Protein and Carbohydrate digestion

Question 1

What is digestion?

Answer 1

the breakdown of nutrients so they can be absorbed across the intestinal wall

Question 2

Where do the two phases of digestion occur?

Answer 2

within the lumen of the gut and within the brush border of enterocytes

Question 3

What is the intestinal brush border covered with?

Answer 3

a secreted layer of glycocalyx

Question 4

How does HCl begin the process of protein digestion?

Answer 4

it partially hydrolyzes some peptide bonds

Question 5

How is pepsin created?

Answer 5

HCl cleaves inactive pepsinogen that is secreted by the chief cells of fundic glands which creates pepsin

Question 6

What does pepsin do?

Answer 6

cleaves peptide bonds next to hydrophobic amino acids with aromatic side chains

Question 7

What is rennin secreted by?

Answer 7

chief cells

Question 8

What does rennin do?

Answer 8

cleaves between phe and met, especially in casein for neonates

Question 9

What happens in the lumenal phase of protein digestion?

Answer 9

peptides activate the receptors of enteroendocrine cells which then secrete CCK, CCK goes to the blood which enters the pancreas which leads to increased pancreatic enzyme secretion

Question 10

Where are digestive enzymed produced by enterocytes generally attaached to?

Answer 10

the apical membrane and they stick out of the glycocalyx of the brush border

Question 11

What do intestinal brush border peptidases do?

Answer 11

they take small peptides to mono, di, or tri amino acids within the brush border

Question 12

How many facilitated carriers are known for a single AA?

Answer 12

4

Question 13

What is always transported with the AA across the apical membrane and why?

Answer 13

Na to provide a driving force to move the large AA across the membrane

Question 14

What do di and tripeptides require to cross the apical membrane?

Answer 14

ATP - active transport

Question 15

What pathways can amino acids follow for absorption?

Answer 15

neutral, basic, acidic, and proline pathways

Question 16

Once inside the cell, what happens to di or tri-peptides that have crossed the apical membrane?

Answer 16

they are rapidly broken down to constituent amino acids via intracellular cytosolic peptidases

Question 17

How do amino acids cross the basolateral membrane?

Answer 17

via facilitated diffusion down a concentration gradient - Na is not needed here

Question 18

Once amino acids cross the basolateral membrane, what are they picked up by?

Answer 18

portal circulation

Question 19

What is an example of an intact protein that is absorbed across the digestive tract?

Answer 19

colostral antibody

Question 20

In monogastrics, what begins the breakdown of starch?

Answer 20

salivary amylase

Question 21

Where does the majority of monogastric CHO digestion occur?

Answer 21

in the small intestine

Question 22

What occurs during the luminal phase of CHO digestion?

Answer 22

pancreatic amylase is secreted and breaks down 1-4 alpha links between glucose molecules in CHO and takes it down to the level of disaccharide maltose and trisaccharides

Question 23

What are the di and tri-saccharide digesting enzymes assocciated with brush border membranes?

Answer 23

sucrase, dextrinase, maltase, lactase, intestinal cell amulase, trehalase

Question 24

In typical diets, what do 80% of carbohydrates end up as?

Answer 24

glucose

Question 25

In typical diets, what do 20% of carbohydrates end up as?

Answer 25

fructose and galactose

Question 26

Why do monosaccharides have no problem reaching the glycocalyx but have issues crossing the hydrophobic cell membrane?

Answer 26

because they are hydrophilic but they are too large to enter the cells by simple diffusion

Question 27

How does the liver utilize carbohydrates?

Answer 27

it uses glucose to produce glycogen

Question 28

How does muscle utilize carbohydrates?

Answer 28

uses glucose to produce glycogen for storage(fed state) or breaks down glycogen (fasted state)

Question 29

What does adipose use carbohydrates for?

Answer 29

it uses glucose and changes it to acetyl CoA or glycerol for triglyceride synthesis

Question 30

What does the nervous system use carbohydrates for?

Answer 30

it uses glucose except during extreme fasts, then it uses ketones

Question 31

What does the reproductive tract use carbohydrates for?

Answer 31

it uses glucose and AA for the fetus for energy or changes glucose into lactose for milk

Question 32

What do red blood cells use carbohydrates for?

Answer 32

it oxidizes glucose into lactate which is then returned to the liver for gluconeogenesis