Re: [HAPS-L] Macula Densa Cells

[Lee Weller <Lee.Weller@xxxxxxxxxxx>]

Title: Re: [HAPS-L] Macula Densa Cells

> I would like some clarification regarding the location
> of the macula densa cells that are part of the JG apparatus in the
> nephron.  Is it considered part of the ascending limb of the loop
> of Henle (distal portion) or part of the distal convoluted
> tubule?  Most textbooks state that it is part of the distal
> convoluted tubule, but I have recently seen one textbook state
> (in the newer edition) that it is part of the ascending limb of the
> loop of Henle. 
>  
> I would
> appreciate your input on this. 
>  
> Thanks,
>  
> Nishi
> Mathew

Okay, folks, I'll climb right out to the tip of this limb (saw in hand) and ask (on the way down, perhaps?), "Does it really matter? And if it does matter, why?".

TH's answer to Nishi's question is "neither" and I (for one) think it's a good answer, and not at all confusing.

Now, the Terminologia Histologica has hit a few snags, I was told the other day, and its publication will be delayed even further.  So we won't know for some time whether the draft version of its kidney terminology will prove to be the final one.

But looking at the draft version (thanks, Bob - my version is buried somewhere), it does seem to me that it presents a very sensible (and functionally meaningful) dividing of the nephron.

In particular, it identifies the thin portion of the nephronic tubule as a single, distinct part ("intermediate tubule"), rather than as two separate parts (thin part of proximal and thin part of distal tubules), and not part of either the proximal or distal tubule.

Also, it identifies the macula densa, too, as a distinct segment of the nephronic tubule, albeit a very short one, and separate from both the distal convoluted tubule and the distal (thick) straight tubule.  The difference, I think, is that TH has enlarged the definition of macula densa to include the whole wall of the tubule in which the special sensor cells (old macula densa?) are located.

Lee

University of Tasmania

(53 days until I retire = 2 quizzes, 5 lectures, 7 pracs, 9 prac quizzes, 148 assignments and 826 exam answers to go... but who's counting???)