The kidney is the site where urine is formed. For this reason it is an indispensable organ for maintaining homeostasis of the body function. In addition to urine formation it is also important for other functions of the body such as regulation of electrolytes and water concentrations in the body.
Several hormones have effect on the kidney function. These are a hormone which regulates the secretion of water in the kidney glomeruli. This hormone is called antidiuretic hormone. It is a polypeptide of 9 amino acids which is secreted by the posterior pituitary gland.
It stimulates the kidney to either conserve or secrete water depending on its concentration in the blood. Low level of blood in the circulation is a stimulant for the kidney to conserve more water. In addition, high plasma osmolality is also a stimulant for the body to conserve more water by the kidney tubules.
Another hormone and which is called aldosterone has an effect on the kidney to conserve the electrolyte sodium. This hormone is secreted by the adrenal cortex in response to increased blood level of of the hormone renin which is secreted by the kidney cells. Renin itself is secreted in response to hypovolemia or low blood volume in the circulation.
Aldosterone stimulates the kidney to conserve the electrolyte sodium and secrete potassium ions in the urine. Due to an osmotic effect that the conservation of sodium makes water starts to flow also in the same direction. Thus causing a state of hypertension and subsequent edema in the case of hyperaldosteronism or increased aldosterone secretion in the blood.
The kidney is composed of functional units that are called nephrons. These nephrons are in turn composed of glomeruli and tubules. The glomeruli are the site where filtration of the blood occurs. The kidney tubules are the site where reabsorption of most important molecules in the body occurs such as the molecule glucose.
Diseases of the kidney are divided to those that affect the glomeruli and those that affect the kidney tubules. Usually diseases that affect the kidney glomeruli are autoimmune in character while those that affect the tubules are due to toxic chemical such as drugs and due to infectious agent such as occurs in pyelonephritis.
Chronic renal failure is a disorder of the kidney tissue which is manifested by oligurea and many other symptoms that are associated with the important function of the kidney. One of the symptoms of chronic renal failure is hyperkalemia or increased concentration of potassium in the blood. In addition acidosis in also another symptom of renal failure. Anemia is also another manifestation to this disease which is caused due to the diminished synthesis and secretion of of the hormone erythropoietin. This hormone is important due to its stimulatory function on red blood cells formation.
The deficiency of eryhtropoietin due to renal failure renders low blood cells in the circulation and subsequent anemia. In hypoxic states this hormone is usually secreted in increased amounts in normal kidney function. In renal carcinoma a state of polycythemia occurs in which increased amount of the hormone eryhtropoietin is secreted to the blood. Thus causing a state of increased red blood cells in the circulation.
In chronic renal failure also vitamin D in the blood is also diminished due to the important function of the kidney in synthesizing this vitamin. Thus one manifestation of renal failure in addition to the afore-mentioned symptoms is vitamin D deficiency in the blood with accompanying hypocalcemia or low calcium ions level in the blood.
As a result of the low level of calcium in the blood the body compensates or tries to compensate by stimulating the parathyroid gland to secrete more parathyroid hormone which in turn stimulates osteoclasts of the bone tissue to release more calcium ions to the blood. This causes a state of parathyroid gland hyperplasia or cellular proliferation and increase in number of this gland cells.