The region of the ascending limb in contact with the granular cells of the afferent arteriole is called the macula densa (fig. 17.25). There is evidence that this region helps to inhibit renin secretion when the blood Na+ concentration is raised.
The cells of the macula densa respond to the Na+ in the filtrate delivered to the distal tubule. When the plasma Na+ concentration is raised, or when the GFR is increased, the rate of Na+ delivered to the distal tubule is also increased. Through an effect on the macula densa, this increase in filtered Na+ inhibits the granular cells from secreting renin. Aldosterone secretion thus decreases, and since less Na+ is reabsorbed in the cortical collecting duct, more Na+ is excreted in the urine. The regulation of renin and aldosterone secretion is summarized in table 17.6.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...