Digestion and absorption processes in the GI tract

Question 1

Where does absorption mainly take place?

Answer 1

the small intestine

Question 2

Where is the first place that we can start digesting proteins?

Answer 2

in the stomach

Question 3

What are the 2 types of digestive activity?

Answer 3

cavital (luminal) digestion

Membrane (contact) digestion

Question 4

What are the longitudinal folds on the surface of the small intestine called?

Answer 4

folds of Kerckring

Question 5

Where are villi longest and shortest?

Answer 5

longest in the duodenum and shortest in the terminal iileum

Question 6

What are enterocytes?

Answer 6

eptihelial cells of the intestine

Question 7

What are globlet cells?

Answer 7

mucus secreting cells

-they protect us

Question 8

What are Paneth cells

Answer 8

Part of the mucosal defenses against infection

Question 9

What does the enterocyte membrane do to control the flux of solutes and fluid between the lumen and blood?

Answer 9

• pinocytosis @ base of microvilli, major mechanism in uptake of protein
• Passive diffusion: particles move through prose in cell membrane or through intercellular spaces
• Facilitated diffusion
• active transport

Question 10

What is the big deal if the terminal ileum is resected?

Answer 10

we can’t absorb vitamin B12 and bile salts

Question 11

What kind of carb is the only one that is absorbed by enterocytes?

Answer 11

ONLY MONOSACCHARIDES!

-we have to get everything to that point somehow

Question 12

What is starch broken down into?

Answer 12

amylase breaks it down to Dextrin, maltose, and maltotriose

-those all get turned into glucose

Question 13

What do trehalose, lactose, and sucrose get broken down into?

Answer 13

trehalose— glucose
lactose= gluc and galactose
sucrose= gluc and fruct

Question 14

What two sugars does sucrase cut?

Answer 14

maltotriose and sucrose

Question 15

What are the 3 end products of carb digestion?

Answer 15

glucose, galactose, and fructose

Question 16

What is the special transporter that Fructose gets?

Answer 16

GLUT 5

Question 17

What transports glucose and galactose into the cell?

Answer 17

SGLT 1

-uses 2ndary active transport with Na

Question 18

What exports all three digested sugars out of the basolateral side?

Answer 18

GLUT 2

Question 19

What results from the lack of the brush border enzyme lactase?

Answer 19

osmotic diarrhea and excess gas

Question 20

what is pepsin made by?

Answer 20

chief cells

Question 21

What are the 4 endo peptidases?

Answer 21

pepsin, trypsin, chymotrypsin, and elastase

Question 22

What are the exopeptidases?

Answer 22

Carbosypeptidase A and B

Question 23

In the small intestine, what activates trypsin?

Answer 23

Enteropeptidase (brush border) and trypsin

Question 24

What does trypsin do?

Answer 24

activates a lot of other enzymes

Question 25

What do we end up breaking proteins into when we are in the small intestine?

Answer 25

aa’s, di and tri peptides

Question 26

What kind of transport is used to bring in aa’s

Answer 26

2ndary active using Na,

-there are 4 separate sotransporters, one for each neutral, acidic, basic, and imino aa

Question 27

What kind of transporter is used to bring in di and tri peptides

Answer 27

H+ cotransporter
-then, a peptidase inside the cell cuts them up and then they go out the basolateral side like all the others through facilitated diffusion

Question 28

What is Cystinuria?

Answer 28

• when we don’t have that transporter for the di-basic amino acids
• those aa’s will be excreted in feces

Question 29

What is Hartnup disease?

Answer 29

when we cannot absorb neutral amino acids like trp

-ppl will have trp and serotonin in their pee or poo

Question 30

Which organ is the first one to fail in CF?

Answer 30

the pnacreas because the stuff is too thick so WE CAN’T FLUSH OUT ACTIVE ENZYMES OUT OF THE DUCT
-may lead to acute pancreatitis

Question 31

What makes the assimilation of lipids rather difficult?

Answer 31

their insolubility

-we need to stick them in micelles

Question 32

What initiates lipid digestion in the stomach?

Answer 32

lingual and gastric lipases

Question 33

What performs the emulsifying action of lipids in the stomach

Answer 33

dietary proteins

-NOT BILE

Question 34

What allows sufficient time for lipid to get digested properly by slowing the rate of gastric emptying?

Answer 34

CCK

-it’s secreted when fat hits the small intestine

Question 35

Where does the most lipid digestion occur?

Answer 35

the small intestine

-that’s where bile salts will emusilfy the lipids

Question 36

What are the 4 pancreatic enzymes that help complete the digestive work in the small intestine?

Answer 36

• pancreatic lipase: inactivated by bile salts, secreted as active form
• Colipase: activated by trypsin, it binds pancreatic lipase displacing bile salts
• cholesterol ester hydrolase: catalyzes production of cholesterol and hydrolzes triglycerides to produce glycerol
• PLA2: also activated by trypsin

Question 37

What is the optimum pH for pancreatic lipase?

Answer 37

6

Question 38

What is the mechanism for processing a lipid?

Answer 38

• solubize in bile salts
• diffusion of micellar content across apical membrane
• reesterification
• chylomicron formation (apoB)
• exocytosis of chylomicron

Question 39

What happens if there’s no Apo B?

Answer 39

there’s no absorption of dietary lipids

• abetalipoproteinemia
• we need that for the chylomicron

Question 40

What is the result of any disorder of lipid assimilation?

Answer 40

steatorrhea

Question 41

What are the key steps in lipid formation?

Answer 41

• pancreatic enzyme secretion
• bile acid secretion
• emulsification
• micelle formation
• diffusion of lipids into intestinal epithelial cells
• chylomicron formation
• transfer of chylomicrons into lymph

Question 42

What is Zollinger Ellison syndrom?

Answer 42

a gastrin-secreting tumor that makes parietal cells secrete a lot of H+ and there’s an overload of acid in the DUODENUM

Question 43

What do bacteria do to bile salts?

Answer 43

deconjugate them… causing a failure of micelle formation

Question 44

What are the 2 examples of deficits in bile salts?

Answer 44

Ileal resection and Small intestinal bacterial overgrowth

Question 45

What is Tropical sprue?

Answer 45

reduction inthe # of intestinal epithelial cells which in turn reduces the microvillar surface area
-lipid absorption is impaired because the surface area for absorption is decreased… steatorrhea

Question 46

What is non-troical (celiac) sprue?

Answer 46

autoimmune disorder

• Ab’s against a component of gluten:GLIADIN
• destruction of villi in SI
• can’t absorb B12 very well

Question 47

What are the fat soluble vitamins?

Answer 47

ADEK

-absorbed in same way as lipids

Question 48

What are the water soluble vitamins?

Answer 48

B1,2,3 and 12, C, biotin, folic acid, nicotinic acid, and pantothenic acid

Question 49

How are the water soluble vitamins absorbed?

Answer 49

via a Na+ dependent cotransport mechanism inthe small bowel

Question 50

What does Vit B12 complex with in order to be absorbed?

Answer 50

• R proteins secreted by slaivary juices
• IF secreted by gastric parietal cells
• and Transcobalamin II

Question 51

What happens if we take the stomach out or bypass it?

Answer 51

lose parietal cells or we can’t absorb Vit B12 anymore

Question 52

What is pernicious anemia?

Answer 52

Where B12 doesn’t get absorbed because IF isn’t there

• could be from chronic inflammation of stomach mucosa leading to no parietal cells
• or could be an autoimmune condition

Question 53

Describe the mechanism of the absorption of Vitamin D

Answer 53

• 7-dehydrocholesterol gets turned into cholecalciferol by the sun
• liver changes that to 25 hydroxy-D3 and it goes to the kidney
• that gets turned into 2 different forms of D3 by 1-alpha-hydroxylase
• increases gut Ca absorption, bone calcification, and bone resorption