Stomach

Question 0

How many layers of smooth muscle in the stomach?

Answer 0

Three:
Oblique
Circular
Longitudinal

Question 1

3 Stomach functions?

Answer 1

Mechanical processing
Digestion
Secretion

Question 2

What are the folds in the stomach called?

Answer 2

Rugae

Question 3

Gastric motility roles of the stomach?

Answer 3

Accepting and holding food
Relaxation
Accommodation

Question 4

What reflex does accommodation require in the stomach?

Answer 4

Vaso-vagal

Question 5

What are the 3 phases of peristaltic waves traveling over the antrum?

Answer 5

Propulsion
Emptying
Retropulsion

Question 6

Which cells secrete HCl and intrinsic factor in the fundus and body of the stomach?

Answer 6

Parietal (oxyntic) cells

Question 8

Where is peptide hormone (gastrin) released from?

Answer 8

G cells of stomach and duodenum

Question 9

What are the 2 forms of gastrin?

Answer 9

G17 (17 amino acids) – main form secreted from antrum

G34 (34 a.a.: the C-terminal 17 are the same as G17) - main form secreted from the duodenum

Question 10

What is the release of gastrin stimulated by?

Answer 10

Lumenal proteins / amino acids

Parasympathetic input (cephalic, and in response to gastric stretch), mediated by gastrin releasing peptide from interneurons

Question 11

What inhibits release of gastrin?

Answer 11

Release inhibited by lumenal [H+] – negative feedback

Question 12

What are the 2 main functions of gastrin?

Answer 12

Main actions on the stomach are to stimulate acid secretion, and promote mucosal growth

an endocrine regulator of acid production

Question 13

In parietal cells, what inhibits acid secretion?

Answer 13

Somatostatin

Question 14

What two things protect the surface epithelium in the stomach?

Answer 14

bicarbonate and mucus

Question 15

What is intrinsic factor and where is it released from?

Answer 15

55 kDa glycoprotein

Released from parietal cells into the stomach

Question 16

What does intrinsic factor do and why is it important?

Answer 16

Binds to cobalamin (Vit B12), but not until the small intestine.

Essential for cobalamin uptake in the ileum.

Question 17

What is the effect of gastrin mediated by?

Answer 17

The effect of gastrin is mediated by CCK-a receptors

Question 18

Where are pepsins secreted from?

Answer 18

from the chief and mucus cells

Question 19

When are pepsins secreted?

Answer 19

Secreted in response to ACh, [H+]. Minor effects of secretin, CCK and gastrin (latter two via CCK-A receptor)

Question 20

How are pepsins initially secreted?

Answer 20

Secreted as prohormones (pepsinogens)
Cleave spontaneously at low pH (<pH3)
Cleaved by pepsin (autolysis)

Question 21

What is the optimum pH of pepsins?

Answer 21

pH 2-3

Question 22

At what pH are pepsins denatured?

Answer 22

pH5-7 (once they reach the small bowel)

Question 23

What does gastric lipase do?

Answer 23

Cleave the outer fatty acids off triglycerides, leaving diacyl glycerol

Question 24

What is the optimum pH of gastric lipase?

Answer 24

pH Optimum is about 4: Stable in the stomach, but denatured by pancreatic proteases. Works together with lingual lipase

Question 25

Which enzyme initially digests polysaccharides?

Answer 25

Ptyalin α-Amylase

Question 26

What is the optimum pH of Ptyalin α-Amylase?

Answer 26

pH 7, denatured at 4.

Still hangs around in the fundus and body, where there is lots of food, but it isn’t well mixed with acid yet.

Question 27

What are 5 causes of vomiting?

Answer 27

• Vagal afferents, in response to irritants in or around the bowel
• Psychogenic: pain, revulsion
• Motion sickness / labyrinthine -disorders
• Drugs or toxins with a direct effect
• Pregnancy

Question 28

How is vomiting controlled?

Answer 28

Centrally controlled: area postrema = chemoreceptor trigger zone

Question 29

What are the consequences of vomiting?

Answer 29

Salivation (waterbrash), Sweating, Hyperventilation
Loss of normal gut motility – retrograde peristalsis
Retching: involuntary contractions of the diaphragm and abdominal wall muscles
Displacement of the cardia into the thorax
Emptying of gastric (+/- small bowel) content