Digestion and Abs 1 (Johnson)

Question 1

Where are digestive enzymes found?

Answer 1

Salivary, gastric, pancreatic secretions, and apical membrane of intestinal epithelial cells

Question 2

Describe the cellular path of absorption

Answer 2

Particle crosses apical membrane to enter the intestinal epithelial cell and is then exported on the basolateral side of the cell and into the blood

Question 3

Describe the paracellular path of absorption

Answer 3

Substances move across tight junctions between intestinal epithelial cells and into the blood

Question 4

increase the surface area of the small intestine, maximizing the exposure of nutrients to digestive enzymes and creating a large absorptive surface

Answer 4

Villi and microvilli and folds of Kerckring

Question 5

What are folds of Kerckring? What projects from them?

Answer 5

Longitudinal folds of small intestine with villi coming off of them

Question 6

Where are the villi the longest?

Answer 6

Duodenum

**where most of the abs and digestion occurs

Question 7

Where are the villi the shortest?

Answer 7

Terminal ileum

Question 8

The villi are covered by

Answer 8

Epithelial cells (enterocytes) interspersed with goblet cells

Question 9

Aka the brush boarder

Answer 9

Microvilli on apical surface of enterocytes

Question 10

What are the carbohydrates that are “absorbable” by the intestinal epithelial cells

Answer 10

Glucose, galactose, or fructose

Question 11

Describe the digestion of starch

Answer 11

Starch is broken down by salivary amylase. Then once in the stomach/duodenum pancreatic alpha amylase digests starch into disaccharides: alpha-dectrins, maltose, and maltotriose. These disaccharides are broken down by alpha dextrinase, maltase, sucrose into glucose.

Question 12

What monosaccharide does trehalose get broken down into? Via what enzyme?

Answer 12

Glucose via trehalase

Question 13

What monosaccharide does lactose get broken down into? Via what enzyme?

Answer 13

Glucose and galactose via lactase

Question 14

What monosaccharide does sucrose get broken down into? Via what enzyme?

Answer 14

Glucose and fructose via sucrose

Question 15

How is glucose abs across the epithelial intestinal cells?

Answer 15

Active transport: Na cotransport via SGLT1 on apical side

Facilitated Diffusion: GLUT2 on basolateral side

Question 16

How is galactose abs across the epithelial intestinal cells?

Answer 16

Active transport: Na cotransport via SGLT1 on apical side

Facilitated Diffusion: GLUT2 on basolateral side

Question 17

How is fructose abs across the epithelial intestinal cells?

Answer 17

Facilitated diffusion via GLUT5 on apical side and GLUT 2 on basolateral side
**dependent on electrochemical gradient to move it across the epithelim

Question 18

What is the source of the energy needed to move glc against its electrochemical gradient via active transport on apial membrane of intestinal epithelial cells?

Answer 18

Na gradient NOT directly ATP

**this gradient is maintained by Na/K ATPase on basolateral side (= indirectly)

Question 19

Difference between the endopeptidases and exopeptidases

Answer 19

Endo hydrolyze the inferior peptide bond in proteins

Exo hydrolyze one amino acid at a time from the C term

Question 20

What are the endopetidases and the expopeptidases?

Answer 20

Endo: pepsin, trypsin, chymotrypsin, and elastase

Exo: carboxypeptidases A and B

Question 21

Describe the process of protein digestion

Answer 21

Begins in the stomach via action of pepsin and continues in the small intestine via action of pancreatic and brush boarder peptidases.
Trypsinogen is activated by enterokinase into trypsin. Trypsin then activates all the other pancreatic proteases (including more trypsin). These proteases hydrolyze proteins into amino acids, dipeptides, tripeptides, and oligiopeptides. The oligiopeptides are then further digested by brush boarder peptides

Question 22

What form of proteins is absorbable?

Answer 22

Amino acids, di, and tri peptides

Question 23

Where does pepsin act? Why does it not continue to work farther down the GI tract?

Answer 23

Stomach—it has a narrow range of pH in which it is active, in the duodenum bicarb is secreted into it from the pancreas, binging the pH out of the range in which it is active

Question 24

Digestion of proteins is dependent on peptidase. How do we know?

Answer 24

F: in pts whose stomach is removed or does not secrete H+ protein digestion and abs is normal

**pancreatic and brush-border proteases alone can adequately digest ingested protein.

Question 25

The L or D form of amino acids is absorbed by intestinal epithelial cells

Answer 25

L

Question 26

How are amino acids absorbed by the intestinal epithelial cells

Answer 26

Na cotransport on apical membrane. There are separate transporters for neutral, basic, acidic, and imino amino acids. They are then transported across the basolateral side via facilitated transport

Question 27

How are di and tri peptides absorbed by the intestinal epithelial cells

Answer 27

H+ cotransport on apical side. Once they are inside they are hydrolyzed into amino acids by cytosolic peptidases and then transported across the basolateral side via facilitated transport. Remaining di and tri peptides are absorbed unchanged

Question 28

What drives the active transport of amino acids across the apical membrane of intestinal epithelial cells

Answer 28

Na gradient (established by Na/K ATPase on basolateral membrane)

Question 29

What drives the active transport of di and tri peptides across the apical membrane of intestinal epithelial cells

Answer 29

H+ gradient (established by Na/H exchanger on apical membrane)

Question 30

a genetic disorder in which the transporter for the dibasic amino acids are absent in both the small intestine and the kidney
What are these amino acids?

Answer 30

Cystinuria: cystine, lysine, arginine, and ornithine

→ increased excretion of these amino acids in the feces and the urine bc they cannot be absorbed by either the kidneys or the intestine

Question 31

What is the role of the stomach in the digestion of lipids

Answer 31

Churn and mix the lipids to break them into small droplets (increases SA) for digestive enzymes.
Peptides present in the stomach emulsify the lipid droplets.

Question 32

Enzymes that initiate lipid digestion in the stomach

Answer 32

Lingual an gastric lipases (Hydrolyze ~10% of ingested triglycerides to glycerol and free fatty acids)

Question 33

still have to

Answer 33

finish