Homeostasis

• Homeostasis


  the regulation of internal conditions in response to internal and external changes to maintain optimum conditions
• what does homeostasis control?

  -body temperature

  -blood pH

  -blood glucose concentration

  -water potential of blood

  -concentration of respiratory gases in the blood

  -metabolic waste
• why is it important to maintain a constant body temperature?

  as enzymes have a specific optimum temperature
• why is it important that body temperature doesn't get too high?

  -at higher temperatures

  the molecules move more quickly and there are more successful collisions and therefore more enzyme-substrate complexes form and the rate of reaction increases

  -at a higher temperature the enzymes denature and the tertiary structure of the enzyme changes and the active site is no longer complementary to the substrate
• why is it important that body temperature doesn't get too low?

  -at lower temperatures the molecules move slower and there are less successful collisions and therefore less enzyme-substrate complexes form

  rate of reaction decreases
• why is it important to maintain a stable pH?

  as enzymes have an optimum pH and will denature when the pH is too high or low
• negative feedback loop


  a feedback loop that helps to maintain a normal range within an organism and reduce the initial effect of the stimulus
• positive feedback loop


  a feedback loop that causes the effect of the original stimulus to be enhanced by producing a response that causes the factor to deviate even more from the normal range
• what happens when BGC increases above a certain level?

  the normal function of cells is distrupted
• what happens when BGC decreases below a certain level?

  cells may not have enough glucose for respiration
• what is the name of the endocrine tissue in the pancreas that secretes glucagon and insulin?

  islets of langerhans
• what cell secretes glucagon?

  a-cells
• what cells secrete insulin?

  b-cells
• how do beta cells secrete insulin

  -they detect a decrease in water potential in the blood, this causes water to move out of the cell and into the blood, the cell shrivels

  -glucose is absorbed by the b-cells via carrier proteins

  this causes insulin-containing vesicles to move towards the cell-surface membrane where they release insulin into the capillaries
• how does insulin cause the blood glucose level to decrease?

  insulin binds to receptors on target cells membrane

  this stimulates a vesicle in the target cell to move towards the membrane and fuse to the membrane, this adds more glucose transport proteins, this increases the permeability of the cells to glucose

  so more glucose is taken up by the target cell

  it also stimulates glycogenesis
• how does glucagon increase the blood glucose concentration?


  -glucagon binds to receptors in the cell surface membranes of hepatocytes

  -this activates adenyl cyclase

  -adenyl cyclase catalyses the conversion of ATP to cyclin AMP

  -cAMP acts as a second messanger and activates protein kinase

  -protein kinase catalyses the breakdown of glycogen to glucose (glycogenolysis)
• how does adrenaline affect blood glucose concentration?

  it increases the blood glucose concentration
• how does adrenaline increase blood glucose concentration?

  by binding to different receptors than glucagon on hepatocytes and activating adenylate cyclase which activated cAMP which activated protin kinase

  this catalyses glycogenolysis
• glycogenesis


  synthesis of glycogen from glucose
• glycogenolysis


  hydrolysis of glycogen to produce glucose
• gluconeogenesis


  the synthesis of glucose from other molecules such as fatty-acids, glycerol and amino acids
• Type I diabetes

  -when the pancreas doesn't produce enough insulin to control BGC

  -begins in childhood when T cells attack beta cells in the islets of Langerhans
• Type II diabetes

  -when the hepatocytes have a reduced sensitivity to insulin (less receptors or receptors no longer respond to insulin)
• Type I diabetes treatments

  monitoring BGC and injecting insulin throughout the day
• Type II diabetes treatment

  maintaining a low-carbohydrate diet and regular exercise to reduce the need for insulin
• why does diabetes cause high blood pressure?

  as an increased BGC decreases the WP, water moves into the blood by osmosis and there is a larger volume of blood which increases blood pressure
• functions of the kidneys

  -regulating the water content of the blood

  -excreting toxic waste products of metabolism (urea) and excess minerals and vitamins
• renal artery


  carries oxygenated blood, to the kidneys (blood contains urea and salts)
• renal vein


  carries deoxygenated blood away from the kidneys (blood that has had urea and excess salts removed)
• ureter


  carries urine from kidneys to bladder
• urethra


  releases urine outside of the body
• structure of the kidney

  contains the fibrous capsule, the cortex, the medulla and the renal pelvis

  
• cortex

  contains the glomerulus, bowmans capsule, proximal convoluted tubule and the distal convoluted tubule
• medulla

  contains the loop of henle and the collecting duct
• renal pelvis


  where the ureter joins the kidney
• where does ultrafiltration take place?

  the bowman's capsule
• ultrafiltration (detailed answer)

  -blood flows into the glomerulus from the afferent arteriole

  -this causes the glomerulus to have a higher hydrostatic pressure than the bowman's capsule

  -small molecules such as glucose, mineral ions, urea and amino acids are forced out of the capillary through the capillary walls and into the lumen of the bowman's capsule, this forms the glomerular filtrate

  -the basement membrane which is made up of collagen fibres acts as a filter and prevents large molecules such as proteins from being removed

  -podocytes provide strength and structure to the capillaries, preventing them from collapsing under the high hydrostatic pressure

  -the podocytes have gaps between them to allow water and small molecules to leave the blood and collect in the bowman's capsule
• how does pressure affect water potential in the glomerulus and bowman's capsule?

  blood pressure is high in the glomerular capillaries this raises the WP of the blood plasma in the glomerular capillaries above the WP of the filtrate in the bowman's capsule

  this causes water to move down its concentration gradient into the bowman's capsule
• how does solute concentration affect the water potential in the glomerulus and the bowman's capsule

  -basement membrane doesn't allow large molecules through so they stay in the blood

  -this causes the blood plasma of the glomerular capillaries to have a higher solute concentration that the filtrate in the bowman's capsule,

  -WP of the blood plasma is lower than in the bowman's capsule

  -therefore water moves down its WP gradient and into the glomerular capillaries from the bowman's capsule
• how does ultrafiltration occur?

  -due to the differences in water potential between the plasma in the glomerular filtrate and in the bowman's capsule

  -pressure outweighs solute concentration so WP of the blood plasma in the glomerulus is higher than the WP of the filtrate in the bowman's capsule

  -water moves down its WP gradient into the bowman's capsule