Definition of Macula densa

In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the cortical thick ascending limb of the loop of Henle, at the transition to the distal convoluted tubule. As such, an increase in sodium chloride concentration would result in vasoconstriction of afferent arterioles, and reduced paracrine stimulation of juxtaglomerular cells. This demonstrates the macula densa feedback, where compensatory mechanisms act in order to return GFR to normal.

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In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the cortical thick ascending limb of the loop of Henle, at the transition to the distal convoluted tubule. The cells of the macula densa are sensitive to the concentration of sodium chloride in the late thick ascending limb. A decrease in sodium chloride concentration initiates a signal from the macula densa that has two effects: (1) it decreases resistance to blood flow in the afferent arterioles, which raises glomerular hydrostatic pressure and helps return GFR toward normal, and(2) it increases renin release from the juxtaglomerular cells of the afferent and efferent arterioles, which are the major storage sites for renin. As such, an increase in sodium chloride concentration would result in vasoconstriction of afferent arterioles, and reduced paracrine stimulation of juxtaglomerular cells. This demonstrates the macula densa feedback, where compensatory mechanisms act in order to return GFR to normal. The release of renin is an essential component of the reninangiotensinaldosterone system (RAAS), which regulates blood pressure and volume.
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