Digestion & absorption

• during digestion large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes.
• describe how carbohydrates are digested?

  -amylase in saliva hydrolyses polysaccharides into disaccharides (maltose).

  • membrane bound disaccharidases (sucrase & lactase) hydrolyse disaccharides into monosaccharides.
  • this is done by breaking glycosidic bonds.
• where is amylase produced?

  salivary glands & pancreas
• how is protein digested?

  -endopeptidases hydrolyse peptide bonds between amino acids in the middle of the chain.

  • exopeptidases hydrolyse peptide bonds between amino acids at the ends of chains.
  • dipeptidases hydrolyse peptide bonds between two amino acids.
• what enzymes are involved in carbohydrate digestion?

  amylase & membrane bound disaccharidases
• what enzymes are involved in protein digestion?

  exopeptidases

  endopeptidases

  dipeptidases
• where does protein digestion occur?

  in the stomach then in the ileum
• where is lipase produced?

  pancreas
• where are bile salts produced?

  liver
• how are lipids digested?

  -lipase hydrolyses ester bonds in triglycerides making monoglycerides & fatty acids.

  • bile salts emulsify lipids to form droplets called micelles, increasing surface area.
• what is the physical digestion of lipids?

  Emulsification & micelles form
• what is the chemical digestion of lipids?

  lipase action
• how are lipids absorbed?

  -micelles are non-polar so can simply diffuse through cell surface membranes and enter the epithelial cell.

  • these will then be modified into triglycerides by the golgi.
  • they will then form vesicles and be transported round the body.
• where does absorption occur in mammels?

  ileum
• what are the adaptations of the ileum?

  The ileum is covered in villi which are covered in microvilli, increasing surface area for absorption.

  The walls are thin, reducing diffusion distance.

  A network of capillaries maintain the concentration gradient.