GI physiology Flashcards
what makes up the upper GI system (5)
- mouth - saliva - pharynx - oesophagus - stomach
lower GI system
- liver - gallbladder - pancreas - small intestine - large intestine
role of the mouth
- lips: speech - palate: roof of oral cavity, uvula seals nasal cavity - tongue: skeletal muscle - teeth: digestion
role of saliva
contains amylase, used for lubrication, antibacterial, controlled by pressure/chemo receptors in the mouth and smell/thought of food
role of pharynx
swallowing is an all or nothing reflex, pharynx prevents bolus from re-entering mouth
role of oesophagus
straight muscular tube with sphincters on each end, peristaltic waves pass through to push food
role of the stomach
stores food, secretes enzymes and mixes
three sections of stomach
fundus - air body - food antrum - mixing
3 secretory cells in stomach
- mucus – thin watery - chief – pepsinogen - parietal – HCL and intrinsic factor
three parts of gastric juice
pepsinogen - HCL -> pepsin which digests peptides mucus - protection intrinsic factor - B12 absorption
three gastric phases
cephalic - increase secretion in response to stimuli gastric - food reaches the stomach intestinal - acid/fat/hypertonicity inhibits secretion
gastric emptying
controlled by duodenum (neural or hormonal)
factors affecting gastric emptying
- chyme in the gut (increases) - fat in duodenum decreases - acid in duodenum decrease - high osmolality in duodenum decreases
role of the liver
metabolic processing of carbs/proteins/fats and production of plasma proteins, stores fats/iron vitamins and produces hormones
role of gallbladder
stores bile made in liver
make up of bile
- aqueous fluid, bile salts, cholesterol, lethicin, bilirubin
role of pancreas
- exocrine and endocrine tissues, release juices
role of small intestine
absorption by enzymes in brush border and digestion (3 sections - duodenum, jejunum and ileum)
role of large intestine
- drying and storage (colon, cecum, appendix, rectum
exocrine pancreatic enzymes
- secretin: stimulates NaHCO3 from duct bells - CCK: stimulates enzyme release from acinar cells- trypsinogen/chymotrypsinogen and procarboxypeptidase: protein digestion once activated by HCL
endocrine function of pancreas
insulin and glucagon release
motility in small intestine
- segmentation: ring like contractions along length of SI initiated by pacemaker cells - response depends on distension, gastrin and extrinsic activity
protein absorption
- hydrolysed to amino acids by pepsin and proteolytic enzymes 2. Na+ co transporters move them into cells 3. exit cell via passive carriers 4. enters the blood via diffusion
carbohydrate absorption
- maltose produced by amylase 2. transformed to monomers by disaccharidases 3. monosaccharides absorbed by SGLT receptor (Na out) - fructose can passively diffuse via GLUT 5 4. monosaccharides move into blood via GLUT 2
fat absorption
- emulsified by bile 2. lipase hydrolyse to monosaccharides 3. carried into cell via water soluble micelles 4. leave micelle and passively diffuse across membrane 5. reform triglycerides 6. aggregate with lipoprotein to form chylomicrons 7. exocytosis to lymph
motility in large intestine
haustral contractions: main motility - autonomous rhythmicity of smooth musclemass movements: big contractions to move contents
taeniae coli
longitudinal bands of muscle
haustra
sacs that change location during contraction
defecation reflex
initiated when stretch receptors in rectum are activated, causes sphincter relaxation and rectal contraction
what does gastrin cause
increases HCL secretion and pepsinogen to increase mass movements
what does secretin do
inhibits gastric emptying and acid secretion until acid in duodenum is neutralised also stimulates NaOH release from duct cells
role of CCK
inhibits gastric motility and secretion and increases pancreatic enzymes
role of glp
stimulates insulin release by pancreas
how is acid secretion caused in the parietal cells
- ACh/histamine or gastrin activates causing Ca influx 2. H+K+ ATPase pumps H out of the cell and K in 3. Cl- and K+ also being pumped out of cell
