Reabsorption Flashcards
How are many substances reabsorbed
Via carrier mediated transport systems
What does Tm (subscript) mean in relation to carriers
Maximum transport capacity
What is Tm (subscript) Due to
Saturation of the carriers
What happens when Tm(subscript) is exceeded
The excess substrate enters the urine
5 substances reabsorbed via carrier mediated transport systems
Glucose Amino acids Organic acids Sulphate ions Phosphate ions
What is renal threshold
Renal threshold is plasma concentration of a substrate at which saturation occurs
Is glucose freely filtered
Yes
Whatever its plasma concentration that will be filtered out
What is the limit of [plasma glucose] that will all be reabsorbed
10mmoles/l
If [plasma glucose] = 15mmoles/l 10 would be reabsorbed and 5 excreted
What is the renal plasma threshold for glucose and how would you know the threshold had been reached
10mmoles/l
It would start appearing in the urine
What is Normal [glucose]
5 mmoles/l
Term for glucose in urine
Glycosuria
Where does the majority of Na+ reabsorption occur
Proximal tubule
How is Na+ reabsorbed
Via active transport not Tm mechanism. (Establishes a Na+ gradient across the tubule wall)
How and where do -ve ions, like Cl- get reabsorbed
why is this?
Passive diffusion down the electrical gradient across the proximal tubule
The electrical gradient is created by the active transport of the + Na+
How is water removed from the tubule
The active transport of Na+ followed by Cl- creates an OSMOTIC FORCE, drawing out water from the tubules.
