Renal IV: Principles of Tubular Transport Flashcards
What does the transport maximum (Tm) refer to?
It refers to the concentration at which there are no more binding sites available for transport of a solute, and saturation is therefore achieved
Is glucose reabsorbed?
Yes, 100% of freely filtered glucose is reabsorbed back into the blood.
Describe the glucose load in terms of F, S, R, and E.
F=R+E, or R=F-E
Why is glucose not a good estimate of GFR?
because the glucose that is filtered through is 100% reabsorbed
At low, or normal plasma concentrations of glucose, is any glucose excreted?
No! Reabsorption perfectly matches filtration.
What is the renal plasma threshold (RPT) for glucose?
220 mg/dL
The concentration of a substance required in the kidneys before it starts appearing in the urine.
renal plasma threshold (RPT)
What is the Tm for glucose, and what does this mean?
375 mg/min; this means that
What are 2 common conditions in which glucosuria may occur?
diabetes and pregnancy
Why does glucosuria cause dehydration and thirst?
Any excess glucose in the tubules holds excess water by osmotic forces, therefore osmotic diuresis results and causes dehydration and thirst.
Describe the PAH load in terms of F, S, R, and E.
F+S=E, or S=E-F (PAH is NOT reabsorbed)
Why is the excreted line above the filtered line for PAH?
because PAH appearing in urine (aka, excretion) comes from filtration AND secretion
What happens at the transport maximum for PAH?
the amount of secretion plateaus, which slows the amount of PAH excreted
Reabsorption in the proximal tubule is _________.
isosmotic
Describe glomerulotubular (G-T) balance?
This describes a situation in which Na+ reabsorption in the PCT varies according to the filtered load, making it such that 2/3 (67%) of the filtered Na+ is reabsorbed in the PCT despite variations in GFR
