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.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.