digestion and absorption

• where is amylase produced

  salivary glands and pancreas
• what does amylase do

  breaks down starch into maltose
• how is maltose broken down into glucose

  by maltase embedded in the epithelial cells of the ileum
• How are monosaccharides absorbed?


  glucose and galactose are absorbed via cotransport with sodium ions

  fructose passes via facilitated diffusion
• what is the process of cotransport of glucose


  1. sodium ions are actively transported out of the epithelial cells by the sodium potassium pump in the blood- takes place in a particular protein carrier molecule found in cell surface of epithelial cells

  2. this maintains a higher concentration of sodium ions in the lumen of the intestine than the epithelial cells

  3, sodium ions diffuse into the epithelial cells down this concentration gradient through a different type of protein carrier. as the sodium ions diffuse in they carry a glucose molecule with them

  4. causes higher glucose conc in cell so moves into blood plasma via facilitated diffusion using a different carrier protein
• why is there ATP near the first carrier protein in co transport

  to provide energy for the active transport of sodium and potassium ions through the sodium potassium pump
• what does lipase do

  breaks down lipids into monoglycerides and fatty acids
• where are lipases made and where else can they be used

  made in pancreas

  work in small intestine
• where are bile salts produced

  liver
• what do bile salts do

  emulsify fats
• how do bile salts aid lipid digestion

  the smaller droplets have a much larger surface area so lipase can hydrolyse them faster
• what is a micelle


  monoglycerides and fatty acids produced surrounded by bile salts
• what are 3 uses of micelles

  - help move monoglycerides and fatty acids towards the epithelium

  - micelles constantly break up and reform so release monoglycerides and fatty acids so they can be absorbed

  - bile salts in micelle make fatty acids more soluble in water

  -maintain a higher concentration of fatty acids outside the cells lining the ileum
• how are monoglycerides and fatty acids absorbed


  directly across the epithelial cell membrane as they are lipid soluble
• once in the epithelial cell what happens


  -in the endoplasmic reticulum they recombine to form triglycerides

  -in the Golgi apparatus the triglycerides combine with proteins to from chylomicrons

  -chylomicrons leave epithelial cell and enter lacteal

  - lymph in lacteal transports chylomicrons away from intestine
• What does endopeptidase do?

  hydrolyse peptide bonds between amino acids in the centre of a polypeptide forming a series of peptide moelcules
• what are 2 examples of endopeptidases synthesised by the pancreas and released into the small intestine


  trypsin

  chymotrypsin
• what is an example of an endopeptidase related into the stomach

  pepsin
• what conditions does pepsin work in

  acidic - maintained by stomach acid
• what does exopeptidase do

  hydrolyses peptide bond at end of polypeptide to remove single end amino acids
• what is a dipeptidase

  a type of exopeptidase that hydrolyses peptide bonds in disaccharides
• where are dipeptidases often found


  In the cell surface membrane of epithelial cells in the small intestine
• how are amino acids absorbed

  co-transport with Na+
• describe the processs of co transport of amino acids


  1. sodium ions are actively transported out of the epithelial cells by the sodium potassium pump in the blood- takes place in a particular protein carrier molecule found in cell surface of epithelial cells

  2. this maintains a higher concentration of sodium ions in the lumen of the intestine than the epithelial cells

  3, sodium ions diffuse into the epithelial cells down this concentration gradient through a different type of protein carrier. as the sodium ions diffuse in they carry an amino acid with them

  4. causes higher amino acid conc in cell so moves into blood plasma via facilitated diffusion using a different carrier protein