Osmoregulation

• Maintains constant osmotic pressure in organism’s fluids by controlling water and salt concentrations with negative feedback (blood plasma ψ changes are detected, so body corrects this, returning it to normal value)
• Hypothalamus (part of the forebrain) detects changes in blood plasma water potential and produces ADH (antidiuretic hormone)
• Pituitary gland stores and secretes ADH in kidney, particularly collecting ducts that respond to ADH concentration in blood plasma
• Organs involved

  A) Pituitary Gland

  B) Hypothalamus

  C) Adrenal gland

  D) Kidney

  
• Diagram brain

  A) Supraoptic Nucleus

  B) Oxytocin

  C) Neurosecretory

  D) Paraventricular Nucleus

  E) ADH

  F) Hypothalamus

  G) Artery

  H) Axon terminals

  I) hormones

  J) Capillary

  K) Posterior pituitary

  L) vein

  M) Anterior pituitary

  
• As filtrate moves down collecting duct, more water is reabsorbed, and urea concentration in filtrate increases; this creates a steep diffusion gradient for urea, so some are reabsorbed into medulla by diffusion
• Re-absorption of urea into medulla helps osmoregulation; as urea concentration increases, medulla’s water potential is lowered, helping the re-absorption of water from the collecting duct