Secretion in the Nephron

[Phantastic]

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EK says most "absorption and secretion" occur in the proximal tubule, whereas TPRH says most absorption occurs in proximal, and most secretion in distal tubule.

So which one is the primary secreter? I know the PCT secretes H+, but doesn't DCT secrete drugs/toxins/K+/HCO3- in larger amounts?

 

[Charles_Carmichael]

I would say most absorption occurs in the PCT. Two-thirds of water/salt and all organic molecules (ie. glucose) are reabsorbed in the PCT. I don't know if I'd say the primary purpose of the DCT is secretion since the secretion/absorption there depends a lot on hormones (ie. aldosterone, PTH, etc).

 

[PiBond]

virtually all secretion is in the proximal tubule

 

[the humming sea]

Keep in mind that filtration, (re)absorption, and secretion are 3 separate things. The majority of reabsorption takes place in the PCT, and the majority of secretion takes place at the DCT and collecting duct.

 

[Phantastic]

I trust Pibond's opinion from previous questions, so now it really begs the question:

should i associate secretion with the PCT or the DCT?

 

[PiBond]

it would depend upon the substance was being secreted. i answered proximal tubule in reference to medications/toxins and a few select other substances. urea is secreted at the DCT, but it's safe to say that almost all secretions occur in the PCT. here's a list i found if you're interested

http://en.wikipedia.org/wiki/Table_of_medication_secreted_in_kidney

 

[Phantastic]

Gotcha.

 

[fahimaz7]

Is the MCAT really asking about selective drug secretion? In reality, it's probably not asking that type of a question.

In general, the PCT is the primary site of reabsorbtion for most ions, AA's, and sugars in the body.

PCT:
67% of Na+ and H20
67% K+
50% Urea reabsorabed
85% Phosphate reabsorbed
90% Ca+ rebsorbed (PCT and TAL)
H+ Secretion for Acid-Base balance
Para-aminohippuric Acid secreted here

Thick Ascending Limb:
25% of Na+ Reabsorbance
20% K+ reabsorbance

DCT/Collecting Duct:
8% Na+ reabsorbance
Urea reabsorbed (under ADH control)
Pricipal cells- Secrete K+
alpha-Intercalated Cells- Secrete H+