1.3. Basic Renal Process - Secretion

Question 1

What is provided in secretion?

Answer 1

This provides a second route into the tubule, so substances may be specifically removed from the body (peritubular capillaries into the tubule lumen)

Question 2

What is secretion important for?

Answer 2

1. Substances which may be harmful (as they can be eliminated rapidly)
2. Protein-bound substances - since filtration at the glomerulus is limited

Question 3

What mechanism allows substances to be secreted?

Answer 3

Tm-limited carrier mediated secretory mechanisms

Question 4

What substances are secreted? And why?

Answer 4

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

Question 5

What ions are actively secreted into the tubule?

Answer 5

1. Hydrogen ions (H)

2. Potassium ions (K)

Question 6

Why are hydrogen ions actively secreted?

Answer 6

For the acid/base balance

Question 7

What is the pathway of renal handling of potassium (K)?

Answer 7

1. K is filtered at the glomerulus into Bowmans Capsuke
2. K is reabsorbed (primarily) at the proximal tubule
3. K is secreted (primarily) at the distal tubule

Question 8

What are changes in serum potassium due to?

Answer 8

Changes in K being secreted:

1. Increase in K concentration leads to an increase in K secretion
2. Decrease in K concentration leads to a decrease in K secretion

Question 9

What regulates K secretion?

Answer 9

Aldosterone

Question 10

What is the pathway for aldosterone?

Answer 10

1. An increase in Extra-cellular fluid K concentration stimulates aldosterone release
2. The aldosterone circulates to the kidney to stimulate an increase in K secretion
3. The aldosterone also stimulates Na reabsorption at the distal tubule - but by a different reflex pathway

Question 11

What can occur as a result of hyperkalaemia?

Answer 11

A decrease in resting-membrane potential of excitable cells

This can lead to Vfib and death

Question 12

What can occur as a result of hypokalaemia?

Answer 12

An increase in the resting-membrane potential of excitable cells (hyperpolarises cardiac / muscle cells)
This can lead to cardiac arrhythmias