Gi physiology Flashcards
what do chief cells do
Release inactive pepsinogen -> pepsin which breaks down protein
what do parietal cells do
Intrinsic factor – for absorption of B12
HCl – denatures proteins and kills microorganisms
what increases stomach emptying
- Increased volume of chyme [increased distension]
- Decreased viscosity of chyme [thinner]
what decreases gastric emptying
Fat decreases gastric emptying as more time required for digestion.
what stimulates and is the action of Gastrin
- peptides/ amino acids in stomach
- increases secretion and promotes intestinal contraction
what stimulates and is the action of Ghrelin
fasting state
- stimulates hunger and satiety
what stimulates and is the action of histamine
food in stomach
- Stimulates parietal cells H+/K+ATPase to release HCl
what stimulates and is the action of serotonin
food in stomach
- decreases secretions and gastric movement
what stimulates and is the action of somatostatin
food in stomach
- decreases secretions and reduces intestinal absorption
what stimulates secretions
Ach
what inhibits secretions
somatostatin
what does prostaglandin E do (PGE2)
reduces histamine and increases mucus / bicarbonate secretion
where are gastrin and somatostatin secreted
at the pyloric antrum
describe the mucosal barrier to the stomach
- Stomach wall coated by thick wall of bicarbonate-rich mucus
- Epithelial cells meet at tight junctions preventing gastric juice from penetrating
underlying tissue layers - Stem cells replace damaged epithelial mucosal cells (completely replaced every 3-6
days)
what does the presence of chyme in the duodenum do
activates receptors that inhibit gastric secretion
adapted for absorption as increase in surface area due to:
- Circular folds
- Villi – lymphatic vessels [lacteals]
- Microvilli – brush border
what does the duodenum mucosa have
Brunner’s glands
Extrinsic innervation of the small intestine:
- Parasympathetic nerve fibres from vagus nerve
- Sympathetic nerve fibres from thoracic splanchnic nerve
describe gastrin
released by G cells
- stimulates secretion of bile and pancreatic enzymes
describe CCK
released by I cells
- stimulates release of pancreatic juices and bile
describe secretin
released by S cells
- stimulates bicarbonate release from pancreas in response to H+ in duodenum
describe motilin
released by M cells
- inhibits gastric secretion, stimulates insulin secretion
what do CCK and secretin do
decrease parietal cell secretion of HCL
describe cholecystokinin
secreted by I cells
- promotes the contraction of the gallbladder, increasing the secretion of the bile into the duodenum at the ampulla of vater
describe Leptin
a hormone secreted by adipose tissue that promotes satiety
- genetic defect in leptin signalling may cause monogenic obesity
what is somatostatin secreted by
D cells
what does secretin do
decrease gastric acid secretion
what are acinar cells
digestive enzymes
what does trypsin do
activate all other protein enzymes
what is the haustra
tonic contractions of taenia coli bunch up into pouches called haustra
what does stomach distension do
promotes gastrocolic reflex increasing motility in colon
what must carbohydrates be converted into for absorption
monosaccarides
what does amylase do
break down a-1,4 linkages as long as they are not terminal
what does HCL do
denature proteins
what does pepsin do
cleaves proteins into peptides
what do pancreatic enzymes do eg
(trypsin, chymotrypsin, elastase)
breakdown proteins into
oligopeptides
what do Peptidases at brush border do
hydrolyse oligopeptides to amino acids
what stabilises the emulsions and how
Amphiphilic molecules stabilise the emulsions by forming a surface layer on droplets of fatty
acids, biliary phospholipids, cholesterol, bile salts.
what are bile salts
Bile salts are amphipathic – hydrophilic and hydrophobic.
They are released from gall bladder in response to CCK and aid in emulsifying lipid droplets.
