Transport of Gases in Blood - 10 Mark Answer

Introduction

PART 1: TRANSPORT OF OXYGEN (O2) IN BLOOD

1. Dissolved Form (Simple Solution)

• Henry's Law - gas solubility pressure ku proportional.
• O2 solubility coefficient = 0.003 mL/dL/mm Hg
• PaO2 = 100 mmHg irundha, dissolved O2 = only 0.3 mL/dL - ithu very less.
• Total O2 transport la ithu minor role mattum.

2. Bound to Hemoglobin (Major Form - 97-98%)

• Hb = 4 heme + 4 protein subunits (2 alpha + 2 beta chains)
• Heme la Fe2+ (ferrous iron) thaan O2 bind aaguthu.
• 1 gram Hb = 1.34-1.39 mL O2 carry pannum.
• Normal Hb = 15 g/dL => arterial blood la ~20 mL O2/dL carry aaguthu.
• Hemoglobin O2 transport capacity dissolved form-a vida 30-100 times more!

Oxygen-Hemoglobin Dissociation Curve

• S-shaped (sigmoid) curve - ithu physiologically important.
• P50 = PO2 at which Hb is 50% saturated = 26.6 mmHg (normal).

• High temperature
• High CO2 (hypercapnia)
• Low pH / acidosis (Bohr effect)
• High 2,3-DPG

• Low temperature
• Low CO2
• High pH / alkalosis
• Low 2,3-DPG

Bohr Effect

• Blood la H+ increase aagum pothu (acidic), Hb la O2 binding decrease aaguthu.
• Tissues la (high CO2, low pH) - O2 release facilitated aaguthu.
• Lungs la (low CO2, high pH) - O2 uptake facilitated aaguthu.

2,3-DPG

• Glycolysis byproduct.
• Anaerobic metabolism la accumulate aaguthu.
• Chronic anemia la compensatory role pannuthu.

PART 2: TRANSPORT OF CO2 IN BLOOD

1. Bicarbonate Formation (Major Route - ~70%)

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

• Carbonic anhydrase (CA) enzyme - RBC la high concentration la irukku - ithu reaction speed pannudhu.
• HCO3- RBC la irundhu plasma ku move aaguthu.
• Chloride Shift (Hamburger Shift): HCO3- out aagum pothu, Cl- plasma la irundhu RBC ku enter aaguthu - electrical neutrality maintain aaguthu.
• H+ ions deoxygenated Hb ku bind aaguthu.

2. Carbamino Compounds (~5-10%)

• CO2 directly Hb protein la ulla NH2 (amino) groups ku bind aaguthu → Carbaminohemoglobin (HbCO2).
• Deoxygenated Hb - CO2 ku more affinity.

3. Dissolved CO2 (~5-10%)

• Plasma la dissolved form la irukku.

Haldane Effect

Deoxygenated blood can carry more CO2 for a given PCO2 than oxygenated blood.

• Tissues la: O2 release aagum pothu → Hb deoxygenate aaguthu → more CO2 binding capacity.
• Lungs la: O2 bind aagum pothu → CO2 release promoted.
• O2 reduces Hb's affinity for CO2 → thereby facilitating CO2 delivery at the lungs.

PART 3: NORMAL PARTIAL PRESSURES (Quick Reference)

Conclusion

• O2 mainly as Oxyhemoglobin transport aaguthu (97%)
• CO2 mainly as Bicarbonate transport aaguthu (70-90%)
• Bohr Effect - O2 unloading at tissues facilitate pannuthu
• Haldane Effect - CO2 loading at tissues and unloading at lungs facilitate pannuthu
• Chloride shift - RBC la HCO3- formation ku associated
• Carbonic anhydrase - CO2 transport la key enzyme