digestion

• ingestion is the intake of food
• mechanical digestion is the breaking up of food by the mouth
• food moves down the oesophagus via peristalsis
• the stomach uses muscles to churn food and fluid into chyme
• chemical digestion is enzymes breaking up large molecules into soluble monomers
• the small intestine completes digestion and processes food for absorption
• waste products are excreted
• membrane proteins allow for facilitated diffusion in the villi of the small intestine
• a rich blood supply means there is a large surface area for absorption in the small intestine
• the single celled epithelial layer in the small intestine means a short diffusion distance
• lacteal in the small intestine allows for the transport of lipids
• the intestinal crypt in the small intestine secretes enzymes
• microvilli in the small intestine increases the surface area, which is better for absorption
• amylase is in the oesophagus and converts starch to maltose
• stomach enzymes

  • protease- proteins to polypeptides
  • stomach acid- used for chemical digestion
• Bile slats in the liver/ gall bladder emulsify lipids
• enzymes in the pancreas

  • amylase- starch to maltose
  • lipase- triglycerides to fatty acids
  • nuclease- DNA/RNA to nucleotides
  • endopeptidase- peptides to amino acids
  • bicarbonate ions- neutralise stomach acid
• membrane bound enzymes in the small intestine includes maltose
• features of an endocrine cell

  • large rough endoplasmic reticulum
  • many mitochondria
  • golgi body and vesicles
  • large nucleus
• co-transport during digestion:

  • glucose and amino acids
  • active transport using membrane proteins
• facilitated diffusion in digestion:

  • monosaccharides
  • uses membrane proteins
• Osmosis:

  • water
  • from an area of high solute concentration to an area of low solute concentration
• simple diffusion in digestion:

  • triglycerides (fatty acids)
  • Monoglycerides pass through the membrane and recombine to form triglycerides (combine with cholesterol and coated in proteins and phospholipids)
• protein digestion:

  • starts in the stomach but mainly carried out in the small intestine
  • enzyme trypin secreted as inactive (otherwise this would digest body cells)
  • breaks proteins into small chains (polypeptides)
• lipid digestion:

  • insoluble so need to be broken up by bile salts
  • produces monoglycerides and fatty acids
  • monoglycerides combine with proteins into chylomicrons
  • then they are transported into the liver in the lymphatic system