L30 – Blood gases, acids and bases Flashcards Preview

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Flashcards in L30 – Blood gases, acids and bases Deck (49):

Healthy pH range of plasma ?



What are the 2 types of acid that threatens normal pH of

1. Volatile (carbonic acid)
2. Nonvolatile (non-carbonic acid)


What process is constant source of CO2?

Metabolism (cellular respiration)


What processes give nonvolatile acids?

Incomplete CHO and fat metabolism


Examples of nonvolatile acids?

e.g. lactic acid, ketone bodies > release H+


What process give strong acids?

Protein metabolism

e.g. sulphuric acid from sulphurous protein metabloism


Net change in acidity by Mixed diet of meat and vegetables?

net acid gain (e.g. oxalic acid, ascorbic acid)


Disturbed pH is detructive to what?

Disturbed pH is destructive to protein structure and functions


How do amino acids behave at different pH?

Amino acids behave like weak acid > protonate / deprotonate in different pH > different charge


What are 3 defenses of the blood pH?

Chemical buffers
Respiratory system


What three chemical buffers are there

Bicarbonate buffer (respiratory system, kidneys)

Proteins buffers (amino acids = weak acids)

Phosphate buffer (e.g. ATP)


What does Bronsted and Lowry acid-base theory state?

 Acid = substance that releases hydrogen ion
 Base = substance that can accept hydrogen ion

 Conjugate base = what’s left from the acid after deprotonation

Acid + base ⇌ conjugate base + conjugate acid


What is Acid dissociation constant (Ka)?

Ka = constant value specific to individual weak acid

Denotes tendency of HA to dissociate and donate H+
to solution

Higher = greater tendency to dissociate H+


What is Ka for weak acid?

Weak acid Partially ionize / dissociate

HA ⇌ A- + H+

Ka = ([H+][A-])/[HA]


What is Henderson-Hasselbalch equation for weak acid? Equation for pH and pKa?

pH = pKa + log [A-]/[HA]

pH = -log[H+]
pKa= -logKa


When pKa= pH, what is the HA & A- distribution?

When pKa = pH
[HA] = [A-]


What is the buffer region of a weak acid?

Buffer region = pKa +/- 1 (pH does not change a lot when base is added)


What forms of CO2 exist in body?

 Gaseous form in lung alveoli (before expiration)
 Dissolved form (H2CO3, HCO3-) (from tissue respiration)


How is dissolved CO2 in equ. with gaseous CO2?

CO2 (gas) ⇌ CO2 + H2O (dissolved) ⇌ H2CO3 ⇌ H+ + HCO3-


What enzyme is involved in blood buffer CO2 conversion?

Carbonic anhydrase:

CO2 + H2O < (carbonic anhydrase) > H2CO3


Does H2CO3 accumulate?

H2CO3 is a transition step so CO2 + H2O almost all converted to H+ + HCO3-


CO2 + H2O ⇌ H2CO3
Keq1 = 5 x 10^-3

H2CO3 ⇌ H+ + HCO3-
Ka1 = 1.58 x 10^-4

How to calculate overall pKa between dissolved CO2 and H+ + HCO3-?

Ka = Keq1 x Ka1 = 7.9 x 10^-7

pKa = -logKa

pKa = 6.1


Given CO2 (dissolved) ⇌ H+ + HCO3- has pKa = 6.1

What is the HH equation for the bicarbonate buffer system for H+?

pH = pKa + log[HCO3-]/[H2CO3]

pH = 6.1 + log [HCO3-]/ (0.0306)pCO2


What is the dissociation of H2CO3 in ALKALINE conditions?

H2CO3 ⇌ H+ + CO3- ⇌ 2H+ + CO3 2-


Blood buffer:

pH = 6.1 + log [HCO3-]/ (0.0306)pCO2

Why is [HA] = 0.0306pCO2?

[CO2(dissolved)] = k [PCO2]

where k = solubility coefficient of CO2 in mmol/L for pCO2


What are the solubility constants, k, used depending on the units of pCO2 measurement?

If pCO2 is measures in kPa, k=0.23

if pCO2 is measured in mmol/L, k=0.0306


Given pH = 6.1 + log [HCO3-]/ (0.0306)pCO2

What happens to pH if [HCO3-] increases or pCO2 decreases?

pH increases


Apart from bicarbonate buffer, name the other two chemical buffers.

Phosphate buffer
Protein buffers


Name some nonvolatile acids.

SO42- + H+
H2SO4 + H+
Urea + H+
Urate + H+
Oxalate + H+
Acetoacetate + H+


Increased nonvolatile acid production from cells (e.g. from Incomplete CHO and fat metabolism) is managed by what?

Increased nonvolatile acid production from cells > nonvolatile acids dissociate to form H+

> H+ buffered by HCO3- in plasma, plasma [HCO3-] falls, plasma pH falls, forms H2CO3

> H2CO3 >> H2O and CO2 and excreted


How is increased volatile acid production from cells (e.g. CO2) managed?

Increased CO2 production from cells > CO2 + H2O from plasma converted by CA to H+ + HCO3-
> Increased [HCO3-] in plasma, Increased [H+] so pH falls


What is the source of:
a)Lactic acid
b)Pyruvic acid
c)Citric acid
d)Acetoacetic acid
e)β-Hydroxybutyric acid
f)Acetic acid
g)Dihydrogen phosphate (H2PO4)
h)Ammonium ion (NH4+)
i)Carbonic acid

All are weak acids*

a)Anaerobic glycolysis
c) TCA cycle and diet
d) Fatty oxidation > ketone bodies
e) Fatty oxidation > ketone bodies
f) Ethanol metabolism
g)Dietary organic phosphates > intracellular
h) Dietary nitrogen containing compounds
i) CO2 from TCA cycle


What happens to CO2 produced INSIDE cells? Name channels, movement...etc

CO2: diffuse out of cell or form H2CO3 in cell

H2CO3 in cell >> H+ + HCO3-

HCO3- move out of cell via Chloride/ HCO3- exchanger

H+ move out of cell via Na+/H+ channel


What happens to CO2 that diffuse out of cells into RBC?

CO2 diffuse into RBC > form carbonic acid inside RBC (catalyzed by CA)

Carbonic acid dissociate:
a) H+ taken up by:
1. (phosphate) H+ + HPO4-2 >> H2PO4
2. (hemoglobin) H+ + Hb >> HHb

b) HCO3-
chloride shift counter act bicarbonate ion shift:
HCO3- exchanged out >
buffer H+ released from nonvolatile acids >> H2CO3 >> H20 + CO2 (excreted)


What happens to fatty acid oxidation products in cell (e.g. Acetoacetate + H+ in hepatocyte)

Fatty Acids > Acetoacetate + H+

H+ taken up by:
a) Propanoic acid: H+ + Pr >> HPr
b) Phosphate buffer: H+ + HPO3 -2 >> H2PO4-

H+ pumped out of cell to be buffered by HCO3- in blood


Explain the effect of H+ on O2 binding by Hb.

CO2 from respiring tissue diffuse into RBC > CA turns CO2 into H2CO3 > H2CO3 dissociate > H+ binds to HbO2, forming HHb and O2 unloading


How is CO2 transported and expired?

CO2 converted to H+ and HCO3- for tansportation to the lungs

At lungs, H+ + HCO3- converted to CO2 and H2O with isoform of Carbonic anhydrase

CO2 expired out


Explain how O2 is loaded and how it causes CO2 unloading?

O2 diffuse from lungs into RBC > O2 binds to HHb to form H+ and HbO2 (cooperative binding) > H+ binds with free HCO3- and form H2CO3 via CA

Chloride shift balance bicarbonate shift

H2CO3 turned into CO2 and H2O by CA, CO2 diffuses out of RBC and exhaled


What pH imbalance is caused by Pulmonary fibrosis/ restrictive pulmonary disease? Explain.

Pulmonary fibrosis > decrease pulmonary gas exchange > increase in pCO2 in body > pH= pKa + log [HCO3-]/kpCO2 > pH falls > respiratory acidosis


What is the approx. CO2 pressure in mmHg for normal pH of 7.4?



Explain the effects of pCO2 on plasma HCO3- concentration and pH? (In hypercapnia for example)

Hypercapnia > Increase pCO2 > increase HCO3- concentration > plasma pH falls > respiratory acidosis


How does hyperventilation change blood pH?

Hyperventilation > increase rate of CO2 removal > plasma HCO3- concentration decreases > plasma pH increases sharply > respiratory alkalosis


What four factors cause Bohr shift in O2 dissociation?

Increase H+ conc.
Increase temperature
Increase DPG conc
Increase pCO2


How does increased pCO2/ acidosis become resolved? (Pathway of receptors and ventilation... etc)

Increase pCO2 or acidosis > Sensed by central or peripheral chemoreceptors > stimulate respiratory control center > Increase ventilation > increase CO2 excretion > Plasma pH increase back to normal


What are some central symptoms of respiratory acidosis?

 Headache
 Sleepiness
 Confusion
 Loss of consciousness
 Coma


What are some muscular symptoms of acidosis?

 Seizures
 Weakness


What intestinal, respiratory, heart and gastric symptoms sappear in acidosis?

Intestinal = diarrhea
Respiratory= shortness of breath, coughing
Heart= arrhythmia, elevate HR
Gastric= Nausea, Vomiting


Scenario: A 26-year-old woman is undergoing a treatment for frequent panic attacks. The attacks are accompanied by
hyper-ventilation, a racing heartbeat (tachycardia) and dizziness. In one particular severe attack, she had to be taken to the A&E. What pH imbalance?

Hyperventilation >urgent need for removal of CO2

Tachycardia >compensatory raised HR to increase pulmonary circulation and removal of CO2

= respiratory alkalosis


Scenario : A 22-year-old man was severely injured in the chest from a motor vehicle accident. A large flail rib segment in his thorax is compromising his breathing.
What pH imbalance?

Breathing compromised, unable to remove CO2 due to insufficient ventilation, increase pCO2 in body = hypercapnia = blood pH falls

= respiratory acidosis

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