Digestion Flashcards
digestion
the mechanical and chemical break down of food so it can be absorbed into the blood
mechanical digestion
breaking down large food by grinding and churning to increase SA available for chemical digestion
chemical digestion
enzymes hydrolyse covalent bonds to break down large molecules into smaller soluble molecules that can be absorbed into te blood
two types of chemical digestion
intracellular and extracellular
intracellular digestion
occurs in epithelial cells of ileum
extracellular digestion
enzymes are secreted out of cells ito the gut lumen
4 examples of extracellular digestion organs and glands
- salivary glands –> mouth
- gastric glands –> stomach
- pancreas –> duodenum
- liver –> duodenum (bile)
2 enzymes involved in intracellular digestion
disaccharidases and dipeptidases
what is the benefit of requiring multiple enzymes to fully digest a food type
the action of the fist enzyme icreases the SA available for the second enzyme so increases rate of digestions
why do different regions ofthe gut have different pHs?
enzymes have different optimum pHs
3 roles of mucus
- important in maintaining correct pH of particular regions of the gut –> neutralise stomach acid in duodenum
- provides lubrication for food to move along gut
- protects gut lining from erosion (acid atack)
what, how, where
2 steps of carbohydrate digestion
- starch is broken down into maltose by salivary and pancreatic amylase in the stomach and duodenum
- maltose is broken down into glucose by maltase in the epithelial cells of the ileum
2 disaccharidases
sucrase and lactase
what, how, where
3 steps of protein digestion
- proteins are broken down into polypeptide chains by endopeptidases (pepsin) in the stomach
- polypeptide chains broken down into shorter polypeptide chains by endopeptidases (trypsin) in the duodenum
- shorter polypeptide chains are proken down into dipeptides and amino acids by exopeptidases in the duodenum
- dipeptides are broken down into amino acids by dipeptidases (exopeptidases) inthe epithelial cells lineing the ileum
peptidases
hydrolyse peptide bonds in a polypeptide chain
endopeptidases
hydrolyse inner peptide bonds in a polypeptide chain
exopeptidases
hydrolyse end (terminal) peptide bonds in a polypeptide
3 types of exopeptidases
- aminopeptidases = N-terminal (left end)
- carboxypeptidases = C-terminal (right end)
- dipeptidases = dipeptides
2 steps of lipid digestion
- mechanical brekadown of lipid droplets into micelles by bile salts in the duodenum
- chemical digestion of micelles into monoglycerides and fatty acids by lipase in the duodenum
what is the role of bile salts in digestion of lipids?
emulsify lipid droplets to increase SA available for action of lipase
function of sodium hydrogencarbonate in lipid digestion
neutralise stomach acid in duodenum
contents of bile
bile salts and sodium hydrogencarbonate
where is bile produced, stored and released?
produced in liver
stored in gall bladder
released via bile duct into the duodenum
advantage of micelles forming
micelles are water soluble so are more easily transported to the epithelial cells in the ileum
pH of mouth
pH 6.5-7.5
mechanical digestion in the mouth
teeth break up food to increase SA for chemical digestion
chemical digestion in mouth
- salivary glands secrete saliva containing amylase, mucus and mineral ions
- starch digested
function of mucus and mineral ions in mouth
mucus = lubrication
mineral ions = maintain neutral pH
oesophagus in digestion
lined by epthelial tissue, containing goblet cells which secrete mucus for lubrication
peristalsis occurs = coordinated contraction of circular and longitudinal muscle
mechanical digestion in stomach
churn contents to form acidic chyme (has extra layer of muscle - oblique - to aid churning
chemical digestion in stomach
gastric gland secrete gastric juice containing hydrochloric acid, endopeptidases (pepsin) and mucus
digest proteins
pH of stomach
2
function of hydrochloric acid in stomach
decrease pH to activate enzyes and kill bacteria by denaturing their enzymes
function of mucus in stomach
lubrication and protection from erosion
two sphincters of the stomach
cardiac sphincter and pyloric sphincter
pH of the duodenum
7-8
where is the main sitee of chemical digestion?
duodenum
what 3 glands secrete juices into the duodenum and what do they secrete??
- pancreas - pancreatic juice
- liver - bile
- Broner’s gland - mucus
what does pancreatic juice contain?
- endopeptidase and exopeptidases
- lipase
- amylase
- hydrogen carbonate ions
function of mucus in duodenum
neutralise stomach acid and protect wall from acid erosion
2 steps of digestion in ileum
- as molecules move across epithelial cell membrane, theyre hydrolysed by proteins in the cell into their monomers
- taken away in blood so maintains concentration gradient from ileum lumen to epithelial cell
what two molecules are digested in the ileum?
disaccharides and dipeptides?
function of the colon
absorbs remaining waater and vitamins from bacteria
absorbs water so we can produce solid faeces as this stimulates peristalsis
contents of faeces
undigested material (cellulose) - fibre
souughed cells
bacteria
function of the rectum
temporary store of faeces before egestion
egestion
removal of undigested and waste material from the body
what are sloughed cells
cells scraped off the gut wall
site of action of amylase
mouth and duodenum
site of action of endopeptidases
stomach and duodenum
site of action of exopeptidases
duodenum and ileum
site of action of lipase
duodenum
site of action of disaccharidases
ileum
