Question

What is the Juxtaglomerular apparatus?

Answer 1

The operating unit of the kidney is the nephron. This suggests that each independent nephron is where the kidney's main function is carried out. The two parts of a nephron are a renal corpuscle and a renal tubule.

Complete answer:
Often known as the juxtaglomerular complex, the juxtaglomerular apparatus is a system in the kidney that controls the activity of each nephron, the functional unit of the kidney. The term juxtaglomerular apparatus is used since it is next to the glomerulus. A specialised structure formed by the distal transformed tubule and the glomerular afferent arteriole is the juxtaglomerular apparatus. It is situated near the glomerular' vascular pole. The key role of the Juxtaglomerular apparatus is to monitor blood pressure and the rate of glomerular filtration.
The juxtaglomerular apparatus consists of two types of cells namely the macula densa, and juxtaglomerular cells. The macula densa is a set of specialised epithelial cells which detect the sodium concentration of the fluid in the tubule in the distal convoluted tubule. It is found immediately adjacent to the afferent and efferent arterioles at the glomerular vascular pole. The macula densa cells activate the afferent arteriole contraction in response to increased sodium, limiting blood flow to the glomerulus and the rate of glomerular filtration. As blood pressure in the arteriole decreases, the juxtaglomerular cells, originating from smooth muscle cells, of the afferent arteriole secrete renin. Sodium chloride accumulation in the lumen is detected by the macula densa cells and activates the juxtaglomerular cells to synthesise and release renin into the bloodstream. This occurs in low sodium chloride concentration states in the blood.

Note: The third type of cell found in the juxtaglomerular apparatus is mesangial extraglomerular cells. It is found near the macula densa, and they are smooth and elongated cells.