excretion

• excretion - the removal of waste products from metabolism fro the body
• hepatic artery - from aorta to the liver, contains oxygen and ATP
• hepatic portal vein - from small intestine to the liver, contains products of digestion
• hepatic vein - from liver to vena cava, contains waste products of respiration
• bile duct - from liver to gall bladder, bile produced by hepatocytes
• sinusoids - channels carrying blood between the rows of cells
• canaliculi - channels carrying bile produced by the hepatocytes
• bile flows from the centre of the lobule to the outside
• sinusoids are lined with kupffer cells (macrophages)
• kupffer cells remove bacteria and damaged red blood cells
• deamination - amino group removed forming ammonia, the remained forms a keto acid which enters the Krebs cycle
• ornithine cycle - metabolic reactions converting toxic ammonia into urea in mitochondria and cytosol
• detoxification - conversion of toxic molecules to less nontoxic molecules
• detoxification of alcohol - broken down in the hepatocytes

  1. ethanol to ethanal using enzyme ethanol dehydrogenase and NAD
  2. ethanal to acetate using enzyme ethanal dehydrogenase and NAD
• ultrafiltration - filtration on a micro scale, small molecules are filtered out of the blood and into the lumen of a nephron. occurs in the Bowmans capsule
• adaptations for ultrafiltration

  • diameter of blood vessels - afferent is greater than the efferent build up of hydrostatic pressure forces fluid into Bowmans capsule
  • capillary endothelium - bigger gaps between cells than usual
  • basement membrane - water, glucose and mineral ions are forced into filtrate
  • podocytes - fingerlike projections allow filtrate to pass between them
• selective reabsorption - filtrate is absorbed back into the blood, in the proximal convoluted tubule
• selective reabsorption process

  1. sodium potassium pumps actively transport sodium out of pct cells
  2. sodium ions enter filtrate by facilitated diffusion. glucose and amino acids transported by cotransporter proteins into pct then into blood by facilitated diffusion.
  3. removal of solute increases water potential, water flows into the blood.
  4. urea enters pct cells by simple diffusion
  5. any large molecules are reabsorbed by endocytosis
• the descending limb loop of henle

  • narrow
  • thin walls
  • highly permeable to water
  • contains aquaporins
• the ascending limb loop of henle

  • wider
  • thicker walls
  • impermeable to water
• loop of henle acts as a counter current multiplier - the longer the loop the greater the effect
• the process of loop of henle

  1. sodium ions are actively transported out of the ascending limb into the medulla
  2. low water potential in the interstitial region, water cannot leave the ascending limb
  3. water leave the descending limb by osmosis
• distal convoluted tubule - region of control of pH and salts under control of aldosterone
• collecting duct - water moves out by osmosis into surrounding medulla tissue where low water potential
• osmoregulation - control of water and salt levels in the blood
• neurosecretory cells - produce ADH in cell bodies, stored in terminal bulbs in the pituitary gland. target cells for ADH = collecting duct
• ADH effect

  1. bind to receptors on collecting duct
  2. activates an enzymes causing vesicles to fuse with the cell surface membrane
  3. vesicles contain aquaporins making the membrane more permeable
  4. more water leave by osmosis `
• pregnancy test

  1. HCG from the urine binds to mobile antibodies on the strip
  2. mobile antibodies bind to immobilised antibodies in the test strip window
  3. any remaining mobile antibodies bind to immobilised antibodies at the end window to show the test worked