week 4 - Homeostatis & Imbalances: K+, Ca++, Mg++

Question 1

Out of following spaces, which ones have the same ion concentration?

Blood plasma (ECF)
Interstitial Space (ECF)
ICF (Intracellular fluid)

Answer 1

Blood plasma (ECF) and Interstitial space (ECF) have the same ion concentration.
Capillary is porous therefore ions in/out freely.
(Due to cell membrane, ions do not move freely between ECF and ICF)

Blood test = checking interstitial space

Question 2

What does phospholipid bilayer prevent from crossing cell membrane?

Answer 2

something charged (ions)
something big (proteins, etc)

Need channel / pump for those to cross the membrane

Question 3

Define Resting Membrane Potential

Answer 3

change difference between ICF and ECF. The difference enables for excitable tissues (neurons / muscles) to take an action

Question 4

What hormone does black licorice have similar substance within?

Answer 4

alsosterone (reabsorb Na+ - water follows)

Question 5

Explain how Resting Membrane Potential (RMP) is created

Answer 5

Resting membrane potential is created by electrical chemical gradient.

Through ATPase (Na+/K+ pump), 3 Na+ are sent out to ECF, and 2 K+ are sent into ICF.
–> one ion worth negative in the cell

Through potassium channel (closed by leaky), K+ sneaks out to ECF
–> more negative in ICF.

–> create Electrical chemical gradient

Question 6

Parathyroid Hormone (PTH)

What stimulates / inhibits its release?

Answer 6

Stimulation/Inhibition
Via Ca++ negative feedback
- Stimulation: by low serum Ca++
- Inhibition: by high serum Ca++

Question 7

What is the function of PTH?

Answer 7

Net effect: elevate blood Ca++ level

–> Bone
Osteoclasts dissolve matrix liberating Ca++ & PO4-

–> Intestine
Absorb Ca++ & PO4-

–> Kidney
Reabsorb Ca++ and eliminate PO4-

Change Active Vitamin D to Active D3 (calcitriol) –> enhance Ca++ absorption at intestine

Question 8

Which ion is the primary factor for Resting Membrane Potential?

Answer 8

K+

Primary ion in the cell determined electric level

Question 9

What is the normal range of serum K+

Answer 9

3.5 - 5 mEq/L

Question 10

To which cells K+ is necessary?

Answer 10

ALL

Especially muscle cells and neuron depends on K+ for their function

Muscle cells - muscle contraction (with Ca++)
Neuron - signal stimulation (with Na+)

Question 11

Explain what happens when extracellular K+ increase.

What happens to RMP by that?

Answer 11

If extracellular K+ increases (hyperkalemia), fewer K+ leave cell through leak channel.
–> more + in cell = cells become more positive (= cell hypopolarized)

RMP is closer to the threshold for depolarization, making it easier to reach action potential
–> too easy, (twitch and then) floppy

Question 12

Explain what happens when extracellular K+ decrease.

What happens to RMP by that?

Answer 12

If extracellular K+ decreases (hypokalemia), more K+ leave cell through leak channel.
–> less K+ in cell = cells become more negative (cell polarized)

RMP is far from (too low) to the threshold for depolarization, making it difficult to reach action potential
–> floppy

Question 13

What causes K+ out of cell?

Answer 13

• K+ leak channel (when RMP is at rest, controlled by gradient)

These makes K+ out of cell
- lack of ATP (Na+/K+ pump failure)
- cell death
- acidosis
- lack of insulin

Question 14

Which can lead more serious medical condition, hypokalemia or hyperkalemia?

Major cause?

What happens?

Answer 14

Hyperkalemia

Causes:
- Renal failure
- Severe hypovolemia
- Oliguria
- Lack of insulin
- Massive tissue trauma / death (–> K+ leaks out of cell into blood)

Can happen:
Cardiac arrhythmia & Cardiac arrest

Question 15

What is the early sign of severe hyperkalemia?

Answer 15

peaked T-wave (tensing) on EKG

Question 16

Know causes, clinical assessment, teaching points for hyper/hypo-kalemia

Answer 16

see list

Question 17

Treatment for severe hyperkalemia

Answer 17

ACLS (Advanced cardiac life support)
- aim to protect the heart from effects of hyperkalemia

• Calcium chloride (IV) to stablize myocardial cell membrane
• Move K+ into cells
  
  • IV sodium bicarbonate
  • glucose & insulin
  • nebulized albuterol
• Promote K+ excretion
  
  • diuresis
  • dialysis etc.

Question 18

What is the normal range of serum Ca++ (total calcium)

Answer 18

9 - 11 mg% (4.5 - 5.5 mEq/L)

Question 19

What is total calcium?

How serum Ca++ is measured?

Answer 19

In blood, there are 3 forms of calcium.
Total calcium (= total of 3 forms) is measured as serum calcium

• Free, ionized, physically active form
• Ca++ bound to albumin (not available while bound)
• Ca++ bound to small organic anions (citrate) (not available while bound)

WHEN TOTAL Ca++ IS HIGH, THEN ionized level measured

Question 20

3 factors associated serum Ca++ level

Answer 20

Vitami D
- needed for calcium absorption at GI tract duodenum

Phosphate
- Plasma Ca++ and phosphate vary inversely

Alkalosis
- decreases available Ca++

Question 21

Calcium function for muscle AP (action potential)

Answer 21

Calcium contribute to:
Motorneuron signaling AP for muscle contraction

• Calcium binds to ACh (acetylcholine) on muscle motor end place
  –> causes influx of Na+
  –> when adequate depolarization muscle contract
  –> Ca++ into muscle cell for contraction

Question 22

Know causes, clinical assessment, teaching points for hyper/hypo-calcemia

Question 23

How liver failure causes hypervolemia?

Answer 23

Liver metabolize aldosterone. When liver failure happens, there’s no further metabolizing of aldosterone. Therefore without the liver function, aldosterone remains in the circular system longer –> leads to hypervolemia

• Aldosterone is produced at kidney / adrenal cortex. High aldosterone also causes hypervolemia *

Question 24

Steatorrhea

Answer 24

fatty stool

Question 25

Tetany

Answer 25

involuntarily contraction of muscle

Question 26

What is total magnesium?

How serum Mg++ is measured?

Answer 26

In blood, there are 3 forms of magnesium.
Total magnesium (= total of 3 forms) is measured as serum magnesium

• ionized magnesium
  the physiologically active form
• Magnesium ions bound to albumin
  physiologically inactive while bound
• Magnesium ions bound to small orgnic anions such as citrate
  Physiologically inactive while they ar ebound

Question 27

Mainly what part of the body absorb Mg++?

Answer 27

Terminal ileum (last part of large intestine)

Question 28

What happen to magnesium balance to an individual who are heavy alcohol user?

Answer 28

Low intake & High output due to diarrhea, urine, emesis –> hypomagnesemia