Absorption and secretion

Question 1

What are the three main functions of the stomach?

Answer 1

Secretion

Motor function meaning it moves a lot (regulating food intake, transit, and mixing)

Humoral regulation (producing hormones like gastrin and somatostatin
*Hormones can regulate secretion

Question 2

List the proximal secretions of the stomach

Answer 2

Hydrochloric Acid (HCl)
Pepsinogens
Intrinsic factor
Mucins
Bicarbonate ions

Question 3

Does the small or large intestine absorb more water?

Answer 3

small

Question 4

list the distal secretion of the stomach

Answer 4

pepsinogen
gastrin
somatostatin

Question 5

what is the secretory layer in the stomach called?

Answer 5

mucosal

Question 6

What are the main secretory cells in the stomach body (oxyntic glands) and their secretions?

Answer 6

Epithelial cells → HCO3-
Mucous neck cells → mucus
Parietal cells → HCl and intrinsic factor
Enterochromaffin-like cells → histamine
Chief cells → pepsinogen
Enterochromaffin cells → serotonin, VIP, substance P
D cells → somatostatin

Question 7

What are the main secretory cells in the stomach antrum (pyloric glands)?

Answer 7

Similar to body but no parietal cells. Key cells include:

G cells → gastrin hormone
D cells → somatostatin

Question 8

Describe the structure and function of parietal cells during acid secretion.

Answer 8

In resting state: Cytoplasmic pool of tubulovesicular membrane on apical side
When stimulated:
Membrane fusion occurs
Surface area increases 50-100x
Microvilli appear
H,K-ATPase pump and K+ and Cl- channels are inserted
Secrete H+ across the apical membrane via H+-K+ ATPase
Absorb HCO3- into the blood via a Cl–HCO3- exchanger

Question 9

Explain the mechanism of HCl secretion by parietal cells

Answer 9

1. H2CO3 dissociates in the cell
2. H+ is secreted across apical membrane via H+-K+ ATPase
3. Cl- follows through channels
4. HCO3- is absorbed into blood via Cl–HCO3- exchanger
5. K+ is recycled into the lumen via K+ channels
   Net result: HCl secretion and HCO3- absorption

Question 10

How does fluid and electrolyte absorption vary along the intestine?

Answer 10

Small Intestine:
Absorbs fluid, Na+, K+, Cl-, HCO3-
Absorbs hydrolyzed food
Has 600x surface area due to folds, villi, and microvilli

Large Intestine:
Net absorption of water, Na+, Cl-
Secretes HCO3- and K+

Question 11

What are the general mechanisms of fluid and electrolyte absorption?

Answer 11

Transcellular movement (usually active transport)

Paracellular movement (passive, through tight junctions)
Fluid movement coupled to solute movement
Regulated by hormones and neurotransmitters
Both SI and LI use active and passive mechanisms

Question 12

How are carbohydrates absorbed in the small intestine?
*use images from PP for help

Answer 12

Glucose and galactose: via SGLT1 (Na+ co-transport) on apical membrane

Fructose: via GLUT5 transporter
All sugars exit cell via GLUT2 on basolateral membrane
Process requires Na+/K+ ATPase on basolateral membrane

Question 13

How are proteins absorbed in the small intestine?
*use images from PP for help

Answer 13

Amino acids: via Na+ co-transporters

Dipeptides and tripeptides: via H+ co-transporters
Peptidases break down peptides into amino acids inside cell
Amino acids exit via facilitated diffusion on basolateral side

Question 14

How are lipids absorbed in the small intestine?

Answer 14

1. Lipids are broken down by pancreatic lipase and solubilized in bile salt micelles
2. Products cross enterocyte membrane via:
   - Diffusion
   - Incorporation into membrane
   - Carrier-mediated transport
3. Products are re-esterified in smooth ER
4. Packaged into chylomicrons
5. Released into lacteals (except glycerol → blood)
6. Bile salts are recycled via enterohepatic circulation