Ions & Electrolytes Concepts

Question 1

Break body fluids down into fluids, ICF, ECF, ISF & blood plasma – on a % basis.

Answer 1

ICF = 40%
ECF = 20%
ISF = 16%
Blood plasma = 4%

Question 2

Name a handful of components of ISF

Answer 2

Lymph
CSF
Aqueous humor
Synovial fluid
NOT urine

Question 3

Define the border between ICF & ISF, and between ISF & blood plasma, naming the types of transport processes that will occur at each border

Answer 3

Between ICF and ISF is the plasma membrane
Facilitated diffusion, active transport, osmosis

Between ISF and blood plasma is the capillary wall
Bulk flow, simple diffusion, osmosis

Question 4

Review ways to hormonally control water loss & water retention by the urinary system

Answer 4

ADH = inserts aquaporin channels into apical membranes of principal cells of collecting ducts to reabsorb water

ANP = increasing urinary loss of Na, which increases water loss

Question 5

Review basic principles of osmosis, hypotonic & hypertonic solutions, and movement of water in and out of cells by osmosis.

Answer 5

Via osmosis, water will always flow from a hypotonic solution to a hypertonic solution

Hypotonic solutions are less concentrated and hypertonic solutions are more concentrated

If ISF has a higher osmolarity than the cytoplasm, water will leave cells and they’ll shrink

IF ISF has lower osmolarity than the cytoplasm, water will enter the cytoplasm and the cells will swell

Question 6

Define an electrolyte and be able to give a brief overview of the most plentiful anions and cations of the ICF, and ECF

Answer 6

Electrolytes are substances that have a natural positive or negative electrical charge when dissolved in water

ICF
Cations = K+, Mg2+
Anions = HPO42-

ECF
Cations = Na+
Anions = Cl- , HCO3-

Question 7

Contrast millimolar with milliequivalents

Answer 7

For monovalent Na+, K+, Cl-, one mM/L is the same as one mEq/L
For divalent Ca2+, Mg2+, HPO42-, one mM/L is two mEq/L

Question 8

Name ONE role of Na, Ca, Cl, K, Mg, HPO4 & HCO3 in the body.

Answer 8

Na = renal reabsorption of water is mostly driven by sodium transport
Ca = excitability of nervous and muscle tissue
Cl = important secretion in the stomach
K = potassium voltage-gated channels allow for repolarization of every AP of the body
Mg = important enzyme cofactor
HPO4 = ECF buffer
HCO3 = very important buffer in blood plasma and ISF

Question 9

Describe an enzyme optima curve, relating it to homeostasis in general, and specifically to acid-base balance.

Answer 9

An enzyme optima curve tells you when an enzyme is functioning perfectly, tells the pH where 100% activity will be produced

An increase or decrease in pH will alter the function of the enzyme and denature it

Must have the perfect environment for the enzyme to function

Question 10

Discuss denaturing & its effect on the structure & function of enzymes.

Answer 10

Denaturing is when proteins lose their 3d shape and decrease their function

Question 11

Describe the 2 oddities of the pH scale and how they work to give various pH’s of various solutions

Answer 11

As acid increases ([H+] increases), pH actually goes down

pH is a logarithmic scale, so to go from pH 7 to pH 6, you increase the proton concentration by 10x

Question 12

Describe a buffer system & contrast the 3 main buffering systems of the body.

Answer 12

• Suck up protons in solutions and “tie them up”
• If you’re going alkalotic, buffers can release tons of protons into ICF and ECF to lower pH
• The free carboxyl group at the one end of every protein can donate a proton (an acid)
• The free amino group at the other end of every protein can accept a proton (a base)

3 buffering systems:
Hemoglobin in RBC
Bicarbonate system in both ICF and ECF
The phosphate system is similar to the bicarb system, just on a smaller scale (good ICF buffer)

Question 13

Describe how respiration rate & depth controls acid-base balance

Answer 13

How frequently and how deeply you breathe will affect your fluid pH

Exhale frequently and deeply and you’ll drive off tons of CO2 at the alveoli

Exhale infrequently and shallowly, and plasma CO2 will build up.

Hydration of CO2 will lead to proton formation and eventual acidification (acidosis) of blood plasma

Question 14

Review proton secretion/reabsorption as part of PCT antiport, and by intercalated cells of the collecting ducts.

Answer 14

• Excreting protons in the kidney
• In the PCT, Na+/H+ antiporters use secondary active transport to secrete H+
• Intercalated cells of collecting ducts secrete H+

Question 15

Contrast acidosis & alkalosis

Answer 15

Acidosis
Occurs when blood pH falls below 7.38

Alkalosis
Occurs when blood pH rises above 7.38

Question 16

Contrast respiratory & metabolic & compensatory responses of acidosis & alkalosis.

Answer 16

Acidosis:
Respiratory= excess build-up of CO2
Metabolic= decrease in blood [HCO3-]

Respiratory compensation= increasing respiration (within minutes to hours)
Metabolic compensation= increased renal secretion of protons and increased reabsorption of bicarb ions (days)

Alkalosis:
Respiratory= excess exhalation of CO2
Metabolic= increase in blood [HCO3-]

Respiratory compensation=decreasing respiration (within minutes to hours)
Metabolic compensation=decreased renal secretion of protons and increased reabsorption of bicarb ions (days)