CHRONIC RENAL FAILURE

THE NEPHRON

A nephron (from Greek νεφρός (nephros) meaning "kidney") is the basic structural and functional unit of the kidney. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbingwhat is needed and excretingthe rest as urine. A nephron eliminates wastes from the body, regulates blood volume and pressure, controls levels of electrolytes and metabolites, and regulates blood pH. Its functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone. In humans, a normal kidney contains 800,000 to one million nephrons.

TYPES OF NEPHRONS

Two general classes of nephrons are cortical nephrons and juxtamedullary nephrons, both of which are classified according to the location of their associated renal corpuscle. Cortical nephrons have their renal corpuscle in the superficial renal cortex, while the renal corpuscles of juxtamedullary nephrons are located near the renal medulla.

Functionally, cortical and juxtamedullary nephrons have distinct roles. Cortical nephrons (85% of all nephrons in humans) mainly perform excretory and regulatory functions, while juxtamedullary nephrons (15% of nephrons in humans) concentrate and dilute urine.

ANATOMY

Each nephron is composed of an initial filtering component (the " renal corpuscle") and a tubule specialized for reabsorption and secretion (the "renal tubule"). The renal corpuscle filters out large solutes from the blood, delivering water and small solutes to the renal tubule for modification.

Two main populations of nephrons are recognizable in the kidney: those possessing a short loop of Henle and those with a long loop of Henle. Humans and most rodents have a larger number of short-looped than long-looped nephrons.

CHRONIC RENAL FAILURE

Chronicrenal failure is a form of total renal failure caused by progressive destruction of individual nephrons over a long period of time. The disease leading to chronic renal failure can generally be classified into two major groups: those causing glomerular pathology, and those causing tubulo-interstitial pathology.

There are two main types of partial renal failure: nephritic syndrome and nephrotic syndrome.

Nephritic syndrome is the result of disturbance of glomerular structure that involves reactive cellular proliferation. This causes reduced glomerular blood flow (leading to reduced urine output oliguria), leakage of red cells from damaged glomeruli (hematuria), and consequent retention of waste products (uremia). The low renal blood flow activates the renin-angiotensin system, with fluid retention and mild hypertension. Small amounts of proteins are also lost in the urine, but this is usually trivial. The hematuria is not gross and is usually manifested as a smoky brown discoloration of urine.

Nephrotic syndrome is the result of abnormality in glomerular basil membranes or mesangium, such that the glomerulus loses the capacity for selective retention of proteins in the blood. This leads to loss of very large amounts of protein, mostly albumin, in the urine (proteinuria), with consequent loss of protein from the blood (hypoalbuminemia) leading to edema. Other indications of renal abnormality are intermittent hematuria and persistent proteinuria which can be thought of as early partial renal failure. The latter may precede the development of a nephrotic syndrome.

Date: 2016-06-13; view: 6