Kidney

The kidneys are the most important excretory organ in vertebrates (the term renal means "related to the kidney").

Function

The major functions of the kidney are to filter wastes from the bloodstream and to regulate the pH, serum osmolality and blood pressure (and secondarily, the volume of the blood).
The basic means to assess excretory function of the kidneys is glomerular filtration rate; usually creatinine clearance test is performed.

The kidney also serves an endocrine function by secreting erythropoietin, a hormone that regulates red blood cell production in the bone marrow. Other hormones produced by the kidneys are renin, active form of vitamin D - 1,25-dihydroxycholecalciferol (calcitriol) and prostaglandins.

Kidney transplants

Peter Bent Brigham Hospital in Boston announced the first successful kidney transplant on March 4, 1954.

Diseases and disorders

Kidney stones are a relatively common and particularly painful disorder.

Pyelonephritis is infection of the kidneys and is frequently caused by complication of a urinary tract infection.

Basic anatomy

The kidneys are 'bean-shaped' organs, and have a concave side facing inwards (medially). On this medial aspect of each kidney is an opening, called the hilus, which admits the renal artery, the renal vein, nerves, and the ureter.

A kidney is divided into a renal cortex, medulla and pelvis. The basic functional unit of the kidney is the nephron, of which there are more than a million in each normal adult kidney. A nephron consists of a Bowman's capsule, a proximal convoluted tubule, a loop of Henle and a distal convoluted tubule which empties into a collecting duct.

In humans the kidneys are the two organs that are located in the posterior part of the abdomen, just below the liver and spleen on the right and left sides of the body respectively. They lie on either side of the spine. Superior to each kidney is an adrenal gland (also called suprarenal gland).

The kidneys are retroperitoneal, which means they lie behind the peritoneum that surounds most of the other abdominal organs. They are approximately at the vetebral level T12 to L3, and the right kidney lies slightly lower than the left, due to the size of the liver.

The upper parts of the kidneys are protected somewhat by the eleventh and twelfth ribs, and each whole kidney is surrounded by layers of fat to cushion it.

In a normal human adult, each kidney is usually about 11 cm long and about 5 cm thick, weighing 150 grams.

Terms:

renal capsule: The membranous covering of the kidney.
cortex: The outer layer over the internal medulla. It contains blood vessels, glomeruli (which are the kidneys' "filters") and urine tubes and is supported by a fibrous matrix.
hilus: The opening in the middle of the concave medial border for nerves and blood vessels to pass into the renal sinus.
renal column: The structures which support the cortex. They consist of lines of blood vessels and urinary tubes and a fibrous material.
renal sinus: The cavity which houses the renal pyramid.
calyces: The recesses in the internal medulla which hold the pyramids. They are used to subdivide the sections of the kidney. (singular - calyx)
papillae: The small conical projections along the wall of the renal sinus. They have openings through which urine passes into the calyces. (singular - papilla)
pyramids: The conical segments within the internal medulla. They contain the secreting apparatus and tubules and are also called malphighian pyramids.
renal artery: Two renal arteries come from the aorta, each connecting to a kidney. The artery divides into five branches, each of which leads to a ball of capillaries. The arteries supply (unfiltered) blood to the kidneys. The left kidney receives about 60% of the renal bloodflow.
renal vein: The filtered blood returns to circulation through the renal veins which join into the vena cava.
renal pelvis: Basically just a funnel, the renal pelvis accepts the urine and channels it out of the hilus into the ureter.
ureter: A narrow tube 40 cm long and 4 mm in diameter. Passing from the renal pelvis out of the hilus and down to the bladder. The ureter carries urine from the kidneys to the bladder.