What are the structures of the excretory system, in order, in the role of producing and eliminating urine?
The functional units of the Kidney are the nephrons .
Metabolic waste is transported to the nephrons by the blood.
One end of each nephron is modified in to a cup-shaped structure called Bowman's Capsule , that surrounds one glomerulus. Glomerulus is a network of capillaries.
Because blood in the glomerulus is under pressure, some of its constituents are forced out of the capillaries in to the lumen of Bowman's Capsule. Apart from wastes, a large amount of water, glucose, and salts are also forced out. This solution is called glomerular filtrate.
This filtrate first passes in to proximal convoluted tubule ; which then narrows in to a hairpin-shaped tube: the loop of Henle ; then in to distal convoluted tubule ; These three parts are surrounded by a second net of capillaries. These collect water, glucose and salts from the nephron, reduces the volume of the filtrate and concentrates the urea in it.
The blood from these capillaries is collected by the renal vein and returns the usable substances in it to the blood circulating through rest of the body.
Several nephrons empty their contents in to a collecting tubule and their final product is urine.