A persistent misconception is that the kidneys are located in the lower back since it is this location that is referred to in case of kidney pain. However, this is an abuse of language: most often the pain comes from the spine at the lumbar level or from the para-vertebral muscles. The kidneys are located way above! 

Indeed, the kidneys are located in the posterior part of the abdomen, on either side of the spine under the last ribs. Each kidney is approximately 11 cm long and is connected to the aorta artery and the inferior vena cava by the renal artery and vein.

Anatomy of the kidney

The kidney is divided into two regions: the cortex, which is responsible for waste filtration, and the medulla.

About a million nephrons (glomerulus + tubule) make up each kidney, and their job is to filter the various substances in the blood and then reabsorb what is still necessary while allowing the waste to be removed through the urine.

The kidneys produce urine, which travels down the ureters to the bladder, where it is stored before being expelled by the urethra during urination.

The role of the kidneys

Each of us normally has two kidneys. They are located in the posterior part of the abdominal cavity, on either side of the spine. The kidneys are vital organs without which we cannot live. They perform several functions.

Filtration/purification function

Eating, drinking, exercising and just plain living produces toxins in our body. These toxins are molecules produced by the normal functioning of the body. These, as well as the excess water, accumulate in the blood which transports them to our kidneys, a true purification station of the body.

The kidneys filter out unwanted toxic substances and remove excess water via urine which will be stored in the bladder before being evacuated. The purified blood, meanwhile, leaves the kidney to reach the body.

Renal blood flow is high, approximately 600 mL/min, or ¼ of cardiac output.

Balancing function

In addition to this purifying function, the kidney ensures the balance “of the internal environment”. This means that the kidneys constantly adapt the “outputs” (volume and composition of urine) to the intake (drink and food) and needs of the body.

This balancing function relates mainly to water and mineral salts, in particular sodium (contained in salt), potassium, calcium, bicarbonate (which regulates the acidity of the blood), and magnesium.

This balancing function is very important because it ensures great freedom in food and drink.

Other kidney functions

  • Regulation of blood pressure: the kidney plays an important role in the regulation of blood pressure by the production of hormones (renin, bradykinins) which cause vasoconstriction or vasodilation and by regulating the right amount of water and sodium (or salt) in the body. High blood pressure is very common in kidney disease.
  • Secretion of vitamin D: the kidney participates in the production of active vitamin D. Vitamin D plays an important role in mineralizing bone and maintaining normal blood calcium levels. A lack of vitamin D is common when there is kidney failure.
  • Secretion of EPO: The kidney produces a hormone called Epoetin (or EPO). The function of EPO is to stimulate the production of hemoglobin and red blood cells by the bone marrow. A lack of EPO is common when there is renal failure, responsible for anemia.