The Kidney

  The kidneys are organs found in all vertebrates and each organism has two kidneys.

Kidneys are bean-shaped and red in colour. They lie near the back of the abdominal cavity about the level of the waistline.

  Each kidney weighs approximately 142.5g, ie about the size of a clenched fist. The right kidney is generally slightly lower than the left. The kidney is surrounded by a layer of fat which helps to cushion and protect it from mechanical or physical injury.

  The kidney is supplied with blood from the general circulatory system via the renal artery which branches off the aorta.

Blood from the kidneys goes back to the general circulation through the renal vein which joins the vena cava.

  A tube called the ureter connects each kidney to the bladder located in the lower abdomen. From the bladder another tube called the urethra opens to the exterior of the organism.

  In males, the urethra is long and is joined to the reproductive system unlike in females hence refered to as urinogenital system.

Two rings of sphincter muscles encircle the urethra and they control the emptying of the bladder.

  The two kidneys, two ureters, the bladder and the urethra make up the urinary system.

The functions of the kidney are;

• Excretion
• Osmoregulation
• Ionic balance
• Regulation of PH

Read the passage above, and draw a well labeled diagram of the urinary system in man.