digestion and absorption

• where does the digestion of carbohydrates take place?

  mouth and small intestine
• where does the digestion of proteins take place?

  stomach and small intestine
• where does the digestion of lipids take place?

  small intestine
• describe the process of the digestion of carbohydrates?

  1. starts in the mouth , salivary glands secrete amylase which hydrolyses glycosidic bonds In starch to produce maltose
  2. in the small intestines , pancreas secretes amylase to also break down starch into maltose
  3. in the ileum , the epithelial cells embedded with membrane bound disachharidases called maltase which hydrolyse maltose into glucose
• how is sucrose digested?

  in the ileum by membrane bound disachharidases called sucrase
• how is lactose digested ?

  in the ileum by membrane bound disaccharide called lactase
• how are proteins digested ?

  • endopeptidase hydrolyse the middle of polypeptides
  • exopeptidase hydrolyse the ends of the polypeptide
  • membrane bound dipeptidase
• how are amino acids absorbed in the ileum?

  co-transport
• what is the ileum?

  longest part of the small intestine
• describe how lipids are absorbed :

  1. glycerol enter the epithelial cells via simple diffusion because they are small and polar
  2. monoglycerides and fatty acids are large and have non-polar regions so combine with bile salts to form micelles (emulsification)
  3. the micelles transport the monoglycerides and fatty acids outside the epithelial cells where they enter via simple diffusion
  4. inside the epithelial cells, the endoplasmic converts them back into triglycerides
  5. tryglycerides aren't soluble in cytoplasm so the Golgi or ER contends trygycerides with proteins and cholesterol to produce chylomicrons
  6. Golgi packages them into vesicles and leave via excosytosis into the lymphatic system (lacteals) eventually the blood
• why do micelles work ?

  their outer shell is polar to is soluble in water
• what are adaptations of the epithelial cells?

  • have micro vili
  • a lot of cotransport protein
  • a lot of mitochondria for ATP