K+ and Ca++ regulation Flashcards
Two primary functions of K+:
- cell metabolism
2. ratio of intra/extracellular K+ creates cell resting membrane potential
% of total body K+ stored intracellularly?
98%
Total body stores of K+:
3,000-4,000 mM
50-55 mM/kg
Two main factors regulating Na-K-ATPase to get K+ back into the cell:
- insulin
2. catecholamines
Three main ideas with insulin K+ regulation:
- increases activity of Na-K-ATPase
- Promotes skeletal muscle uptake
- eating –> inc insulin –> prevents sharp rise in serum K+
How does exercise affect K+ in serum?
Muscle cells release K+ –> proportional to degree of exercise
How does serum pH affect K+?
H+ uses up bicarb in serum
To balance charge, K+ leaves cell
Acute treatment for acidotic patient with hyperkalemia:
Insulin
glucose
Ca++ (to stabilize cardiac myocytes)
% of total body K+ handled by principal cells (late distal tubule and cortical collecting duct):
10%
Two principal cell channels facilitating excretion of K+:
ROMK
BK
Aldosterone action with respect to K+:
Directly stimulated by high K+
Upregulates ROMK
Stimulates Na-K-ATPase
What does Angiotensin II do to ROMK?
Inhibits
What can block ROMK to help retain intracellular K+?
Mg++
When is BK active?
High K+ diet
What is the function of the a-intercalated cell in the distal convoluted tubule/collecting duct?
reabsorption of K+
What channels are necessary for K+ reabsorption in the alpha-intercalated cells?
K-H-ATPase
H-ATPase
*these two bring K back in from tubule lumen
bicarb also needed to antiport with Cl-
PTH generally does what to free calcium?
Increase it
How does PTH affect kidney role in free Ca?
- Increases reabsorption?
- Increase activation of vit D
- Increases PO4 secretion
What is active vit D’s role in Ca homeostasis?
Increases gut absorption
Where is vit D activated?
kidney
What is PTH regulated by?
Ca levels (free)
Increased Ca = decreased PTH
(see page 7 lecture notes)
Route of Ca reabsorption in the distal tubule?
Transcellularly
Pathology that can activate vit D?
granulomas
What gets released from cortical bone along with calcium by PTH activity?
PO4
How does free Ca get from inside the cell to the blood?
Bound to Calbindin
–> Ca-ATPase
