Digestion and absorption Processes in the GI Tract

Question 1

cellular absorption

Answer 1

lumen to apical membrane to intestinal epithelial cells to basolateral membrane to blood
transporters in membranes

Question 2

paracellular absorption

Answer 2

intestinal epithelial cells to lateral intercellular space to intestinal epithelial cells
tight junctions

Question 3

cavital (luminal) digestion

Answer 3

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

Question 4

membrane (contract) digestion

Answer 4

refers to hydrolysis by enzymes synthesized by epithelial cells

Question 5

structure of the intestinal mucosa

Answer 5

kerckring - longitudinal folds
villi and microvilli increase surface area of the small intestine (longer in duodenum and shorter in ileum)
all increase the intestine total surface area by 600 fold

Question 6

enterocytes

Answer 6

function in digestion, absorption and secretion
turnover rate cells are replaced 3-6 days
susceptible to irradiation and chemotherapy

Question 7

goblet cells

Answer 7

mucus secreting cells

physical chemical and immunologic protection

Question 8

paneth cells

Answer 8

part of the mucosal defense against infection

secrete agents that destruct bacteria or produce inflammatory responses

Question 9

pinocytosis

Answer 9

at the base of the microvilli

major mechanism in the uptake of proteins

Question 10

passive diffusion

Answer 10

particles move through pores in the cell membrane or through intercellular spaces

Question 11

barriers crossed during absorption into enterocyte

Answer 11

unstirred layer of fluid 
glycocalyx 
apical membrane 
cytoplasm of the cell 
basolateral membrane 
basement membrane 
wall of blood capillary or lymphatic vessel

Question 12

end products of carbohydrate digestion

Answer 12

only monosaccharides are absorbed by the enterocytes

glucose, glactose, and fructose

Question 13

transport mechanisms in absorption of carbohydrates

Answer 13

co-transport and facilitated diffusion

SLGT1 - secondary active transport

Question 14

lactose intolerance

Answer 14

failure to digest carbohydrates
brush border lactase is deficient or lacking
undigested lactose remains in the lumen and holds water and causes osmotic diarrhea
undigested and unabsorbed lactose is fermented into methane and H gas causing excess gas

Question 15

Stomach proteases - endopeptidase

Answer 15

pepsin
trypsin
chymotrypsin
elastase

Question 16

stomach proteases - exopeptidases

Answer 16

carbocypeptidase A

carboxypeptidase B

Question 17

small intestine proteases

Answer 17

trypsin
chymotrypsin
elastase
carboxy peptidase A
carboxy peptidase B

Question 18

transport mechanism in absorption of proteins

Answer 18

4 separate cotransporters - neutral, acidic, basic, and imino AA
4 separate facilitated diffusion mechanisms - one each for neutral acidic basic and imino AA

Question 19

chronic pancreatitis and cystic fibrosis

Answer 19

deficiency of pancreatic enzymes

Question 20

congenital trypsin absence

Answer 20

in the absence of trypsin it seems like all the pancreatic enzyme are gone

Question 21

cystinuria

Answer 21

defect in or absence of Na amino acid cotransporters
transporter for di basic amino acids is absent from the SI and kidney
genetic disorder
as a result of the intestinal deficiency amino acids are secreted in feces

Question 22

hartnup disease

Answer 22

cannot absorb neutral aa
recessive genetic disorder
symptoms resemble those caused by pellaga (deficiency of niacin)
symptoms - diarrhea, mood changes, neurologic problems, red, scaly skin rash, usually which skin is exposed to sunlight , photosensitivity, short stature, uncoordinated movements
urine same have high excretion of neutral aa

Question 23

mutations in cystic fibrosis transmembrane conductance regulator

Answer 23

regulated anion channel that is located at the apical surface of the duct cells
loss of bicarb secretion

Question 24

insolubility of lipids

Answer 24

lipids need to be solubilized in micelles and transported to the apical membrane of intestinal epithelial cells for absorption

Question 25

stomach and lipid digestion

Answer 25

lingual and gastric lipases initiate lipid digestion in the stomach CCK allows sufficient time for lipids to get digested properly by slowing gastric emptying

Question 26

small intestine and lipid digestion

Answer 26

most lipid digestion occurs in the small intestine bile salts emulsify lipids pancreatic enzymes are secreted into the small intestine to complete the digestive work

Question 27

pancreatic lipase

Answer 27

inactivated by bile slats colipase solves this problem

Question 28

colipase

Answer 28

secreted as inactive form it is activated by trypsin | once activated it binds to pancreatic lipase displacing bile salts

Question 29

cholesterol ester hydrolase

Answer 29

in addition to catalyze the production of cholesterol it also hydrolyzes triglycerides to produce glycerol

Question 30

phospholipase A2

Answer 30

proenzyme is activated by trypsin

Question 31

mechanism for processing lipids

Answer 31

``` solubilization by micelles diffusion of micellar contents across apical membrane reesterfication chylomicron formation exocytosis of chylomicrons ```

Question 32

abnormalities of pancreatic enzyme secretion

Answer 32

failure to secrete adequate amounts of pancreatic enzymes regulation of acidity of duodenal contents is critical for the integrity of pancreatic enzyme function Zollinger-Ellison syndrome Pancreatitis

Question 33

deficiency of bile salts

Answer 33

interferes with the formation of micelles ileal resection interrupts the enterohepatic circulation of bile salts small intestinal bacterial over growth

Question 34

decreased intestinal epithelial cells

Answer 34

tropical sprue - lipid absorption is impaired because the surface area for absorption is decreased

Question 35

fat soluble vitamins (A, D, E and K)

Answer 35

same mechanism of absorption as lipids

Question 36

water soluble vitamins (B1, B2, B3, B12, C, biotin, folic acid, nicotinic acid, and pantothenic acid)

Answer 36

absorbed via Na dependent cotransport mechanism in the small bowel

Question 37

Vitamin B12

Answer 37

form complexes with other proteins in order to be absorbed

Question 38

pernicious anemia

Answer 38

type of vitamin B12 anemia stomach does not produce enough IF which decreases B12 due to atrophic gastritis and autoimmune conditions

Question 39

absorption of vitamin D

Answer 39

D3 from diet converted to 15 hydroxy D3 in liver converted to 1,2 dihydroxy D3 and 24,25 dihydroxy D3 in liver leads to increase gut Ca2 absorption, bone calcification, bone reabsorption

Question 40

abnormalities of vitamin D absorption

Answer 40

inadequate Ca2 absorption - rickets and osteomalacia | no D3 and no 1,23 dihydroxy D3