Osmoregulation (Edexcel GCSE Biology)

• 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

• Two key functions of the urinary system are:
  • To filter waste products from the blood and expel it from the body as urine
  • To control the water levels of the body (osmoregulation)

• The urinary system consists of two kidneys (found at the back of the abdomen) joined to the bladder by two tubes called the ureters
• Another tube, the urethra, carries urine from the bladder to outside the body
• Each kidney is also connected to:
  • The renal artery which comes from the aorta and delivers oxygenated blood to the kidney
  • The renal vein which delivers the deoxygenated blood from the kidney to the vena cava

The urinary system in humans

Main Structures of the Urinary System Table