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.