B16 homeostasis

• homeostasis is the maintenance of a constant internal environment in an organism, within restricted limits
• the internal environment of an organism is made up of tissue fluids that bathe each cell, which supply nutrients and remove waste
• homeostasis is important because maintaining the features of the fluid protects the cells from changes to the external environment
• the control mechanism for homeostasis involves the stages: optimum point, receptor, coordinator, effector, feedback mechanism
• in homeostasis, the optimum point is conditions where the system operates best
• in homeostasis, the receptor detects any change from the optimum point
• in homeostasis, the coordinator coordinates information from receptors and sends instructions
• in homeostasis, an effector is usually a muscle or gland, which responds by creating a stimulus
• in homeostasis, a feedback mechanism is how a receptor responds to the stimulus created by the effector
• the final stage of homeostasis is feedback mechanisms
• negative feedback = changes in conditions are reversed to restore optimum conditions
• positive feedback = changes in conditions are increased to achieve extreme conditions
• having separate feedback mechanisms that control the same condition gives a greater degree of homeostatic control
• hormones are different chemically but all have similar features
• hormones are produced in glands which secrete them directly into the blood
• hormones are carried in the blood plasma to the cells where they act, which are called target cells
• hormones are complementary to the receptor on a specific target cell
• hormones are effective in very low concentrations
• hormones have widespread and long-lasting effects
• the second messenger model is a mechanism of hormone action used for the control of blood glucose concentration
• in the second messenger model:

  • adrenaline/glucagon binds to a transmembrane protein receptor in the cell-surface membrane of a liver cell
  • this causes the protein to undergo a conformational change
  • this activates the enzyme adenyl cyclase
  • adenyl cyclase converts ATP to cyclic AMP
  • cyclic AMP acts as a second messenger which binds to the enzyme protein kinase
  • protein kinase catalyses the conversion of glycogen to glucose
  • glucose moves out of the liver cell by facilitated diffusion and into the blood
• the pancreas contains groups of cells called islets of langerhans which have alpha cells and beta cells
• alpha cells are larger and produce glucagon
• beta cells are smaller and produce insulin
• glycogenesis is the conversion of glucose to glycogen
• glycogenolysis is the breakdown of glycogen to glucose
• gluconeogenesis is the production of glucose from other sources
• blood glucose concentration is influenced by three factors:

  • directly from diet
  • hydrolysis of glycogen in the small intestine
  • from gluconeogenesis using amino acids or triglycerides
• insulin has the following roles:

  • attaches to receptors on the surface membrane of target cells
  • causes a conformational change in the carrier proteins so they allow more glucose through by facilitated diffusion
  • activates enzymes which convert glucose to glycogen
• glucagon has the following roles:

  • attaches to receptors on the surface membrane of target cells
  • activates enzymes which convert glycogen to glucose
  • activates enzymes which convert amino acids and glycerol to glucose
• adrenaline has the following roles:

  • attaches to receptors on the surface membrane of target cells
  • activates enzymes which convert glycogen to glucose
• diabetes is a metabolic disorder caused by an inability to control blood glucose concentration, due to either a lack of insulin or a loss of responsiveness to insulin
• there are two types of diabetes, called type I and type II
• type I diabetes causes the organism to be insulin-dependent as the body is unable to produce insulin as a result of the immune system attacking the beta cells of the islets of langerhans
• type II diabetes causes the organism to be insulin-independent as the body loses responsiveness to insulin as a result of glycoprotein receptors on body cells being lost or losing responsiveness to insulin
• type I diabetes is controlled by injections of insulin, the dosage of which is controlled using biosensors which detect the blood glucose concentration of an organism
• type 2 diabetes is controlled by diet and exercise, sometimes supplemented by insulin injections or other drugs
• kidneys have the following structures: fibrous capsule, cortex, medulla, renal pelvis, ureter, renal artery, renal vein
• in the kidneys, the fibrous capsule is an outer membrane that acts as protection
• in the kidneys, the cortex is a lighter outer region made up of Bowman's capsules, convoluted tubules, and blood vessels