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Breathing and Exchange of Gases - Exchange of gases, transport of gases and regulation of respiration

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Exchange of gases occurs primarily in the alveoli and tissues via simple diffusion, driven by a partial pressure gradient. The solubility of gases (where CO2CO_2 is 20−2520-25 times more soluble than O2O_2) and the thickness of the diffusion membrane are critical factors.

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The diffusion membrane is composed of three layers: the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries, and the basement substance between them. Its total thickness is less than 11 mm.

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Partial pressure of gases (in mmHgmmHg): In Alveoli, pO2=104pO_2 = 104 and pCO2=40pCO_2 = 40. In deoxygenated blood, pO2=40pO_2 = 40 and pCO2=45pCO_2 = 45. In oxygenated blood, pO2=95pO_2 = 95 and pCO2=40pCO_2 = 40. In tissues, pO2=40pO_2 = 40 and pCO2=45pCO_2 = 45.

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Transport of O2O_2: 97%97\% is transported by Red Blood Cells (RBCs) as oxyhaemoglobin, and 3%3\% is carried in a dissolved state through plasma. Each Haemoglobin (HbHb) molecule can carry a maximum of 44 molecules of O2O_2.

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The Oxygen-Haemoglobin dissociation curve is sigmoid. Factors like high pO2pO_2, low pCO2pCO_2, lesser H+H^+ concentration, and lower temperature in the alveoli favour the formation of oxyhaemoglobin. Opposite conditions in tissues (low pO2pO_2, high pCO2pCO_2, high H+H^+, high temperature) favour dissociation.

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Transport of CO2CO_2: Nearly 20−25%20-25\% is transported as carbamino-haemoglobin, 7%7\% in dissolved state in plasma, and the majority 70%70\% as bicarbonate (HCO3−HCO_3^-) ions, facilitated by the enzyme Carbonic Anhydrase.

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Regulation of Respiration: The 'Respiratory Rhythm Centre' is located in the medulla oblongata. The 'Pneumotaxic Centre' in the pons can moderate its functions by reducing the duration of inspiration. A chemosensitive area near the rhythm centre is highly sensitive to CO2CO_2 and H+H^+ concentrations.

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Receptors in the aortic arch and carotid artery also recognize changes in CO2CO_2 and H+H^+ concentration and send signals to the rhythm centre for remedial actions. The role of O2O_2 in the regulation of respiratory rhythm is quite insignificant.

📐Formulae

CO2+H2O→Carbonic AnhydraseH2CO3→Carbonic AnhydraseHCO3−+H+CO_2 + H_2O \xrightarrow{\text{Carbonic Anhydrase}} H_2CO_3 \xrightarrow{\text{Carbonic Anhydrase}} HCO_3^- + H^+

Hb+4O2⇌Hb(O2)4\text{Hb} + 4O_2 \rightleftharpoons \text{Hb}(O_2)_4

Partial Pressure (pGas)=Total Pressure×Fractional concentration of the gas\text{Partial Pressure (pGas)} = \text{Total Pressure} \times \text{Fractional concentration of the gas}

💡Examples

Problem 1:

Calculate the amount of O2O_2 delivered to the tissues by 500500 ml of oxygenated blood under normal physiological conditions.

Solution:

Under normal conditions, every 100100 ml of oxygenated blood can deliver around 55 ml of O2O_2 to the tissues. Therefore, for 500500 ml: 500100×5=25\frac{500}{100} \times 5 = 25 ml.

Explanation:

This demonstrates the efficiency of O2O_2 transport from the lungs to the tissues via haemoglobin.

Problem 2:

During exercise, if the pCO2pCO_2 levels in the blood increase and pH decreases, what happens to the oxygen-haemoglobin dissociation curve?

Solution:

The curve will shift to the right.

Explanation:

An increase in pCO2pCO_2, increase in H+H^+ (which decreases pH), and increase in temperature (Bohr Effect) decrease the affinity of haemoglobin for O2O_2, facilitating the release of O2O_2 to the active tissues.

Problem 3:

How much CO2CO_2 is delivered to the alveoli by 100100 ml of deoxygenated blood?

Solution:

44 ml.

Explanation:

Every 100100 ml of deoxygenated blood carries approximately 44 ml of CO2CO_2 to be released into the alveolar air.

Exchange of gases, transport of gases and regulation of respiration Revision - Class 11 Biology CBSE