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✅ Chapter 17: Breathing and Exchange of Gases – Part 4

🔬 Respiratory Volumes, Capacities, and Transport of Gases

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🧪 Respiratory Volumes:

These are the measurements of air movement during different phases of breathing.

Let’s understand each volume in detail:

Volume	Definition	Average Value
Tidal Volume (TV)	Volume of air inspired or expired during normal breathing	~500 mL
Inspiratory Reserve Volume (IRV)	Additional air inspired with force after normal inspiration	~2500–3000 mL
Expiratory Reserve Volume (ERV)	Additional air expired forcefully after normal expiration	~1000–1100 mL
Residual Volume (RV)	Air remaining in lungs even after forced expiration	~1100–1200 mL

✅ Key point:

Residual Volume prevents lung collapse.

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🧪 Respiratory Capacities:

These are combinations of two or more volumes.

Capacity	Formula	Average Value
Inspiratory Capacity (IC)	TV + IRV	3000–3500 mL
Expiratory Capacity (EC)	TV + ERV	1500–1600 mL
Functional Residual Capacity (FRC)	ERV + RV	2100–2300 mL
Vital Capacity (VC)	TV + IRV + ERV	3500–4500 mL
Total Lung Capacity (TLC)	VC + RV	~5000–6000 mL

✅ Vital Capacity is the maximum air a person can expel after maximum inspiration.

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🌬️ Important Definitions:

• Spirometer: Instrument used to measure lung volumes and capacities.

• Eupnea: Normal breathing (12–16 breaths/min).

• Apnea: Temporary stoppage of breathing.

• Dyspnea: Difficulty in breathing (as in asthma).

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🚚 Transport of Gases:

Now let’s see how oxygen and carbon dioxide are transported in the blood.

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🩸 Transport of Oxygen:

Oxygen is transported in two ways:

1. 98.5% by binding to hemoglobin (Hb) forming oxyhemoglobin.

2. 1.5% dissolved directly in plasma.

✅ Reaction:

$$\text{Hb} + \text{O}_2 \rightleftharpoons \text{HbO}_2$$

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🔵 Hemoglobin and Oxygen:

• Each hemoglobin molecule can bind four molecules of oxygen.

• The binding is reversible and depends on conditions like:

  • Partial pressure of oxygen (pO₂)

  • Partial pressure of carbon dioxide (pCO₂)

  • Temperature

  • Hydrogen ion concentration (pH)

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📈 Oxygen Dissociation Curve:

• A graph between pO₂ and percentage saturation of hemoglobin.

• Shape: Sigmoidal (S-shaped).

✅ Key Points:

• High pO₂ → more oxygen binding.

• Low pO₂ → oxygen released to tissues.

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🔵 Factors Affecting Oxygen Binding:

Factor	Effect on O₂ binding
↑ pO₂	Increased binding
↓ pO₂	Decreased binding
↑ pCO₂	Decreased binding
↓ pCO₂	Increased binding
↑ Temperature	Decreased binding
↓ pH (acidic)	Decreased binding (Bohr Effect)

✅ Bohr Effect:

Increased CO₂ or H⁺ → facilitates release of O₂ at tissues.

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🚚 Transport of Carbon Dioxide:

CO₂ is transported in three forms:

1. 70% as bicarbonate ions (HCO₃⁻).

2. 20–25% bound to hemoglobin (as carbaminohemoglobin).

3. 7–10% dissolved in plasma.

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🧪 Formation of Bicarbonate:

CO₂ reacts with water inside RBCs:

$$\text{CO}_2 + \text{H}_2O \xrightarrow{\text{Carbonic Anhydrase}} \text{H}_2CO_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$$

• Enzyme: Carbonic Anhydrase (very fast reaction)

• Bicarbonate ions diffuse into plasma for transport.

✅ At the lungs:

Reaction reverses → CO₂ is released and exhaled.

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🔵 Chloride Shift:

• As bicarbonate ions move out of RBCs, chloride ions (Cl⁻) move in to maintain electrical neutrality.

✅ Key Term:

Chloride shift = Hamburger phenomenon.

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📉 Haldane Effect:

• Oxygenation of blood in lungs displaces CO₂ from hemoglobin.

• Helps CO₂ unloading at lungs.

✅ In simple words:

When hemoglobin binds oxygen, its affinity for CO₂ decreases.

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🎯 Quick Summary:

Gas	Main Transport Method
O₂	Oxyhemoglobin (98.5%)
CO₂	Bicarbonate ions (70%)

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🔍 Important Facts for NEET:

• Each hemoglobin molecule = 4 oxygen molecules (fully saturated).

• Normal pO₂ in alveoli: ~104 mm Hg.

• Normal pCO₂ in alveoli: ~40 mm Hg.

• O₂ affinity is affected by: CO₂ concentration, pH, temperature.

✅ Remember:

More CO₂ or more H⁺ → oxygen release increases at tissues → essential for metabolism!

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🌟 Related Blogs to Explore:

👉 biologyatease1.blogspot.com
👉 neetpyqall.blogspot.com