The juxtaglomerular apparatus/complex is found where the most distal part of the ascending limb of the nephron loop (loop of henle) touches the afferent arteriole contains a region of chemoreceptor cells called the macula densa in the distal nephron loop (loop of henle) contains granular (juxtaglomerular) cells in the afferent arteriole that sense blood pressure.

In the afferent arteriole that sense blood pressure.

Explanation:

Background Knowledge:

Nephron: Nephron is the basic structural and functional unit of kidney. It regulates salt and water balance. Structure of nephron is divided in to two parts.

1) Renal Corpuscles: Renal Corpuscles further divided into

a) Glomerulus and

b) Bowman capsule.

Blood from Arteries enters into glomerulus  through afferent arterioles and leaves through Efferent arterioles for filtration. During this process waste material become filtered from Glomerulus containing blood into the Bowam capsule.

2) Renal Tubules: Renal tubules are further divided into

a) Proximal Convulated tubules

b) Loop of Henle and

c) Distal Convulated Tubules

Waste material pass through these tubes in sequential order. Components which are needed by body become reabsorbed in to capillaries present around these tubules while rest of material pass out of the body.

Juxtaglomerular apparatus: This is specialized structure. This structure is formed by the distal convulatd tubules and glomerular afferent arteriole.  Juxtaglomerular apparatus is located near the vascular pole of the glomerulus.

Function: Its main function is the regulate blood pressure and the filtration rate of the glomerulus. This structure contains specialized epithelial cells in the distal convoluted tubule. Purpose of these cells is to detect sodium concentration in the tubule. These cells trigger contraction of the afferent arteriole in case if the sodium level is present in elevated state in filtrate fluid. This whole procedure reduces glomerulus blood flow and glomerular filtration rate.