|
Nephrotic syndrome is a nonspecific kidney disorder characterized by three signs of disease: large proteinuria, hypoalbuminemia, and edema.〔http://wordnetweb.princeton.edu/perl/webwn?s=nephrotic%20syndrome〕 Essentially, loss of protein through the kidneys (proteinuria) leads to low protein levels in the blood (hypoalbuminemia), which causes water to be drawn into soft tissues (edema). Very low hypoalbuminemia can also cause a variety of secondary problems, such as water in the abdominal cavity (ascites), around the heart or lung (pericardial effusion, pleural effusion), high cholesterol (hence hyperlipemia), loss of molecules regulating coagulation (hence increased risk of thrombosis). Large proteinuria is due to an increase in permeability of the "filtering membrane" of the kidney which normally separates the blood from the urinary space in Bowman's capsule. This is composed of the capillary walls of the glomerulus which are wrapped by highly specialized cells called podocytes. Alterations in their capacity to filter the substances transported in the blood mean that proteins but not cells pass into the urine (hence no haematuria). By contrast, in nephritic syndrome red blood cells pass through the pores, causing haematuria. ==Signs and symptoms== Nephrotic syndrome is characterized by large proteinuria (>3.5g perday per 1.73m2 body surface area > or 40 mg per square meter body surface area per hour 〔(【引用サイトリンク】title=ELECTRONIC LEARNING MODULE for KIDNEY and URINARY TRACT DISEASES )〕), hypoalbuminemia (< 2,5 g/dl), hyperlipidaemia, and edema (which is generalized and also known as anasarca or dropsy) that begins in the face. Lipiduria (lipids in urine) can also occur, but is not essential for the diagnosis of nephrotic syndrome. Hyponatremia also occurs with a low fractional sodium excretion. Hyperlipidaemia is caused by two factors: * Hypoproteinemia stimulates protein synthesis in the liver, resulting in the overproduction of lipoproteins. * Lipid catabolism is decreased due to lower levels of lipoprotein lipase, the main enzyme involved in lipoprotein breakdown.〔http://www.hawaii.edu/medicine/pediatrics/pedtext/s13c02.html〕 Cofactors, such as Apolipoprotein C2 may also be lost by increased filtration of proteins. A few other characteristics seen in nephrotic syndrome are: * The most common sign is excess fluid in the body due to the serum hypoalbuminemia. Lower serum oncotic pressure causes fluid to accumulate in the interstitial tissues. Sodium and water retention aggravates the edema. This may take several forms: * * Puffiness around the eyes, characteristically in the morning. * * Pitting edema over the legs. * * Fluid in the pleural cavity causing pleural effusion. More commonly associated with excess fluid is pulmonary edema. * * Fluid in the peritoneal cavity causing ascites. * * Generalized edema throughout the body known as anasarca. * Most of the patients are normotensive but hypertension (rarely) may also occur. * Anaemia (iron resistant microcytic hypochromic type) maybe present due to transferrin loss. * Dyspnea may be present due to pleural effusion or due to diaphragmatic compression with ascites. * Erythrocyte sedimentation rate is increased due to increased fibrinogen & other plasma contents. * Some patients may notice foamy or frothy urine, due to a lowering of the surface tension by the severe proteinuria. Actual urinary complaints such as haematuria or oliguria are uncommon, though these are seen commonly in nephritic syndrome. * May have features of the underlying cause, such as the rash associated with systemic lupus erythematosus, or the neuropathy associated with diabetes. * Examination should also exclude other causes of gross edema—especially the cardiovascular and hepatic system. * Muehrcke's nails; white lines (leukonychia) that extend all the way across the nail and lie parallel to the lunula The main signs of nephrotic syndrome are:〔(【引用サイトリンク】Manifestaciones clínicas del síndrome nefrótico )〕 * A proteinuria of greater than 3.5 g /24 h /1.73 m² s or 40 mg/h/m2 in children (between 3 and 3.5 g/24 h is considered to be proteinuria in the nephrotic range).〔 〕〔(【引用サイトリンク】Síndrome nefrótico y proteinuria en rango no nefrótico )〕 The ratio between urinary concentrations of albumin and creatinin can be used in the absence of a 24-hour urine test for total protein. This coefficient will be greater than 200–400 mg/mmol in nephrotic syndrome. This pronounced loss of proteins is due to an increase in glomerular permeability that allows proteins to pass into the urine instead of being retained in the blood. Under normal conditions a 24-hour urine sample should not exceed 80 milligrams or 10 milligrams per decilitre.〔(【引用サイトリンク】Valores normales de proteína en orina de 24 horas )〕 * A hypoalbuminemia of less than 2.5 g/dL,〔 that exceeds the ''hepatic clearance'' level, that is, protein synthesis in the liver is insufficient to increase the low blood protein levels. * Edema is thought to be caused by two mechanisms. The first being hypoalbuminemia which lowers the oncotic pressure within vessels resulting in hypovolemia and subsequent activation of the Renin-angiotensin system and thus retention of sodium and water. Additionally, it is thought that albumin causes a direct effect on the epithelial sodium channel (ENaC) on the principal cell that leads to the reabsorption of sodium and water. Nephrotic syndrome edema initially appears in parts of the lower body (such as the legs) and in the eyelids. In the advanced stages it also extends to the pleural cavity and peritoneum (ascites) and can even develop into a generalized anasarca. It has been recently seen that intrarenal sodium handling abnormality is related to Atrial Natriuretic Peptide resistance is associated with decreased abundance and altered subcellular localization of dopamine receptor in renal tubules. * Hyperlipidaemia is caused by an increase in the synthesis of low and very low-density lipoproteins in the liver that are responsible for the transport of cholesterol and triglycerides. There is also an increase in the hepatic synthesis of cholesterol. * Thrombophilia, or hypercoagulability, is a greater predisposition for the formation of blood clots that is caused by a decrease in the levels of antithrombin III in the blood due to its loss in urine. * Lipiduria or loss of lipids in the urine is indicative of glomerular pathology due to an increase in the filtration of lipoproteins.〔(【引用サイトリンク】La pérdida de lipoproteínas en la orina )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nephrotic syndrome」の詳細全文を読む スポンサード リンク
|