Resorption and secretion Flashcards
What is Tm?
maximum transport capacity - occurs when carriers all become saturated
What is renal threshold?
Renal threshold = plasma threshold at which saturation occurs.
Up to what plasma glucose concentration is all glucose reabsorbed from the urine?
10mmoles/L - renal plasma threshold for glucose
What is a normal plasma glucose concentration?
5mmoles/L
What % of Na reabsorption occurs at the proximal tubule?
65-75%
Where are active Na pumps located?
Basolateral surfaces where there is a high density of mitochondria
What does the rate of reabsorption of non-actively reabsorbed solutes depend on?
Ie passive movement of solutes like Cl-
o Amount of H2O removed, which will determine the extent of the concentration gradient.
o The permeability of the membrane to any particular solute.
Give two examples of substances that cannot be reabsorbed
Inulin
Mannitol
What is the 2nd route into the tubule?
Active secretion
Where does tubular secretion take place?
Proximal tubule
What is normal [K+] in ECF?
Normal ECF [K+] ≈ 4mmoles/l.
Define hyperkalaemia
[K+] ECF of 5.5mmoles/L or above = hyperkalaemia
What are the clinical dangers of hyperkalaemia?
↓ resting membrane potential of excitable cells and eventually ventricular fibrillation and death
Define hypokalaemia
[K+] < 3.5 mmoles/L = hypokalaemia
What are the clinical dangers of hypokalaemia?
↑ resting membrane potential i.e. hyperpolarizes muscle, cardiac cells → cardiac arrhythmias and eventually death.
