Digestion + enzymes

• What is digestion?


  - the breakdown of large, insoluble molecules into smaller, soluble molecules which can be absorbed into the bloodstream
• What is mechanical digestion?

  - physical breakdown of large pieces of food into smaller pieces

  - chemical nature of food remains unchanged

  - increases surface are of food upon which enzymes can act

  - occurs in mouth (teeth) and stomach
• What is chemical digestion?


  - the changing of large food molecules into smaller molecules by the action of digestive enzymes

  - usually takes place in stages

  - each stage is catalyses by a different enzyme
• What are enzymes?


  - proteins which act as biological catalysts
• What do enzymes do?

  - speeds up rate of a chemical reaction without being used up

  - but not used in the reaction itself

  - left unchanged afterwards so it can catalyst more reactions

  - there are a large number of them in the alimentary canal (oesophagus)
• How is food digested in the mouth?

  - food is bitten off by incisors + chewed by molars (makes it easier to swallow + increases surface area)

  - food is also mixed with saliva (produced in salivary glands + released via salivary ducts)

  - saliva has a neutral pH

  - amylase in saliva breaks down starch (polysaccharide) into maltose (disaccharide)

  - once the food is chewed enough it's swallows
• Where is the epiglottis and what is its purpose?

  - entrance to the trachea

  - prevent chocking
• What happens in the oesophagus?

  - muscles in walls of oesophagus contract and relax in process called peristalsis

  - this pushes the dood downwards

  (You can swallow while upside down)
• Digestion in the stomach?

  - muscular wall churns food (mechanical digestion)

  - chemical digestion occurs due to gastric juices (containing HCl and protease)

  - protease breaks down proteins into amino acids

  - the food (in semi liquid state) is released into top of small intestine (duodenum)
• What does HCl do in the stomach?

  - reduces stomach pH to pH2 which:

  —> kills bacteria

  —> makes a closer pH for protease's optimum temp
• Why does digestion of starch stop in the stomach?

  - stomach's pH is too acidic for amylase
• Two parts of the small intestine? What occurs here?

  Duodenum: where bile and digestive enzymes are added

  Ileum (longer): where digested food is absorbed
• Where is bile made, stored and transported to?

  - made by the liver

  - stored in gallbladder

  - transported into small intestine via bile duct
• Functions of bile?


  - emulsification of fats

  —> BUT IT DOES NOT CONTAIN ENZYMES

  - this increases surface area for lipase enzymes to work on the fat droplets

  - alkaline as well so neutralizes acidity from the stomach
• What is emulsification?


  - the breakdown of a large fat droplet into smaller droplets (globules)
• What is pancreatic juice?


  - an alkaline mixture containing several digestive enzymes
• Different types of digestive enzymes?


  - amylase

  - lipase

  - protease

  - maltase
• Function of salivary amylase?

  - found in the salivary glands

  - works in the mouth

  - released by the salivary ducts via saliva

  - breaks down starch into maltose
• Function of amylase?


  - made in pancrease

  - works in the duodenum

  - breaks starch down into maltose
• Function of lipase?


  - produced in pancreas

  - works in duodenum

  - breaks down lipids into fatty acids and glycerol

  - also contains sodium hydrogen carbonate which helps neutralizes acidic stomach contents
• Function of protease?


  - produced in pancreas + stomach

  - works in stomach + duodenum

  - breaks down proteins into amino acids
• Function of maltase?


  - found in intestinal juice secreted by the lining of the small intestine

  - breaks down maltose into glucose
• What is the mouth?


  - where food enters alimentary canal

  - digestion begins
• Function of salivary glands?


  - produces saliva containing amylase
• What is the oesophagus?

  - muscular tube which moves ingested food into stomach
• Function of stomach?


  - muscular organ where digestion occurs
• Function of the pancreas?

  - produces digestive enzymes
• Function of the liver?


  - produces bile
• Function of the gallbladder?


  - stores bile before releasing it into the duodenum
• Function of the duodenum?


  - where food is mixed with digestive enzymes and bile
• Function of the colon?

  - where water is reabsorbed
• Function of the ileum?


  - where digested food is absorbed into the blood and lymph
• Function of the rectum?

  - where faeces are stored
• Function of the anus?

  - where faeces leave the alimentary canal
• What is absorption?


  - when small food molecules move from the small intestine into the bloodstream
• What is assimilation?


  - small food molecules being used to build large molecules
• What is egestion?


  - the removal of undigested food from the anus
• Where does absorption occur?


  - ileum
• Why is the ileum an efficient areas for absorption?

  - really long (large surface area aver which to absorb end products)

  - have folds and millions of villi and microvilli (increase the surface area by about 600x)

  - lining of the ileum is is very thin (one cell thick) so molecules pass through rapidly (shorter diffusion path)

  - dense capillary network + a branch of the lymphatic system called the lacteal (to transport digested food away from ileum to liver + body, speeds up diffusion)
• What are villi and microvilli?

  (villi) fingerlike projections of the sheets of cells in intestinal tract

  (microvilli) hairlike projections on each cell of every villus