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Urinary System.
The urinary system (also called excretory system or the
genitourinary system) is the organ system that produces, stores, and eliminates
urine. In humans it includes two kidneys, two ureters, the bladder, the urethra,
and the penis in males.
Kidney
The kidneys are bean-shaped organs, which lie in the abdomen, retroperitoneal to
the organs of digestion, around or just below the ribcage and close to the
lumbar spine. The organ is about the size of a human fist and is surrounded by
what is called Peri-nephric fat, and situated on the superior pole of each
kidney is an adrenal gland. The kidneys receive their blood supply of 1.25 L/min
(25% of the cardiac output) from the renal arteries which are fed by the
abdominal aorta. This is important because the kidneys' main role is to filter
water soluble waste products from the blood. The other attachment of the kidneys
are at their functional endpoints the ureters, which lies more medial and runs
down to the trigone of urinary bladder.
The kidneys perform a number of tasks, such as: concentrating urine, regulating
electrolytes, and maintaining acid-base homeostasis. The kidney excretes and
re-absorbs electrolytes (e.g. sodium, potassium and calcium) under the influence
of local and systemic hormones. pH balance is regulated by the excretion of
bound acids and ammonium ions. In addition, they remove urea, a nitrogenous
waste product from the metabolism of amino acids. The end point is a
hyperosmolar solution carrying waste for storage in the bladder prior to
urination.
Humans produce about 2.9 liters of urine over 24 hours, although this amount may
vary according to circumstances. Because the rate of filtration at the kidney is
proportional to the glomerular filtration rate, which is in turn related to the
blood flow through the kidney, changes in body fluid status can affect kidney
function. Hormones exogenous and endogenous to the kidney alter the amount of
blood flowing through the glomerulus. Some medications interfere directly or
indirectly with urine production. Diuretics achieve this by altering the amount
of absorbed or excreted electrolytes or osmalites, which causes a diuresis.
Urethra
The endpoint of the urinary system is the urethra. Typically the urethra in
humans is colonised by commensal bacteria below the external urethral sphincter.
The urethra emerges from the end of the penis in males and between the clitoris
and the vagina in females.
The urinary system cleans the blood and regulates the amount of water in a body.
The urinary system is composed of kidneys, ureters, urinary bladder, urethra
sphincter that works together in the collection, storage and elimination of urine.
