Deck 26: Digestion and Absorption of Basic Nutritional Constituents

Question 1

The digestion and absorption of starch involves hydrolysis to glucose

A) followed by an antiport mechanism of absorption.
B) followed by phosphorylation and absorption of the glucose phosphate.
C) followed by absorption after conjugation with glutathione.
D) followed by absorption via a symport mechanism.
E) after endocytosis of starch by intestinal epithelial cells.

Answer 1

followed by absorption via a symport mechanism.

Question 2

Which enzyme is an endopeptidase secreted as a zymogen by the pancreas?

A) trypsin
B) pepsin
C) amylase
D) enterokinase
E) carboxypeptidase

Answer 2

trypsin

Question 3

Sucrose is composed of

A) two residues of D-glucose.
B) one residue each of D-glucose and D-fructose.
C) one residue each of D-glucose and D-galactose.
D) one residue each of D-galactose and D-fructose.
E) two residues of D-fructose.

Answer 3

one residue each of D-glucose and D-fructose.

Question 4

Pancreatic lipase is an enzyme which

A) hydrolyzes triglycerides to glycerol plus fatty acid.
B) specifically attacks the 2-position of triglycerides.
C) specifically attacks the 1- and 3-ester linkages of triglycerides.
D) specifically hydrolyzes 2-monoglycerides to glycerol and fatty acid.
E) specifically hydrolyzes phospholipids.

Question 5

bile salts are stored in the

A) gall bladder.
B) liver.
C) small intestine.
D) all of the above.

Question 6

Human bile contains all of the following EXCEPT

A) glycocholic acid.
B) mucin.
C) phosphoglycerides.
D) triacylglycerol.
E) taurocholic acid.

Question 7

Which of the following compounds would you suggest be eliminated from the diet of a patient suffering from galactosemia?

A) leucine
B) starch
C) lactose
D) glucose
E) none of the above

Question 8

Which molecule is a zymogen activated by hydrolysis in the intestine?

A) trypsinogen
B) chymotrypsin
C) carboxypeptidase
D) enterokinase
E) pepsinogen

Question 9

Chymotrypsin is

A) an enterokinase.
B) an endopeptidase.
C) a carboxypeptidase.
D) the precursor of trypsin.
E) an aminopeptidase.

Question 10

What are the total products of triglyceride digestion in the lumen of the small intestines?

A) Free glycerol and free fatty acids.
B) 2-Monoglycerides and free fatty acids.
C) 1-Monoglycerides and free fatty acids
D) 2-Monoglycerides, free glycerol and free fatty acids.
E) Diglycerides and free fatty acids.

Question 11

What type of cells have secretagogue receptors?

A) Autocrine
B) Endocrine
C) Exocrine
D) Juxtacrine
E) Paracrine

Question 12

The action of pancreatic amylase followed by maltase on starch would yield

A) fructose, isomaltose and glucose.
B) maltose, alpha-dextrins and lactose.
C) amylose and alpha-dextrins.
D) maltotriose, glucose and alpha-dextrins.
E) maltose, maltotriose and amylose.

Question 13

Which enzyme is responsible for the conversion of pepsinogen to pepsin?

A) enteropeptidase
B) gastrin
C) pepsin
D) trypsin
E) Both B and C are correct.

Question 14

All of the following statements are correct EXCEPT which one?

A) triglyceride digestion requires a lipase produced by the pancreas.
B) triglycerides can be emulsified in the gut using bile salts.
C) Phospholipids can aid emulsification of triglycerides in the gut.
D) lipases use water as a cosubstrate.
E) Long chain acyl-CoA's are products when lipases degrade triglycerides.

Question 15

Which enzyme of intestinal origin activates trypsinogen?

A) pepsin
B) carboxypeptidase
C) chymotrypsin
D) enterokinase
E) cholecystokinin

Question 16

An enzyme present in saliva which hydrolyzes starch to produce free maltose is

A) sucrase.
B) alpha-amylase.
C) phosphorylase.
D) debranching enzyme.
E) limit dextrin.

Question 17

In the transport of glucose from the intestinal lumen through the epithelial cells, which of the following is NOT true?

A) A metabolic poison (cyanide) or absence of oxygen would have no effect.
B) It requires sodium, potassium ATPase.
C) It is unidirectional.
D) It is stereospecific.
E) Cotransport with sodium occurs.

Question 18

All of the following are true of mixed micelles formed in the intestine EXCEPT which one?

A) They provide a vehicle for the absorption of fat soluble vitamins.
B) They are absorbed directly into the lymphatic system via the lacteals.
C) Cholesterol is often a component of micelles.
D) Micelles contain mainly free fatty acids and monoacylglycerols.
E) The non-polar ends of lipids are oriented toward the center of the micelles.

Question 19

Which of the following is the main carrier for the transport of digested fat?

A) chylomicron
B) VLDL
C) LDL
D) HDL
E) albumin

Question 20

The formation of chylomicrons takes place in the

A) adipose tissue where stored triacylglycerols are mobilized.
B) small intestine where dietary triacylglycerols are digested and absorbed.
C) liver where cholesterol and apolipoproteins are synthesized.
D) blood where circulating lipoproteins are degraded by lipases.

Question 21

All of the following occur at or in the brush border (microvilli) of intestinal mucosal cells EXCEPT which one?

A) Na⁺-driven cotransport of amino acids.
B) Na⁺-driven cotransport of fatty acids.
C) Na⁺-driven cotransport of glucose.
D) conversion of dipeptides to amino acids.
E) uptake of monoglycerides.

Question 22

Which molecule is synthesized in the stomach as a precursor of a proteolytic enzyme?

A) pepsinogen
B) trypsinogen
C) chymotrypsin
D) enterokinase
E) progastrin

Question 23

The processes involved in the secretion of enzymes and electrolytes in the digestion system are regulated and coordinated by which of the following substances?

A) acetyl choline
B) histamine
C) serotonin
D) gastrin
E) all of the above

Question 24

Which of the following is produced by the liver?

A) trypsinogen
B) chymotrypsinogen
C) carboxypeptidase
D) enterokinase
E) glycocholic acid

Question 25

Most nutrients are absorbed in the:

A) Colon
B) Large intestine
C) Small intestine
D) Stomach

Question 26

Cellulose is not digested by humans because it

A) is a relatively insoluble protein-carbohydrate complex inaccessible to digestive enzymes.
B) is a mucopolysaccharide, which is not a substrate for digestive enzymes.
C) is highly sulfated, making it inaccessible to the action of most glycosidases.
D) is a polymer of glucose molecules in beta 1-4 linkage for which we have no digestive enzymes.
E) resists enzyme action due to its highly branched structure.

Question 27

Which statement about protein digestion in the stomach and intestines is FALSE?

A) Trypsin can activate all zymogens of pancreatic proteases.
B) pepsin is irreversibly inactivated when the pH is above 5.
C) Chymotrypsin and trypsin show similar specificity in catalyzing the hydrolysis of peptide bonds.
D) The action of pepsin in the stomach produces primarily peptide fragments of proteins.
E) Intestinal peptidases are required to digest di- and tri-peptides.

Question 28

What do cardiac glycosides inhibit?

A) Cl-/HCO3- transporter
B) Electrogenic Na+ flux
C) Na⁺/H⁺ transporter
D) Na⁺/K⁺/2Cl- cotransporter
E) Na⁺/K⁺-exchanging ATPase

Question 29

Which transport mechanism is unique to parietal cells for the transport of HCl?

A) Cl^-/HCO3^- exchanger
B) Cl^-/Na⁺ antiporter
C) Electrogenic Cl- flux
D) K⁺/H⁺ -exchanging ATPase
E) Na⁺/H⁺ transporter

Question 30

Which of the following statements about bile acids is CORRECT?

A) bile acids are required for the absorption of vitamins A and K
B) Taurodeoxycholic acid is a primary conjugated bile acid.
C) Glycochenodeoxycholic acid is a secondary conjugated bile acid.
D) The presence of high concentrations of bile acids stimulates the synthesis of additional bile acids.
E) The rate-limiting step in their synthesis is decarboxylation.

Question 31

Pancreatic enzymes cannot catalyze the complete digestion of dietary proteins to amino acids in the intestine because

A) pancreatic proteases are zymogens.
B) the pH in the small intestine is unfavorable for activity of pancreatic proteases.
C) pancreatic proteases are endopeptidases.
D) bacteria destroy pancreatic proteases in the small intestine.
E) pepsin from the stomach is required to activate pancreatic proteases.

Question 32

Enzymes involved in the digestion of dietary protein in the small intestine include all of the following EXCEPT

A) trypsin
B) elastase
C) chymotrypsin
D) carboxypeptidase A
E) pepsin

Question 33

The major site of digestion of dietary fats is the

A) stomach.
B) liver.
C) small intestine.
D) duodenum.
E) large bowel.

Question 34

Monoglycerides formed by digestion of unmodified animal fats usually contain

A) a saturated fatty acid residue.
B) an unsaturated fatty acid residue.
C) about equal amounts of saturated and unsaturated fatty acid residues.

Question 35

Which type of reaction BEST characterizes the process of digestion?

A) hydrolysis
B) dehydration
C) dehydrogenation
D) phosphorolysis
E) hydrogenation

Question 36

A typical property of a detergent is the formation of a micelle in solution. Under which of the following conditions is a detergent least likely to form micelles?

A) at high detergent concentrations
B) in the presence of other amphipathic molecules
C) in the presence of low amounts of lysolecithin
D) at low detergent concentrations
E) None of the above; detergents always form micelles.

Question 37

Dietary triacylglycerols are mainly hydrolyzed in the intestinal tract by

A) hepatic lipase to glycerol and fatty acids.
B) hormone-sensitive lipase to glycerol and fatty acids.
C) hormone-sensitive lipase to monoacylglycerol and fatty acids.
D) pancreatic lipase to diacylglycerol and fatty acids.
E) pancreatic lipase to monoacylglycerol and fatty acids.

Question 38

Alpha-1,6-glucosidase is an enzyme in humans which is

A) found in salivary and pancreatic secretions.
B) secreted by cells of the gastric mucosa.
C) located in the epithelium of the large intestine.
D) elaborated by cells in the duodenum.
E) a constituent of bile.

Question 39

All of the following are part of the process of protein digestion EXCEPT

A) denaturation of many proteins at the pH of gastric juice.
B) the action of enteropeptidase (enterokinase) on pro-aminopeptidase.
C) conversion of pepsinogen to pepsin by the action of pepsinogen.
D) catalysis of protein hydrolysis by both endo- and exopeptidases.
E) the action of specific dipeptidases.

Question 40

Absorption of all the major nutrients (fat, protein, polysaccharide) from the gut has which of the following characteristics?

A) Active transport is required.
B) ATP hydrolysis, when employed, results in heat production, not useful work.
C) The products absorbed are typically derived by hydrolysis of larger molecules.
D) Absorption results exclusively in entry into the portal circulation.
E) In each case where ATP is employed, the absorbed substance is phosphorylated.

Question 41

Lactose intolerance is caused by deficient activity of

A) galactose 1-phosphate uridylyltransferase.
B) amylase.
C) lactose dehydrogenase.
D) lactase.
E) galactokinase.

Question 42

Bile salts are synthesized in the

A) gall bladder.
B) liver.
C) small intestine.
D) all of the above.

Question 43

Concerning the bile acids, which of the following statements is/are CORRECT

A) glycocholic and taurocholic acids are the major conjugated bile acids.
B) some of the conjugated bile acids are returned to the liver from the intestine via the enterohepatic circulation.
C) the major lipid components of bile, besides the conjugated bile acids, are phosphatidyl choline and cholesterol.
D) all of the above.
E) none of the above.

Question 44

All of the following would be able to function as emulsifying agents in water EXCEPT which one?

A) sphingomyelin
B) 2-acylglycerol
C) phosphatidylcholine
D) sodium stearate
E) cholesterol ester

Question 45

All of the following statements about alpha-amylase are correct EXCEPT which one?

A) Small branched dextrins are poor substrates for the enzyme.
B) Amylopectin and glycogen are normal substrates.
C) The major product of its action on amylose is glucose.
D) The enzyme catalyzes the hydrolysis of alpha-1,4-glucosidic linkages.
E) For humans, the most important occurrence of the enzyme is in the secretion of the pancreas.

Question 46

The intestinal cell is probably unique in that it can

A) Synthesize lipoprotein.
B) Acylate monoglyceride to form triglyceride.
C) Synthesize phosphatidic acid.
D) Absorb free fatty acids.
E) Utilize glucose to form glycerol phosphate.

Question 47

Which of the following is involved in the conversion of a zymogen into an active enzyme in the intestine?

A) carboxypeptidase
B) cholecystokinin
C) pepsin
D) enterokinase
E) all of the above

Question 48

Which protein is synthesized in the intestine?

A) trypsinogen
B) chymotrypsinogen
C) procarboxypeptidase
D) enterokinase
E) pepsin

Question 49

In a patient who has had a significant portion of the stomach removed in surgery, the action of which of the following enzymes would be significantly reduced?

A) trypsin
B) enteropeptidase
C) elastase
D) pepsin
E) carboxypeptidase A

Question 50

The major function of chylomicrons is transport of

A) cholesterol from the liver to peripheral cells.
B) dietary triglycerides to peripheral tissues.
C) fatty acids from the adipose tissue to energy-requiring tissues such as skeletal muscle.
D) endogenous triglycerides from the liver.
E) cholesterol from peripheral tissues to the liver for disposal.

Question 51

Which of the following statements is true concerning secretagogues?

A) They are secreted by exocrine glands into the digestive tract
B) They stimulate the secretion of calcium ions into the digestive tract
C) They may be comprised of neurotransmitters and hormones that act on exocrine cells
D) They are cleaved by digestive enzymes and absorbed into small intestine
E) They are released as zymogens from exocrine cells

Question 52

Glucose absorption:

A) occurs without the need for a transport protein in muscle cells.
B) needs an active Na+ pump in liver cells.
C) requires insulin in the brain.
D) is stimulated by glucagon in the liver.
E) occurs against a concentration gradient in the intestinal mucosa.

Question 53

What is the principal physiological function of bile salts?

A) To permit cholesterol catabolism.
B) To catalyze lipid digestion.
C) To permit gastrointestinal absorption of dietary lipid.
D) To control enterohepatic circulation.
E) To regulate blood cholesterol levels.

Question 54

Lactase catalyzes which of the following?

A) galactose --> glucose + glucose 6-phosphate
B) sucrose --> glucose + fructose
C) lactate --> glucose + galactose
D) lactose --> glucose + galactose
E) lactate --> pyruvate

Question 55

Which digestive enzyme is NOT synthesized in the pancreas and secreted into the lumen of the intestine as a zymogen?

A) aminopeptidase
B) trypsin
C) chymotrypsin
D) elastase
E) carboxypeptidase B

Question 56

Chylomicrons are

A) produced in the gut, and contain triglycerides, cholesterol, cholesteryl esters, protein, phospholipids.
B) produced in the liver and contain triglycerides, cholesterol, cholesteryl esters, protein, phospholipids.
C) produced in the intestine and the liver and contain largely cholesterol and phospholipids.
D) produced in the intestine and contain bile salts in addition to triglycerides, cholesterol and phospholipids.
E) the smallest of the serum lipoprotein particles.

Question 57

Digestive enzymes operating within the gastrointestinal tract may be contributed by each of the following EXCEPT

A) synthesis in the liver.
B) synthesis in the gastric mucosa.
C) synthesis in the pancreas.
D) synthesis in the intestinal mucosa.
E) bacterial flora.

Question 58

Zymogens of gastric and pancreatic proteases are activated by

A) aggregation of monomers.
B) glycosylation.
C) formation of covalent crosslinks.
D) proteolysis.
E) association with coenzymes.

Question 59

The major site of carbohydrate digestion is the

A) mouth.
B) stomach.
C) small intestine.
D) large intestine.
E) pancreas.

Question 60

Dietary triglycerides are absorbed primarily as

A) 1,3 diglycerides.
B) intact triglyceride.
C) 1,2 diglyceride.
D) 1 monoglyceride.
E) 2 monoglyceride.

Question 61

The incorporation of iron is required in the biosynthesis of each of the following molecules EXCEPT

A) hemoglobin
B) immunoglobulin G (IgG)
C) cytochrome c
D) myoglobin
E) catalase

Question 62

The primary function of ferritin is best described as

A) providing storage of iron within cells.
B) providing storage of iron within the intestinal lumen.
C) providing storage of iron within the renal tubules.
D) providing transport of iron through the plasma.

Question 63

How is iron transfer across the mucosal-capillary interface regulated?

A) Change in the number of mucosal cells
B) Changes in pH
C) Degradation of heme-associated iron
D) Synthesis of apoferritin
E) Synthesis of transferrin

Question 64

Iron is stored in tissue primarily as

A) transferrin
B) heme enzymes
C) ferritin
D) ferrous salts
E) ferric salts

Question 65

Iron uptake in the intestine is promoted by all of the following except:

A) a low pH.
B) a high pH.
C) ascorbic acid (vitamin C) to maintain iron in the ferrous form.
D) a diet rich in heme.

Question 66

In order for cells to acquire iron all of the following are required except:

A) transferrin receptors to be expressed on the surface of cells.
B) binding of transferrin to transferrin receptors.
C) alkalization of the endosome containing the transferrin_transferrin receptor complex.
D) endocytosis of the transferrin-transferrin receptor complex.

Question 67

Which of the following statements is correct?

A) iron absorption into mucosal cells of the gut is a simple diffusion process.
B) Hemosiderin is produced by denaturation of ferritin with the loss of some apoprotein.
C) Apotransferrin is a large protein complex capable of binding thousands of iron hydroxide molecules.
D) iron is transported in blood chiefly as part of ferritin.
E) oxidizing agents promote the absorption of iron from the intestine.

Question 68

All of the following statements about iron metabolism are correct EXCEPT

A) iron is absorbed by the intestinal mucosa in the free Fe3+ form
B) overloading of iron in the body can occur as a result of repeated transfusions
C) transferrin is a glycoprotein that binds iron in the plasma
D) specific receptors for transferrin are probably required for delivery of iron to liver and erythropoietic tissue
E) ferritin stores iron in an oxidized form within a central cavity formed by its 24 subunits

Question 69

The cell responds to an influx of toxic iron by:

A) transcription of the ferritin gene to make new ferritin mRNA
B) splicing of stored ferritin pre-mRNA to produce new ferritin mRNA.
C) stabilizing the ferritin protein against proteolytic degradation.
D) derepressing the translation of ferritin mRNA.
E) converting an inactive form of ferritin to an active, iron-binding form.

Question 70

Primary bile acids are

A) any bile acids found in the small intestine.
B) any bile acids reabsorbed from the small intestine.
C) synthesized in the small intestine by bacteria.
D) synthesized in the liver from cholesterol.
E) converted to secondary bile acids by conjugation with glycine or taurine.

Question 71

The measurement of the iron binding capacity of serum is an indirect measurement of

A) ceruloplasmin level
B) transferrin level
C) albumin level
D) total body stores of iron
E) hemoglobin concentration in red blood cells

Question 72

Medium-chain triacylglycerols

A) are absorbed intact in the small intestine and are transported in the thoracic duct to blood as chylomicrons.
B) are not utilized in man because of a lack of pancreatic lipase specific for medium-chain triacylglycerols.
C) are readily absorbed in the small intestine and are transported in the portal vein.
D) contain mostly fatty acids having a chain length of 14-16 carbons.
E) none of the above.

Question 73

All of the following proteins bind iron EXCEPT

A) ferritin.
B) ceruloplasmin.
C) haptoglobin.
D) transferrin.
E) calmodulin.

Question 74

The excretion of iron

A) is regulated by the rate of iron absorption.
B) occurs mainly as a result of desquamation of cells.
C) involves transfer of iron from transferrin to renal tubular cells.
D) is the process by which total body iron is regulated.

Question 75

Which is classified as an exopeptidase?

A) trypsin
B) chymotrypsinogen
C) carboxypeptidase
D) enterokinase
E) pepsin

Question 76

Hemochromatosis is:

A) Treated with blood transfusions
B) An acquired anemia
C) Treated with a high carbohydrate diet
D) A consequence of hemorrhagic disease
E) Accompanied by saturated transferrin

Question 77

Normal cellular uptake of iron from the blood occurs by the process of

A) ATP-dependent active transport.
B) erythrocytosis.
C) hemochromatosis.
D) passive diffusion.
E) receptor-mediated endocytosis.

Question 78

Which of the following statements is correct?

A) iron absorption from the gut occurs at a rate which is independent of the quantity of body iron stores
B) ferritin is responsible for storage of most of the body iron
C) transferrin is a large spherical cluster of protein molecules capable of binding thousands of iron hydroxide molecules
D) iron is transported in blood chiefly as hemosiderin
E) iron is transported as both Fe+2 and Fe+3

Question 79

The complete digestion by humans of starch or glycogen to glucose requires

A) only amylase.
B) only phosphorylase.
C) amylase, an oligo-alpha-1,6-glycosidase, and a maltase.
D) amylase and sucrase.
E) a poly-alpha-1,4-glucosidase.

Question 80

Iron is transported in blood almost entirely as

A) free ferric ion.
B) ferritin.
C) free ferrous ion.
D) transferrin.
E) hemosiderin.