Alimentary System

Question 1

describe the stimuli for the different phases of gastric activity

Answer 1

cephalic phase
- mechanical stimuli from muscles of mastication
- chemical stimuli from taste and smell
- pyschic stimuli from sight and emotion

gastric phase
- mechanical stimuli from distension
- chemical stimuli from food in the stomach

intestinal phase
- mechanical stimuli from distension
- chemical stimuli from acids and protein in the duodenum

Question 2

describe the controls of the different phases of gastric activity

Answer 2

cephalic phase
- controlled by long reflex nerves that go to the brain

gastric phase
- controlled by long and short reflex nerves
- gastrin hormone

intestinal phase
- long and short reflex nerves
- gastric inhibitory peptide inhibits stomach acid secretion, stimulates insulin secretion, stimulates glucagon release and the accumulation of fat
- secretin is produced in the duodenum and reduces secertions from parietal cells of acid, increases the production of bicarbonate from the pancreas.
- controls in this phase tend to slow gastric emptying

Question 3

describe the control of the release of pancreatic juice in the different phases of gastric activity

Answer 3

cephalic
- vagus nerve
- small effect

gastric phase
- small effect
- could be from vagus

intestinal phase
- secretin - released from duodenum in response to acid, stimulates secretion of bicarbonate rich pancreatic juice
- cholecystokinin - promotes digestion of fat and protein, appetite suppressant, weak stimulatory effecton bicarbonate secretion
- vasoactive intestinal poypeptide - in the gut this breaks down glycogen and relaxes the smooth muscle of the gall bladder and the stomach

Question 4

describe the control of the secretion of bile at the different phases of gastric activity

Answer 4

cephalic phase
- vagus nerve stimulate relaxation of the sphincter of oddi

gastric phase
- small stimulatory effect by the vagus nerve

intestinal phase
- cck is released from duodenum in response to fat and protein, stimulates contraction of the gall bladder and relaxation of the sphincter of oddi
- secretin has the same effect as cck but weaker

Question 5

describe the neural control in the large intestine

Answer 5

segmentation controlled by local reflexes

long reflexes are triggerd by food entering the stomach to increase the motility in the intestines

gastroileal reflex is when the gastric activity is increased in the ileum

gastrocolic reflex is when the gastric activity leads to increased motility on the colon
related to mass movements

control is mainly neural. in the large intestine and rectum it is autonomic control. the vagus controls to the splenic flexure. after that, the pelvic nerves (sacral, 2,3,4) control the descending colon and rectum.

control of the anal canal
- autonomic control of internal anal sphincter and voluntary control of the external anal sphincter.

somatic nerves are sacral.