The Macula Densa is important in Tubuloglomerular feedback, the localised mechanism to control fluid flowing through the nephron. The Macula Densa is adjacemt to the afferent arteriole that leads to the Bowman's capsule. This part of the afferent arteriole is specialized smooth cells known as juxtoglomerular cells. These cells secrete renin in response to increased pressure on the afferent arteriole walls leading to increased levels of NaCl. The increased NaCl levels causes the Macula Densa cells to send paracrine signals to the adjacent afferent arteriole cells causing the arteriole to constrict causing a decrease in Glomerular Filtrate Resistance.