RENAL CIRCULATION AND JG APPRATUS

 

1.      SPECIAL FEATURES OF RENAL CIRCULATION

a.      Renal Blood Flow (RBF): The normal blood flow to kidney is about 1200 ml. This forms about 25% of cardiac output. Kidney receives the maximum blood flow next to liver.

b.      Portal circulation: An arteriole is interposed between two capillaries. Glomerulus (capillary tuft) – Efferent arteriole – Peritubular capillary

c.       High pressure system: The pressure in the glomerular capillaries is 45 mmHg. This is much higher compared to the pressure in the systemic capillaries which is 30 mmHg. This high pressure is the main driving force for glomerular filtration

d.      Vasa recta: Longest capillaries in the form of hairpins. It runs parallel to LOH of juxtamedullary nephron. It acts as countercurrent exchanger and maintains the osmotic gradient from the cortex towards the inner medulla of kidney

e.       Autoregulation: The ability of kidney to regulate its own blood flow is called autoregulation. This helps the kidney to maintain the blood flow constant between a systemic pressure of 90 – 220 mmHg. Autoregulation is achieved by myogenic principle and tubuloglomerular feedback mechanism

f.       Regional blood flow: Cortex receives the maximum blood flow whereas the inner medulla receives the minimum blood flow

g.      Arterio-venous difference of oxygen is minimal compared to the other organs

h.      Renal O₂ consumption is high

2.      JUXTAGLOMERULAR APPARATUS

Juxta Glomerular Apparatus refers to the collection of specialized cells located very near to the glomerulus

   Components:

a)      Juxtaglomerular cells

b)      Macula densa cells

c)      Mesangial cells

Juxtaglomerular cells:

-          Modified smooth muscle cells of afferent arteriole

-          Secrete renin

Macula densa Cells:

-          Specialized tubular epithelial cells at DCT

-          Act as chemoreceptors ( detect the changes in the concentration of sodium and chloride in tubular fluid)

Messangial cells:

-          Supporting cells present around glomerulus

-          Contractile in nature

Functions of JG Apparatus:

1.      JG cells secrete renin that activates Renin- Angiotensin system which takes part in regulation of blood volume and pressure

2.      Macula densa cells act as sensor in Tubuloglomerular feedback which takes part in autoregulation of renal blood flow and GFR

3.      JG apparatus helps to regulate the volume and osmolarity of ECF

4.      It secretes erythropoietin which influences erythropoiesis