Digestion

• What is digestion


  When large insoluable biological molecules hydrolysed into smaller soluble molecules that can be absorbed across cell membranes into blood stream and delivered to cells in body
• why are enzymes used in digestion

  catalyse precess of digestion
• what are products of digestion used for

  small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy(via respiration) or to build other molecules for cell growth, repair and function
• what are proteins ,carbohydrates and lipids hydrolysed into

  • Proteins are hydrolysed into amino acids
  • Carbohydrates are hydrolysed into simple sugars
  • Lipids are hydrolysed into a mixture of glycerol and fatty acids
• What do glands do in digestion

  salivary glands and glands in pancreas produce digestive enzymes
• what does the liver do in digestion

  produces bile which breaks down fats into fatty acids
• what does small intestines do in digestion

  where nutrients are absorbed into blood
• what does large intestines do in digestion

  site of water reabsorption
• Function of mouth in digestion

  The mouth contains teeth which break food into smaller pieces and increase its surface area to volume ratio

  • Carbohydrate digestion begins here as salivary glands excrete amylase

  The food is shaped into a bolus (ball) by the tongue and lubricated in saliva so it can be swallowed easily
• Function of oesophagus 


  A hollow tube with muscular walls through which food passes from the mouth to the stomach

  • Contractions of the smooth muscle in the wall of the oesophagus help move food down towards the stomach
• function of stomach in digestion

  where protein digestion occurs

  gland up tissue produces enzymes and stomach acid

  muscle tissue churns food

  acid unravels proteins for enzyme action whilst lowering ph

  lower ph kills microorganisms
• which digestion occurs in small intestines

  carbohydrate , protein and lipid mainly in duodenum with enzymes produced in pancreas and small intstines
• 3 sections of small intestines

  duodenum , jejunum and ileum
• how do molecules diffuse from small intestines into blood stream 


  by diffusion and active transport mainly in ileum and jejunum
• ileum adaptions for absorption

  long and lined with villi to increase surface area
• what are the 3 main types of digestive enzyms

  carbohydrase protease and lipids
• Digestion of carbohydrates by amylases and membrane bound disaccharides

  • The digestion of carbohydrates takes place in the mouth and the small intestine
  • Amylase is a carbohydrase that hydrolyses  starch into maltose
  • Maltose is then hydrolysed into glucose by the enzyme maltase
  • Amylase is made in the salivary glands, the pancreas and the small intestine
  • Maltase is a disaccharides which is found in cell-surface membranes of the epithelial cells lining the small intestine
• how is small intestine adapted to digest carbohydrates

  small intestines folded and microvilli present which increases surface area allowing more membrane bound disaccharides to fit and more absorption
• Digestion of proteins by proteases

  digestion begins in lumen of stomach by protease

  Endopeptidase hydrolyses middle of peptide bonds creating protein chunks

  exopeptidases - hydrolyse bonds at ends of a polypeptides • dipeptidases - break dipeptides into individual amino acid
• how are amino acids absorbed by cells lining ileum

  d by facilitated diffusion through specific carrier molecule in the surface membrane of epithelial cells. With each amino acid, one Na+ is also taken up, therefore amino acid absorption occurs via co-transport.
• digestion of lipids 


  lipids emulsified into micelles by bile salts(from liver) increasing surface area . 

  The digestion of lipids takes place solely in the lumen of small intestines

  • Lipase enzymes break down lipids (fats) to glycerol and fatty acids
  • Lipase enzymes are produced in the pancreas and secreted into the small intestine by the pancreas