The principal function of the urinary
system is to maintain the volume and composition of
body fluids within normal limits. One aspect of this
function is to rid the body of waste products that accumulate
as a result of cellular metabolism, and because of this,
it is sometimes referred to as the excretory system.
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Although the urinary system has a major role in excretion,
other organs contribute to the excretory function. The lungs
in the respiratory system excrete some waste products, such
as carbon dioxide and water. The skin is another excretory
organ that rids the body of wastes through the sweat glands.
The liver and intestines excrete bile pigments that result
from the destruction of hemoglobin. The major task of excretion
still belongs to the urinary system. If it fails the other
organs cannot take over and compensate adequately.
The urinary system maintains an appropriate fluid volume
by regulating the amount of water that is excreted in the
urine. Other aspects of its function include regulating the
concentrations of various electrolytes in the body fluids
and maintaining normal pH of the blood.
In addition to maintaining fluid homeostasis in the body,
the urinary system controls red blood cell production by secreting
the hormone erythropoietin.
The urinary system also plays a role in maintaining normal
blood pressure by secreting the enzyme renin.
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