1.3. Basic Renal Process - Secretion Flashcards
What is provided in secretion?
This provides a second route into the tubule, so substances may be specifically removed from the body (peritubular capillaries into the tubule lumen)
What is secretion important for?
- Substances which may be harmful (as they can be eliminated rapidly)
- Protein-bound substances - since filtration at the glomerulus is limited
What mechanism allows substances to be secreted?
Tm-limited carrier mediated secretory mechanisms
What substances are secreted? And why?
Large numbers of endogenous and exogenous substances, due to them not being specific
e.g. the mechanism for lactic acid secretion is also used for penicillin and aspirin
What ions are actively secreted into the tubule?
- Hydrogen ions (H)
2. Potassium ions (K)
Why are hydrogen ions actively secreted?
For the acid/base balance
What is the pathway of renal handling of potassium (K)?
- K is filtered at the glomerulus into Bowmans Capsuke
- K is reabsorbed (primarily) at the proximal tubule
- K is secreted (primarily) at the distal tubule
What are changes in serum potassium due to?
Changes in K being secreted:
- Increase in K concentration leads to an increase in K secretion
- Decrease in K concentration leads to a decrease in K secretion
What regulates K secretion?
Aldosterone
What is the pathway for aldosterone?
- An increase in Extra-cellular fluid K concentration stimulates aldosterone release
- The aldosterone circulates to the kidney to stimulate an increase in K secretion
- The aldosterone also stimulates Na reabsorption at the distal tubule - but by a different reflex pathway
What can occur as a result of hyperkalaemia?
A decrease in resting-membrane potential of excitable cells
This can lead to Vfib and death
What can occur as a result of hypokalaemia?
An increase in the resting-membrane potential of excitable cells (hyperpolarises cardiac / muscle cells)
This can lead to cardiac arrhythmias
