stomach physiology (demonaco)

Question 1

intrinsic factor and the stomach

Answer 1

IF binds to B12, which is required for B12 to be absorbed in the ileum

Question 2

How does the stomach sterilize food?

Answer 2

Via gastric acids (HCl, pepsin)

Question 3

What do the parietal cells of the proximal portion of the stomach secrete?

Answer 3

HCl, IF

stimuli: Ach, histamine, gastrin

Question 4

What do the Chief cells of the proximal portion of the stomach secrete?

Answer 4

Pepsinogen
- inactive form of pepsin
- proteolytic enzyme of the gastric juice

stimuli: vagal cholinergic NTs (Ach)

Question 5

What do the endocrine cells of the proximal & distal portions of the stomach secrete?

Answer 5

gastrin, histamine

stimuli: protein digestion, vagal stimuli

Question 6

HCl and pepsinogen relationship

Answer 6

Food present in stomach –> parietal cells stimulated (via Ach, histamine, gastrin) –> HCl is secreted –> HCl breaks down pepsinogen –> pepsin breaks down peptide bonds via hydrolysis

= the start of gastric digestion in the stomach!

Question 7

What hormones inhibit HCl secretion?

Answer 7

Secretin
peptide hormone released by duodenal S-cells
- inhibits gastric acid secretion (as contents move out of stomach and into dudoedenum)
- in response to acid

CCK (cholecystokinin)
- in response to fat

GIP (Gastrin Inhibitory peptide)
- in response to carbohydrates

Question 8

What hormones stimulate HCl secretion?

Answer 8

• gastrin (produced by gastric endocrine cells)
• histamine (produced by gastric mast cells and binds to H2 receptor – non-gastric MCTs can cause GI ulceration due to histamine release)
• Ach (vagal – gastric distention)

All 3 bind to parietal cell receptors to promote gastirc acid release!

Question 9

What drug works best at inhibiting gastric acid secretion?

Answer 9

Proton pump inhibitors (PPIs) – Omeprazole, pantoprazole

Question 10

Gastrinoma

Answer 10

• tumor of G-cells (endocrine cells that release Gastrin)
• excessive amts. of gastrin secreted –> GI ulceration, gastric hypertrophy
• tx = PPIs

Gastrin = a “trophic factor” – causes small growth (hypertrophy) of the gastric mucosa

Question 11

5 gastric protective mechanisms against its own acids

Answer 11

tight junctions = in mucus layer (gap junctions are in the muscular layer)

Question 12

3 layers of the gastric mucosal barrier

Answer 12

submucosa -> gastric epithelial cells -> mucosa

Question 13

What mediates gastric blood flow?

Answer 13

Prostaglandin
- NSAIDs and corticosteroids decrease gastric mucosal blood flow

Question 14

The 3 phases of gastric activity

Answer 14

1. Cephalic Phase – promotes gastric activity/anticipation phase (conscious awareness or thought of food – vagal stimulation)
2. Gastric Phase - promotes gastric distension via vagal and local neural reflexes, mostly in response to gastrin. -> HCl (parietal cells) & Pepsinogen (chief cells) released
3. Intestinal Phase – inhibits gastric activity - reflexes & negative hormonal feedbacks from SI mucosa by CCK & GIP (in response to CHO, fat and acid present in the duodenum)

Question 15

Interdigestive phase

Answer 15

“housekeeper” – phase in between meals
- moves fasting content (larger particles) into the duodenum (pylorus does not close)

Question 16

What diets move fastest -> slowest through stomach (gastric emptying)

Answer 16

Carbs > proteins > fat

The presence of fat, such as oleate, in the meal results in stimulation of cholecystokinin (CCK) secretion in the duodenum; in turn, this inhibits antral motility, stimulates pyloric tone and delays gastric emptying

Question 17

What part of stomach allows food to enter?

Answer 17

Cardia

the cardiac spincter (LES)

Question 18

What part of the stomach allows for storage of food, has mild peristaltic waves and no mixing or mechanical digestion occurs?

Answer 18

Fundus

Question 19

What part of the stomach is highly mobile where strong peristaltic and reverse peristaltic waves occur, mixing food with enzymes and HCl?

Answer 19

Body

Question 20

What part of the stomach is the “real grinder” where strong contractions occur and mechanical digestion is completed?

Answer 20

Antrum – delivers tiny digesta to the pylorus – pyloris returns bits too large for the dudoenum back to gastric antrum or body

Question 21

The pylorus only allows particles through to the duodenum of what sizes?

Answer 21

No larger than 1-2mm

Question 22

During filling, the stomach ?. During empyting, the stomach ?.

Answer 22

relaxes; contracts