Maintaining Water Balance in the Body

Our bodies are like finely tuned machines, and water plays a crucial role in keeping them running smoothly. Too much or too little water can lead to harmful changes in our cells due to osmosis. If body cells lose or gain too much water, they do not function efficiently. 

  • Too much water in the blood can cause cells to swell and they may possibly burst
  • Too little water can lead to cell death

So, how does our body maintain this delicate balance? The answer lies with our kidneys, which are organs of the urinary system. These vital organs filter our blood, selectively reabsorbing useful materials such as glucose, salt ions and water. They also produce urine, which helps maintain water balance.

The kidneys contain over one million microscopic filtering units called nephrons, which remove urea and excess water and mineral ions from the blood.

But our kidneys aren’t the only organs that help us maintain water balance in the body. Our lungs and skin also play important roles. 

KidneysFilter blood, remove waste products and control water balance
SkinLose water, ions and urea in sweat
LungsExhale water vapour

How Our Kidneys Maintain Water and Ion Balance

Stage 1Filtration: Kidneys act like a super filter. Blood rushes into nephrons, where small molecules like water, ions, glucose and urea are separated out. Big molecules, like proteins, stay in the blood.

Stage 2Reabsorption: The kidneys reabsorb useful molecules like glucose, needed water and ions back into the bloodstream. The remaining substances continue their journey.

Stage 3Urine Formation: Other molecules like urea, excess water and ions form urine, which travels to the bladder, where it exits the body.

  • The renal veins carry deoxygenated blood away from the kidneys, whereas the renal arteries deliver oxygenated blood to the kidneys.

Also, do not confuse the ‘ureter’ with the ‘urethra’. The ureter is the tube that carries urine from the kidneys to the bladder , while the urethra is the tube that expels urine out of the body.

Keeping Water Levels in Check

Our body cannot regulate the amount of water lost through breathing or sweating, but it can control how much water is lost through urine. This job is also carried out by our kidneys.

The brain has a gland called the pituitary gland, which releases a hormone known as ADH (anti-diuretic hormone). The amount of ADH released depends on how much water our kidneys need to reabsorb from the filtrate.

  • If our blood has too much water, less ADH is released, leading to less water being reabsorbed by the kidneys
  • If our blood doesn’t have enough water, more ADH is released, leading to more water being reabsorbed

When Kidneys Fail

We can live with just one working kidney, but if both kidneys fail, harmful wastes quickly build up in our bodies. People with kidney failure can be treated with a kidney transplant or by using a machine that acts like an artificial kidney, called a dialysis machine.

Dialysis is a common treatment for kidney failure. It involves a machine that removes most of the urea and helps maintain the water and salt balance in the blood.