What is the role played by renin - angiotensin in the regulation of kidney function?

Explanation

### Step-by-Step Solution:

1. **Introduction to Renin-Angiotensin System**:
The renin-angiotensin system (RAS) is a hormone system that plays a crucial role in regulating blood pressure and fluid balance, which in turn affects kidney function.

2. **Release of Renin**:
Renin is an enzyme released from the juxtaglomerular apparatus (JGA) of the kidneys. Its release is triggered by a decrease in glomerular blood flow or blood pressure.

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