homeostasis

• ADH is released by the posterior pituitary gland
• ADH increases water potential in the blood by causing the kidneys to reabsorb more water
• ADH increases the number of aquaporins in the collecting duct membrane so makes it more permeable to water
• insulin is released by b-cells in the islets of langerhans
• glucagon is released by a-cells in the islets of langerhans
• insulin lowers blood glucose levels by causing cells to absorb more glucose
• insulin stimulates glycogenesis
• gluconeogenesis is the synthesis of glucose from glycerol and amino acids
• glucagon stimulates gluconeogenesis and glycogenolysis
• adrenaline is released from adrenal glands
• adrenaline can act as a primary messenger in the same way as glucagon to increase blood glucose concentration
• insulin attaches to receptors on muscle or liver cells which cause the shape of protein channels to change and become more permeable to glucose
• insulin causes vesicles within the cell to bind with the membrane and add more protein channels to the membrane, making it more permeable to glucose
• secondary messenger model

  • glucagon or adrenaline bind to receptors on liver cells
  • adenylyl cyclase becomes activated
  • catalyses the conversion of ATP to cyclic AMP (cAMP)
  • cAMP activates protein kinase
  • protein kinase converts glycogen into glucose (glycogenolysis)
• glycogenolysis is the breakdown of glycogen into glucose
• glycogenesis is the conversion of glucose to glycogen
• selective reabsorption occurs in the proximal convoluted tubule
• osmoregulation occurs in the collecting duct
• ultrafiltration occurs in the Bowman's capsule and glomerulus
• glucose, amino acids and ions are reabsorbed into the blood during selective reabsorption
• proteins, red and white blood cells and and urea are not reabsorbed into the blood
• nephrons are the small functional units that make up the kidney
• too high water potential of blood is bad as cells will shrivel and become crenated
• if the water potential of the blood is higher than in the cells, water will move by osmosis into cells and cause them to burst
• changes in blood water potential are detected by osmoreceptors in the hypothalamus
• ADH binds to receptors on the collecting duct and DCT which activates a phosphorylase enzyme. Phosphorylase causes vesicles to fuse with the membrane of the collecting duct and add aquaporins to the membrane, making it more permeable to water
• ADH increases water potential of the blood
• substances move out of the glomerulus into the Bowman's capsule as there is a high hydrostatic pressure because the afferent arteriole branches into smaller capillaries that make up the glomerulus.
• the descending limb is thinner than the ascending limb so it is more permeable to water
• sodium ions are actively transported out of the ascending limb into the interstitial space which decreases the water potential. Water can then move out of the descending limb into the blood
• the filtrate passes out of the glomerulus into the bowman's capsule through fenestrations in the capillary endothelium, the basement membrane and podocytes
• homeostasis can only maintain the internal conditions of the body within certain limits
• adrenaline can activate enzymes involved in the conversion of glycogen to glucose (glycogenolysis) so increases the blood glucose levels
• the afferent arteriole is wider than the efferent arteriole
• selective reabsorption

  1. sodium actively transported into blood
  2. sodium ion concentration in epithelial cells decreased
  3. sodium diffuses from lumen into lining through co-transport carrier proteins with glucose/amino acids
  4. glucose/amino acids diffuse into the blood
• longer loops of henle have a greater concentration gradient so can make the urine more concentrated. More water is able to be reabsorbed along the longer length of the descending limb. Animals adapted to desert conditions will have this
• counter current multiplier effect means filtrate in the collecting duct meets interstitial fluid with a lower water potential so water can enter the blood.
• the nephron has a cortex (lighter coloured) and a medulla