Definition:
The excretory system is comprised of two parts, the upper tract, the kidney
composed of renal tissue, and the lower tract, a collecting system.
Structure:
The excretory sustem is made up of four parts: the kidneys, tubes (ureters)
that connect to a storage site, the bladder, and an exit tube (urethra).
The exit tube in some species is a shared cavity with the reproductive
system, and is then called a cloaca. The
renin-angiotensin system is found in the juxta-glomerular cells of the
kidneys.
Function:
The main functions of the excretory system is the control the amount of
water in the body, and removal of metabolic wastes from the circulatory
system. Some species with primative systems, like salamanders,
use the skin for this function.
Excretion of food wastes and bacteria from the intestines
is separate from the excretion of fluid. Hormones from the endocrine
system acting on the kidneys control the water and inorganic ions,
such as Na+, K+, Ca++ balance in the body. Angiotensin II is an important
regulator of blood pressure.
