Lecture 8: Regulation of Potassium Balance Flashcards
Where is most K+ located?
ICF
How is ICF K+ controlled?
Na+/K+ pump
Internal K balance
Distribution of K+ across cell membranes
External K Balance
Renal mechanisms to manage variations in K+ intake
What pump helps with internal K+ balance and with buffering when needed?
H+/K+ pump
Alkalemia is accompanied by what condition
Hypokalemia
What is the mechanism that causes Alkalemia
Hydrogen in blood decreases, so H+ leaves to enter ECF and K+ enters cells
Acidemia is accompanied by what condition
Hyperkalemia
What is the mechanism that causes acidemia?
Hydrogen in blood increases, so H+ enters and K+ leaves the cell exchange
Do acid-base disturbances always cause a K+ shift across membranes?
No (particularly if disturbance is respiratory acidosis or respiratory alkalosis)
Hyperkalemia leads to what kind of cells
Hyperexcitable
Hypokalemia leads to what in cells
Hyperpolarization
Why does hyperkalemia lead to hyperexcitable cells?
More potassium outside of cell and concentration of K more equal than between inside and outside. Decreased concentration gradient so less driving force for K+ to leave inside of cell –> RMP more positive/closer to threshold
Why does Hypokalemia lead to hyperpolarization
K+ shifts into cells, so have more K inside than normal. Concentration gradient increases even more, so K leaves via channels because driving force is increase, so RMP even more negative and harder to reach threshold
Insulin increases what pump activity
Na+/K+ ATPase activity
Insulin increases uptake of what into cells
K+
What condition does insulin prevent?
Hyperkalemia
What happens if insulin is deficient (Type 1 diabetes)?
Decreases K intake after meals –> Hyperkalemia
What are the 6 major factors that disturb internal K+ balance?
Catecholamines
Osmolarity
Cell lysis
Exercise
Insulin
Acid-base abnormalities
Beta-2 adrenergic agonists increase activity of what
Na+/K+ ATP (increase potassium in cell, hypokalemia)
Alpha-adrenergic agonist cause shift in K+ where
Out of cells - hyperkalemia
Alkalemia
Less hydrogen in blood
Acidemia
More hydrogen in blood
How does hyperosmolarity impact internal K+ balance?
Water moves from ICF to ECF to increase concentration of K+ inside cells, drives diffusion of K into ECF
How does cell lysis impact internal K+ balance?
Breakdown of cell membranes releases K+ from ICF
How does exercise impact internal K+ balance?
Causes shift of K+ out of cells
Can result in hyperkalemia in those with renal failure, or if taking beta2 adrenergic antagonist
K+ balance = ? + ?
Daily urinary excretion of K+ + dietary K+ intake
If excretion of K+ less than intake then what kind of K balance?
Positive K balance
If excretion of K+ greater than intake, then what kind of K balance?
Negative K balance
Filtration/filtered load is dependent on
Blood K concentration
Reabsorption is dependent on
Need to conserve (increases if need to conserve increases)
Secretion is dependent on
If need to excrete more, increased secretion
What part handles 67% K+ filtered?
PCT
Where is K+ reabsorption relatively constant?
PCT and TAL
What part reabsorbs ~20% of K+ in filtered load?
TAL
What transporter is used in the TAL for K
Na/K/2Cl transporter
Distal tubule and collecting ducts are responsible for
Fine tuning of K+ excretion
What part of the renal tubule is K+ excretion dependent upon diet
CD and DT
If there is a low K+ diet, then what happens and what cells do it
Reabsorption by alpha-intercalated cells
If there is normal to high K+ diet then what happens and what cells do it
Secretion by principal cells
What pump controls K+ reabsorption by alpha intercalated cells on luminal membrane?
H+/K+ ATPase
What pump controls K+ reabsorption by alpha intercalated cells on basolateral membrane?
K+ channel
How do principal cells move K+ from blood to lumen of tubule (what transporter)
Na/K ATPase
Magnitude of K+ secretion is determined by what
Size of electrochemical gradient for K across the luminal membrane (ie how much K is entering cells?)
What factors influence magnitude of secretion of K?
Dietary K
Presence of aldosterone
Acid-base disturbances
Alkalosis
Acidosis
What does dietary K+ do to influence magnitude of secretion of K+? (High and low)
High: Causes K+ to enter principal cells, increases ICF K+ concentration, driving force for K+ secretion
Low: K+ decreases K+ in principal cells
How does presence aldosterone affect K+ secretion?
K+ will be secreted more by principal cells (because aldosterone increases Na+ reabsorption)
Increase potassium in cells is driving force for
Secretion
How does alkalosis impact secretion of K+
Less H+ in ECF, H+ leaves cells, K+ enters cells, driving force for secretion
How does acidosis impact secretion of K+
Usually decreases K+ secretion (hyperkalemia)
More H+ in ECF, so H+ enters cells
K+ leaves, decreases K+ in cells, so less secreted
