Talk:Macula densa

Why

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)

I too won't change the article as I have only just been learning about this, but here's my take. I assume we discuss a healthy human kidney.

"Blood pressure" is rather vague in this context. The glomerular filtration pressure is the sum of the hydrostatic pressure in the capillary and the oncotic pressure (osmotic pressure due to the impermeability to protein) which is in the opposite direction. The short term variable is the hydrostatic pressure, which increases or decreases with pressure in the afferent arteriole. The article as it stands implies a direct effect of pressure. The effect on salt concentration passing the macula densa is indirect, as follows.

When the GFR increases, the filtrate passes faster through the ascending loop so the ion channels remove less salt per unit volume. The concentration of salt at the distal tubule adjacent to the macula densa increases. Conversely it decreases with lower GFR.

The macula densa cells detect changes in salt concentration in the distal tubule and send signals to the juxtaglomerular cells to increase or decrease release of renin, the rate limiting step in the production of angiotensin II. This is a homeostatic mechanism, as low mean arterial pressure leads to afferent arteriole pressure, low GFR, high reabsorption of ions, low concentration of salt passing the macula densa, increased renin release, and the various effects of angiotensin II increasing MAP.

There is significant new information on the macula densa. It would be great if someone more competent than me could update the article.

Alkhowarizmi (talk) 01:35, 11 October 2021 (UTC)

References

Macula densa releases ATP

After sensing an increased salt concentration the macula densa releases ATP from its basolateral surface. ATP causes contraction of mesangial cells and afferent arterioles (purinergic receptros, P2). ATP may also be metabolized to adenosine, which has the same effect. —Preceding unsigned comment added by 69.57.241.245 (talk) 19:38, 14 November 2008 (UTC)

According to three physiology textbooks, including one devoted fully to renal physiology, the function of the macula densa as described here is almost bordering on incorrect. The fact of the matter is that the macula densa is an autoregulatory mechanism - not a primary sensor in terms of providing a driving force to establish renin secretion. In effect, the macula dense is a "braking" mechanism - not a primary sensor of sodium. The way this is worded here is highly suspect and in need of serious revision. —Preceding unsigned comment added by 174.54.155.108 (talk) 19:43, 3 February 2010 (UTC)

Reversion Dec 2008

I've just reverted an IP edit with no edit summary: [1]. The edit, beyond introducing a spelling error, seemed to radically alter the sense of the previous wording ("increased" vs. "decreased"). I've based this reversion entirely on instinct, not on biological knowledge. Someone with better information is welcome to review, or perhaps the IP who made the initial edit could explain their rationale. Franamax (talk) 01:27, 6 December 2008 (UTC)

Simplify

The function section is wordy and difficult to follow. If someone could add or edit so as to make it easier to understand that'd be great. Perhaps it could start with "if a person lacked these macula densa cells then...<consequences>.."

Thanks

macula densa figure

The figure is correct, but isn't clear. I understand that the current figure lists most of the glomerulus, but is that all necessary when the focus should be on the macula densa? maybe a big figure of the whole nephron, with the glomerulus correctly facing the distal tubule and the macula densa circled would be good here. —Preceding unsigned comment added by 74.179.96.106 (talk) 14:04, 26 September 2010 (UTC)

The figure is not correct. ACE is present at high levels in the lung, but this is not the primary site of conversion from Angiotensin I to Angiotensin II. ACE is present at lower but still physiologically significant levels within the kidney itself, and this is where conversion occurs. See: "Systemic Versus Local Renin Angiotensin Systems. An Overview", by Walmor C. DeMello and Richard N. Re. RENIN ANGIOTENSIN SYSTEM AND CARDIOVASCULAR DISEASE Contemporary Cardiology, 2010, 1-5, DOI: 10.1007/978-1-60761-186-8_1. — Preceding unsigned comment added by 130.15.171.64 (talk) 02:26, 11 December 2011 (UTC)