The Kidney
- The kidneys are located in the back of the abdomen and have two important functions in the body:
- They regulate the water content of the blood (vital for maintaining blood pressure and osmoregulation)
- They excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
Waste substances removed by the kidney
Osmoregulation
- 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
