The Excretory Systems

• As your body performs chemical activities to keep you alive, waste products, such as carbon dioxide and ammonia, are made

• These waste products are toxic to cells• Excretion is the process of removing waste

products from the body• Three of your body systems play a role in excretion:

integumentary system releases waste and water when you sweat

respiratory system releases carbon dioxide when you exhale urinary system removes waste from the blood

The Urinary System

• The urinary system organs produce, store and eliminate urine• The kidney removes waste from the

blood• The ureters are tubes that connect the

kidneys to the bladder• The bladder is a saclike organ that stores

urine• The urethra is the tube urine exits the

body from

The Kidneys

• The kidneys are a pair of organs that constantly clean the blood• They filter about 2000 liters of blood

each day – our bodies hold only 5.6 liters of blood• Inside each kidney are more than a

million nephrons – microscopic filters in the kidney that remove harmful substances from the blood – ex. Urea

How the Kidneys Filter Blood

• A large artery brings blood into the kidney• Tiny blood vessels branch off and pass through part of

each nephron• Water and other substances are forced out of the blood

vessels and into the nephrons• As these substances flow through the nephrons, most

of the water and some nutrients move back into blood vessels – the remaining waste is left behind in the nephron

• The cleaned blood leaves the kidney • The yellow fluid that stays in the nephrons is urine• Urine leaves the kidneys through the ureter and goes

into the urinary bladder• Urine leaves the body through the urethra

Water In, Water Out

• You drink water every day and you lose water every day in sweat and urine

• You must get rid of as much as you drink – if you don’t you will swell up

• The balance of fluids is controlled by chemical messengers in the body called hormones

• When you are warm, you lose a lot of water in the form of sweat and water content in the blood drops

• A hormone is released that signals the kidney to conserve more water and make less urine

• If there is too much water, less of the hormone is released and more urine is produced

Urinary System Problems

• Bacterial infections – bacteria can get into the bladder and ureters through the urethra and cause painful infections

• Kidney stones – salts and other wastes collect inside the kidney and form kidney stones – may interfere with urine flow

• Kidney disease – damage to nephrons can prevent normal kidney function – may lead to dialysis – a machine that performs the job of the kidneys