GFR is regulated by-----------

Answer

**Step-by-Step Solution:**

1. **Understanding GFR**: GFR stands for Glomerular Filtration Rate, which is the volume of filtrate produced by both kidneys per minute. It is a crucial indicator of kidney function.

2. **Normal GFR Value**: The normal GFR is approximately 125 ml per minute, which translates to about 180 liters of filtrate produced daily. However, most of this filtrate is reabsorbed back into the bloodstream.

3. **Role of Juxtaglomerular Apparatus**: The regulation of GFR is primarily managed by a structure known as the juxtaglomerular apparatus (JGA). This apparatus is located at the junction of the distal convoluted tubule (DCT) and the afferent arteriole.

4. **Function of Juxtaglomerular Apparatus**: The JGA contains specialized cells that are sensitive to changes in blood pressure and sodium concentration. When blood pressure drops or sodium levels decrease, the JGA responds by secreting an enzyme called renin.

5. **Renin-Angiotensin System**: Renin acts on a plasma protein called angiotensinogen, converting it into angiotensin I. Angiotensin I is then converted into angiotensin II, primarily in the lungs.

6. **Effects of Angiotensin II**: Angiotensin II has multiple effects, one of which is stimulating the adrenal cortex to release aldosterone. Aldosterone promotes the reabsorption of sodium and water in the distal convoluted tubule, which helps to increase blood volume and, consequently, blood pressure.

7. **Conclusion**: Therefore, the GFR is regulated by the juxtaglomerular apparatus through the renin-angiotensin-aldosterone system, which adjusts the filtration rate based on the body's needs.

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