How The Kidneys Work

Date: 15/12/21

We recently discussed how the bladder works and how the body maintains a fluid balance. Both of these processes are directly linked to the kidneys. These are the organs that maintain your body’s fluid levels, as well as filtering the blood to produce the waste that we call urine.

What are the kidneys?

The kidneys are a pair of organs located just below your ribs towards the back of the torso, either side of the spine. They are around 10-12cm long and 5-7cm wide and the right kidney is slightly lower than the left due to displacement by the liver. The kidneys are fed by the renal arteries, which carries blood to be cleaned. Clean blood leaves the kidneys via the renal veins, while waste leaves via the ureters as urine and flows down to the bladder.

What do the kidneys do?

The kidneys perform a remarkable range of functions that are essential for keeping the body in a healthy, constant state, known as homeostasis. These include:

  • Filtering the blood to remove the waste products of metabolism, such as urea and uric acid. 
  • Maintaining fluid balance within the body
  • Regulating minerals such as sodium, potassium, calcium and phosphorous
  • Producing hormones that regulate red blood cell production and calcium absorption
  • Helping to control blood pressure
  • Creating vitamins, such as calcitriol, the active form of vitamin D

The structure of the kidneys


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The kidneys have two distinct regions: the dark outer layer called the cortex and a more complex inner region called the medulla. The cortex is used in hormone production while the medulla holds the renal pyramids where filtration takes place. There are around 8-12 pyramids, each containing tens of thousands of nephrons.

How do the kidneys work?

The kidneys filter around 300-400 pints of blood every day with all of your blood passing through around 40 times every 24hrs. The blood enters via the renal artery, which splits into smaller and smaller vessels until it reaches tiny structures called nephrons. There are over a million nephrons in the kidney and each has two parts: the glomerulus and the tubule. The glomerulus filters the blood, then the tubule returns what is needed, such as salts, glucose, amino acids and water, and excretes the rest as urine.


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The body maintains fluid and electrolyte balance by changing the amount of water and salt that is reabsorbed by the blood after filtration. This is controlled by the hypothalamus and the pituitary gland. If your fluid level drops, a hormone called anti-diuretic hormone is released, which makes the walls of the tubule more permeable, so more water is reabsorbed.

The kidneys and urine

From the 300-400 pints of blood that pass through the kidneys every day, between two and four pints of urine are produced, though this will obviously increase if you drink more. It is important to remember that urine is not just excess water that is being excreted from the body, but also contains a number of waste products. This is why reducing your fluid intake is not a good strategy for managing incontinence, as these waste products can become concentrated and irritate the bladder, making your symptoms feel worse despite there being a lower volume in the bladder.

It is far better to maintain a healthy fluid intake and manage your output using the wide range of Tena incontinence products available from IncoDirect. We can help all ages, from child incontinence pants to discreet Tena incontinence pads. Talk to our team today about the best way to manage your incontinence while keeping your kidneys and bladder healthy. To find out more about Tena incontinence products visit our shop:

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