chapter 5 - digestion in humans Flashcards
nutrition
process by which organisms obtain food and energy for growth, repair and maintenance of the body
ingestion
food is taken into the digestive system
digestion
process where large, complex, insoluble molecules are broken down to small, simple, soluble molecules for absorption into body cells
describe the different forms of digestion
physical process : mechanical breakdown of food into smaller pieces through chewing
(eg. chewing, peristalsis, emulsification), which increases the food molecules’ surface area to volume ratio for faster chemical digestion
chemical process : mechanical break of bonds in molecules which involves enzymes
(eg. hydrolytic reaction)
absorption
digested food substances such as glucose and amino acids will be taken up by the body cells and absorbed into the bloodstream through the wall of the ileum of the small intestine by process like active transport and diffusion. the absorbed food substances in the bloodstream will then be diffused into the body cells for assimilation
assimilation
uptake of absorbed food substances into cells and tissues to be converted into protoplasm or used to release energy
egestion
removal of undigested material
describe the mouth and the processes happening in it
-the salivary gland in mouth secretes saliva, which is mixed with the food by the tongue
- the saliva contains mucin which softens the food
the chewing action of teeth breaks up larger pieces of food into smaller pieces to increase surface area to volume ratio
- the tongue rolls the food into small, slippery round masses (boli)
describe the pharynx, larynx and epiglottis
- pharynx connects buccal cavity to the oesophagus and larynx, and the trachea to the lungs
- the larynx has a slit-like opening known as glottis, which is covered by a flap-like tissue known as the epiglottis. during breathing, air passes into the trachea and into the lungs, the larynx moves downwards and the glottis is open. during swallowing, the larynx moves upwards and the epiglottis covers the glottis, preventing food particles from entering the trachea.
oesophagus
- made up of two antagonistic muscles : circular and longitudinal
- peristalsis in the walls of the oesophagus and the gravity pushes the bolus into the stomach
stomach
food in the stomach is digested by enzymes found in the gastric juice produced and secreted by the gastric glands. when the bolus enters the stomach, it stimulates the release of gastric juices by the gastric glands. peristalsis in the walls of the stomach mixes the food with the gastric juices
what is in the gastric juice secreted by the gastric glands in the stomach?
dilute solution of hydrochloric acid, mucus and pepsin
what does the hydrochloric acid in gastric juice do?
- denatures salivary amylase
- converts inactive pepsinogen into pepsin
- provides an acidic medium (pH 2) for the action of pepsin
- kills harmful microorganisms in food
small intestine
- consists of the duodenum, jejunum and ileum
- chyme enters the duodenum and stimulates release of pancreatic juice by pancreas, bile by gall bladder, and intestinal juice by the small intestine. the alkaline fluids neutralises the acidic chyme. the alkaline medium is needed for the action of intestinal and pancreatic enzymes.
what do the juices released at the small intestine consist of?
- pancreatic juice : secreted by pancreas, contains pancreatic amylase, pancreatic lipase, trypsin
- bile : secreted by gall bladder, passes through bile duct into duodenum
- intestinal juices : secreted by intestinal glands, contains maltase, sucrase, lactase, peptidase and intestinal lipase
liver
- 3 important blood vessels found at its lower surface : hepatic artery, hepatic vein and hepatic portal vein
- produces and releases bile
- regulate the blood glucose concentration in blood plasma
functions of liver
- produces bile involved in the emulsification of fats, which is the physical breakdown of large fat globules into smaller fat globules for faster chemical digestion of fat molecules into fatty acids and glycerol by lipase
- regulate blood glucose concentration by secreting insulin and glucagon
- uses amino acids to synthesise plasma proteins such as prothrombin and fibrinogen for clotting of blood
- after worn-out red blood cells are destroyed in the spleen, haemoglobin will be released and transported to liver
- haemoglobin broken down to produce iron and bile, iron stored in liver
- detoxification of harmful substances like alcohol, into less harmful substances
what is bile made up of?
- alkaline, greenish-yellow liquid
- made up of bile salts and pigments which aids in fat digestion by emulsification of fats
describe the role of bile in the digestion process
- physical digestion of fat molecules
- used for emulsification of large fat globules to smaller fat droplets
which increase the fat molecules’ SA2VR for faster chemical digestion by lipase into glycerol and fatty acids
describe the fate of amino acids in the liver
- used to synthesise plasma proteins in the liver
- excess amino acids undergoes deamination in the liver
- amino group will be removed and converted into urea, that will be excreted in the kidneys
- carbon residue converted into glucose, excess glucose converted and stored as glycogen in liver
gallbladder
- temporarily stores bile produced by the liver
- when gallbladder contracts, bile would flow through the bile duct and the duodenum
pancreas
- connected to the duodenum by the pancreatic duct and joins to the bile duct before it opens into the duodenum
- produces and secretes pancreatic juices that contains enzymes
- produces and secretes hormones like insulin and glucagon
peristalsis
rhythmic, wave like muscular contractions in the wall of the alimentary canals where the circular and longitudinal muscles contract and relax alternately
what does peristalsis do?
- helps to move food along the gut
- helps food to be mixed with digestive juices
- occurs in oesophagus, stomach, small/large intestine