carbohydrates

• Explain the digestion of starch: Mouth and stomach

  The food containing starch is physically broken down using the teeth. The salivary glands produce salivary amylase. This hydrolyses starch into maltose. The salivary amylase contains mineral salts, which maintains the PH at around neutral, this is the optimum PH for the amylase to work at. The food is then swallowed into the stomach, here the conditions are acidic, this denatures the salivary amylase so that there is no further hydrolysis of starch. The food then enters the small intestine after a while.
• Explain the digestion of starch: Small intestine

  Once the food is in the small intestine, the pancreas releases pancreatic juices this contains pancreatic amylase. Tis hydrolyses any remaining starch into maltose. the pancreas releases alkaline salts to maintain the PH at around neutral as this is the optimum PH for the pancreatic amylase to work best at. The intestinal wall pushes the food along the ileum. On the cell-surface membrane of the epithelial cells that line the ileum there are membrane-bound disaccharidases known as maltase these hydrolyse the maltose into alpha glucose.
• Explain the digestion of lipids

  the liver makes bile salts this emulsifies lipids into tiny droplets called micelles, these increase the surface area for lipase to act on. The lipase is then released by the pancreas it hydrolyses the ester bonds in triglycerides forming fatty acids and monoglycerides. The fatty acids monoglycerides and glycerol as well as the bile salts all associate forming structures called micelles. These micelles are water soluble vesicles they transport the monoglycerides, fatty acids etc to the epithelial cells that line the ileum.
• Explain the digestion of lipids: the epithelial cells

  The micelles break down releasing the fatty acids, monoglycerides into the epithelial cells. They are transported to the endoplasmic reticulum where they re-combine to become triglycerides. They are then transported to the golgi-apparatus where they are combined with lipoproteins and cholestrol forming chlyomicrons, these then leave the epithelial cell by exocytosis and enter the lymphatic system via the lymphatic capillaries called lacteals. it is then transported into the blood stream by the lymphatic vessels.
• Explain the digestion of lipids: in the blood- final stage

  The triglycerides in the chylomicrons are hydrolysed by the enzymes in the endothelial cells in the blood. The triglyceride is then released and diffuses into cells where it is needed