DSA - K, Ca, P, Mg

Question 1

Normal Plasma K+ concentration

Answer 1

3.5-5.0 mEq/L

Question 2

What is the distribution of K+ throughout the body?

Answer 2

98% intracellular
(80% muscle cells; 20% other cells)

2% extracellular

Question 3

What channels regulate K+ concentrations?

Answer 3

Na-K-atpase
NKCC2
K+ Channels

Question 4

How is Hypokalemia defined and what is the most common cause?

Answer 4

Plasma [K+] <3.7 mEq/L

Caused by vomiting/diarrhea, insulin excess, dietary deficiency, alkalosis

Question 5

How is hyperkalemia defined and what is the most common cause?

Answer 5

Plasma [K+] > 5.2 mEq/L
> 10 mEq/L is lethal

Excessive intake (dietary), tissue release (rhabdimyolosis, burns, hemolysis), shifts from ICF to ECF (acidosis, insulin deficiency, tissue damage, hyperglycemia)

Question 6

How is pseudohyperkalemia defined and what is the most common cause?

Answer 6

Artificially high plasma [K+] due to lysis of RBCs while blood is drawn

Question 7

How much K+ should we intake per day and where does it go once ingested?

Answer 7

70 mmol/day

Muscle has largest amount of K+, followed by bone, then liver and RBCs

Of the 70 mmol/day, 10 mmol/day is excreted in feces while 60 mmol are absorbed through the gut into the ECF

60 mmol of K+ is excreted in urine per day

Question 8

How does extracellular K+ levels affect normal nerve and muscle function?

Answer 8

HYPOkalemia causes resting membrane potential to hyperpolarize (become more negative) in neuromuscular cells

HYPOkalemia causes muscle weakness, muscle paralysis, intestinal distention, respiratory failure

HYPERkalemia causes resting membrane potential to hypopolarize (become more positive) in neuromuscular cells

HYPERkalemia causes an initial increase in muscle excitability, but later causes muscle weakness/paralysis

Question 9

How does K+ levels affect cell volume?

Answer 9

Net loss of K+ causes cell shrinking

Net gain of K+ causes cell swelling

Question 10

How does K+ levels affect intracellular pH?

Answer 10

Low plasma [K+] causes cellular acidosis

High plasma [K+] causes cellular alkalosis

Question 11

How does K+ levels affect vascular resistance?

Answer 11

Low Plasma [K+] causes vasoconstriction

High Plasma [K+] causes vasodilation

Question 12

How does extracellular K+ levels affect normal cardiac function?

Answer 12

Cardiac Cells respond in the opposite direction to neuromuscular cells

HYPOkalemia causes hypopolarization (more positive) of cardiac cell resting membrane potential

HYPOkalemia causes prolonged repolarization, slowed conduction, abnormal pacemaker activity, leads to tachyarrhythmias

HYPERkalemia causes hyperpolarization (more negative) of cardiac cell resting membrane potential

HYPERkalemia causes enhanced repolarization, slowed conduction, leading to bradyarrhytmias and cardiac arrest

Question 13

What is the effect of insulin on K+?

Answer 13

Enhances cell uptake (reduces ECF K+ levels)

Question 14

What is the effect of Beta-Catecholamines on K+?

Answer 14

Enhanced cell uptake (reduces ECF K+ levels)

Question 15

What is the effect of Alpha-Catecholamines on K+?

Answer 15

Impaired cell uptake (increases ECF K+ levels)

Question 16

What is the effect of Acidosis on K+?

Answer 16

Impaired cell uptake (increases ECF K+ levels)

Question 17

What is the effect of Alkalosis on K+?

Answer 17

Enhanced cell uptake (reduces ECF K+ levels)

Question 18

What is the effect of Cell damage on K+?

Answer 18

Impaired cell uptake (increases ECF K+ levels)

Question 19

What is the effect of Hyperosmolality on K+?

Answer 19

Enhanced cell efflux (increases ECF K+ levels)

Question 20

What is the normal approximate value of daily Ca2+ intake?

Answer 20

~1000 mg/day (adults)

Absorption is best at doses <500 mg, thus splitting up Ca2+ intake is preferable

Question 21

What are the major storage pools for Ca2+ in the body and what are the major routes of loss from the body?

Answer 21

The general body and Bones pool Ca2+

Majority of Ca2+ is lost through Stool (~800 mg) and the rest is lost in urine (~200 mg)

PTH and calcitriol inhibit urinary excretion of Ca2+ by promoting Ca2+ renal tubular resorption. Additionally they both promote calcium resorption from bone.

Calcitriol promotes absorption of Ca2+ from gut

Calcitonin promotes bone formation and also inhibits Ca2+ excretion by promoting renal tubule resorption of Ca2+

Question 22

What are the effects of Hypocalcemia on neuromuscular excitability?

Answer 22

Hypocalcemia hyperpolarizes the membrane threshold potential, causing a reduction in the potential difference between resting membrane potential and threshold potential, thus INCREASING neuromuscular excitability (hypercalcemic tetany/spasticity)

Question 23

What are the effects of Hypercalcemia on neuromusclar excitability?

Answer 23

Hypercalcemia hypopolarizes the membrane threshold potential, causing the potential difference between resting membrane potential and threshold potential to increase, thus DEPRESSING neuromuscular excitability

Question 24

What differential diagnoses could cause an elevated serum calcium?

Answer 24

Primary hyperparathyroidism

Malignancy

Question 25

What differential diagnoses could cause a reduced serum calcium?

Answer 25

Hypoparathyroidism Renal disease Vitamin D deficiency

Question 26

What is the normal daily dietary intake of Phosphate?

Answer 26

1500 mg

Question 27

What are the major storage pools for Phosphate?

Answer 27

Bone (majority) Cells Serum

Question 28

What are the major routed of phosphate loss from the body?

Answer 28

Stool Urine Bone formation

Question 29

What are the 4 main regulators of phosphate metabolism?

Answer 29

Dietary Calcitriol - increases phosphorus resorption from bone and absorption form the gut PTH - increases phosphorus resorption from bone and indirectly promotes absorption from intestines by activating calcitriol Renal Tubular Resorption - Stimulated by tubular filtered load of phosphorus; inhibited by PTH

Question 30

What are the major storage pools for Mg2+?

Answer 30

50% in bone 49% in ICF (especially muscle) 1% in ECF

Question 31

What are the major routes of Mg2+ absorption and excretion from the body?

Answer 31

Most ingested Mg2+ is excreted in stools; the remaining Mg2+ is absorbed from the gut into the blood Mg2+ leaves blood to enter cells where it is stored and used Remainder in blood gets excreted through urine

Question 32

What is the state of serum Mg2+ and how much is there?

Answer 32

Total serum Mg2+ = 1.8 mEq/L (1.8-2.2 mg/dL) Free serum Mg2+ = 0.8-1.0mEq/L (not bound to protein) Non-diffusable (protein bound Mg2+) makes up almost 1/3 of serym Mg2+ while DIffusible and Ionized Mg2+ make up a little over 2/3.