AEMCA Practice Exam

What is the major function of the juxtaglomerular apparatus?

1. Filtration of blood plasma

2. Regulation of blood pressure

3. Secretion of erythropoietin

4. Reabsorption of water

The correct answer is: Regulation of blood pressure

The major function of the juxtaglomerular apparatus is the regulation of blood pressure. This specialized structure, located near the glomerulus of the nephron in the kidney, plays a crucial role in monitoring and responding to changes in blood pressure and sodium levels. It includes specialized cells such as the juxtaglomerular cells, which are responsible for the secretion of renin, an enzyme that initiates a cascade of reactions resulting in increased blood pressure. When blood pressure drops or when there is a decrease in sodium concentration, the juxtaglomerular cells sense these changes and release renin into the bloodstream. Renin then converts angiotensinogen, a plasma protein produced by the liver, into angiotensin I, which is subsequently converted to angiotensin II. Angiotensin II has potent vasoconstrictive properties, raising blood pressure, and it stimulates the release of aldosterone from the adrenal glands, promoting renal reabsorption of sodium and water, which also helps to increase blood volume and pressure. Thus, the primary function of the juxtaglomerular apparatus is vital for maintaining homeostasis of blood pressure, ensuring adequate perfusion to tissues and organs throughout the body. The other options, although important kidney functions,