Whatis the significance of juxtaglomerular apparatus (JGA) in kidneyfunction?

Juxtaglomerularapparatus (JGA) is a complex structure made up of a few cells ofglomerulus, distal tubule, and afferent and efferent arterioles. Itis located in a specialised region of a nephron, wherein the afferentarteriole and the distal convoluted tubule (DLT) come in directcontact with each other.

Thejuxtaglomerular apparatus contains specialised cells of the afferentarteriole known as juxtaglomerular cells. These cells contain theenzyme renin that can sense blood pressure. When glomerular bloodflow (or glomerular blood pressure or glomerular filtration rate)decreases, it activates juxtaglomerular cells to release renin.

Reninconverts the angiotensinogen in blood into angiotensin I and furtherinto angiotensin II. Angiotensin II is a powerful vasoconstrictorthat increases the glomerular blood pressure and filtration rate.Angiotensin II also stimulates the adrenal cortex of the adrenalgland to produce aldosterone. Aldosterone increases the rate ofabsorption of sodium ions and water from the distal convoluted tubuleand the collecting duct. This also leads to an increase in bloodpressure and glomerular filtration rate. This mechanism, known asrenin-angiotensin mechanism, ultimately leads to an increased bloodpressure.