Digestion and absorption

Question 1

What is the vagovagal reflex?

Answer 1

reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli

Question 2

What are the 3 phases of GI secretion?

Answer 2

Cephalic phase
Gastric phase
Intestinal phase

Question 3

Describe the cephalic phase

Answer 3

Anticipatory response and feed forward control as GI secretion before food enters the mouth
Stimuli such as smell/look up regulate GI secretions
- Presence of active enzymes
- Lubrication with saliva
- Presence of bicarb
- Increases gastric acid secretion
Mediated by parasymmpathetic nervous system ( vagus nerve)

Question 4

Describe the gastric phase

Answer 4

Presence of food in the stomach stimulates gastric acid secretion via 2 major mechanisms ( distension and protein digestion)

Distension: Stretch sensitive neurones in stomach are activated by food in the stomach
Vagovagal reflex causes parasympathetic stimulation via acetylcholine to acinar and duct cells stimulating secretions

Protein digestion
G cells in the stomach secrete gastrin in response to AA + peptones in the stomach. Gastrin causes release of gastric acid
CCK stimulates acinar cells
Maintains optimal pH for enzymatic digestion

Question 5

Describe the intestinal phase

Answer 5

Acidic chyme enters the duodenum and stimulates S cells to release secretin
Secretin stimulates pancreatic duct cells to release HCO3-
Slows H+ secretion by parietal cells and also contracts pyloric sphincter
Fatty acids and peptones in the stomach stimulate a vasovagal reflex -> parasympathetic stimulation of duct and acinar cells

G cells in stomach secrete gastrin

Fatty acids and peptones stimulate duodenal I cells to release CCK : Contract pyloric sphincter and gall bladder, relaxes sphincter of oddi