kidney disorders
DEFINITION:
The kidneys are susceptible to a wide range of disorders. However, only one normal kidney is needed for good health, so disease is rarely life-threatening unless it affects both kidneys and has reached an advanced stage.
Hypertension (high blood pressure) can be both a cause and effect of kidney damage. Other effects of serious disease or damage include the nephrotic syndrome (in which large amounts of protein are lost in the urine and fluid collects in body tissues) and acute or chronic renal failure.
Congenital and Genetic Disorders
Congenital abnormalities of the kidneys are fairly common. In horseshoe kidney, the two kidneys are joined at their base. Some people are born with one kidney missing, both kidneys on one side, or a kidney that is partially duplicated and gives rise to two ureters (duplex kidney). These conditions seldom cause problems. In rare cases, a baby is born with kidneys that are so underdeveloped that they are barely functional.
Polycystic disease of the kidneys is a serious inherited disorder in which multiple cysts develop on both kidneys. In Fanconi's syndrome and renal tubular acidosis (which are rare), there are subtle abnormalities in the functioning of the kidney tubules, so that certain substances are inappropriately lost in the urine.
Impaired Blood Supply
Various diseases may cause damage to, or lead to obstruction of, the small blood vessels within the kidneys, impairing blood flow. Diabetes mellitus and hemolytic-uremic syndrome are examples. In physiological shock, blood pressure and flow through the kidneys are seriously reduced; this can cause a type of damage known as acute tubular necrosis. The larger blood vessels in the kidney may be affected by periarteritis nodosa and systemic lupus erythematosus. In rare cases, there is a defect of the renal artery supplying a kidney, which may lead to hypertension and tissue damage.
Autoimmune Disorders
Glomerulonephritis refers to an important group of autoimmune disorders in which the glomerular filtering units of the kidneys become inflamed. It sometimes develops after infection with streptococcal bacteria.
Tumors
Benign kidney tumors are rare. They may cause hematuria (blood in the urine), although most cause no symptoms. Malignant tumors are also rare. Renal cell carcinoma, the most common type, occurs mostly in adults over 40; nephroblastoma (Wilms' tumor) affects mainly children under 4. (See also kidney cancer.)
Metabolic Disorders
Kidney stones are common in middle age. They are usually caused by excessive concentrations of various substances (such as calcium) or lack of inhibitors of crystallization in the urine. In hyperuricemia, there is a tendency for uric acid stones to form. (See also calculi.)
Infection
Infection of a kidney is called pyelonephritis. An important predisposing factor is obstruction of the flow of urine through the urinary tract, leading to stagnation and subsequent infection spreading up from the bladder. The cause of the obstruction may be a congenital defect of the kidney or ureter, a kidney or ureteral stone, a bladder tumor, or, in a man, enlargement of the prostate gland.
Tuberculosis of the kidney is caused by infection carried by the blood from elsewhere in the body, usually the lungs.
Drugs
Allergic reactions to certain drugs can cause an acute kidney disease, with most of the damage affecting the kidney tubules. Other drugs may directly damage the kidneys if taken in large amounts for prolonged periods. For example, renal failure can develop after many years of taking excessive amounts of analgesics. Some potent antibiotics can damage the kidney tubules, producing acute tubular necrosis.
Other Disorders
Hydronephrosis refers to a kidney swollen with urine as a result of obstruction further down the urinary tract. In the crush syndrome, kidney function is disrupted by proteins (released into the blood from severely damaged muscles) that block the filtering mechanisms.
See also nephrogenic diabetes insipidus.
Investigation
Kidney disorders are investigated by kidney imaging techniques such as ultrasound scanning, intravenous or retrograde pyelography, angiography, and CT scanning; by renal biopsy (removal of a small amount of tissue for analysis); by blood tests; and by kidney function tests, such as urinalysis.
protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
protein
DEFINITION:
Any of a group of complex organic compounds which contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur, the characteristic element being nitrogen, and which are widely distributed in plants and animals. Proteins, the principal constituents of the protoplasm of all cells, are of high molecular weight and consist essentially of combinations of a-amino acids in peptide linkages. Twenty different amino acids are commonly found in proteins, and each protein has a unique, genetically defined amino acid sequence which determines its specific shape and function. They serve as enzymes, structural elements, hormones, immunoglobulins, etc., and are involved in oxygen transport, muscle contraction, electron transport, and other activities throughout the body, and in photosynthesis.
binding protein - any of a number of plasma proteins (See below) that bind to hormones of low solubility (chiefly the thyroid and steroid hormones), thus providing a transport system for them; some are specific for particular hormones, while others bind to any sparingly soluble hormones. Called also carrier protein or transport protein (See below).
carrier proteins - A binding protein (See above).
plasma proteins - The hundreds of different proteins present in blood plasma, including carrier proteins (such as albumin, transferrin, and haptoglobin), fibrinogen and other coagulation factors, complement components, immunoglobulins, enzyme inhibitors, precursors of substances such as angiotensin and bradykinin, and many other types of proteins.
transport protein - binding protein (See above).
