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
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