Macula densa is a pa of

The thick end of the ascending limb of the loop of Henle reaches the glomerulus of the nephron from which the tubule arose and nestles between its afferent and efferent aerioles. Specialized cells at the end form the macula densa, which is close to the afferent and paicularly the afferent aeriole. The macula, the neighboring lacis cells, and the renin-secreting juxtaglomerular cells in the afferent aeriole form the juxtaglomerular apparatus.Ref: Ganong&;s review of medical physiology,23rd edition, page: 641