The correct option is Renin.
Explanation
The regulation of kidney function involves hormonal feedback mechanisms to maintain homeostasis, particularly regarding blood pressure and glomerular filtration rate (GFR). The Juxtaglomerular apparatus (JGA) is a specialized region formed by the distal convoluted tubule and the afferent arteriole.
Analysis of the Options:
- Renin Renin: Correct. Juxtaglomerular (JG) cells are specialized smooth muscle cells located in the afferent arterioles of the kidney. When there is a fall in glomerular blood pressure or glomerular blood flow, these cells activate and release the enzyme Renin. Renin initiates the Renin-Angiotensin-Aldosterone System (RAAS) by converting Angiotensinogen in the blood into Angiotensin I, eventually leading to an increase in blood pressure.
- Insulin Insulin: Incorrect. Insulin is a peptide hormone produced by the beta cells of the Islets of Langerhans in the pancreas. It regulates blood glucose levels.
- Pepsin Pepsin: Incorrect. Pepsin is a proteolytic enzyme secreted by the chief cells (peptic cells) of the stomach lining. It is responsible for the digestion of proteins into proteoses and peptones.
- Trypsin Trypsin: Incorrect. Trypsin is a proteolytic enzyme produced by the pancreas in an inactive form (trypsinogen) and released into the small intestine for protein digestion.
Key Takeaway:
Renin is the specific enzyme secreted by the Juxtaglomerular cells of the kidney in response to low blood pressure, triggering the RAAS pathway to restore physiological balance.