CBSE Class 10 Answered

• A kidney is composed of an enormous number of uriniferous tubules.They are also known as nephrons or renal tubules or kidney tubules.
• Nephrons are the structural and functional units of the kidney.
• Each kidney is formed of about 1 million nephrons.
• Nephrons are held together by a connective tissue.

Structure of nephron:

• Each nephron is made of a glomerulus and a renal tubule.

Glomerulus:

• It is a tuft of anastomosing blood capillaries formed by the fine branches of the
  afferent arteriole. 
• These capillaries of the glomerulus again unite to form the efferent arteriole.
• The afferent arteriole is wider than the efferent arteriole.
• The afferent arteriole brings blood into the glomerulus, while the efferent arteriole collects blood from the glomerulus.

Renal Tubule:

The renal tubule comprises the following regions:

Bowman’s Capsule

• The Bowman’s capsule lies in the cortex.
• It is a thin double-walled, cup-like depression.

It is the blind end of the nephron.

• The glomerulus is located in the concave depression of the Bowman’s capsule.
• The Bowman’s capsule and the glomerulus together are called Malpighian Capsule or Renal Capsule.
• The outer layer of the Bowman’s capsule is made of flattened epithelial cells.
• The inner layer is in close contact with the glomerulus and bears special cells called podocytes.
• Podocytes have many feet-like processes called pedicels and minute slit-like pores called slit pores.     

Proximal Convoluted Tubule (PCT)

• PCT lies in the cortex.
• It is also known as the first convoluted tubule.
• The Bowman’s capsule continues into the PCT.
• It is lined with a layer of columnar epithelial cells.
• The columnar cells are with numerous microvilli to increase the surface area of absorption.   

Loop of Henle

• It lies in the medulla.
• It is U-shaped.
• It is not convoluted.
• It has a descending limb and an ascending limb.
• Each limb has a thick region towards the cortex and a thin region towards the medulla.
• Thick regions are lined with columnar epithelial cells.
• Thin regions are lined with flat epithelial cells.          

Distal Convoluted Tubule (DCT)

• It lies in the cortex.
• Its short terminal part is called a collecting tubule.
• The collecting tubule opens into the collecting duct.
• DCT in lined with ciliated columnar epithelial cells.
• The collecting duct receives the contents of many renal tubules.

• The collecting duct is a larger duct which receives collecting tubules of several nephrons.
• Collecting ducts pass into the renal medulla and join with each other to form the ducts of Bellini.
• The ducts of Bellini run through the renal pyramids and open into calyces.
• All calyces open into the pelvis.
• From the pelvis, urine is carried to the urinary bladder through the ureters.