Water regulation

• Water

  Plays a key role in the human body, and it is regulated via the process of osmoregulation
• Too much or too little water

  The body will use stimulus-response models to adjust
• Osmolality

  Concentration of solute in a given weight of water
• Extracellular fluid

  • All cells within the body sit within it
  • Its composition has to be "just right" for cells to function properly
• Intracellular fluid

  There is lots of water in it, and it's vital that water remains in the cell
• If the solute concentration is high outside the cell (hypertonic)

  Water will rush out of the cell via osmosis, causing it to crenate (shrink) and lose function
• If the solute concentration is low outside the cell (hypotonic)

  Water will rush into the cell via osmosis, causing it to swell or potentially burst (lyse)
• Osmoregulation

  Regulating the osmolality of the extracellular fluid to prevent cells from shrinking or bursting
• Easier for body to change the fluid levels than the solute levels
• If more water is added to the body

  Osmolality will decrease, as the concentration will be lower
• If water is removed from the body

  Osmolality will increase as concentration will be higher
• Stimulus-Response Pathway - General

  1. Stimulus: change in osmolality of blood or change in blood pressure or blood volume

  2. Receptors: osmoreceptors in the hypothalamus and baroreceptors in the aortic arch, carotid artery in the neck, and in the kidneys

  3. Modulators: osmoreceptors send signals to the hypothalamus and pituitary gland, baroreceptors will also send signals to the kidney too

  4. Effectors: distal tubules and collecting duct in the kidneys, of the hypothalamus

  5. Response: alteration in reabsorption of water
• Decrease in water levels (increase osmolality)

  1. Stimulus + receptors: Decrease in osmolality will be detected by hypothalamus, increase in B.P by baroreceptors in the carotid artery, neck, and kidneys

  2. Modulator: hypothalamus & kidneys

  3. Effector + Response 1 (ADH): hypothalamus will release antidiuretic hormone (a.k.a vasopressin) to the kidneys, which embed aquaporins (membrane protein) in the distal tubule to allow for more water reabsorption from the kidneys

  4. Effector + response 2 (renin): Baroreceptors release renin from the kidneys, triggering the adrenal glands to release aldosterone (hormone), triggering sodium pumps within nephron, allowing increase in water reabsorption in kidneys
• Increase in water levels (decrease osmolality)

  1. Stimulus + receptors: decreased osmolality detected by osmoreceptors and decrease B.P detected by baroreceptors carotid artery and kidneys

  2. Modulator: hypothalamus

  3. Effector + response: hypothalamus will tell pituitary gland to slow production of ADH, to reduce aquaporins embedded into the distal tubule. Further, your thirst centre will be suppressed,decreasing consumption of fluid.