Transport of other molecules Flashcards
The highest rate (e.g., mg/min) at which the renal tubules can transfer a substance either from the tubular luminal fluid to the interstitial fluid or from the interstitial fluid to the tubular luminal fluid.
Transport maximum
T/F: Typically all glucose goes back into the body in the proximal tubule.
True
Tx = absorption rate. What is the formula?
Tx = filtered load - excretion rate
What is the equation for filtered load?
GFR * Px (concentration in the plasma)
What is the equation for excretion rate?
Ux (concentration in the urine) * V (urine flow rate)
Reabsorption of glucose continues to increase as plasma concentration increases until it is eventually seen in the ______.
Urine (excretion)
So, below the Tm of glucose, is glucose seen in the urine?
No! It is reabsorbed!
In a plasma concentration vs. excretion graph of glucose, where does Tm occur?
Above the point where the line curves up linearly and exponentially. Not when the first drop of glucose is seen in the urine. It’s referred to as splay.
An example of an antidiabetic drug used to block the reabsorption of glucose so that it may be excreted
Phlorizin
Explain the effect of a glucose transport inhibitor
Typically, you don’t begin to excrete glucose in the urine until you reach Tm and max out the transporter for reabsorption. However, with a glucose transport inhibitor, you can get glucose to be excreted at a lower plasma concentration
Why is urine flow increased with diabetes?
Because glucose and sodium are transported together. So, if you have a large conc of glucose in the urine, you will also have more salt. As a result, more water will be pulled in. High glucose concentration will retain water in the lumen of the tubule
If a molecule has a lesser clearance than inulin, what could explain this?
It is being reabsorbed
If a molecule has a greater clearance than inulin, what could explain this?
It is being secreted
Why is inulin a flat line on a clearance scale?
If it gets into the tubule, it is excreted. 100% of the filtered load is excreted.
When PAH enters a cell, it is accompanied by an _______ going the other direction.
Anion
This molecule is used as a transport blocker
Probenecid
What’s happens to PAH when concentration is below Tm? What about when it is greater than Tm?
100% of it will be excreted in the urine and secretion will occur; if it is above Tm, maximum amount of PAH is being secreted, so some will go back into the blood stream
When PAH enters the plasma, will it be found immediately in the urine?
Yes
So, compared to the curve of inulin clearance which is a straight and steady line, explain the clearance curve for PAH as its concentration in the plasma increases.
The curve will have a decreased slope once it hits Tm, because some of the PAH will have to be reabsorbed into the bloodstream.
Is clearance higher when the plasma concentration is above or below Tm?
Clearance is higher when plasma concentration is below Tm, because then it is 100%.
Inulin becomes _______ as concentrated in the urine as it was in the plasma
125 times
PAH becomes ______ as concentrated in the urine as it was in the plasma
585 times
In gout, this is blocked by a transporter, so that uric acid cannot get out of body, and will build up to toxic levels
Probenicid
T/F: Uric acid is both reabsorbed and secreted in the nephron.
True.
