GUT- Intro to function and control of alimentary tract Flashcards
outline how the ANS enables the storage of food in the stomach
mechanical stimuli in the pharynx - receptive relaxation - signal to the vagus centre - relaxation
adaptive relaxation - inhibitory vagal fibre - NANC - inhibitor
feedback relaxation - when food is within the duodenum - acidic has to be neutralised - no more food into the duodenum
how does parasympathetic and sympathetic innervation of the GI tract different
parasympathetic - stimulates digestive activity, stimulates gallbladder, relaxes rectum
sympathetic - inhibits digestive activity, causes release of glucose from the liver
what mediates contraction and relaxation of the GI system with a bolus of food
behind the bolus of food - contraction - acetylcholine
before the bolus of food - relaxation - VIP/ NO
describe the movement of food through the oesophagus to the anus
ripples of contraction move the food towards the antrum
pyloric sphincter is often relaxed by the opening of pyloric sphincter
small partially digested foods is squirted into the duodenum
repulsion of antral contents towards body = mixing
how is the rate of emptying dependent on the material ability to be absorbed
carbohydrates - empty quickly into the duodenum
proteins - slow emptying
fatty food- slowest emptying - this is because they have to be emulsified first
fatty acids in the duodenum - decrease gastric emptying- increase in contractility of pyloric sphincter
describe the role of the enteric nervous system in mediating peristalsis in the small intestine
two nerve fibres are intrinsic to the gut
myenteric plexus - motor function
submucosal plexus - intestinal secretions
what are the neurotransmitters of the ENS
Ach, NO, 5-HT, GABA, ATP
describe the roles of gastric acid secretions
mucus - lubricant - protection
lipase- converts triglycerides
lipase- converts triglycerides to fatty acids adn glycerol
pepsin - active form of pepsinogen - protein digestion
HCL- defence, conversion of pepsinogen to pepsin
IF - vitamin B12 absorption
describe the role of paracrine secretions
they are local hormones secreted from cells in the mucosa
act on locally adjacent cells via interstitial fluid
somatostatin inhibits gastrin
too much HCL (G cells) - somatostatin secreted by D cells
describe the function of exocrine secretions in reference to alimentary tract
salivary glands - lubrication; lipase
gastric glands - HCl, pepsin, mucus
pancreas - bicarbonate ions, enzymes (amylase, lipase, carboxypeptidase)
liver - bile salts, bile acids
what is the function of gut motility
movement from one region to another (law of gut) - mass evacuation
mechanical degradation - gastric antrum
mixing lumen contents - small intestine
transport of nutrients, water, urea, and electrolytes
digestion and absorption
describe the function of absorption
for food to be used it needs to be digested and then the resulting nutrients needs to be transported across the intestinal epithelium into the blood
absorption occurs in the small intestine mostly
absorption of fluid occurs in small intestine and colon
disorders of fluid secretion and absorption are important in the pathogenesis of diarrhoea
describe the function of excretion
drugs and some products leave the body in
saliva
bile
faeces
vomit
describe the function of defence
sight / smell/ taste - alters us to harmful food substances
vomit reflex
acid in stomach
mucus secretions
natural bacterial
payer’s patches
maintenance of repair and integrity; growth factors
describe the function of gastrin
neurone stimulates gastrin releasing peptide
binds to g cells allows gastrin to be released
acts on parietal cells to cause acid secretion
act on enterochromaffin like cells (secrete histamines)
Ach can act on parietal cells / ELC cells to cause acid secretion
prostaglandins negative regulate by inhibiting parietal cells and increase bicarbonate secretion and mucous secretion
