Talk:Macula densa

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why should the decreased blood pressure result in decreased sodium concentration ? that makes no sense. it should be : low sodium can lead to low blood pressure (because of low volume) so there will be an upregulation (after sensing by the macula densa) of renin release... —The preceding unsigned comment was added by 130.60.68.45 (talk • contribs) .

I believe the reason that decreased blood pressure results in decreased sodium concentration in the distal convoluted tubule is that the filtration by the glomerulus is less efficient when there is decreased blood pressure. That is, less filtrate enters the proximal convoluted tubule when blood pressure is low. This filtrate passes through the nephron and becomes concentrated, but because there was less fluid there to begin with (and thus less sodium) the resulting concentrate does not have as high a sodium concentration. If you were to boil down a gallon of saltwater to a pint of saltwater, the resulting pint would be less concentrated than you would get if you boiled down two gallons of the same saltwater to a pint. Robotsintrouble 19:07, 27 November 2006 (UTC)

However the GFR should not change that much with change in Renal blood flow (dependent on blood pressure), this is regulated by constriction of arterioles.

The reason NaCl supply to the PT drops is that the peritubular capillaries have less pressure due to efferent arteriole contriction. This means there is less pressure in the capillaries slowing reabsorption of solutes, and less backflow. This means less NaCl left in the PT lumen reaching the Macula Densa.

I won't change the article as I'm not 100% sure, but if someone can confirm this? 87.194.31.172 (talk) 13:49, 9 December 2007 (UTC)