Page 111 - Science Class 07

Ammonia, Urea and Uric Acid present in the abdomen, just above the waist
Pro en metabolism results in nitrogenous
wastes such as ammonia, urea and uric acid.
These wastes come out in the form of urine
and sweat. Urine is formed in urinary bladder
while sweat is formed in sweat glands present
under the skin. Sweat is an aqueous fluid which
contains water, dissolved salts and urea. Sweat
comes out of the body through small pores
present in our skin.
Carbon Dioxide
During respira on, oxygen is u lised to
produce energy from the food. It results in the
forma on of carbon dioxide and water. Carbon
dioxide is a gaseous waste which is expelled
out of the body. This process is called
exhala on.
EXCRETORY SYSTEM IN HUMAN BEINGS
Human excretory or urinary system consists of
two kidneys, ureters, urinary bladder and
urethra. Let’s study about these organs and
their func ons.
Vena Cava Aorta
Right Le
Kidney Kidney
Ureters
Urinary
Bladder
Urethra
Excretory System
Kidneys
Kidneys are paired bean shaped organs about
10 cm long. These are dark red in colour and
Science-7
on either side of the backbone.
Each kidney consists of about one million
func onal units called nephrons. Each nephron
has bowman’s capsule at one end and the rest
part of the nephron is differen ated into a
coiled proximal convoluted tubule, a 'U' shaped
thin tubule and a distal tubule. Nephrons filter
blood which passes through the kidneys and
the waste products are collected here in the
form of urine. Urine comprises 95% water, 2.5%
urea and 2.5% other waste products in a
healthy body.
Inner View of Kidney
Ureters
These are narrow tubes which transport urine.
Ureter runs from the inner side of each kidney.
It joins the two kidneys to the urinary bladder.
Urinary Bladder
It is a muscular bag in which urine collects. The
ureter transports urine to this urinary bladder.
It is situated in the pelvic cavity of a human
body.
Urethra
The urine collected in urinary bladder passes
through a muscular tube called urethra. This is
a very thin tube and its opening is regulated by
sphincter muscles.
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