Digestive Physiology

Question 1

Process that mostly occurs in the small intestine

Answer 1

Digestion
◦Enzymes secreted to the lumen hydrolyze (break
down by reacting with water) larger molecules into monomers

Question 2

Absorption of molecules in the intestine involves:

Answer 2

◦Entering epithelial cells across apical membrane
from the intestinal lumen
◦Movement across the basolateral membrane of
epithelial cells into the intestinal fluid
◦Diffusion into capillaries or lacteals

Question 3

Digestion begins in the mouth with

Answer 3

Salivary amylase splitting starch into oligosaccharides (chains of 3–10 simple sugars)

Question 4

Digestion continues in the intestine with

Answer 4

◦Pancreatic amylase breaking down starch &
glycogen into oligosaccharides & disaccharides
(chains of 2 simple sugars)
◦Brush border enzymes breaking oligosaccharides & disaccharides into monosaccharides (single simple
sugars)

Question 5

monosaccharides (glucose, galactose, fructose) are moved across apical membrane of absorptive cells via

Answer 5

Transporters

Question 6

Monosaccharides glucose & galactose move across the apical membrane via

Answer 6

Na+ dependent secondary active transport (SGLT1) ◦ Na+K+ ATPase pumps Na+ across basolateral membrane to maintain Na+ gradient (maintains low Na+ inside of cell) necessary for SGLT1 to function

Question 7

Fructose is moved across the apical membrane via

Answer 7

facilitated diffusion (GLUT5)

Question 8

Monosaccharides move into the interstitial fluid across basolateral membrane via

Answer 8

facilitated diffusion (GLUT2) & then enter capillaries via intercellular clefts

Question 9

Percentage of adults that can’t digest lactose

Answer 9

60-70%

Question 10

Lactose is hydrolyzed into glucose & galactose by

Answer 10

Lactase

Question 11

Producing lactase throughout your life is

Answer 11

Lactase persistence

Question 12

Deficient amounts of lactase is

Answer 12

Lactose intolerance
◦ Microbial metabolism of undigested solutes
produces large amounts of gas (H 2, CO2 & CH4) → bloating, flatulence, & cramping pain
◦ Undigested lactose creates an osmotic gradient in
intestine that prevents water from being absorbed → diarrhea

Question 13

In the stomach hydrolysis of denatured proteins begins via

Answer 13

Pepsin (secreted by chief cells)

Question 14

In the small intestine hydrolysis of proteins continues via

Answer 14

◦Pancreatic proteases breaking down proteins &
protein fragments into smaller pieces & some
amino acids (Trypsin, chymotrypsin, carboxypeptidase B)
◦Brush border peptidases break oligopeptides
into di- & tripeptides, & amino acids
◦Intracellular peptidases hydrolyze di- & tr- peptides

Question 15

Proteins are absorbed via

Answer 15

Transporters moving amino acids or small peptides across apical membrane of absorptive cells (active transport)
◦ Amino acids use primary active transport and Na+-dependent secondary active transport (like monosaccharides)
◦ Di- & tri-peptides use H+-dependent secondary active transport

Question 16

In protein digestion amino acids move into interstitial fluid across basolateral membrane via

Answer 16

Facilitated diffusion & then enter capillaries via intercellular clefts

Question 17

Allergies result from

Answer 17

Intact proteins being taken up by intestinal epithelial cells via endocytosis & being released into body where the immune system detects them as foreign antigens

Question 18

The primary site for lipid digestion is

Answer 18

The small intestine

Question 19

Lipid digestion begins with

Answer 19

The emulsification of lipids with bile salts
◦ ↑ SA exposed to water-soluble lipase enzymes

Question 20

2nd step of lipid digestion is

Answer 20

Pancreatic lipases breaking down triglycerides to monoglycerides & free fatty acids

Question 21

3rd step of lipid digestion is

Answer 21

Monoglycerides & fatty acids grouping with bile salts to form micelles
◦Helps transport lipids to absorptive surfaces of
intestinal cells
◦Also combine with fat-soluble vitamins (A, D, E,
K) & cholesterol to aid with their absorption

Question 22

At plasma membrane, using simple diffusion, fatty acids & monoglycerides

Answer 22

Dissociate from micelles & move into epithelial cells

Question 23

Within epithelial cells monoglycerides & fatty acids are converted back to

Answer 23

Triglycerides

Question 24

Chylomicrons are

Answer 24

Protein-coated combinations of triglycerides with cholesterol & other lipids that move into interstitial fluid via exocytosis & are taken into lacteals for transport in lymph (too large to enter blood capillaries)

Question 25

Pancreatic nucleases hydrolyze nucleic acids (DNA & RNA) into

Answer 25

Nucleotide monomers

Question 26

Nucleosidases & phosphatases (brush border enzymes) break down nucleotides into

Answer 26

Free nitrogenous bases, pentose sugars, & phosphate ions; which are then actively transported by special carriers in the epithelium of the villi

Question 27

Vitamins are

Answer 27

Organic cofactors that help with metabolism (mostly absorbed in the small intestine)

Question 28

Vitamins mostly absorbed by specific active or passive transporters

Answer 28

Water-soluble vitamins (B’s & C)
◦Vitamin B 12 – a large polar molecule, is bound by intrinsic factor (produced by stomach) & absorbed in ileum by endocytosis

Question 29

Vitamins carried by micelles of lipids & absorbed by simple diffusion

Answer 29

Fat-soluble vitamins (A, D, E & K) – Vitamins K & B 7 – made available through bacterial metabolism & absorbed by large intestine

Question 30

Most electrolytes are absorbed via

Answer 30

Active transport along the entire length of the small intestine
◦Calcium & iron – mainly absorbed in duodenum

Question 31

The most abundant substance in chyme is

Answer 31

Water

Question 32

90% of the water in chyme is

Answer 32

Reabsorbed via osmosis in the small intestine (remaining 10% in the large intestine)