Introduction to Regulation of K, Ca, Pi and Mg: DSA

Question 1

State the normal ranges of plasma K+ concentration.

Answer 1

3.5-5.0 mEq/L

Question 2

Describe K+ distribution in the body

Answer 2

Total in body: 3500 mEq K+ in the body

K+ is primary concentrated intracellularly (98%).

80% in muscle cells (150 mEq/L)

20% other cells

Question 3

_____ difference in concentration of K+ between ICF and ECF

Answer 3

30-fold.

This is primarily d/t Na/K ATPase pump and NKCC2.

Question 4

Hypokalemia

Answer 4

Plasma [K+] < ~3.7 mEq/L

D/t [vomiting, diarreah, too much insulin, not enough K, alkalosis]

Question 5

Hyperkalemia

Answer 5

Plasma [K+] > ~5.2 mEq/L

More than 10 is lethal

D/t: Excessive intake, tissue release, shifts from ICF–>ECF (lk in acidosis, not enough insulin, tissue damage and hyperglycemia)

Question 6

Pseudohyperkalemia

Answer 6

Artificially high plasma [K+] d/t lysis of RBC while blood is being drawn.

Question 7

Identify the major routes of K+ loss from the body

Answer 7

We intake about 70mmol/day. Input=output.

1. Gut via feces
   
   1. Output 10mmol/day
2. Kidneys via urine
   
   1. Output 60mmol/day

Question 8

Define the role of extracellular K+ in maintaining normal nerve and muscle function.

Answer 8

Regulating K+ is important to maintain RMP and membrane excitability.

Hyperkalemia hypopolarizes the membrane, causing the RMP to become less negative.

• More excitable

Hypokalemia hyperpolarizes the membrane, causing the RMP to become more negative (hyperpolarized)

• Less excitable

Question 9

How do cardiac cells respond to hyperkalemia and hypokalemia?

Answer 9

Hyperkalemia–> cardiac cells actually become refractory (hyperpolarize), which induces bradycardia.

Hypokalemia–> the cells become over excitable, resulting in tachycardia and arrhythmia.

Question 10

What are the classic signs of K+ abnormalities on the ECG?

Answer 10

1. Low T wave–> hypo
2. Tall peaked T wave–> hyper

Question 11

What are the 4 roles of intracellular K+?

Answer 11

1. Maintains cell volume
2. Regulates intracellular pH
3. Needed for some enzymes to function
4. Needed for DNA/protein synthesis.

Question 12

How does K+ maintain cell volume?

Answer 12

A loss of K intracellularly can be thought of as a simple loss in osmolality. This causes cell shrinkage to compensate. The opposite is true if potassium is gained.

Question 13

How does K+ regulate intracellular pH?

Answer 13

Low K+–> low pH

High K+–> high pH

Question 14

· Potassium establishes and maintains the cell membrane potential. Since a low plasma pH results in hypopolarization of skeletal muscle cells, it results in muscle weakness, paralysis, intestinal distention, and respiratory failure. On the other hand, hyperkalemia initially increases muscle excitability, but later causes muscle paralysis.

Question 15

Low plasma potassium causes ________, and high plasma potassium causes _______

Answer 15

Low plasma potassium causes vasoconstriction, and high plasma potassium causes vasodilation

Question 16

Normal range of dietary Ca2+ intake:

Answer 16

~1000 mg/day (adults)

Question 17

Major storage pools of Ca2+

Answer 17

1. · Bone
2. · Kidneys
3. · GI tract

Question 18

Our body’s calcium pool is moderated by what?

Answer 18

1. calcitonin
   
   1. ​Calcitonin opposes the effects of parathyroid hormone (PTH), which acts to increase the blood calcium level. Calcitonin lowers blood calcium levels by suppressing osteoclast activity in the bones and increasing the amount of calcium excreted in the urine.
2. calcitriol & PTH
   
   1. PTH and calcitriol assist with resorption from bone, increasing Ca2+ levels in the blood.

Question 19

Thus, 3 ways Ca2+ can enter circulation:

Answer 19

1. Resorption from bone

2. Reabsorbed from the kidneys

3. Absorbed from the GI tract

Question 20

Major routes of Ca2+ loss from the body

Answer 20

· Most of the Ca2+ ingested in excreted as feces (~800 mg)

· 200 mg as urine

Question 21

Calcium can also act on the resting membrane potential of skeletal muscle cells.

How do?

Answer 21

Opposite of K+.

Hypocalcemia–> increases neuromuscular excitability by decreasing threshold to a more negative value.

• Predisposes to hypocalcemic tetany/spasticity

Hypercalcemia–> decreases neuromuscular excitability by increasing threshold to a less negative value.

Question 22

Phosphorus dietary intake required.

Answer 22

~1500 mg

Question 23

Phosphate Body Pools

Answer 23

85% bone

Question 24

How is P lost?

Answer 24

1. Feces
2. Urine
3. Distribed into bone

Question 25

What are the 4 regulators of phosphate metabolism

Answer 25

1. Dietary- amount we ingest

2. Calcitroil–>reabsorbs phosphate from the bone and absorption from intestines

3. PTH–> reabsorbs phosphate from the bone and indirectly increses absorption from GI tract via calcitriol

4. Renal tubular reabsorption: PTH increases phosphate excretion by the kidneys (opposite of calcium). Thus, it can be reasorbed via the kidkneez

Question 26

Mg Pools

Answer 26

1. 50% bone
2. 49% ICF (esp in muscle)
3. 1% in ECF

Question 27

Total serum Mg2+

Answer 27

1.8 mEq/L (1.8-2.2)

Question 28

Free serum Mg2+

Answer 28

0.8- 1 mEq/L

Question 29

98% of K is intracellular while 2% is extracellular, this 30fold difference is due to the NaKATPase and NKCC2 transporters. How is the ICF K+ divided and what is the input and out put?

Answer 29

K+ is concentrated higher intracellular.

80% will be inside the muscle cells and 20% inside other cells.

We exrete most in urine (90%) and 10% in stool

Question 30

A majority of K+ is stored in

Answer 30

1. muscle
2. liver
3. bone
4. RBCs

Question 31

Hyperosmolality, alkalosis, B-catecholamines, and insulin all do what to K+ cell uptake?

Answer 31

increase

Question 32

A-catecholamines, acidosis, and cell damage all do what to K+ cell uptake?

Answer 32

decrease/impair

Question 33

Describe K+ in alkalosis/acidosis

Answer 33

Alkalosis–> low K+ in the ECF/ high K+ in the cell–> hypokalemic

Acidosis–> high K+ in the ECF/low K+ in the cell–> hyperkalemic