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Flashcards in Regulation Of Potassium Deck (21)
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1

Distribution and balance of potassium

1) Intake 70 mmol /day via GI system
- 60 mmol is actually absorbed

2) ECF possesses 65 mmol at any given time, shuttling potassium to and from liver/muscles/bone/RBCs
- Muscles use the most/have the most potassium at any time!

3) kidneys reabsorb 800 mmol/day, filter 810 mmol/day and secrete 50 mmol/day

4) urine excretes roughly 60 mmol per day

2

Distribution and balance of sodium

1) Intake 120 mmol /day via GI system
- 110 mmol is actually absorbed

2) ECF possesses 2450 mmol at any given time, shuttling sodium to the ICF in all cells of the body.
- The ECF possess the most sodium at any time (other than kidneys when they are filtering)

3) kidneys reabsorb 25,400 mmol/day, filter 25,500 mmol/day

4) urine excretes roughly 100 mmol per day

3

How does the resting membrane potential change with potassium concentration?

High levels = lowers the threshold for action potential (makes the membrane potential more (+)
- easier to fire action potentials
- Nernst equation potential decreases

Low levels = increases the threshold for action potentials (makes the membrane potential more (-)
- harder to fire action potentials
- Nernst equation potential decreases

4

How do ECG’s change with respect to hypo and hyperkalemia?

Hypokalemia
- u waves become present
- T waves decrease in amplitude

Hyperkalemia
- T waves increase in amplitude (peak)
- PR interval prolongs
- V. Fib if bad enough

5

Normal balance of ECF and ICF potassium

ECF
- 4.2 mEq/L x 14L = 59mEq

ICF
- 140 mEq/L x 28L = 3920mEq

6

What happens in the body when you eat potassium in order to maintain normal potassium gradients?

**the primary goal is to maintain ECF concentrations of potassium (dont change much)**

1) the body net translocates K+ INTO cells (ICF) (typically kidneys)
- this is done via insulin and activation of K+/Na+-ATPase pumps in the CD

2) cumulative renal excretion of K+ occurs in order to get rid of excess potassium

7

Specific physiology steps to move potassium intracellularly

1) acute plasma K+ increase in blood is noted by the B-cells in the pancreas and both chromaffin (medulla) and glomerlousa (cortex) cells of the adrenal gland

2) these cells all activate to produce insulin, epinephrine and aldosterone respectively

3) epinephrine increases cAMP in muscle cells, insulin increases glucose reabsorption in muscle cells via activation of GLUT 4 and aldosterone activates mineralcorticoid receptors on muscle cells

4) everything in #3 works synergistically to increase sodium and potassium pump actions in muscle cells which casues them to uptake excess potassium

8

Factors that promote movement of potassium from ECF -> ICF
(Hypokalemia)

Insulin

Aldosterone

B2-adrenergic agonists via epinephrine/albuterol/etc
- these increase the activity of the Na+/K+/ATPase pumps which shifts K+ into cells

A-adrenergic antagonists
- these increase the activity of the Na+/K+/ATPase pumps which shifts K+ into cells

Alkalosis conditions
- body wants to throw H+ ions into the blood to correct, which causes K+ to move into cells

9

Factors that promote movement of potasssium from ICF -> ECF
(Hyperkalemia)

Insulin deficiency (diabetes mellitus)
- Na/K+/ATPase pump doesnt work efficiently

Aldosterone deficiency (addisons disease)

B-adrenergic antagonists
- Na/K+/ATPase pump doesnt work efficiently

A-adrenergic agonists
- Na/K+/ATPase pump doesnt work efficiently

Acidosis conditions
- body wants to get H+ ions out of blood so it absorbs H+ ions intracellularly while excreting potassium

Cell lysis

Strenuous exercise
- depletion of ATP causes K+ channels to open and icnreases K+ potential to move out of the cell

Increased ECF osmolarity

**causes hyperkalemia and acidemia**

10

Why does potassium move out of the cell in conditions of high ECF total osmolarity?

Higher total ECF osmolarity pulls water out of the cells

This causes the potassium specific gradient to favor potassium movement out of the cell
(Too high concentration of K+ inside of cells = moves K+ ICF -> ECF)

**the exact opposite happens in low osmolarity conditons of ECF**

11

What is the relationship between kalemia levels and H+ ions (alkalosis/acidosis)

Hypokalemia always leads to alkalemia (and vise versa)
- potassium needs to move out of cells to balance hypokalemia which requires H+ ions to move into the cell in order for this to occur

Hyperkalemia always leads to acidemia (and vise versa)
- potassium needs to move into cells to balance hyperkalemia which requires H+ ions to move out of the cell in order for this to occur

**the vise versa of each are seen as well, so these are direct relationships**

12

Where does most potassium reabsorption occur along the nephron?

67% is seen in the PCT

20% is seen in thick ascending limb

13

Where does most sodium reabsorption occur along the nephron?

67% is in the PCT

25% is in the thick ascending limb

**tends to follow potassium reabsorption

14

How does K+ get reabsobed in the PCT and the TAL?

Two ways in the PCT
1) solvent drag (gets “dragged” with water through PCT)

2) paracellular diffusion

Two ways in the TAL
1) Na+/K+/Cl- cotransporters (primary)

2) paracellular diffusion

15

How does the principal and intercalated cells move potassium?

Principal cell
- moves potassium OUT of the cell via Na+/K+ co-exchanger (moves Na+ in and K+ out) And via K+/Cl- cotransporter out of the cell
- moves potassium IN the cell via the Na+/K+ ATPase pump

(A)-intercalated cell
- moves potassium IN the cell via H+/K+ cotransporter and via Na/K+ ATPase pumps

16

Factors that increase potassium secretion

High K+ diet
- stimulates insulin to increase intercellular K+ in all cells to prevent hyperkalemia. This increases electrochemical gradient in principal cells and promotes Na+/K+/ATPase pump activity

Hyperaldosteronism
-increases ENaC channels which indirectly increases Na+ inside cells as well as upregulates a-intercalated Na+/K+/ATPase channels on basolateral surface and brings more K+ into cells. Both of these mechanisms promote K+ excretion due to charge

Alkalosis

Thiazide diuretics

Loop diuretics

Luminal anions in high concentrations

17

Factors that decrease K+ secretion

Low K+ diet

Hypoaldosteronism

Acidosis

K+-sparing diuretics (spironolactone)

18

What is the physiological properties behind how increased tubular flow rate causes increased K+ secretion?

1) flow rate increases and bends the cillia of the PCT

2) cillia bending activates PKD1/PKD2 channels and Ca+ entry

3) increases in Ca+ activates K+ secretion channels which causes excess secretion of potassium

19

How does aldosterone work?

1) in levels of increased serum potassium, aldosterone is secreted via zona glomerulosa cells in the medulla of the adrenal cortex

2) increased aldosterone goes to principal cells of the DCT/ collecting duct and causes them to hyper stimulate

3) hyper stimulation of principal cells causes increased potassium excretion due to excess sodium uptake (causes increased positive charge of cell which repells K+ into lumen)

20

What are the three stimuli for aldosterone to be released?

1) Increased plasma potassium

2) angiotensin-2 presence

3) ACTH release from the anterior pituitary

21

How does increased sodium intake affect potassium excretion?

Increased sodium intake causes increased volume in the body and inactivates RAAS system
- decreases aldosterone and decreases K+ secretion

HOWEVER, it also increases GFR and DCT flow rates which promote K+ secretion

**overall is unchanged potassium excretion**