Neural & Hormonal Control of Gastrointestinal Function 1 Flashcards
What are the basic functions of the GI tract?
Digestion of food, absorption of nutrients, excretion of waste, prevention of invasion by pathogens
What are the key regulatory requirements of the GI tract?
smooth muscle contraction, secretion of enzymes and solvents, reabsorption of water, coordinate regions
What are the interstitial cells of cajal?
Pacemaker cells that produce rhythmic activity in the muscle - act independently of neural activity
What provides local control in the GIT?
The enteric nervous system
What provides distant control of the GIT?
endocrine system
What is the function of the enteric nervous system?
regulate contractile activity and secretion of water and salt
What is the function of the endocrine system?
secretion of enzymes and solvents, regulate appetite
What are the two layers of the enteric nervous system?
The myenteric plexus and the submucosal plexus
What mediators do enteroendocrine cells contain?
Many different mediators depending on their type e.g. CCK, secretin, somatostatin, serotonin, glucagon like peptides 1 and 2 - may contain one or more
Where do the hormones of enteroendocrine cells get secreted?
Into the interstitial space and into blood vessels
Do the hormones also have a local role?
Yes - paracrine action to excite enteric neurons and extrinsic sensory neurons
What do enterochromaffin cell like cells release?
histamine
What does the vagus nerve control?
control of swallowing, acid secretion in the stomach, coordinates contraction of stomach an duodenum
What controls intestino-intestinal reflexes?
some via vagus, some via DRG and spinal cord
What is the role of viscerofugal neurons?
They project from the GIT to pre vertebral sympathetic ganglia to produce reflex inhibition of proximal regions when distal regions are distended
What is the cephalic phase of digestion?
The phase triggered by site, smell and taste of food - causes salivation, gastric acid secretion, pepsin secretion and relaxation of gastric corpus and fundus
What does the cephalic phase operate via?
Vagus nerve
Which cells does the vagus nerve release acetylcholine onto?
parietal cell, ECL cell, D cell and G cell as well as enteric neurons
What does the parietal cell secrete?
acid
What does the ECL cell secrete?
histamine
What does the D cell secrete?
somatostatin
What does the G cell secrete?
gastrin
How does gastrin and somatostatin reach parietal cells?
Via the portal vein and the liver
What excites ECL cells?
acetylcholine
What inhibits ECL cells?
somatostatin
What else does somatostatin inhibit?
parietal cells and G cells
What stimulates D cells?
acid and gastrin
What controls peristalsis along the oesophagus?
vagus
What is the normal position of the lower oesophageal sphincter?
closed
What is GORD?
gastro oesophageal reflux disease
What is the response of gastric distension?
Activation of enteric and vagal reflexes, acid and pepsin secretion
What causes constriction of the stomach?
interstitial cells of cajal
What does food entering the antrum trigger?
Inhibition of acid secretion in the corpus
What contributes to the separation of the fat from the food?
acid, protease and mechanical activity
Where does the fat go to?
It floats to the fundus and forms a separate layer
