Human excretory system

In humans, excretion of nitrogenous waste is the job of a compact, four-part system: a pair of kidneys that do the actual filtering, a pair of ureters that carry the urine away from each kidney, a single urinary bladder that stores it temporarily, and a urethra through which it finally leaves the body. The kidneys are reddish-brown, bean-shaped organs, each weighing 120-170 g, tucked against the back wall of the abdominal cavity at the level of the last thoracic to third lumbar vertebrae; because the liver takes up space on the right side, the right kidney sits slightly lower than the left. Blood reaches each kidney through a renal artery branching off the aorta and leaves through a renal vein draining into the vena cava - this blood supply is what makes continuous filtration possible. The two subsections that follow zoom in first on the int …