Glomerulus As the name implies ju.aglomerulus apparatus (JGA) lies at hilum of glomerulus Juxtaglornerulus apparatusThe juxtaglomerular apparatus is a microscopic structure in the kidney, which regulates the function of Lech nephron. The juxtaglomerular apparatus is named for its proximity to the glomerulus: it is found between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron. This location is critical to its function in regulating renal blood flow and glomerular.filtration rate.The three microscopic components of the apparatus are the macula densa, extraglomerular mesangial cells (lacis cells), and juxtaglomerular cells.Juxtaglomerular cellJuxtaglomerular cells (JG cells, also known as granular cells) are the site of renin secretion.The JG cells are found in the media of afferent aerioles of the glomerulus and act as an intro-renal pressure sensor Lowered pressure leads to decreased pressure on the JG cells stimulating renin secretion. Renin then acts to increase systemic blood pressure (while maintaining GFR) the resi angiotensin systemMacula densaAt the point where the afferent aeriole enters the glomerulus and the efferent leaves it, the tubule of the nephron touches the aeriole of the glomerulus from which it arose.At this location, which marks the sta of the distal convulation, there is the modified region of tubular epithelium called the macula densaThe macula densa senses sodium chloride concentration in the distal tubule of the kidney and secretes a locally active (paracrine) vasopressor which acts on the adjacent afferent aeriole to decrease glomerular filtration rate (GFR), as pa of the tubuloglomerular feedback loop. Specifically, excessive filtration at the glomerulus or inadequate sodium uptake in the proximal tubule / thick ascending loop of Henle brings fluid to the distal convoluted tubule that has an abnormally high concentration of sodium. Na/K/2C1 cotranspoers move sodium into the cells of the macula densa. The increased Na+ conc. triggers a signal that causes constriction of the afferent aeriole thus reducing the GFRLacis cells or extraglomerular mesangial cellsThe function of the extraglomerular mesangial cells remains somewhat mysterious. They contain actin and myosin, allowing them to contract when stimulated by renal sympathetic nerves, which may provide a way for the sympathetic nervous system to modulate the actions of the juxtaglomerular apparatus. In addition, extraglomerular mesangial cells are strategically positioned between the macula densa and the afferent aeriole, and may mediate signalling between these two structures