digestion and absorption

ingestion

taking food into the alimentary canal

digestion

hydrolysis of large insoluble food molecules into small soluble molecules

absorption

movement of small soluble products of digestion across the epithelial cell membrane then into the bloodstream- this occurs via both diffusion and active transport

egestion

removal of undigested waste material from the body

physical digestion

mechanical process whereby food is manually broken down by chewing

chemical digestion

enzymes breaking down food

salivary glands

produces saliva containing salivary amylase

oesophagus

carries food from mouth to stomach

stomach

contains hcl, inner layer produces and secretes proteases, two rings of muscle on either side called cardiac and pyloric sphincter

pancreas

produces amylase, lipase and protease and secretes them into the duodenum

liver

produces bile but it is stored in the gall bladder

ascending limb of large intestine

absorbs water

small intestine

inner walls contain villi and microvilli for increased absorption, produces and secretes enzymes, thin walls to reduce diffusion distance, rich capillary network to maintain conc gradient

duodenum, jejunum, ilium

3 sections of small intestine, d - where lipid and carb digestion occurs, other 2 for absorption

rectum

stores faeces

anus

egests faeces

amylase

secreted by salivary glands and pancreas, not in stomach because too acidic so denatures enzyme, breaks down starch into sugar

sucrase and lactase

made in ileum then bound as extrinsic proteins in epithelial cells, breaks down sucrose into glucose and fructose, breaks down lactose into glucose and galactose

carb digestion

salivary amylase hydrolyses alternate glycosidic bonds of starch to form maltose, enzyme denatures in acidic stomach, pancreatic amylase released in small intestine after maltose neutralised by bile and alkaline salts

lipid digestion

bile emulsifies lipids to form micelles (increased sa to v ratio for lipase to act on), lipase hydrolyses ester bonds and a monoglyceride and 2 fatty acids are formed, transported to ileum increasing conc of fatty acids outside epithelial to increase conc gradient for simple diffusion, endoplasmic reticulum reconstructs triglyceride, golgi modifies and packages to form lipoproteins, chylomicron formed (cholesterol and lipoprotein) which is then packaged into a vesicle and exocytosed into lacteal transporting via lymph system until drains into capillary, lipase lines endothelial cells, hydrolyses ester bonds to form fatty acids and monoglyceride

digestion of proteins

endopeptidases e.g. pepsin in stomach and trypsin from pancreas hydrolyses peptide bonds in middle of protein, exopeptidases e.g. dipeptidase from ileum hydrolyses peptide bonds between terminal amino acids to form single amino acids which are small enough to be absorbed across small intestine