9.9 osmoregulation

• structure of urinary system

  • kidney
  • renal artery
  • renal vein
  • urethra
  • bladder
• structure of kidney

  • fibrous capsule - protects kidneys
  • cortex - consist of bowman's capsule, distilled convoluted tubule and vessels (outer region)
  • medulla - consist of collecting duct, loop of henle and vessels (inner region)
• What is urea? How is it removed?

  • produced in the liver
  • deaminates excess acids into ammonia
  • ammonia converted to urea - by reacting with carbon dioxide
  • which is less toxic
• structure of nephron

  as shown...

  
• blood vessels in nephron

  wide afferent arteriole:

  • from the renal artery
  • enters bowman's capsule
  • forms glomerulus

  narrow efferent arteriole:

  • knot of capillaries
  • form capillary network around tubules
• Ultrafiltration

  used to remove urea from blood stream

  • high hydrostatic pressure in glomerulus
  • due to narrow efferent arteriole
  • small substances such as glucose pass through
  • fenestrations in the capillary endothelium
  • cross the capillary basement membrane
  • pass through podocytes and enter lumen
• adaptations of bowman's capsule

  • fenestrations
  • podocytes which filtrate passes through
• selective reabsorption

  • occurs in proximal convoluted tubule
  • reabsorbs useful molecules
  • water via osmosis
  • glucose and amino acids via co-transport with Na+ and active transport
  • ions via facilitated diffusion
  • urea via diffusion
• loop of henle - concentrated urine

  
  

  • acts as a counter current multiplier
  • Na+ and Cl- ions are actively transported out of ascending limb
  • ascending limb is impermeable to water. (osmosis of water out of descending limb)
  • water potential of medulla decreases
  • collecting duct are permeable to water
• distal convoluted tubule

  reabsorbs...

  • water via osmosis
  • ions via active transport and facilitated diffusion

  walls are permeable and depend on hormone action
• collecting duct (decreased water conc)

  • osmoreceptors in the hypothalamus detects water potential
  • sends signal to posterior pituitary gland
  • to release ADH
  • ADH released in collecting duct
  • increases permeability of cells
  • forms aquaporins
  • which reabsorb water
• Collecting duct (increase water conc)


  • osmoreceptors in the hypothalamus detects water potential
  • sends signal to posterior pituitary gland
  • to release less ADH
  • less ADH released in collecting duct
  • decreases permeability of cells
  • less reabsorbed water
• permeability of collecting duct and distal convoluted tubule is determined by ADH level.

  more ADH = more permeable
• osmoregulation

  • control of negative feedback
  • via negative feedback mechanisms
• role of hypothalamus in osmoregulation

  • contains osmoreceptors which detect change in water potential levels
  • triggers release of ADH
• Kangaroo Rats

  • desert animal
  • doesn't drink water
  • gains water through food and metabolism
• adaptations of Kangaroo Rats

  • long loop of henle
  • low water potential in renal medulla - (more effective counter current multiplier)
  • microvilli and mitochondria
• ectotherm


  • regulates temperature using external sources
  • e.g behavioural methods
• endotherm


  • use physiological methods (metabolic) and behavioural to regulate temperature
  • contain thermoreceptors - detect temperature and send signal to hypothalamus
• the thermoregulatory centre is located in the hypothalamus.

  receives impulses from receptors.