3. The urinary system filters out the waste products collected by
the blood from all over the body, and expels it as urine.
This system consist of two kidneys, a urinary bladder, two
ureters and the urethra, a small tube in which urine is
expelled.
The kidneys are bean shaped organs situated behind the
stomach, on each side of the spine.
Each kidney has about a million tiny filters called nephrons.
4. A nephron looks like a small cup or funnel with a longish
tube attached to it.
There is a mesh of capillaries in each of these cups.
Water and wastes like urea and salt filter in to the cups
from the blood in the capillaries, the way tea filters
through a strainer.
Blood cells and other large particles remain in the blood
in the capillaries the way tea leaves remain in the
strainer.
5. The clean blood leaves the kidneys, while the wastes flow
in to the tubes of the nephrons.
These tiny tubes join up to form bigger tubes, which in
turn join the ureter.
The waste flow through the ureter and are collected in
the urinary bladder in the form of urine.
The bladder is like an elastic bag.
It can hold about half a litre of urine, but the urge to
urinate begins much before the bladder is completely
stretched.
6. An adult human passes between 1L and 1.5L
urine a day.
