- The excretory system of mammals centers on a pair of kidneys.
- In humans, each kidney is about 10cm long and is supplied with blood by a renal artery and drained by a renal vein.
- Blood flow through the kidneys is voluminous.
- The kidneys acount for less than 1% of human body mas but receive roughly 25% of he blood exiting the heart.
Urine exits each kidney through a duct called the ureter
, and both ureters drain into a common urinary bladder
- During urination, urine is expelled from the bladder through a tube called the urethra, which empties to the outside near the vagina/penis.
- Urination is regulated by sphincter muscles close to the junction of the urethra and the bladder.
The mammalian kidney has an outer renal cortex
and an inner renal medulla
Microscopic extretory tubules and their associated blood vessels pack both regions.
- Weaving back and forth across the cortex and medulla is the nephron, the functional unit of the vertebrate kidney.
- A nephron consists of a single long tubule as well as a ball of capillaries called the glomerulus.
The blind end of the tubule forms a cup-shaped swelling, called bowman's capsule
, which surrounds the glomerulus.
Each human kidney contains about a million nephrons, with a total tubule length of 80km.