Digestion

• Digestion breaks large insoluble molecules via hydrolysis to smaller soluble molecules that can be absorbed across cell membranes
• Ingestion is the taking in of solid food through the mouth
• absorption is when soluble molecules are absorbed across cell membranes into the blood stream
• Egestion is the elimination of undigested material from the body
• Peristalsis is the relaxation and contraction of muscles in the intestines to move digested food through the system
• Ileum is the smallest part of the small intestine that furthered digests food from the stomach
• Disaccharidases are enzymes that catalyse the hydrolysis of disaccharides to monosaccharides
• Micelle are water soluble vesicles formed of fatty acids, glycerol, mono glycerine’s and bile salts
• Emulsification is the break down of fats into tiny droplets (micelles) which are water soluble
• Villi are finger like projections which have a rich blood supply which helps the absorption of nutrients in the intestine by increasing surface area
• Lumen is the space within the bodies tracts, tubes and cavities and cells
• Chlylomicrons are formed in the intestine and are the transport vesicles for fat to the liver
• Lacteal are lymphatic capillaries that absorbs fats in the villi of the small intestine
• Bile salts are produced in the liver directly from cholesterol and used in the emulsification of fats
• Oesophagus is a circular muscle which does peristalsis to push food down to the stomach
• The mouth is where mechanical digestion (mastication) takes place and uses salivary amylase
• Pancreas produces pancreatic amylase, lipase and peptidase which are digestive enzymes used in the small intestine
• large intestine absorbs water by osmosis as well as minerals and vitamins
• Bile is made in the liver and stored in the gall bladder. It helps emulsify fats and increases pH to 7/8 after the stomach with mineral salts
• The duodenum is the first part of the small intestine and is where pancreatic enzymes and bile from the liver works.
• The stomach is a muscular sac with a 1/2 pH as it contains HCl. It does mechanical digestion to break down large food prices into smaller ones to increase its surface area.
• Physical breakdown breaks down large food pieces to smaller food pieces to increase surface area to allow enzymes to work more efficiently
• Chemical digestion uses enzymes to catalyse hydrolysis reactions to break down insoluble molecules to smaller soluble molecules. This is down by breaking bonds within the substrate
• Enzymes used in digestion

  • carbohydrases which breaks down carbohydrates to monosaccharides
  • lipases hydrolysis lipids to fatty acids and glycerol
  • proteases hydrolyse proteins to amino acids
• amylase breaks down polysaccharides to disaccharides
• Disaccharidase enzymes break down disaccharides to monosaccharides
• Salivary amylase denatures in the stomach due to pH decrease
• Dissacharidases

  • Disaccharidase breaks down maltose to alpha glucose
  • sucrase breaks down sucrose to glucose and fructose
  • lactase breaks down lactose to galactose and glucose
• Endopetidase breaks down a protein to a polypeptide in the stomach
• Exopeptidase breaks down polypeptides to dipeptides in the duodenum
• Dipeptidase breaks down dipeptides to amino acids in the ileum
• Lipids are hydrolysed by lipase to fatty acids and glycerol
• Before lipase can work bile is used to emulsify large fat molecules
• Villi are 1mm long
• Structure of the small intestine for maximal absorption

  • Thin walls
  • muscle contractions maintain concentration gradient
  • Villi and micro villi
  • rich blood supply
• Amino acids and monosaccharides are absorbed by co transport in the epithelial cells of the ileum
• Facilitated diffusion moves monosaccharides and amino acids from the epithelial cell into the blood stream
• In order to absorb amino acids and monosaccharides we use the potassium and sodium ion pump.
• Once monoglycerides have been absorbed into the cell they are converted to triglycerides where they become chylomicrons in the golgi and endoplasmic reticulum
• Chylomicrons are too big to be absorbed into the blood so are absorbed by lacteals via exocytosis into the thoracic duct where they are absorbed into the lymph.