Digestion & Absorption-1/26/16

Question 1

___ digestion refers to digestion resulting from the action of enzymes secreted by the salivary glands, stomach, and pancreas

___ digestion refers to hydrolysis by enzymes synthesized by epithelial cells

Answer 1

Cavital (luminal)

Membrane (contact)

Question 2

Villi are longest in the ___ of the SI and shortest in the ____ of the SI

Answer 2

Duodenum

Terminal ileum

Question 3

____ are epithelial cells whose function is digestion, absorption, and secretion. These are susceptible to irradiation and chemotherapy

___ are mucus-secreting cells which provide a physical, chemical, and immunologic protection

___ cells are part of the mucosal defenses against infection and secrete agents that destroy bacteria or produce inflammatory responses

Answer 3

Enterocytes

Goblet cells

Paneth cells

Question 4

On the enterocyte, where does pinocytosis occur?

Answer 4

At the base of the microvilli. It is a major mechanism in the uptake of protein

Question 5

If the terminal ileum is resected, absorption of ___ is abolished

Answer 5

Vitamin B-12 and bile salts

Question 6

Lactase converts lactose to ____

Sucrase converts sucrase to ____

The 3 end-products of carbohydrate digestion are ____

Answer 6

Glucose and galactose

Glucose and fructose

glucosa, galactose, and fructose

Question 7

List the 3 main carbohydrate transporters on the apical membrane of the SI:

Answer 7

Na-Glucose cotransporter (SLGT1)

Na-Galactose cotransporter (SLGT1)

Fructose transporter (GLUT5)

SLGT1 is secondary active transport and all of these bring Na and the sugar from the lumen into the cell

Question 8

List the Main transporters on the basolateral (blood) side of the SI:

Answer 8

Na-K ATPase–> creates the energy gradient

GLUT2 brings glucose, galactose, and fructose in individually

Question 9

How does lactose intolerance cause diarrhea?

Answer 9

Lactase is deficient on the brush-border and lactose remains in the lumen. As a result, undigested lactose holds water in the lumen and causes osmotic diarrhea

Undigested and unabsorbed lactose is fermented into methane and H+ gas, causing flatulence

Question 10

In the stomach, what converts pepsinogen to pepsin?

Answer 10

Low pH

Question 11

In the SI, what initially converts trypsinogen to trypsin?

Answer 11

Enteropeptidase (brush-border)

Question 12

Chymotrypsinogen –> chymotrypsin, Proelastase –> elastase, Procarboxypeptidase a/b –> carboxypeptidase a/b

All of these rxns are catalyzed by ___ in the SI

Answer 12

Trypsin

Question 13

What are the co-transporters for amino acids and di/tri-peptides on the apical (lumen) side in the SI?

Answer 13

Na-AA co-transporter

H-Di/tri-peptide cotransporter

Both co-transporters bring them from the lumen into the cell

Also a Na-H exchanger –> Na into the cell, H into the lumen

Question 14

Once di and tri-peptides are co-transported from the lumen into the cell via the H+-Di/tri-peptide cotransporter, what converts the di/tri-peptides into AAs?

Answer 14

Peptidase

Question 15

How are AA’s absorbed from the cells of the SI into the blood?

Answer 15

Na-K ATPase creates energy gradient

AA’s absorbed via facilitated diffusion

Question 16

___ is a genetic disorder that occurs when there is a defect or absence of Na+ - AA cotransporters and the transporter for di-basic AAs is absent from the SI and kidneys.

As a result of the intestinal deficiency, AAs are secreted in feces

Answer 16

Cystinuria

Question 17

___ is a recessive genetic disorder (SLC6A19 gene) where you cannot absorb neutral AAs, such as Trp. Urine samples from these patients reveal an abnormally high excretion of neutral AAs and their by-products

Answer 17

Hartnup disease

Question 18

Mutations in the ___ is associated with a deficiency of pancreatic enzymes

Answer 18

CFTR (Cystic Fibrosis Transmembrane conductance Regulator)

Question 19

Triglycerides are converted to monoglyceride and 2 FA’s via these enzymes:

Answer 19

Lingual, gastric, pancreatic lipases

Question 20

Cholesterol esters are converted to cholesterol and FA via these enzymes:

Answer 20

Cholesterol ester hydrolases

Question 21

Phospholipids are converted to lysolecithin and FA via this enzyme:

Answer 21

Phospholipase A2

Question 22

Most lipid digestion occurs in the ___ and ___ emulsifies the lipids in this region

Answer 22

SI

Bile salts

Question 23

Procolipase is converted to colipase via this enzyme:

Once colipase is activated, it bind to ___ to displace bile salts

Answer 23

Trypsin

Pancreatic lipase

Question 24

The proenzyme of Phospholipase A2 is activated by ____

Answer 24

Trypsin

Question 25

The pH optimum for pancreatic lipase is ___

Answer 25

6

Question 26

List the steps for the mechanism(s) of absorbing lipids:

Answer 26

1) solubilization by micelles
2) diffusion of micellar content across the apical membrane
3) Re-esterification
4) Chylomicron formation
5) Exocytosis of chylomicron

Question 27

The absence of ApoB on a chylomicron leads to ___

Answer 27

Abetalipoproteinemia–> impaired absorption of dietary lipids

Question 28

Steatorrhea is a result of ____

Answer 28

Disorder of lipid assimilation

I.e., abnormalities in: pancreatic enzyme secretion,bile acid secretion, emulsification, micelle formation, diffusion of lipids into intestinal epithelial cells, chylomicron formation, transfer of chylomicrons into lymph

Question 29

___ is the result of a gastrin-secreting tumor of the pancreas that leads to increased H+ secretion by gastric parietal cells and an overload of acid in the duodenum

Answer 29

Zollinger-ellison syndrome

Question 30

___ leads to impaired HCO3- secretion and impaired enzyme secretion, i.e., lipase and amylase

Answer 30

Pancreatitis

Question 31

____ is the reduction in the number of intestinal epithelia cells which in turn reduces the microvillar surface area. Cause is unknown and lipid absorption is impaired because the SA for absorption is decreased (steatorrhea). Diarrhea is the main symptom.

Answer 31

Tropical Sprue –> nutritional deficiencies especially Folate and B12. Treatment with Tetracycline and folate for 6 months

Question 32

____ is an autoimmune disorder thought to begin in childhood with the introduction of wheat gluten. Abs develop against gliadin that leads to destruction of the villi in the SI as well as hyperplasia of the intestinal crypts. Symptoms include abdominal pain, constipation, diarrhea

Answer 32

Non-tropical sprue (celiac sprue)

Malabsorption related to deficiencies in B12, folate, Fe, Ca, Vit D, and Vit A

Most common in caucasians and persons of European ancestry. Women affected more than men

Question 33

What is the mechanism for the absorption of fat-soluble vitamins (A,D,E,K)?

Answer 33

Same mechanism of absorption as lipids

Question 34

What is the mechanism of absorption of water-soluble vitamins (B1/2/3/12, Biotin, folic acid, nicotinic acid, pantothenic acid)

Answer 34

Most are absorbed via a Na+-dependent cotransport mechanism in the small bowel

Question 35

Vitamin B12 forms complexex with these proteins in order to be absorbed:

Answer 35

R Proteins (secreted in salivary juices)
IF (secreted by gastric parietal cells)
Transcobalamin II

Question 36

____ is a type of vitamin B12 anemia where the stomach does not produce enough IF, which leads to decreased B12

Answer 36

Pernicious anemia

Common causes:

• Atrophic gastritis–> chronic inflamm of stomach mucosa, leads to parietal cell loss
• Autoimmune condition –> IS attacks IF protein or gastric parietal cells

Question 37

The production of 1,25-dihydroxy-D3 leads to:
___ gut Ca absorption
___ bone calcification
___ bone resorption

Answer 37

All increase

Question 38

Inadequate Ca2+ absorption leads to:

Answer 38

Rickets (Children)

Osteomalacia (adults)

Question 39

Describe the cellular path of absorption:

Answer 39

Lumen–> apical membrane –> intestinal epithelial cell–> basolateral membrane–> blood

Transporters in membrane