nutrition in humans Flashcards
what is peristalsis and how does it work
-longitudinal muscle on outside of gut and circular muscle on inside of gut work antagonistically causing rhythmic wave like contractions gut wall
-when circular muscle contract, longitudinal muscle relax, wall of gut constrict becoming narrower and longer, food is pushed forward
-when longitudinal muscle contract, circular muscle relax, wall of gut becomes wider and shorter allowing food to enter
what and where is physical digestion
-mechanical break up of food into small particles
-in the mouth when you chew food
-in the stomach when churning breaks up food particles and mixes it with digestive enzyme
-increase SA:V of indigested food so that digestive enzyme can act on it more efficiently
what is chemical digestion
-breaking down of food molecules such as fats, proteins and starch into small soluble molecules which can be absorbed, involving hydrolytic reactions by digestive enzyme
digestion in mouth
-food enters mouth, stimulating salivary glands to secrete saliva
-saliva is mixed with food, mucin in saliva helps soften food
-saliva contains salivary amylase, enzyme digesting starch to maltose, active due to saliva neutral pH
-chewing breaks food up into smaller pieces, increase SA:V for salivary amylase to work on
-tongue rolls food into small slippery bolus which is swallowed and pass down the oesophagus via the pharynx
digestion in stomach
-food passes into stomach, stimulating gastric glands to secrete gastric juices into stomach cavity
-peristalsis in stomach wall churns and breaks up food, also mixing it with the gastric juices
-gastric juice is dilute solution of hydrochloric acid, renin and pepsin
-food normally remains in stomach for 3-4 hours, partially digested food becomes liquified, forming chyme that passes in small amounts into duodenum when pyloric splinter relaxes and opens, entering small intestine
what does dilute hydrochloric acid and rennin and pepsin do
-stop action of salivary amylase by denaturing it
-changes inactive form of enzyme, pepsinogen and prorennin in the gastric juice into active forms, pepsin and rennin
-provides acidic medium suitable for action of gastric enzyme
-kills certain potentially harmful microorganisms in food
-protease pepsin digest proteins into polypeptides
-protease rennin curdles milk proteins by converting the soluble protein caseinogen into casein so that milk proteins will pass through duodenum as easily as water, would not be digested by pepsin
-insoluble casein remains long enough in the stomach to be digested by pepsin
what does chyme stimulates
-chyme enters small intestine stimulating intestinal glands to secrete intestinal juice
-pancreas to secrete pancreatic juice that passes through pancreatic duct into duodenum
-gall bladder to secrete bile
components of bile
-does not contain enzymes, passes through bile duct into duodenum
-in small intestine, bile salt emulsify fats by lowering surface tension of fats, reducing attractive forces between fat molecules, this causes fats to break into tiny fat droplets suspended in water to form an emulsion
-emulsion increase SA:V ratio of fats, speeding up rate of digestion by lipase
-emulsified fats are digested by intestinal and pancreatic lipase into fatty acids and glycerol
components of pancreatic juice
-contains amylase which digests starch to maltose
-trypsin that digests proteins into polypeptides
-lipase that digests fats into fatty acids and glycerol
components of intestinal juice
-enterokinase that activates trysinogen
-disaccharidases (maltase, sucrase, lactase) that digest disaccharides into monosaccharides
-erepsin which digests polypeptides into amino acids
-lipase digesting fats into glycerol and fatty acids
where do digested fats go
-pass through the cell membrane of villi cells in ileum
-fat molecules are then formed again and transported by exocytosis out of cells into lacteal of villi in ileum
adaptations of the small intestine
-increased SA in folded internal walls, villi, microvilli which is the finger like projections of the plasma membrane of the epithelial cells of the villus
-villi move back and forth independently where movement increase after meals increase absorption rate
-one cell thick membrane allows for easy absorption through diffusion or active transport
-dense capillary network close to epithelium to carry away absorbed food particles quickly and maintain concentration gradient between ileum and blood capillaries to aid diffusion
where is amino acids and simple sugars and fatty acids and glycerol absorbed to
-amino acids and simple sugars are absorbed mainly through active transport and diffusion to capillaries to the hepatic portal vein
-fatty acids and glycerol absorbed by lacteal to be transported to lymphatic system
function of hepatic portal vein, hepatic vein and hepatic artery
-HPV transports absorbed sugars and amino acids, water soluble foods from ilium to liver, blood is nutrient rich but deoxygenated
-HV transports waste products away from liver, carrying deoxygenated and nutrient poor blood
-HA transport oxygenated blood but nutrient poor from aorta to the liver
assimilation of glucose
-excess glucose is converted to glycogen and stored in the liver where it is converted back to glucose when body needs energy and blood sugar level is low
-further excess of glucose is stored as fats in the adipose tissue
-used in cellular respiration
