What is the Juxtaglomerular Apparatus?

The juxtaglomerular apparatus is a structure found within the kidneys. Kidneys are made up of hundreds of thousands of units known as nephrons, which filter fluids so that the body can express waste, maintain the right balance of salts, and regulate its blood pressure. Each nephron contains a juxtaglomerular apparatus, which is involved in the regulation of the function of the nephron. Working together, the nephrons of the kidneys play a complex role in human physiology.

This structure is located near the glomerulus of the nephron, the network of tangled and twisted tubes that act as a filtration system. Viewed under magnification, the tiny apparatus can be seen surrounding the afferent arteriole, the tube that brings fresh blood into the kidney for filtration. As the blood is forced through the tubes, it is filtered, and the nephron can express waste or selectively reuptake liquids and salts to balance the blood pressure.

When blood volume is low, it triggers the juxtaglomerular apparatus to produce a hormone called renin. Renin stimulates the production of angiotensin, a hormone that contracts the blood vessels. This causes blood pressure to rise, as the same amount of blood is suddenly forced through a series of smaller blood vessels. Angiotensin also promotes the production of aldosterone, a hormone that tells the kidneys to retain more fluid and salts, which will increase blood volume over time.

As blood volume rises, the juxtaglomerular apparatus reduces renin production. This keeps the blood pressure in balance. If there are errors with this system, blood pressure can get too high, or drop too low, depending on the nature of the problem. This structure is one among many in the kidney that perform a range of functions, including releasing and responding to hormones that are intended to regulate blood pressure and blood volume throughout the day in response to changing environmental factors.

People with kidney disorders can experience a variety of health problems related to the organs, including illness as a result of being unable to express wastes and unregulated blood pressure, which can put strain on other systems of the body, such as the heart. Disorders are usually diagnosed starting with bloodwork to learn more about the hormones present and the balance of salts in the blood, and can include medical imaging of the kidneys to look for signs that they are not functioning as they should be.