The urinary system (also called the excretory system) is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder, the urethra, and two sphincter muscles.
Physiology of urinary system
Main article: Kidney
The kidneys are bean-shaped organs that 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 acidsammonium 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. and
Humans produce about 2.9 litres
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.