The Urinary System

Chapter 37.3

Urinary System• Function: Helps maintain the

homeostasis of body fluids.

• Structure: – 2 kidneys– 2 ureters– 1 urinary bladder– 1 urethra

The Kidney• The kidneys are main organs of the urinary

system.• Function:

– Filters and removes waste from blood

– Regulates body water volume, blood volume and blood pressure

– Regulates the amount of ions and salt in the body.

– Produces urine.

• Protein is broken down for energy in the body– this releases ammonia (very toxic)

• Ammonia is converted into urea by the liver (less toxic)

• Some of the urea is removed by the skin in perspiration (sweating). Most is removed from the blood by the kidneys.

Waste is removed in the kidney by Nephrons.

• 1 million nephrons per kidney• Blood entering the nephron carries water,

glucose, salt, vitamins, amino acids, ions, urea and waste.

• 1st step is filtration– Small molecules, salt and water, and other

waste are removed from the blood.

• 2nd step is reabsorption– Important material (water, glucose, and salt)

are reabsorbed into the blood.

The remaining fluid is urine.

• Urine is water and solutes.– Solutes = excess elements,

ions, salt, and vitamins, urea, toxic substances and drugs

• Approx. 1-2 Liters of urine produced a day.

• Ureters– Carries urine from the

kidneys to the bladder.

– About 25 cm long

• Urinary Bladder– Stores the urine– Muscular sac on the bottom of the pelvic

cavity.– Average volume = ½ Liter– Max capacity = ¾ Liter

• Urethra– Passes urine out of the body– Female approx 3-4 cm– Male approx 18 cm