coupled.
(c) contain neuromuscular junctions.
(d) are larger than skeletal muscle cells.
(e) contain actin and myosin filaments running parallel to each other.
8. Esophageal peristalsis
(a) is abolished by vagotomy.
(b) is under hormonal control.
(c) can occur in the absence of a swallow.
(d) moves a bolus by decreasing the pressure in front of it.
(e) is not effective for liquids.
9. Receptive relaxation of the stomach
(a) is abolished by vagotomy.
(b) is triggered by relaxation of the LES.
(c) occurs primarily in the antrum.
(d) results in large increases in intragastric pressure following a meal.
(e) depends entirely on the enteric nervous system.
10. Gastric emptying
(a) is more rapid for solid than liquids.
(b) is stimulated by CCK.
(c) of hypotonic solutions is more rapid than emptying of isotonic solutions.
(d) is inhibited when acid enters the duodenum.
(e) of fats is inhibited by receptors in the mucosa of the stomach.
11. Contractions of intestinal circular smooth muscle may be influenced by each of the following EXCEPT:
(a) Parasympathetic nerves.
(b) Chemicals present in the lumen.
(c) Somatic nerves.
(d) Gastrointestinal hormones.
(e) Enteric nerves
12. Gastrointestinal smooth muscle can be considered different from skeletal muscle in that action potentials are ________ (L, long; S, short) duration, the ________ (A, absence; P, presence) of well defined end plates, and the ________ (A, absence; P, presence) of troponin C.
13. Effective peristalsis ________ (S, is; X, is not) dependent upon the myenteric plexus, and is ________ (I, increased; N, not significantly affected; D, decreased) by sympathetic nerve stimulation.
14. Carbohydrates:
(a) start to be digested in the stomach.
(b) are ultimately broken down at the brush border of intestinal mucosal cells.
(c) have about the same calorific value weight for weight as fat.
15. With reference to gastric function:
(a) the average meal has moved on from the stomach after half an hour.
(b) when the quantity of ingested material increases, the intragastric pressure increases.
(c) the longitudinal muscle coat has a basic electrical rhythm.
(d) enterogastrone secretion inhibits the production of gastric acid.
(for multiple choice, select all correct answers)
1. What are the functions of salivary secretion? Which glands are involved, and what are the pathways and mechanisms of innervation?
2. List the secretory functions of the stomach and compare the cell-types and secretory activities for various regions of the gastric mucosa.
3. For a duodenal ulcer patient, would you expect more or less HCl secretion than a "normal" subject? Will the abolition or diminution of HCl secretion heal an ulcer? Will it prevent the recurrence of the ulcer? Why?
4. What factors influence the rate of gastric emptying?
5. Digestive enzymes are secreted by (a) the acinar cell, (b) the intercalated duct cell,
(c) the chief cell, (d) the parietal cell, (e) the jejunal enterocyte, (f) the hepatocyte.
6. All digestive enzymes are secreted in an inactive or pro-enzyme form, T or F. What is the function of enterokinase (enteropeptidase)?
7. What are the principal differences between hepatic bile and gall bladder bile? What accounts for the differences?
8. The total body contains about 2-4 gm of bile salts, and yet daily output of bile salt by the liver amounts to about 20-30 gms/day. How is this accomplished?
9. Distinguish bile salts and bile pigments in terms of synthesis, secretion, function, and pathological alterations.
10. Salivary secretion
(a) is stimulated by both parasympathetic and sympathetic activation.
(b) contains high concentrations of K+ relative to the blood.
(c) is hypotonic.
(d) can occur at large volumes relative to the weight of the glands.
11. As saliva moves from the acinus toward the duct opening, its
(a) concentration of K+ increases.
(b) total ionic concentration increases.
(c) chloride concentration decreases.
(d) sodium concentration increases.
12. Bile
(a) Contains bilirubin, which been synthesized by the hepatocytes.
(b) is concentrated in the gallbladder so that its osmotic pressure increases.
(c) is produced only during times food is present in the GI tract.
(d) secretion decreases in volume if the enterohepatic circulation is interrupted .
13. ________ (G, gastrin; P, pepsin), the principal proteolytic enzyme of gastric juice, is secreted in an ________ (A, active; I, inactive) form by ________ (O, oxyntic; C, chief) cells.
14. Mucous neck cells and chief cells, ______ (W, as well as; N, but not) parietal cells, are components of the ______ (C, cardiac; F, fundic; P, pyloric) glands.
15. Hydrochloric acid in the stomach
a. breaks down proteins into amino acids
b. converts pepsinogen into active pepsin
c. solubilizes fats and lipids
d. stimulates the release of gastrin by antral cells
16. Gastric secretion, ______(L, like; U, unlike) salivary secretion, is regulated by ______ (N, only neural; H, only hormonal; B, both neural and hormonal) mechanisms.
17. Secretin produces a ______ (S, scanty; C, copious) flow of pancreatic secretion with a high concentration of ______ (E, enzymes; Cl−, chloride ions; HCO3, bicarbonate ions).
18. Bile is secreted ______ (I, intermittently, C, continually) by the liver and contains significant amounts of ______ (S, only bile salts; E, only digestive enzymes; B, both bile salts and digestive enzymes) which contribute to the gastrointestinal digestive processes.
with a twist (any given question may be T or F)
19. On the left is a list of gastric secretions. Are the items on the right appropriately associated with each secretion?
(a) Hydrochloric acid — Increase in bicarbonate in gastric venous blood
(b) Hydrochloric acid — Necessary to life
(c) Pepsinogen — Remains inactive above pH6
(d) Intrinsic factor — Another name for vitamin B12
(e) Gastrin — Secretion stimulated by vagal activity
20. Concerning gastric secretion in a normal adult:
(a) the histamine receptors in the stomach can be pharmacologically stimulated without significant stimulation of histamine receptors in the lungs.
(b) pentagastrin injection can cause a maximal secretion of acid by the stomach.
(c) gastrin comes mainly from cells in the fundus of the stomach.
21. Concerning gastrointestinal secretions:
(a) gastrointestinal hormones are steroids.
(b) secretin results in a flow of pancreatic secretion with a high concentration of bicarbonate ions.
(c) the pancreas secretes more than one litre of juice per 24 hours.
22. In the normal human:
(a) cholecystokinin is the most important hormone concerned in the neutralization in the small bowel of acid from the stomach.
(b) the emulsification of dietary lipid by bile salts assists intestinal absorption of lipid.
(c) at least 95% of bile pigments secreted by the liver are reabsorbed in the gut.
23. Bilirubin released into the circulation from the reticulo-endothelial system:
(a) is bound by plasma proteins.
(b) contains ferric ions.
24. Concerning bile:
(a) most of the water is absorbed from the bile in the gall bladder.
(b) a high ratio of bile salts to cholesterol favors the formation of gall stones.
(c) the cholesterol normally present in bile is derived mainly from the breakdown of steroid hormones.
(d) the volume of bile entering the duodenum is about 500 ml/day.
(e) about 10% of the bile salts entering the duodenum is lost in the feces.
(for multiple choice, select all correct answers)
1. Describe the cephalic, the gastric, and the intestinal phases of gastric secretion.
2. (T or F) Gastric HCl secretion is likely to be reduced (but not necessarily abolished) by (a) atropine, (b) carbamylcholine, (c) histamine, (d) secretin, (e) H-1 antagonists, (f) H-2 antagonists, (g) low gastric pH, (h) low duodenal pH, (i) vagotomy, (j) antrectomy.
What are the mechanisms for the above effects?
3. Describe the principal gastrointestinal responses to
(a) gastrin, (b) secretin, (c) CCK, (d) VIP, (e) GIP, and (f) urogastrone.
4. What neural and hormonal mechanisms of interdependence are available for gastric secretion, pancreatic secretion and biliary secretion? Can we call the gastric antrum and the duodenum endocrine organs?
5. Acid in the duodenum
(a) inhibits gastric acid secretion,
(b) stimulates gall bladder contraction,
(c) stimulates bile production,
(d) stimulates pancreatic bicarbonate secretion.
6. Vagotomy will decrease
(a) pancreatic secretion in response to intestinal stimuli,
(b) the amount of gastrin released during the cephalic phase,
(c) pepsin secretion in response to a meal,
(d) acid secretion in response to gastric distension.
7. Antral gastrin release is increased by
(a) somatostatin.
(b) fat in the antrum of the stomach.
(c) protein digestion products in the antrum.
(d) lowering antral pH from 5.5 to 2.0.
(e) infusion of secretin.
8. Gastrointestinal peptides
(a) are often found in nerves of the gastrointestinal tract.
(b) are all hormones.
(c) are present in discrete endocrine organs.
(d) are destroyed in the liver after being released into the bloodstream.
(e) have only one physiological action per peptide.
For questions 9-14 select one of the following (a - d):
(a) Gastrin
(b) Cholecystokinin
(c) both
(d) neither
9. Stimulates gallbladder contraction physiologically.
10. The entire molecule is necessary for biological activity.
11. Released from antral mucosa by acid (pH <3.0).
12. Inhibits gastric emptying.
13. Sulfated tyrosyl residue is necessary for physiological effect.
14. Released by protein digestion products.
For questions 15 through 18, select one of the following (a - d):
(a) Secretin
(b) VIP
(c) Both
(d) Neither
15. Belongs to the same family as glucagon.
16. Primarily acts as a paracrine.
17. Relaxes smooth muscle.
18. Stimulates bicarbonate secretion in response to acid in the duodenum.
19. Regulation of gallbladder emptying through the action of ________ (C, cholecystokinin; V, villikinin; S, secretin), is functionally significant as bile ________ (P, pigment; T, salts) assist in the digestion and absorption of fats.
20. The vagus nerve ______ (I, is; N, is not) essential to the cephalic phase of gastric secretion, it ______ (I, is; N, is not) responsible for the flow of salivary juice, and it ______ (C, can; CN, cannot) influence the secretion of gastrin.
with a twist (any given question may be T or F)
21. Concerning pancreatic secretion:
(a) secretin can produce a greater flow of pancreatic juice than the maximal flow in response to vagal stimulation.
(b) atropine blocks the secretogogue effects of vagal stimulation.
(c) atropine blocks the secretogogue effects of secretin.
22. With respect to regulation
(a) carbohdrate digestion products are important gastric stimuli
(b) acid or low pH in the antrum stimulates gastric output
(c) acid or low pH in the duodenum stimulates pancreatic enzyme output
(d) the vagus nerve is primarily an efferent nerve
(for multiple choice, select all correct answers)
1. Compared to the small intestine, we can say that the large intestine has a ________ surfacea area, a ________ capacity for absorption of salts and water, and a ________ "leakiness" of tight junctions. (S, smaller; G, Greater)
2. Glucose absorption across the intestinal ______ (BB, brush border; BL, basolateral) membrane is stimulated by Na+, and is competitively inhibited by ______ (G, galactose; F, fructose; C, cyclic AMP).
3. Differentiate between passive diffusion, carrier-mediated transport, primary active transport, and secondary active transport.
4. What are the mechanisms for the intestinal absorption of Na+, Cl−, H2O, Ca2+, Fe2+, vit B12, D-glucose, L-glucose, lipids?
5. Cite the experimental evidence to support the Na+-coupling hypothesis for intestinal absorption of glucose and certain amino acids.
6. Given the following clinical and experimental examples of lipid malabsorption, describe the primary site of the dysfunction.
a. pancreatic enzyme insufficiency
b. decreased lipid esterification capacity in enterocytes, e.g., non-tropical sprue, or adrenal hormone insufficiency
c. genetic impairment of synthesis of beta-lipoprotein.
d. bile salt insufficiency
e. treatment of intestine with protein synthesis inhibitor, e.g., puromycin
f. severe liver cirrhosis
g. prevention of bile salt absorption in the ileum
h. lymphatic obstruction
7. Contrast mechanisms for fluid and salt balance in the normal intestine and one exposed to bacterial toxins, such as cholera toxin.
8. Poorly absorbed solutes, such as MgSO4 or Mg-Citrate, are often used as a laxative, or cathartic. Explain. What would be some predictable differences in response to drinking milk of two individuals, one with and one without the intestinal disaccharidase, lactase?
9. Blood samples were taken from an individual before and after a meal. By comparison, the plasma shortly after the meal (a) was more alkaline, (b) was hyperglycemic, (c) had a slightly higher concentration of bile salts, and (d) was somewhat turbid, or milky, in appearance. Detail the events in specific regions of the gastrointestinal tract that would account for these changes.
10. Diarrhea-producing toxins of cholera, certain colon bacilli, and staphylococci appear to ________ (I, inhibit; S, stimulate) an active transport mechanism involving chloride ________ (A, absorption; E, secretion) and water (A, absorption; E, secretion).
Note: Take on question 11 & 12 only if we have covered experiments on isolated intestinal membrane vesicles.
11. Glucose uptake is being measured in a preparation of isolated brush border membrane vesicles. Arrange the following experimental conditions in order of expected increase in initial rates of glucose uptake by the vesicles.
outside soln. — intravesicular soln.
(a) 150 mM NaCl — 150 mM NaCl
(b) 150 mM NaSCN — 0
(c) 150 mM NaCl — 0
(d) 75 mM Na2SO4 — 0
(e) 150 mM KCl — 0
What would you predict for the glucose concentration gradient at equilibrium for each of the above conditions?
12. For a preparation incubated as in (a) from the question above, describe an experimental manipulation that would tend to drive net NaCl into the vesicles. . . . out of the vesicles.
with a twist (any given question may be T or F)
13. The small intestine absorbs less salt and water each day than is taken in the diet.
14. The large intestine has a greater absorbing surface than the small intestine.
15. Concerning intestinal absorption:
(a) a volume of fluid of about 8 liters per day is absorbed from the gut.
(b) most protein is absorbed in the form of dipeptides.
(c) absorption of the products of protein digestion depends on active transport mechanisms for sodium.
16. The ileum is the principal site for the absorption of:
(a) glucose.
(b) the products of fat digestion.
(c) bile salts.
(d) vitamin K.
(e) iron.
17. Concerning fat digestion and absorption:
(a) in a healthy human, 5 % is the upper limit of ingested fat which appears in the feces.
Malabsorption of lipids is likely to occur as a result of:
(b) hepatocellular damage.
(c) obstructive jaundice.
(d) failure of pancreatic secretion.
(e) removal of the gastric antrum in a partial gastrectomy.
18. In the colon:
(a) the secretions lack significant digestive enzymes.
(b) sympathetic stimulation results in enhanced motility.
(c) more than half the water is absorbed from its contents.
(d) bacterial synthesis of vitamin K is of vital importance.