Gastrointestinal Physiology MCQ

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1. Which of the following statements about liver failure are correct? [Select all that apply]
a) Severe hyperglycemia develops
b) Plasma levels of ammonia will rise
c) The digestion and absorption of fats is impaired
d) The plasma oncotic pressure will rise
e) There is an increased chance of a venous thrombosis
ANSWERS
b) Plasma levels of ammonia will rise
c) The digestion and absorption of fats is impaired
REVISION NOTES
The wide variety of functions performed by the liver in health is reflected by the number of physiological processes that are disrupted in liver failure. Severe hypoglycemia (plasma glucose concentration below the normal range) develops in liver failure because the liver plays a central role in maintaining plasma glucose. Plasma ammonia levels will rise because the ammonia formed by the deamination of amino acids will no longer be converted to urea by the liver. Bile production will slow or cease and this will impair the digestion and absorption of fats, which depends on bile salts. The plasma oncotic pressure will fall because the hepatic synthesis of plasma proteins will be impaired in liver failure. The synthesis of clotting factors decreases so there is a reduced chance of developing a venous thrombosis.

2. Concerning the major dietary constituents:
a) The body cannot store glucose.
b) All essential amino acids are found in meat.
c) Plant oils mainly consist of saturated fats.
d) Ketones are likely to be present in the urine of an individual eating a predominantly carbohydrate diet.
ANSWER
b) All essential amino acids are found in meat.
REVISION NOTES
Glucose is stored in the liver, skeletal muscle and some other tissues as glycogen. Animal protein is complete protein and contains all 20 of the amino acids used by the body to synthesize new proteins. Plant oils are rich in unsaturated fats. Ketones are by-products of fat metabolism and appear in the urine of individuals who are eating little or no carbohydrate.

3. Regarding dietary requirements of the major foodstuffs:
a) Adults can synthesize all of the amino acids found in proteins.
b) Children who have a protein deficient diet may develop kwashiorkor.
c) Edema is a characteristic feature of marasmus.
d) People whose diets are low in fats often suffer from fatty acid deficiency diseases.
ANSWER
b) Children who have a protein deficient diet may develop kwashiorkor.
REVISION NOTES
Adults cannot synthesize the 8 essential amino acids, which must be supplied by the diet. Children whose diet is protein deficient are at risk of developing kwashiorkor. Such children have edema; those suffering from marasmus do not. Fatty acid deficiency is rare, even in those whose diet is low in fats.

4. Concerning disorders due to vitamin deficiency or excess:
a) Excess intake of vitamin A can cause severe toxic reactions.
b) Vitamin B2 deficiency may cause severe muscular disorders.
c) Vitamin B12 deficiency results in microcytic anemia.
d) Rickets can be prevented by large doses of vitamin C.
ANSWER
a) Excess intake of vitamin A can cause severe toxic reactions.
REVISION NOTES
Excess vitamin A is highly toxic and can cause a variety of neurological problems. Vitamin B2 deficiency is comparatively rare. Symptoms include cracking at the edges of the lips and skin lesions. Neurological disorders are seen in deficiency of Vitamins B1, B3 and B6. Vitamin B12 deficiency results in macrocytic (or pernicious) anemia. Rickets can be prevented by administration of vitamin D.

5. Regarding gastric motility:
a) Gastric emptying is inhibited by the enterogastric reflex
b) The antral region of the stomach is important for the storage of food.
c) Contractions of the stomach wall do not begin until food enters the stomach.
d) The contractions of the stomach depend on activity in the vagus nerve.
ANSWER
a) Gastric emptying is inhibited by the enterogastric reflex
REVISION NOTES
The enterogastric reflex is a general term that is used to describe all the hormonal and nervous mechanisms that control gastric emptying. The most vigorous mixing movements in the stomach take place in the antral region. Storage takes place in the main body of the stomach. Although during fasting the stomach wall shows only weak contractions, short periods of powerful contractions occur in extreme hunger (“hunger pangs”). The vagus plays only a minor role in the control of gastric motility, intrinsic nerves are much more important.

6. Regarding pancreatic secretion:
a) Pancreatic secretion is inhibited by gastrin secreted by the G cells of the antrum
b) Pancreatic acinar cells contain trypsin.
c) Cholecystokinin inhibits secretion from the exocrine pancreas.
d) The introduction of acid into the duodenum stimulates pancreatic secretion.
ANSWER
d) The introduction of acid into the duodenum stimulates pancreatic secretion.
REVISION NOTES
The G cells of the antrum stimulate enzyme secretion by the pancreas. The pancreatic acinar cells contain trypsinogen, which is converted to trypsin in the small intestine by enteropeptidase. Cholecystokinin stimulates enzyme secretion by the pancreatic acinar cells. Acid in contact with the duodenal wall causes the secretion of secretin, which stimulates a copious alkaline secretion by the cells of the pancreatic ducts.

7. Regarding digestion and absorption by the small intestine:
a) Intestinal digestive enzymes are secreted by cells of the crypts of Lieberkuhn.
b) About half of the digested carbohydrate is absorbed in the small intestine.
c) Small peptides are absorbed in the small intestine
d) The liver is the first organ to receive the digestion products of dietary fats.
ANSWER
c) Small peptides are absorbed in the small intestine
REVISION NOTES
The enzymes of the small intestine are associated with the brush border of the epithelial cells. The crypts secrete isotonic fluid. Virtually all the digested carbohydrates are absorbed in the small intestine. Although absorbed sugars and amino acids pass from the small intestine to the liver via the portal vein, the digested fats first pass to the general circulation via the lymph.

8. Regarding gastro-intestinal function:
a) The presence of large amounts of fat in the chyme will accelerate gastric emptying.
b) Distension of the ileum stimulates gastric motility.
c) Total gastrectomy leads to malabsorption of vitamin B12.
d) Aldosterone inhibits the absorption of sodium and water by the large intestine
ANSWER
c) Total gastrectomy leads to malabsorption of vitamin B12.
REVISION NOTES
Fatty chyme leaves the stomach more slowly than chyme that contains little fat. Both cholecystokinin (CCK) and GIP are released from the duodenal wall in response to the presence of fatty acids in the duodenum, and both hormones delay gastric emptying. Distension of the ileum inhibits gastric motility. Intrinsic factor secreted by the parietal cells of the gastric glands is needed for the absorption of vitamin B12. Aldosterone stimulates the absorption of sodium and water by the large intestine – this is an aspect of the sodium conserving action of aldosterone

9. Bile salts
A. Are the only constituents of bile necessary for digestion
B. Have a characteristic molecule, part water-soluble and part fat-soluble.
C. Are reabsorbed mainly in the upper small intestine.
D. Are derived from cholesterol.
E. Inhibit bile secretion by the liver
REVISION NOTES
A. True – They emulsify fat creating a greater surface area for lipase to act on.
B. True – This property allows them form to micelles for fat transport.
C. False – They are absorbed in the terminal ileum.
D. True – They are synthesized from cholesterol in the liver.
E. False – They are ‘choleretics’, substances which stimulate bile secretion.

10. Absorption of
A. Fat is impaired if either bile or pancreatic juice is not available.
B. Undigested protein molecules can occur in the newborn.
C. Laevo-amino acids occurs more rapidly than absorption of the dextro-forms.
D. Iron is at a rate proportional to body needs.
E. Sodium is at a rate proportional to body needs.
REVISION NOTES
A. True – If either is absent, undigested fat appears in the feces.
B. True – Maternal antibodies (globulins) in colostrum are so absorbed.
C. True – Transport mechanisms are isomer-specific.
D. True – An active carrier-mediated transport mechanism is involved which reduces the danger of iron toxicity with excessive intake.
E. False – Most ingested sodium is absorbed; if absorption is above the body requirements, the excess is excreted by the kidneys.

11. The passage of gastric contents to the duodenum may cause
A. Copious secretion of pancreatic juice rich in bicarbonate
B. Decreased gastric motility
C. Contraction of the gallbladder
D. Contraction of the sphincter of Oddi
E. Release of pancreozymin.
REVISION NOTES
A. True – This is caused by the hormone secretin released from the duodenal mucosa.
B. True – This postpones further gastric emptying.
C. True – Due to the action of cholecystokinin released from the mucosal cells.
D. False – The sphincter of Oddi must relax to allow bile to enter the gut.
E. True – Pancreozymin stimulates the pancreas to secrete a scanty, enzyme rich juice.

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