Reabsorption & secretion Flashcards
How are glucose, amino acids sulphate & phosphate ions reabsorbed?
Carrier mediated transport system
Why do carriers have a maximum transport capacity (Tm)?
They can become saturated
What happens if Tm is exceeded?
Excreted in the urine
What is the renal threshold?
Plasma threshold at which saturation occurs
What is the renal plasma threshold for glucose?
10mmol
What is glucose in the urine called?
Glycouria
How will an increase in PTH effect reabsorption of phosphate?
Reduce reabsorption
What is the most abundant ion in the ECF?
Na
Where does 65-75% of Na reabsorption occur?
Proximal tubule
How is Na absorbed?
Active transport
What drives the process of Na reabsorption?
Na/K pump
How does Na move across the apical membrane of the proximal tubule cell?
Passively down concentration gradient (diffusion)
Where is the Na/K pump found?
Basolateral surfaces
How do Cl move across the tubular epithelium?
Passively -Down electrical gradient created by Na
What facilitates the movement of water out of the tubule? How does it move?
NaCl, passively
What can glucose be coupled to to transport across the membrane?
SGLT
During secretion, where does fluid move from/to?
Peritubular capillary to tubular lumen
How is substances secreted into the tubular lumen?
Via carrier mediated secretory transport
What substances are mainly secreted?
Exogenous substances (drugs)
Where does secretion occur?
Proximal tubule
What occurs when K levels rise?
Hyperkalaemia
Decreased resting membrane potential > VF
What occurs when K levels drop?
Hypokalaemia
Increased resting membrane potential > Arrythmias
What determines K excretion?
Secretion at the distal tubule
How is K secretion regulated?
Aldosterone secreted by the adrenal cortex
