co 2 transport in blood: 1. dissolved approx 7% 2. combined with hemoglobin10–20%
DESCRIPTION
CO 2 transport in blood: 1. Dissolved approx 7% 2. Combined with Hemoglobin10–20% 3. As bicarbonate83%. red cell. CO 2 + Hb carbamino-hemoglobin. CO 2. H. H. R—N. R—N. CO 2 +. H. COOH. Note: not the same combining site as O 2 - PowerPoint PPT PresentationTRANSCRIPT
CO2 transport in blood:
1. Dissolved approx 7%
2. Combined with Hemoglobin 10–20%
3. As bicarbonate 83%
CO2
red cell
CO2 + Hb carbamino-hemoglobin
CO2 + R—NH
HR—N
H
COOH
Note:
• not the same combining site as O2
• reaction is in deoxygenated Hb
• reaction is relatively slow quantitatively not as important as the next slide
CO2
red cell
CO2 + H2O H2CO3
HCO– + H+
HHb H+ + Hb–plasma
H2OCl–
carbonic acid
carbonic anhydrase
HCO3–
ie Combination of CO2 + H2O produces a weak acid – buffered by Hb
Effect of O2 on CO2 transport: Deoxygenated Hb is a better buffer than HbO2
deoxygenated Hb has a greater carrying capacity for CO2 (Haldane effect)
Haldane Effect
% C
O2
in b
loo
d
(ml /
10
0 m
l blo
od
)
35 40 45 50
50
55
45
B Lung capillaries
PO2 = 100 mmHg
PCO2 (mmHg)
A
PO 2 = 40 mmHg
Tissue capillaries
Carrying capacity for CO2 is low when PO2 is high
= Lungs ~easier unloading of CO2
Carrying capacity for CO2 is high when PO2 is low
= Tissues ~easier loading of CO2
1. CO2 carrying capacity >> O2 carrying capacity
2. CO2 carrying capacity almost linearly with PCO2 in physiological range.
Buffers: HA H+ + A–
Law of mass action:[H+] [A–]
[HA]= K (2)
now pH = negative log of [H+]rearranging (2)
pH = pK + log [A–]
[HA]
Henderson-Hasselbach equation
[H+] = 0.00004 mmol/L pH = 7.4range
7.0 — 7.7
R
Buffers (biological):
Proteins:
1. RCOOH RCOO + H+ ~large conc
RNH3 + RNH2 + H+
Collectively
Protein Protein + H+
2. pK 7.4 Hb (histidine) - 36 per molecule
NH+
HC
H N
H C C
R
N
HC
H N
H C C
+ H+
• Deoxygenated Hb is a better buffer than HbO2
Phosphate:
H2PO4 H+ + HPO4
2
pH = pK + log [A–]
[HA]
pK 6.8
H2CO3 H+ + HCO3–
pH = pK1 + log [HCO3
–]
[H2CO3]
but CO2 + H2O H2CO3
so [H2CO3] is proportional to [CO2]
pH = pK + log [HCO3
–]
[H2CO3]
= pK1 + log [HCO3
–]
0.03 x PCO2
CO2 at 37C dissolves at 0.03 mmol/L/mmHg pK1= 6.1
• [HCO3–] regulated by kidneys cf
• PCO2 regulated by lungs.
Isohydric principle:
• all buffer systems are in equilibrium with one another: e.g.
pH = pK1 + log [A1
–]
[HA1] = pK2 + log
[A2–]
[HA2] = etc
pH = a constant +kidneys
lungs
Respiratory disturbances
• may cause changes in pH
e.g. ventilation PCO2 and pH
respiratory acidosis
HCO3– retention by kidney
• tends to return pH to near normal
Renal compensation takes days to occur
Hyperventilation
PCO2 cerebral vaso-constriction
lightheaded / dizziness
+ Alkalosis
Ca2+ + albumin Ca—Alb
and Ca2+ spontaneous firing nerves
so pH Ca2+
pins and needles
parasthesiae
Respiratory system may also compensate for other problems of acid base balance:
Metabolic acid eg lactic acid, ketones
or losses HCO3–
from severe vomiting of intestinal contents
severe diarrhoea
• injection of H+ pH ventilation
CO2tends to return pH to
near normal
Summary
• CO2 transport and acid base balance
• CO2 in blood
dissolved
carbamino—Hb
bicarbonate
Haldane effect CO2 carried if PO2 is low• biological buffers• respiratory disturbances of acid-base balance• respiratory compensation for acid-base
disturbances