• Osmoregulation?is the process of maintaining water and salt concentrations (osmotic balance) across membranes within the body
• It is an example of?homeostasis?in the human body

The importance of osmoregulation

• The?cytoplasm?of all cells is largely composed of water, as is the?blood plasma
• Maintaining water levels in the body is vital to prevent harmful changes occurring to cells of the body as a result of?osmosis
• If body cells lose or gain too much water by osmosis they do not function efficiently:
  • Too much water?in the blood results in cells swelling as water moves into them, this has a diluting effect and can lead to cell lysis (bursting)
  • Too little water?in the blood (or too high an ion concentration) and the cells lose water by osmosis, this has a dehydrating effect and can lead to cell death

   

The effect of water concentration on body cells due to osmosis

Water content of the body

• There are two?sources?of water in the body:
  • Water produced as a result of?aerobic respiration
  • Water in the?diet

   

• Water is?lost?from the body in the following ways:
  • Via the lungs during exhalation (breathing out)
  • Lost from the skin as?sweat?(along side?mineral?ions?and?urea)

   

• Water lost through the lungs or skin?cannot be controlled, but the volume of water lost in the production of urine can be?controlled by the kidneys

• Water reabsorption occurs along the nephron tubules in the kidneys
• The control of water reabsorption by the tubules is an example of?negative feedback
• If the water content of the blood is too high then less water is reabsorbed, if it is too low then more water is reabsorbed
  • This is controlled by the hormone?ADH

   

• The pituitary gland in the brain constantly releases a hormone called?ADH
• How much ADH is released depends on how much water the kidneys need to reabsorb from the filtrate
• ADH affects the permeability of the tubules to water
• If the?water?content of the blood is too?high:
  • The pituitary gland releases?less?ADH?which leads to?less water being reabsorbed?in the tubules of the kidney (the tubules become less permeable to water)
  • As a result, the kidneys produce a large volume of dilute urine

   

• If the?water?content of the blood is too?low:
  • The pituitary gland releases?more?ADH?which leads to?more water being reabsorbed?in the tubules of the kidney (the tubules become more permeable to water)
  • As a result, the kidneys produce a small volume of concentrated urine

   

The kidney controls water levels using the hormone ADH. It is an example of a negative feedback mechanism.

• Urine?produced by the kidneys contains a mixture of
  • Urea
  • Excess mineral ions
  • Excess water

   

• The?colour?and?quantity?of urine produced in the body can change quickly
  • Large quantities?of urine are usually?pale yellow?in colour because it contains a lot of water and so the urea is?less concentrated
  • Small quantities?of urine are usually?darker yellow / orange?in colour because it contains little water and so the urea is?more concentrated

   

• There are various reasons why the concentration of urine will change, including:
  • Water intake?- the more fluids drunk, the more water will be removed from the body and so a?large quantity of pale yellow, dilute urine?will be produced
  • Temperature?- the higher the temperature the more water is lost in sweat and so less will appear in the urine, meaning a?smaller quantity of dark yellow, concentrated urine?will be produced
  • Exercise?- the greater the level of exercise, the more water is lost in sweat and so less will appear in the urine, meaning a?smaller quantity of dark yellow, concentrated urine?will be produced

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