digestion ins human 6.2

• 1. physical digestion

  • involves mechanical break up of food into smaller particles
  • by chewing and peristalsis
• 2. chemical digestion

  • involves break down of large molecules in food into small soluble molecules than can be adsorbed
  • involves hydrolytic reaction catalysed by digestive enzyme
• • in the mouth...

  the chewing action of teeth break up larger pieces of food into smaller pieces (physical digestion)
• • in the mouth...

  the tongue rolls the food into small, slippery, round masses or boli
• • in the mouth...

  salivary glands in the mouth secrete saliva, mixed with the food by the tongue, saliva contains mucin which softens the food
• salivary digest starch to maltose
• • in the oesophagus...

  peristalsis in the walls of the oesophagus and gravity push the bolus into the stomach
• • in the stomach...

  when bolus enters the stomach, it stimulates the release of gastric juice by the gastric glands
• • in the stomach...

  peristalsis in the walls of the stomach mixes the food with the gastric juice
• enzyme made of protein
• • gastric juice

  is a dilute solution of hydrochloric acid and two enzymes, pepsin and renin
• pepsin breaks down proteins into peptides
• rennin coagulates milk (milk curdles)
• • hydrochloric acid

  1. denatures salivary amylase
  2. converts pepsinogen to pepsin
  3. converts prorennin into renin
  4. provides an acidic medium for the action of pepsin and renin
  5. kills harmful microorganisms in food
• pepsin and rennin act on proteins
• • actions of pepsin

  digest proteins to polypeptides
• • actions of rennin

  converts soluble caseinogen into soluble casein
• food remains in the stomach for 3 to 4 hours
• • pyloric sphincter

  a muscular valve that opens to allow food to pass from the stomach to the top of the small intestine
• partially digested food aka chyme passes into the duodenum when the pyloric sphincter relaxes
• • in the small intestine...

  chyme enters the duodenum and stimulates the release of:

  1. intestinal juice by the intestinal glands
  2. pancreatic juice by the pancreas
  3. bile by the gall bladder

  these alkaline fluids neutralise the acidic chyme
• • in the small intestine...

  alkaline medium is needed for the action of intestinal and pancreatic enzymes
• • in the small intestine...

  gall bladder release its stored bile, bile passes through the bile duct into the duodenum
• • in the small intestine...

  pancreas secretes pancreatic juice which contains the enzymes pancreatic amylase, pancreatic lipase and trysinogen
• lactase breaks down the lactose in food so your body can absorb it
• • in the small intestine...

  intestinal juice secreted by the intestinal glands contains the enzymes peptidas, maltase, sucrase, lactase and inestinal lipase

  these enzymes digest food molecules
• • how are different food digested ?

  carbohydrates, proteins and fats in food are broken down into smaller molecules by specific enzymes

  amylases act on carbohydrates

  proteases act on proteins

  lipase act on fats
• small intestine is the last organ for digestion