The kidneys are a pair of bean-shaped organs that are found high in the back of the abdominal cavity, just below the rib cage; one on either side of the spine. The right kidney is slightly lower than the left because of the position of the liver.
Adult kidneys measure approximately 10 to 12cm in length and 5 to 7 cm in width, and weigh approximately 150g.
If you were to cut a kidney in half you would see that it is divided into a dark outer area (the cortex) and an inner lighter-coloured area (the medulla). Within the medulla there are between 10 and 18 renal pyramids; triangular structures which have a striped appearance. They have this appearance because of the renal tubules and associated blood vessels. The renal cortex and the pyramids make up the renal parenchyma. It is here that approximately one million nephrons are the working centres of the kidneys.
The kidneys filter the blood to remove waste products, which they convert into urine. Urine is carried from each kidney, through a tube called a ureter to the bladder, where it is stored. The ureter and blood vessels enter and exit the kidney through the renal hilum.
When you are ready to pass urine, it leaves the bladder through a tube called the urethra. The urethra opens immediately in front of the vagina in women and at the tip of the penis in men.
The kidneys have several other functions, such as blood pressure regulation, acid-base balance, toxin removal, red blood cell production, activation of vitamin D, water balance and electrolyte balance.