homeostaisis

• insulin is when blood glucose gets too high
• glucagon is when blood glucose gets too low
• Glycogenesis: formation of glycogen from glucose
• Glycogenolysis: breakdown of glycogen to glucose
• Islets of Langerhans: endocrine cells scattered throughout the pancreas, which release insulin and glucagon
• negative feedback process

  -stimulus is detected by a receptor

  -receptor sends information through the nervous system

  -central control in the brain or spinal cord instructs an effector to carry out a response

  -the stimulus is constantly monitored by receptors so that it fluctuates around a set value
• Why is it important to maintain a core body temperature?

  If the body temperature is too high then enzymes may denature - the enzyme vibrates too much which breaks the H bonds causing a change in 3D structure

  • If temperature is too low then enzyme activity is reduced
• Why is it important to maintain a constant pH?

  If blood pH is too high or too low enzymes become denatured

  The hydrogen bonds are broken so the 3D structure is changed, causing the active site to change shape

  • Metabolic reactions are slowed.
• Why is it important to maintain a constant concentration of glucose in the blood?

  Too high = water potential of blood is reduced, water diffuses out of the cell and cells shrivel up and die

  • Too low = cell can't carry out normal activities because there isn't enough glucose for respiration to provide energy
• gluconeogenesis: glucose is formed from glycerol and amino acids
• How does insulin lower blood glucose concentration?

  1)Binds to specific receptors on liver and muscle cells

  2) Increases the permeability of muscle-cell membranes to glucose by creating more channel proteins

  • vesicles containing glucose transporters move towards the membrane and fuse with it when insulin binds, forming more channel proteins

  3) Activates enzymes in liver and muscle cells that convert glucose into glycogen

  4) The cells can store glycogen as an energy source in the cytoplasm

  5) Also increases the rate of respiration of glucose, especially in muscle cells
• How does glucagon increase blood glucose concentration? (second messenger model)

  1)Binds to its specific receptors on the liver cell

  2) Activates an enzyme called adenylate cyclase

  3) This converts ATP into cyclic AMP (cAMP), the second messenger

  4) cAMP activates the enzyme protein kinase A

  5) Protein kinase A activates a chain of reactions which break glycogen into glucose
• type 1 diabetes: pancreas produces little or no insulin
• type 2 diabetes: insulin resistance, insulin deficiency
• 2 main ways urine is formed- ultrafiltration, selective re-absorption
• selective absorption occurs at the glomerulus filtrate, the useful substances leave the tubules and enter capillary
• the use of mitochondria in the bowman's capsule is to provide ATP for active transport
• the use of a folded membrane in the Bowman's capsule is to increase the surface area and speed up the rate of diffusion (out of)
• the use of microvilli in the Bowman's capsule is to increase the surface area and speed up the rate of diffusion (into )
• basal- bottom
• apical- top/ apex
• active transport of sodium, glucose and water back into the blood:

  1. Na+ are actively transported out of epithelial cells in the wall of proximal convoluted tubule and into capillaries
  2. this creates a low Na+ concentration gradient in epithelial cells
  3. Na+ diffuses across their concentration gradient into epithelial cells from the lumen into proximal convoluted tubule (facilitated diffusion)
• active transport of sodium, glucose and water back into the blood P2:

  4. glucose/ amino acids/ chloride ions are co-transported by sodium glucose co-transport protein into epithelial cells

  5. then diffuse down the concentration gradient into capillaries

  6. water moves, via osmosis, down water potential gradient from lumen of proximal convoluted tubule into the capillaries
• loop of henle: main function is to reabsorb sodium ions and water to create a concentration gradient in the medulla of the kidney

  • is made of an ascending and descending limb
• decending limb: has thin cell wall, permeable to water
• ascending limb: thick cell wall, impermeable to water
• what leads to a decrease in blood water potential

  • sweating
  • not drinking enough
  • ingesting solutes and ions
• osmoregulation: the water potential of the blood is maintained to an optimal level
• what happens when water pot of blood goes too high?

  increase in blood water potential is detected by osmorecpetors in the hypothalamus, the pituitary gland releases less ADH, walls of distal convoluted tubule become less permeable to water, more water leaves body as dilute urine
• what happens when water pot becomes too negative?

  decrease in blood water potential is detected by osmorecpetors in the hypothalamus, the pituitary gland releases more ADH, walls of distal convoluted tubule become more permeable to water, less water leaves body as concentrated urine
• osmoregulation process:

  • ADH travels to kidney from pituitary gland, binding to specific receptors in collecting duct cells of epithelium
  • binding of ADH activates phosphorylase that leads to phosphorylation of aquaporins (signalling cascade)
  • vesicle containing aquaporins fuses with collecting duct cells
  • meaning it contains more aquaporins, more permeable so water can move down the water potential gradient into tissue fluid