When glomerular filteration rate falls which of the following hormone is released to stimulate glomerular blood flow?

Question

Accepted Answer

When the glomerular filtration rate (GFR) falls, the body needs to take action to restore adequate blood flow and filtration in the kidneys. The correct answer to which hormone is released to stimulate glomerular blood flow is Option 2: Renin.

1. **Explanation for Option 2 (Renin):**
   - Renin is an enzyme secreted by the juxtaglomerular cells of the kidney in response to a decrease in blood pressure, blood volume, or sodium concentration. When the GFR falls, it often indicates a drop in blood pressure or blood flow to the kidneys. In response, the kidneys release renin into the bloodstream.
   - Renin initiates the renin-angiotensin-aldosterone system (RAAS), which ultimately leads to the production of angiotensin II. Angiotensin II is a potent vasoconstrictor that increases blood pressure by constricting blood vessels and stimulating the release of aldosterone, which helps retain sodium and water, thereby increasing blood volume and pressure. This cascade of events helps restore glomerular blood flow and filtration rate.

2. **Explanation for why other options are incorrect:**

- **Option 1 (ADH - Antidiuretic hormone):**
     - ADH is primarily involved in regulating water balance in the body by increasing water reabsorption in the kidneys, which concentrates urine and conserves water. While ADH can affect blood volume and pressure indirectly, it is not directly responsible for stimulating glomerular blood flow when GFR falls.

- **Option 3 (Angiotensin):**
     - Angiotensin, specifically angiotensin II, is indeed a key player in increasing blood pressure and stimulating glomerular blood flow. However, it is not the hormone initially released in response to a fall in GFR. Instead, it is produced as a result of the renin-angiotensin-aldosterone system activation initiated by renin.

- **Option 4 (Aldosterone):**
     - Aldosterone is a hormone that promotes sodium and water reabsorption in the kidneys, which helps increase blood volume and pressure. However, like angiotensin, it is part of the downstream effects of the RAAS and is not the initial hormone released when GFR falls. Its release is stimulated by angiotensin II, which is produced following the release of renin.

In summary, renin is the correct answer because it is the initial hormone released by the kidneys in response to a decrease in GFR, setting off a chain reaction that ultimately restores glomerular blood flow and filtration rate.