In the kidney, the macula densa is an area of closely packed specialised cells lining the distal convoluted tubule (DCT) where it lies next to the glomerular vascular pole. It is a component of the juxtaglomerular apparatus. Its cells are taller and have more prominent nuclei than surrounding cells. They are thought to be sensitive to the concentration of sodium ions in the fluid within the DCT. A decrease in blood pressure results in a decreased concentration of sodium ions. Together with the juxtaglomerular cells which have mechano-receptors for blood pressure, they lead to a release of renin which enters the renin-angiotensin-aldosterone system (RAAS).