Collects wastes produced by cells Removes wastes from body (excretion)

Kidneys Ureters Urinary bladder Urethra

Two kidneys are the major organs of the excretory system

They act like filters by removing waste from blood

They eliminate◦ Urea – a chemical that comes

from the breakdown of proteins◦ Excess water ◦ Other waste materials

All come out in the form of urine (a watery fluid)

From the kidneys, urine travels through…

Two narrow tubes called ureters

To the urinary bladder

Finally through the urethra – a small tube

A sack-like muscular organ that stores urine When full enough, and the walls are

stretched, you feel the need to urinate

Two stages◦ First, wastes and needed materials like glucose

are removed from the blood◦ Second, much of needed material is returned to

blood

Kidneys filter every drop of blood in your body more than 300 times a day

Each kidney contains approximately 1 million nephrons or filtering factories◦ These are tiny filters that remove waste

Blood enters kidney and travels through smaller and smaller arteries until it reaches capillaries in a nephron

◦ In the capillary clusters (capsules), urea, glucose, water, and other chemicals move from blood into the capsules

◦ Blood cells and proteins do not move in

Forms from filtered material in the capsule Needed materials for the body are

reabsorbed into the blood (glucose, much of water, small amounts of other materials)

Urea and other wastes remain

When urine is analyzed◦ Check for glucose and protein (not normally

present)◦ Glucose could be a sign of diabetes (body can’t

absorb glucose)◦ Protein can be a sign that kidneys are not

functioning properly

Kidneys help maintain homeostasis◦ Regulate amount of water in body◦ Amount of water reabsorbed depends on outside

conditions Sweat a lot more absorbed, small amount of urine