nutrition ✧

• nutrition is the process which organisms obtain food & energy for growth, repair & maintenance
• ingestion: is the process of food being taken into body
• digestion: is the process where large food molecules are broken down into smaller soluble & diffusible molecules that can effectively be absorbed into the body cells physically & chemically
• absorption: is the process where digested food substances/molecules are absorbed from the small intestine into the bloodstream
• assimilation: is the conversion of absorbed food substance into protoplasm or to provide energy
• egestion: removal of undigested matter from the body
• egestion is poop
• egestion is not the same as excretion
• peristalsis is how food moves down the alimentary canal
• the wall of the oesophagus is made up of circular & longitudinal muscles
• circular & longitudinal muscles are antagonistic muscles
• peristalsis allows food to be mixed with digestive juices
• peristalsis helps the movement of food along the intestinal tract & in the mechanical digestion of food
• peristalsis starts as soon as food enters the oesophagus
• outer muscles: longitudinal
• inner muscles: circular
• examples of physical digestion: chewing, peristalsis, bile action
• chemical digestion involves hydrolytic reactions catalysed by digestive enzymes
• teeth: chewing breaks up food into smaller pieces to increase surface area to volume ratio of the food for salivary amylase to act on it per unit time
• tongue: mixes the food with saliva and rolls food into food bolus
• mucin in saliva softens food
• salivary amylase + starch = maltose
• saliva contains salivary amylase which digests starch to maltose at pH 7
• salivary amylase optimal pH: 7
• stomach is a muscular distensible bag
• stomach as highly folded stomach walls with pits that lead to gastric glands which secrete gastric juice
• pyloric sphincter relaxes to allow chyme to leave the stomach to enter the small intestine after about 3 hours
• peristalsis occurs to churn & mix the food with gastric juices
• churning breaks up the food & allows it to mix digestive juices
• digestion of proteins by pepsin to polypeptides at pH 2
• hydrochloric acid denatures salivary amylase & stops its enzymatic reaction
• hydrochloric acid converts pepsinogen into active form pepsin
• hydrochloric acid converts prorennin into active form rennin
• hydrochloric acid provides optimal pH of 1 - 2.5 for gastric enzymatic actions
• hydrochloric acid kills potentially harmful microorganisms in the food
• importance of rennin: to curdle milk proteins so that they will not pass through the stomach to duodenum as readily as water
• protein is digested in stomach and small intestine by pepsin and trypsin
• small intestine

  1. duodenum
  2. jejunum
  3. ileum
• lining of small intestine walls contains glands which secrete intestinal juice
• when chyme enters small intestine:

  1. gall bladder releases by produced by liver
  2. pancreas to secrete pancreatic juice
  3. intestinal glands to secrete intestinal juice