The Excretory System

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

Organs/Structures Involved Kidneys Ureters Urinary bladder Urethra

The Kidneys 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)

Urinary Tract From the kidneys, urine travels through… Two narrow tubes called ureters To the urinary bladder Finally through the urethra – a small tube

The Bladder A sack-like muscular organ that stores urine When full enough, and the walls are stretched, you feel the need to urinate

Urine Formation Two stages First, wastes and needed materials like glucose are removed from the blood Second, much of needed material is returned to blood

Filtering Process 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

Capillary Clusters/Capsules 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

Urine 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

What Urine Tells a Doctor 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

Water Balance 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