Physiology

Question 1

Pancreatic Secretions: flow

Answer 1

Isotonic fluid;

low flow –> high Cl-

high flow –> high HCO3-

Question 2

Pancreatic Secretions (4)

Answer 2

alpha-amylase

lipases

proteases

trypsinogen

Question 3

Alpha-amylase

Answer 3

Pancreatic secretion

Role: starch digestion (1,4-glycosidic bonds)

secreted in active form

Question 4

Lipases

Answer 4

Pancreatic secretion

Role: fat digestion

Question 5

Proteases

Answer 5

Pancreatic secretion

Role: protein digestion

Includes: trypsin, chymotrypsin, elastase, carboxypeptidases

Secreted as proenzymes (zymogens)

Question 6

Trypsinogen

Answer 6

Pancreatic secretion

Role: Converted to active enzyme trypsin (activation of other zymogens and cleaving of additional trypsinogen molecules into active trypsin –> positive feedback loop)

Converted to trypsin by enterokinase/enteropeptidase, brush border enzyme on duodenal and jejunal mucosa

Question 7

Carb absorption

Answer 7

ONLY monosaccharides (glucose, galactose, fructose) absorbed by enterocytes

Glucose/galactose –> SGLT1 (Na+ dependent)

Fructose –> facilitated diffusion by GLUT-5

All transported to blood via GLUT-2

Question 8

D-xylose absorption test

Answer 8

distinguishes GI mucosal damage from other causes of malabsorption

D-xylose = monosaccharide that does not require enzymes for digestion prior to absorption

Question 9

Vitamin/mineral absorption

“Iron Fist, Bro”

Answer 9

• Iron - absorbed as Fe2+ in duodenum
• Folate - absorbed in small bowel
• B12 - absorbed in terminal ileum (along with bile salts) / requires IF

Question 10

Peyer patches

“Intra-gut Antibody”

Answer 10

Unencapsulated lymphoid tissue

Found in lamina propria and submucosa of ileum

Contains specialized M cells that sample and present antigen to macrophages –> macrophages present processed antigen to lymphocytes –> triggers secretory immunity –> stimulates B cells in germinal centers of Peyer’s patches to differentiate into IgA-secreting plasma cells that reside in ileal lamina propria

Question 11

Bile

Rate-limiting step of bile acid synthesis

Functions

Answer 11

Composed of bile salts (bile acids conjugated to glycine or taurine, changes pKa to make them water soluble), phospholipids, cholesterol, bilirubin, water, ions

Cholesterol 7alpha-hydroxylase catalyses rate-limiting step of bile acid synthesis

Functions:

Digestion and absorption of lipids and fat-soluble vitamins

Cholesterol excretion (body’s only means of eliminating cholesteroal)

Antimicrobial activity (via membrane disruption)

Question 12

Bilirubin

Heme metabolism

Unconjugated bilirubin

Direct bilirubin

Indirect bilirubin

Answer 12

yellow-colored byproduct of hemoglobin (heme) metabolism

Heme is metabolized by heme oxygenase to biliverdin –> reduced to bilirubin

Unconjugated bilirubin removed from blood by liver, conjugated with glucuronate, and excreted in bile

Direct bilirubin - conjugated with glucuronic acid; water soluble

Indirect bilirubin - unconjugated, water insoluble