macula densa

noun

macula den·​sa -ˈden-sə 

: a group of modified epithelial cells in the distal convoluted tubule of the kidney that lie adjacent to the afferent arteriole just before it enters the glomerulus and control renin release by relaying information about the sodium concentration in the fluid passing through the convoluted tubule to the renin-producing juxtaglomerular cells of the afferent arteriole