Urinary system

Kidneys

A pair of organs found in the abdominal cavity. Located against the back muscles on either side of the spine.

Ureters

Two tubes that run from the kidney to the bladder. Urine is conveyed through the ureters by peristalsis and gravity.

Urinary bladder

The bladder is a hollow sac situated towards the front of the lower part of the abdomen. The bladder stores urine.

Urethra

Urine is conveyed from the bladder through the urethra. In the female the urethra is about 10cms long; in the male the urethra is about 20cms long and also conveys semen. The opening at the end of the urethra is called the urinary meatus.

The nephron

The nephron is the basic working unit of the kidney. Blood enters the nephron under pressure and passes through the structures of the nephron to be filtered. Most of the water and many substances that are needed by the body are returned to the circulation. The kidneys produce 1-1.5 litres of urine on average per 24 hrs. Many factors effect the production of urine. These include age, illness, the amount of and type of fluids ingested, the amount of salt in the diet, caffeine, alcohol and medications.

The main functions of the urinary system:

• Removes metabolic wastes from the circulatory system.
• Plays a part in red blood cell formation.
• Assists in the regulation of blood pressure.
• Maintains the balance of body fluids in the body.

Excretion of urine

Urination is the process of emptying the bladder. As the bladder fills with urine, nerve impulses carry the message to the spinal chord that the bladder is filling. The spinal chord then sends a message back to the bladder via the motor nerves causing the bladder to contract and the sphincter to relax. This is a ‘reflex’ that gives rise to the urge to urinate.