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Respiratory Physiology > Acid-Base Homeostasis > Flashcards

Acid-Base Homeostasis Flashcards

1
Q

pH

A

-log[H] (no units)

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2
Q

[CO2]

A

(0.0301 mM/ mm Hg) x PCO2

units of mM OR mmol/L

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3
Q

strong acid

A

completely dissociated at physiologic pH

HCl -> H+ + Cl-

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4
Q

strong cations

A

completely dissociated

ex: Na+, K+, Mg2+ and Ca2+

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5
Q

strong anions

A

completely dissociated

ex: Cl-, SO4(2-)

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6
Q

weak acid

A

exists in both dissociated and undissociated forms

-> act as buffers

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7
Q

buffer

A

molecule or molecular system that resists changes in [H+]

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8
Q

acid dissociation constant

A

Ka = [products]/[reactants]

*[H20] concentration can be ignored because it’s concentration in the body is generally constant

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9
Q

equilibrium expression for bicarbonate buffer

A

Ka’ = [H+][HCO3-]/[CO2] = 800 x 10^-9M

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10
Q

equilibrium constant for bicarbonate buffer

A

800 x 10^-9M

800 nM

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11
Q

normal values in arterial blood for H+, HCO3- and CO2 concentrations

A 
[H+] = 40 nM (40 x 10^-9M)
[HCO3-] = 24 mM (24 x 10^-3M)
[CO2] = 1.2 mM (1.2 x 10^-3M)

*carbonic acid occurs 1:320 to CO2 -> 4 uM

So,
[H+] < [H2CO3] < [CO2] < [HCO3-]

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12
Q

hyperchloremia

A

bicarbonate anion is replaced by the chloride anion

HCl + HCO3- = CO2 + H2O + Cl-

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13
Q

closed system

A

retains CO2

large change in pH with each addition of acid

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14
Q

open system

A

elimination of CO2

small change in pH with each addition of acid

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15
Q

PCO2 isobar

A

In an open system, dissolved [CO2] remains constant. So the pH-bicarbonate diagram illustrates the relationship that forms a line called the PCO2 isobar

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16
Q

Henderson-Hasselbalch equation

A

mathematical rearrangement of the equilibrium expression for CO2-bicarbonate
-> generates family of PCO2 isobars by choosing various [HCO3-] for given

pH = 6.1 + log ([HCO3-]/(.0301 x PCO2))

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17
Q

CO2-bicarbonate system

A

effectively buffers hydrogen ions from non-carbonic acids

-cannot buffer itself

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18
Q

isohydric principle

A

pH can be known if [CO2] (or PCO2) AND [HCO3-] are both known

19
Q

CO2-bicarbonate rxn

A

CO2 + H20 H+ + HCO3-

futile cycle of buffering bc the CO2 that is added is regenerated

THUS the body requires other buffers to remove free H+ without regenerating CO2

*not good for respiratory (carbonic acid) challenge

20
Q

buffer line

A

formed by pH-bicarbonate values

flat is undesirable, ex: increasing PCO2 -> no change in bicarbonate and pH drops

steep is desirable- large amounts of bicarbonate formed with little change in pH

21
Q

metabolic acidosis

A

increase in non-carbonic acid

22
Q

respiratory acidosis

A

increase in PCO2 (hypoventilation)

23
Q

advantages of other buffers

A

1) buffer H+ produced by CO2

2) transport added CO2 as HCO3- not as dissolved CO2

24
Q

other buffers

A

1) plasm and interstitial phosphate
2) plasma and interstitial protein
3) red cell
4) intracellular buffering
5) bone

25
Q

plasm and interstitial phosphate

A

H+ + HPO4(2-) H2PO4-

26
Q

plasma and interstitial protein

A

H+ + (protein) (protein-H+)

27
Q

red cell buffer

A

a) dissolve CO2 crosses cell membrane
b) some remains dissolved, some becomes carbamino compound on hemoglobin
c) rest catalyzed by carbonic anhydrase -> H+ and HCO3-
d) H+ is buffered by hemoglobin, cannot rapidly diffuse across membrane
e) HCO3- diffuses out of cell and is exchanged for Cl- (chloride shift)

*not metabolic acid challenge

28
Q

intracellular buffering

A

H+ enters cell and then either:

a) Cl- follows
b) Na+ or K+ leaves (could lead to hyperkalemia)

29
Q

bone buffering

A

may lose calcium carbonate -> lose bone density

30
Q

Renal System

A

compensation and correction of acid-base homeostasis

31
Q

time course of buffering

A

ECF:
millisec- plasma and hemoglobin in rbc
10-30min- interstitial fluid compartment

ICF:
2-4hrs- intracellular buffering
several days- renal system
minutes-years- bone

32
Q

buffer value

A

= d(HCO3-)/d(pH)
units = slykes (sl) or mmol/L per pH
ability of all boady buffer systems other than CO2-bicarbonate to buffer a change in [H+] caused by changes of PCO2 ie how effective can they turn CO2 into HCO3-

high value is preferred
-> can indicate relationships on pH-bicarb diagram

plasma (4sl) < ECF (11sl) < blood (25sl)

individual variation of buffer values

33
Q

base excess

A

amount of strong acid to return blood to pH of 7.4

represent increase in bicarbonate cause by:

1) intracellular/bone buffering and renal compensation for chronic respiratory acidosis
2) metabolic alkalosis
3) administration of sodium bicarbonate

34
Q

base defecit

A

amount of strong base to return blood to pH of 7.41)
represent decrease in bicarbonate cause by:
1)intracellular/bone buffering and renal compensation for chronic respiratory alkalosis
2) metabolic acidosis

35
Q

metabolic acidosis

A

caused by

a) bicarbonate loss due to renal or diarrheal disease
b) bicarbonate loss due to buffering of metabolic acids (lactic acid and ketoacids increase H+ load)
c) gain of non-carbonic acid (“metabolic” or “non-volitle”)
d) inability to excrete H+ thus bicarbonate is consumed- renal disease

dx: < 22mM
compensation: hyperventilation PCO2, 35 mmHg

correction: increasing plasma HCO3-
a) administer NaHCO3 (dangerous)
b) kidney restores bicarbonate by excreting H+

36
Q

ABG

A

arterial blood gases
pH 7.35-7.45
Pa(CO2) 35-45 mmHg
HCO3- 22-26mM

37
Q

acid-base disorder

A
  • respiratory and/or renal abnormality

- acid-base load exceeds capacity of these systems to handle it (ex: diarrhea)

38
Q

respiratory acidosis

A
  • abnormal PCO2 from hypoventilation
    compensation: renal creation and retention of bicarbonate
    correction: treating respiratory problem if possible
    dx: PCO > 45 mm Hg, pH < 7.35, normal or above HCO3-

causes:

a) depressed ventilation (drug overdose)
b) obstructive lung disease (COPD and pulmonary fibrosis)
c) chest wall/ muscle disorders
d) pulmonary fibrosis

39
Q

respiratory alkalosis

A
  • abnormal PCO2 from hyperventilation
    compensation: renal secretion of bicarbonate
    correction: treating respiratory problem
    dx: PCO2 < 35mm Hg, pH > 7.45, normal or below HCO3-

causes:
1) hypoxia -> hypoxic drive
2) pain/ anxiety -> psychogenic hyperventilation
3) dyspnea
4) mechanical overventilation

40
Q

metabolic alkalosis

A
  • loss of non-carbonic acid
  • gain of bicarbonate

dx: >7.45pH and HCO3- > 26mM
compensation: hypoventilation (PCO2 > 45 mmHg)

causes:

a) GI loss of H+ due to vomiting bc pancreas secretes bicarbonate
b) hypokalemia (K+ leaves cell, H+ enters so ECF becomes alkaline)
c) contraction alkalosis (from diuretics -> loss of NaCl->H2O follows salt-> ECF volume decreases -> [HCO3-] increases

stages:

1) initiation
2) maintenance

41
Q

compensation

A

physiologic adjustment when acid-base homeostasis is disturbed to restore pH

->PCO2 or bicarbonate will become abnormal bc pH is priority

42
Q

correction

A

resolution or cure when acid-base homeostasis is disturbed to restore pH

43
Q

plasma anion gap

A

= [Na+] - ([HCO3-] + [Cl-])

normal range is 8-16mM

Respiratory Physiology (4 decks)

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