49- Acid Base Terminology and Control Mechanisms

Acids are / bases are H+ ____

acids = H donors

bases = H acceptors or give up OH- in solution

example of a strong acid or base that dissociates completely in solution

acid- HCl

base- NaOH

example of a weak acid that dissociates only partially in solution

carbonic acid (H2CO3)

holy grail of acid/base

H+

normal H ion conc = pH of 7.4 

t or f: most enzymes have a broad function range.

also, what happens if they go out of range

f- narrow pH range and is membrane potential is altered it usually becomes less negative (depolarizes) leading to hormones becoming less effective

normal extracellular fluid pH

7.4

blood pH

7.35-7.45

< 6.8 or >8.0 death occurs

acidosis value 

below 7.35

alkalosis value

above 7.45

why does the body produce more acids than bases?

• acids are taken in w foods

• acids are produced by metabolism of lipids and proteins

• cellular metabolism produces CO2

What equation describes the relationship between blood pH, bicarbonate, and carbon dioxide?

Henderson–Hasselbalch equation:

pH=6.1+log⁡ [HCO3−] / 0.03×PCO2

Why does CO₂ appear in the Henderson–Hasselbalch equation if the problem is about H⁺?

Because dissolved CO₂ forms H₂CO₃ (carbonic acid), which releases H⁺.
So ↑ CO₂ = ↑ acid = ↓ pH = acidosis

what organ regulates P(CO2) in the Henderson hasselbalch equation

Lungs

Adjusts acid load via ventilation (fast)

which organ regulates [HCO3] 

kidneys 

Adjusts base reserve via reabsorption / generation (slow)

What happens to pH if CO₂ rises or bicarbonate falls?

↑ CO₂ → ↑ H⁺ → ↓ pH (respiratory acidosis)
↓ HCO₃⁻ → ↓ base → ↓ pH (metabolic acidosis)
Opposite changes cause alkalosis

describe the CO2 hydration equation

• describes what happens when carbon dioxide (CO₂) dissolves in water (like in blood plasma or inside red blood cells).

• CO₂ + H₂O combine to form carbonic acid (H₂CO₃).
  Then dissociates into H⁺ (acid) and bicarbonate (HCO₃⁻) (base).

So, this single reaction explains how CO₂ levels directly affect pH.

what joins CO2 and H20 in the body and what does it form

carbonic anhydrase enzyme joins them 

forms carbonic acid 

what does carbonic acid dissociate into

H and HCO3 

an acid and a base 

lungs remove CO2 and control the ____ side

acid

• acts fast seconds to minutes

kidneys save or make HCO2 and control the _____ side

base

• acids hours to days

what is the henderson hasselbalch equation and whats pK dervied frmo

pH = pKa + log 10 [A] / [HA] 

pK is 6:1 and under normal conditions the HCO3 to H2CO3 ratio is…

20:1

volatile acid (lung) is mostly

CO2

fixed acids (kidney) are non volatile and include….

1. phosphorus acid from membrane lipid breakdown

2. sulfuric acid from protein breakdown

3. lactic acid from ischemia, hypoxia

4. keto-acids from disease (diabetes)

fixed acids (kidney) react with what to form CO2 and salt?

NaHCO3

describe buffer systems

resist a change in pH by taking up H or releasing H as conditions change

results in much smaller change in pH

describe buffer pairs

weak acid and base like H2CO3-HCO3 (carbonic acid/bicarb pair)

effective buffers have a pK within ____ 

1 pH unit of 7.4

what does breathing have to do with acid

it controls acid levels! more co2 = acidosis, less alkalosis

normal arterial pH range 

7.37 - 7.42 to coincide w a [H] of 43-36

why is body pH important

It is crucial for maintaining enzyme function, metabolic processes, and overall homeostasis. Deviations can lead to significant health issues.

even small changes in H alter…

1. enzyme structure and activity by changing metabolic rxn rates

2. membrane potentials: acids depol cells, alkalosis hyperpol them

3. hormone-receptor binding: less effective when protein charge or shape changes

normal venous pH

7.32-7.38

normal [H] arterial and venous value

arterial: 43- 48

venous: 48-42 nEq/L

normal arterial and venous P(CO2)

arterial: 40 mm Hg

venous: 46 mm Hg

normal arterial and venous [HCO3]

arterial: 24 mEq/L

venous: 27 mEq/L

explain why small pH changes can cause disturbances

even a 0.03 pH change equals a 3 nEq/L [H] shift which is enough to alter nerve, muscle, enzyme function

how is H produced

from CO2 (volatile acid) from aerobic metabolism

CO2 + H2O ← → H2co3 ← → H+ + HCO3

• about 15-20k mmol Co2 produced daily

how much fixed / non volatile acid is produced a day

50 mmol H from protein / lipid metabolism → sulfuric acid and phosphoric acids

list some pathologic acids

lactic (hypoxia) and ketoacids (diabetes, starvation)

describe volatile acids

normal metabolism that produces CO2

lungs breathe it out (can turn into gas and leave thru breathing)

examples: carbonic acid (H2CO3) from CO2

describe fixed (non volatile) acids 

comes from protein, phospholipid, or fat breakdown

cant blow off and stay dissolved in blood until kidneys remove them

• kidneys excrete H and make new HCO3

• examples: sulfuric acid (H2SO4), phosphoric acid (H3PO4), lactic acid, ketoacids

why dont we pee out carbonic acid (H2CO3)

bc its volatile and we can just exhale Co2

what happens if you cant get rid of CO2

resp acidosis

t or f: since you only make 50 mmol of non volatile acid/day, its not a big deal

F- if kidneys didnt remove it pH would fall below 7 in hours

how kidneys secrete non volatile acids

1. secrete H into urine

2. buffer H using phosphate (HPO4) and ammonia (NH4)

3. reabsorb or create new HCO3 to replace what was used up by acid

takes hours to days but is a long term stabilizer

name that organ: rapid adjuster in minutes, controls CO2 (volatile acid)

lungs

name that organ: long term correction in hours-days, controls fixed acids and HCO3

kidneys

what is the main ECF buffer

bicarbonate buffer system 

• if H increases it binds to HCO3 to form H2CO3 → CO2 + H2O → CO2 is exhaled 

• if H decreases carbonic acid dissociates to release H

describe the organic phosphates intracellular buffer

• found in cells and in kidney tubular fluid

• pka = 6.8 import inside cells for urinary acid excretion

• H + HPO4 → H2PO4

describe the protein (amino side chain) intracellular buffer

• found in cytoplasm of cells and plasma membranes

• large # of ionizable groups makes proteins excellent buffers

• COOH → COO- + H and NH3 → NH2 + H

describe hemoglobin as a intracellular buffer

• found in RBC

• most imp intracellular buffer in blood, deoxygenated Hb binds H as O2 is released (haldane effect)

• Hb + H → HHb

pKa of ECF and relative importance

6.1

most important overall

pKa of ICF and relative importance

6.8-7

major ICF buffers and urinary acid buffer