Complete information on the structure of a nephron

Nephron (Uriniferous tubule):

This is the ba­sic filtering unit of the kidney. It has been esti­mated that nearly one million nephrons are present in the human kid­ney. The nephron basi­cally consists of two parts. The secretory tu­bule and the excretory portion.

1. Secretory tubule:

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The secretary tubule consists of the Bowman’s cap­sule, the proximal convo­luted tubule, the loop of Henle and distal convo­luted tubule.

Bowman’s capsule:

At the closed end which is dilated the nephron con­sists of a baloon shaped structure called the Bowman’s capsule. The Bowman’s capsule is a cup shaped structure. It lies in the cortex of the kidney and contains an invigilated tuft of capil­lary vessels called the glomerulus (pi. glomeruli). The Bowman’s capsule and the glomerulus together constitute the malpighian corpuscle (pygmalion corpuscle or Re­nal corpuscle). The Malphigian corpuscles were first described by Morcello Malpighi in the year 1966.

The inner layer of the wall of the Bowman’s capsule is a visceral layer and along with the endothelium of the glomerulus forms an endotheliocapsular membrane. This membrane has three parts namely the Endothelium of the glomerulus (porus membrane), Basement membrane (This is between the endothelium of the blood vessels and Epithelium of Bowman’s capsule.

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This is without pores and helps as a dialyzing mem­brane) and the epithelium of the Bowman’s capsule (This layer is made up of epithelial cells called podocytes. The podocytes have foot like pedicels arranged parallel to the glomerulus and cover the basement membrane except for spaces called slit pores or Alteration slits).

Proximal convoluted tubule:

The Bowman’s capsule opens thorough a narrow constricted passage into a greatly contorted tube called the convo­luted tubule which also lies in the cortex. This tubule is about 14 milimeters in length. The wall of the tubule is made up of cuboidal epithelial cells which have microvilli. Each cell has about 150 microvilli per square mi­cron. Each microvillus is about 1 micron in length. The microvilli to­gether form a brush border region.

Loop of Henle:

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The proximal convoluted tubule takes a straight course down into the medulla region. This descending limb is called the loop of Henle. This loop of Henle is divided into three segments namely –

a) Thick descending segment which is the straight portion of the proximal convoluted tubule.

b) A thin segment which takes a direct radial course in the medulla. This segment takes a sharp hairpin bend extending past the tip of the Henle’s loop.

c) A thick ascending segment. This is a straight radial tubule. In this region the squamous epithelial cells suddenly change into cuboidal epi­thelial cells. This segment is relatively impermiable to salts and water.

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Distal convoluted tuhule:

The tubule that comes out of the Limb of Henle leads to the distal convoluted tubule. This tubule is made up of cuboidal cells and has less microvillus than in the proximal tubule. There is no brush border formation. The tubule lies near a malphigian corpuscle. At the region of the contact with the Bowman’s capsule the cells of the tubule are columnar and are aggregated together. Hence this region is called the macula densa or crowded spot.