We all know that urine is made of water, certain electrolytes and the colour of urine i.e. yellow is due to a chemical which is called urobilins. Its original name was urochrome. It was assumed that this pigment has given colour to urine but later on it was found that many pigments were responsible for the colour of urine, so the name has been changed.
Urine is formed mainly by the breakdown
of product in the blood cells. Kidney’s functional units are called nephrons.
They are found in millions of numbers in kidneys. These nephrons are
responsible for the formation of urine by way of filtration, re-absorption and
secretion. A normal 170 litres of waste should be excreted out of our bodies in
the form of urine. But we never drink this much of water or secrete out. Some
amount of water is also re-absorbed into our blood through the process of
passive re-absorption.
The nutrition that we consume never gets
wasted. Some ions like sodium and urobilins are not re-absorbed into the blood
stream. As we drink, large amount urine starts looking clear as urobilin
dilutes into water.
When a person drinks less amount of
water, the urobilin content decreases in urine and urine looks dark yellow. It
looks dark yellow as body tries to maintain some amount of water in the body.
So, when a person takes less amount of
water the posterior pituitary gland secretes antiduretic hormone {ADH}. This
secretion of hormone causes the urobilin concentration to increase and makes
urine dark yellow. This is a sign of dehydration. When a person takes lot
amount of water, ADH decreases and the water is eliminated in order to maintain
water content.