Structure and function of the kidney
You have two kidneys that are located to the left and right of the spine below the diaphragm and look similar in shape to beans. A kidney is on average 12 cm long and weighs about 150 grams. In spite of their small size, your kidneys perform a number of complex and vital functions that help keep the body in balance.
Some of these important functions are:
Help remove waste products and excess fluid
The kidneys ensure that waste substances (substances not required by our body) are removed from the body in the urine. Some medicines are also eliminated through the urine. Urine is collected in the middle of each kidney (the renal pelvis). From there it passes through a tube (the ureter) into the urinary bladder which collects and stores urine from both kidneys. When going to the toilet, the bladder is emptied and the waste products leave the body in the urine.
Regulation of water and electrolyte balance as well as acid and base balance
The kidneys’ job is to eliminate excess fluid or salts (electrolytes) from the body and maintain the balance between the water we take in and the water we lose. If you take in only a little fluid, the amount of urine is reduced accordingly and the water coming in and going out is balanced. The kidneys also regulate the pH of blood (the balance between acidity and alkalinity).
Hormone production and red cell production control
The kidneys produce various hormones such as calcitriol (vitamin D3, involved in bone metabolism), erythropoietin (stimulates red blood cell formation) and renin (involved in regulating blood pressure).
This is how your kidneys perform their important functions:
1. Blood goes into the kidneys through an artery that comes from the heart.
2. Once inside the kidneys, that blood is cleaned by passing through millions of tiny blood filters (called 'nephrons').
3. All of the waste material that was removed from the blood, passes through the ureter and is stored in the bladder as urine.
4. The newly cleaned blood returns to the circulation by way of veins.
5. The bladder keeps receiving urine until it's full. Once it becomes full, you receive a signal that you need to go to the toilet. Urine then passes out of the body through the urethra.
The kidneys filter about 200 liters of fluid every 24 hours. Approximately 2 liters per day are eliminated from the body in the form of urine, while the remainder, about 198 liters, is retained in the body. The urine we excrete has been stored in the bladder for approximately one to eight hours.
- Adapted from Findlay’s and Isles’ “Clinical Companion in Nephrology”, Springer Ed., 2015.
- Adapted from “Comprehensive Clinical Nephrology”, 6th edition, Elsevier Ed., 2015.
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