NEPHRON

                                                       NEPHRON   

Introduction : 

• Nephron is defined as functional unit of the kidney . 
• Each kidney consists of 1 to 1.3 millions of nephrons. 
• The number of nephrons starts decreasing after about 45 to 50 years of age at the rate of 0.8 to 1 % every year. 
• Each nephrons is formed by two parts :

1. A blind end called renal corpuscle or malpighian corpuscle .
2. A tubular portion called renal tubule.

RENAL CORPUSCLE : 

• Renal corpuscle or Malpighian corpuscle is a speroidal and slightly flattened structure with a diameter of about 200 µ.
• Function of the renal corpuscle is the filtration of lood which form the first phase of urine formation.  
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STRUCTURE OF RENAL CORPUSCLE AND MALPIGHIAN CORPUSCLES : 

  Renal corpuscle is formed by the two portions : 

1. Glomerulus .
2. Bowman capsule.   

 1. Glomerulus : Glomerulus  is a tuft of capillaries enclosed by Bowman capsule. It consists of glomerular capillaries interposed afferent arteriole on one end and efferent arteriole on the other end . 

Function : 

   Glomerular capillaries are made up of single layer of endothelial cells, which attach to the basement membrane . Endothelium has many pores called the filtration pores . this presence shows the filtration is the functuion of the glomerulus.

2. Bowman Capsule :  Bowman capsule is a capsular structure, which encloses the glomerulus . 

         It is formed by the two layer : (a) Inner visceral layer , (b) Outer parietal layer. 

   Visceral layer covers  the glomerular capillaries . It is continued as the parietal layer at the visceral pole . 

 

Function : 

        Functional anatomy of the bowman capsule resembles a funnel with filter paper. Diameter of bowmans capsule is 200µ .

 TUBULAR PORTION OF THE NEPHRON :

 

  Tubular [portion of the nephron is continuation of the Bowman capsule .

         It is made up of three parts : 

1. Proximal convulated tubule  (PCT ). 
2. Loop of the Henle.
3. Distal convulated tubule (DCT) . 

1. Proximal convulated tubule  (PCT ).  : Proximal convulated tubule is the coiled porion arising from the Bowman capsule . It is situated in the cortex . It is continued as descending limb of loop of Henle.  length of proximal convulated tubule is 14 mm and diameter is 55 µ .   Proximal convulated tubule is continued  as Loop of Henle. 
2.  Loop of Henle :  Loop of Henle is consists  of :  (a) Descending limb (b) Hairpin Bend   (c) Ascending limb. 

•  (a) Descending limb : Descending limb of   Loop of Henle is made up of two segments,  i.e. is (1) Thick descending segment (2) Thin descending segment .  

           (1) Thick descending segment : Thick descending segment is direct continuation of the Proximal convulated tubule. It is descent into medulla.  

            (2) Thin descending segment : Thick descending segment is continued as thin descending segment . And it is continued as the hairpin bend of the loop .

• (b) Hairpin Bend :   Hairpin Bend formed by the flattened epithelial cells without brush border and it is continued as the ascending limb of loop of the Henle. 
•      Ascending limb : Ascending limb made up of two parts , (1) Thick ascending segment (2) Thin ascending segment . The Thick ascending segment ascends to the cortex and continues as distal convulated tubule . 

 3. Distal convulated tubule (DCT) : Distal convulated tubule is continuation of the thick ascending segment and occupies the cortex of the kidney. It continues s a collecting duct . The length distal convulated tubule is 14.5 to 15 mm It has diameter of 22 to 50 µ. 

 

Collecting duct : 

Distal convulated tubule is continues as the intial or arched collecting duct , which is in cortex. The lower part of the collecting duct is lies in the medulla. Length of the collecting duct is 20 to 22 mm and its diameter is 40 to 200 µ .