Digestion and Absorption in the GI Tract

Question 1

Lactose intolerance

Answer 1

Lactase enzyme activity is deficient or absent
Lactose converted to SCFAs and hydrogen
Remains in lumen, holds H2O in lumen resulting in osmotic diarrhea
Ferments into methane and H+ gas

Question 2

Type of transport for glucose, galactose and fructose in small intestine

Answer 2

Concentration gradient established by Na/K ATPase
Secondary active transport for glucose and galactose via SGLT1 cotransport w/Na
Facilitated diffusion for fructose via GLUT5
GLUT2 facilitated transport of these sugars into blood

Question 3

Most starch breakdown occurs where

Answer 3

Small intestine via pancreatic amylase

Breaks starch down into maltose and longer (3-9) polymers of glucose

Question 4

Congenital trypsin absence

Answer 4

All pancreatic enzymes are gone because trypsin cleaves/activates the pancreatic enzymes
Trypsinogen (enterokinase) catalyzes trypsinogen–>tryspin

Question 5

Cystinuria

Answer 5

Defect in transport or absence of di-basic AA transporter
Cystine, lysine, arginine, ornithine are not reabsorbed at proximal tubule
Cystine is most problematic because it is not very soluble and aggregates

Question 6

Hartnup disease

Answer 6

Cannot absorb neutral AA
Symptoms resemble pellagra (niacin deficiency)
High excretion of tryptophan & its byproducts like serotonin
Diarrhea, mood changes, neurological problems, red/scaly skin, photosensitivity

Question 7

Cystic fibrosis

Answer 7

CFTR Cl channel is defective
Pancreatic problems early in life
Some CFTR mutations associated w/loss of HCO3 secretion which means pancreas cannot move enzymes from ducts - leads to acute/chronic pancreatitis

Question 8

Pancreas protein digestion - enzymes/functions

Answer 8

Mostly breaks proteins into di/tripeptides and some AAs

Trypsin, chymotrypsin, carboxypeptidase, elastase

Question 9

Small intestine protein digestion

Answer 9

Aminopolypeptidase, dipeptidases

AAs, di/tri-peptides are absorbed into enterocytes

Question 10

Amino acid vs Di/tri-peptide cotransport

Answer 10

AAs cotransported with sodium

Di/tripeptides cotransported with hydrogen

Question 11

Folds of Kerckring

Answer 11

Longitudinal folds in the small intestine containing villi and microvilli
Increasing surface area for absorption
Duodenum has longest villi

Question 12

Fat digestion in the stomach

Answer 12

Lingual and gastric lipase act on TAGs
10% of TAG digestion
Cholesterol ester hydrolase separates cholesterol from FAs
CCK inhibits gastric emptying for more mixing along with activating gallbladder emptying

Question 13

Small intestine fat digestion

Answer 13

Most digestion of lipids occurs here - bile salts emulsify

Pancreatic lipase - inactivated by bile salts - colipase prevents pancreatic lipase from being inactivated by bile salts

Question 14

ApoB

Answer 14

Found on chylomicrons

Lack leads to abetalipoproteinemia - no lipid absorption leading to steatorrhea

Question 15

Overlying theme of pancreatic insufficiency, Zollinger-Ellison syndrome and Pancreatitis

Answer 15

Duodenum is too acidic due to lack of HCO3 containing pancreatic secretions

Question 16

SIBO

Answer 16

Bacteria deconjugate bile salts, impairing micelle formation
Can damage intestinal mucosa
Too little gastric secretion and small intestinal dysmotility
Methane and hydrogen detected in breath test

Question 17

Causes of IF deficiency

Answer 17

Atrophic gastritis- chronic inflammation of stomach mucosa leading to loss of parietal cells
Autoimmune metaplastic atrophic gastritis- immune system attacks IF protein or parietal cells

Question 18

Water soluble vitamin vs fat soluble vitamin absorption

Answer 18

Fat soluble ADEK- same mechanisms as lipids

Water soluble BC- most are absorbed via Na depended cotransport except B12

Question 19

Iron absorption

Answer 19

Occurs in duodenum
Liver secretes apotransferrin into bile, enters duodenum
Apotransferrin binds free iron and hemoglobin forming transferrin
Transferrin binds intestinal epithelial cell receptors and is absorbed via pinocytosis
Ferroportin transports iron into the blood and transferrin transports to liver/spleen/bone marrow

Question 20

Jejunum vs ileum electrolyte absorption

Answer 20

Jejunum- absorbs lots of sodium

Ileum- sodium absorbed, HCO3 secreted

Question 21

Colon electrolyte absorption

Answer 21

Na absorption and K+ secretion

Aldosterone modulates- stimulates Na absorption

Question 22

Cholera

Answer 22

Increases cAMP causing increased Cl secretion, accompanied by Na and H2O secretion
Volume of fluid secreted into the intestinal lumen overwhelms the absorptive mechanisms of the small intestine/colon leading to massive secretory diarrhea

Question 23

Calcium absorption occurs where

Answer 23

Small intestine - duodenum/jejunum