Regulation of Water Balance

• Importance of osmolarity


  • It helps regulate the concentration of ions
• How water is gained and lost in the body

  1. Osmosis - water moving across a semi-permeable membrane for a lower solute concentration to a region of higher concentration

  2. Osmolarity goes up water goes down - detected by osmoreceptors in the hypothalamus

  
• Osmoregulation


  • Increase in salt consumption
  • Increase in sweating
• Urine is less concentrated


  • Decreases sodium reabsorption
  • Less water in the blood stream
  • Kidney less permeable to water
• Water content of the blood too high

  stimuli response: Drinking lots of H2O
• Water content of the blood too low

  Stimulus Response: Sweating or eating salty food
• Receptors


  • Baroreceptor - Heart
  • Osmoreceptors - Hypothalamus
• Effector

  Pituitary Gland - Releases ADH
• Decrease in ADH


  More water in urine (decrease in kidney permeability)
• Increase in ADH


  Less water in urine (Increase in kidney permeability)
• How water enters the body

  • Drinking
  • Eating
  • Metabolic (water from cellular respiration)
• Plug holes


  • Sweating, breathing, urination and defaecation
• Tonicity


  Concentration of dissolved solutes
• Aquaporin


  A channel protein specific to water molecules
• Most water lost in the body is lost in ways that are unavoidable and cannot be regulated
• The amount of water in urine can be controlled
• Anti-diuretic hormone (ADH)


  A peptide hormone secreted in response to high blood tonicity that stimulates water reabsorption in the kidney
• How ADH regulates water balance

  1. ADH goes into the collecting tubules where it stimulates the production of aquaporins

  2. The aquaporins enable water to leave the collecting duct to be reabsorbed into vessels instead of getting lost through plug holes