Notes on Gas Transport and Regulation of Respiration

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CO2 Diffusion:

CO2 is more soluble than O2, and it diffuses more quickly.

Oxyhemoglobin attachments:

Site 4: least affinity; requires greatest PO2.

Site 3: slightly greater affinity; requires a slightly larger PO2.

Site 2: more affinity; requires a small PO2.

Site 1: very high affinity; requires lowest PO2; is always attached under normal conditions.

Oxygen-Hb Dissociation Curves:

Oxygen-Hb Dissociation Curves

Oxygen-Hb Dissociation Curves:

Right shifting:


• CO2, temperature, 2,3-DPG; and decreased pH. (CO2 is acidic)

• There is a general decreased affinity of Hb to carry O2; tissues suck out O2 easily. Eg., exercise (?)

Left shifting:


• CO2, temperature, 2,3-DPG; and increased pH.

• There is a general increased affinity of Hb to carry O2; tissues find it hard to suck out O2. Eg., CO-poisoning.

Role of CO2:

CO2 is more soluble in blood compared to O2.

CO2 in blood is transported as bicarbonate (90%) and bound to Hb (5%). Bicarbonate is formed in the RBC with the help of carbonic anhydrase, but carried in plasma.

CO2 is converted into bicarbonate in systemic capillaries.


• Decreased Hb.


• Increased Hb.

Central chemoreceptors:

• Located in CNS; close to medulla; monitor CSF H+ and CO2.

Peripheral chemoreceptors:

• Located in carotid bodies (near CN IX) and aortic bodies (near CN X); monitor H+ / CO2 and PO2.

• PO2 = O2 not bound to Hb.

Special conditions:

• Chronic hypoventilation: only peripheral chemoreceptors work.

• Anemia/CO poisoning: PO2 is normal; no ventilatory response.

Medullary center:

• Rhythm of respiration.

Apneustic breathing:

• Prolonged inspirations and short expirations; developed when connection between pneumotaxic center and apneustic center is severed.

High altitude:

• Increased erythropoietin; adaptive polycythemia.

Hyperbaric environment:

• Can lead to O2 toxicity and N2 narcosis.

Additional Reading:

Basic Pulmonology

1. Lung Mechanics
2. Alveolar-Blood Gas Exchange
3. Gas Transport and Regulation of Respiration
4. Four Causes of Hypoxemia
5. Control of Respiration
6. Systemic vs Pulmonary Circulation FAQ
7. Principles of Gas Exchange in Lungs
8. Hypoxia, Hypoxemia & Hemoglobin-Oxygen Saturation Curve
9. FAQ on Mechanics of Breathing
10. FAQ on Control of Breathing
11. Criteria for Transudate Pleural Effusion
12. Light's Criteria for Exudate Pleural Effusion
13. Notes on Lung Sounds
14. Patient with Acute Respiratory Distress Syndrome (ARDS)
15. Management of Acute Deep Venous Thrombosis
16. Notes on Asthma Treatment

Pulmonology Videos

1. Video of Pulmonology Examination in a Clinical Setting

Related Topics

1. Histology of the Respiratory System
2. Upper and Lower Respiratory Disorders
3. Pulmonary Examination for Internal Medicine

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