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🌬️ Chapter 15: Breathing and Exchange of Gases – Part 2

🔄 Exchange of Gases and Transport of Oxygen

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🔁 Gaseous Exchange: External and Internal Respiration

🫁 1. External Respiration (Pulmonary Gas Exchange)

• Takes place between the alveoli and blood capillaries.

• Oxygen from alveolar air diffuses into the blood.

• Carbon dioxide from blood diffuses into alveolar air.

• Both gases move by simple diffusion due to partial pressure gradients (ΔpO₂ and ΔpCO₂).

Fun fact: Alveolar surface area is ~70 m² — almost like a tennis court!

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🧬 2. Internal Respiration (Tissue Respiration)

• Occurs between blood capillaries and tissue cells.

• Oxygen moves from blood to tissues.

• Carbon dioxide moves from tissues to blood.

• Driven by differences in partial pressures:

  • Tissue cells: Low pO₂, High pCO₂

  • Arterial blood: High pO₂, Low pCO₂

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📊 Partial Pressure (pO₂ and pCO₂)

Location	pO₂ (mm Hg)	pCO₂ (mm Hg)
Alveolar air	104	40
Oxygenated blood	95	40
Deoxygenated blood	40	45
Tissues	40	45

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🩸 Transport of Oxygen in Blood

Oxygen is transported in two ways:

1️⃣ Bound to Haemoglobin (Hb) – 97%

• Each Hb molecule binds to 4 O₂ molecules, forming oxyhaemoglobin (HbO₂).

• Binding is reversible and cooperative (once one O₂ binds, others bind more easily).

Reaction:
Hb + 4O₂ ⇌ HbO₈ (Oxyhaemoglobin)

• Oxygen binding depends on partial pressure of O₂, temperature, pH, and CO₂ levels.

2️⃣ Dissolved in Plasma – 3%

• Minimal, but enough to maintain pO₂ for diffusion.

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🧪 Oxygen Dissociation Curve

This graph shows the relationship between pO₂ and % saturation of haemoglobin with O₂.

• S-shaped (sigmoid) curve

• At high pO₂ (lungs): Hb is fully saturated.

• At low pO₂ (tissues): Hb releases O₂.

🧠 Factors Shifting the Curve

• Right Shift (less affinity, more O₂ release):

  • ↑ CO₂

  • ↑ Temperature

  • ↓ pH (Bohr Effect)

• Left Shift (more affinity, less release):

  • ↓ CO₂

  • ↓ Temperature

  • ↑ pH

Bohr Effect: High CO₂ and low pH reduce Hb’s affinity for O₂, helping in unloading at tissues.

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🧪 NEET PYQs – Oxygen Transport

1. Oxyhaemoglobin formation occurs in:

   • A) Tissues

   • B) Lungs

   • C) Liver

   • D) Heart
     ✅ Answer: B) Lungs

2. Which of the following shifts the oxygen dissociation curve to the right?

   • A) Low CO₂

   • B) High pH

   • C) Low temperature

   • D) High CO₂
     ✅ Answer: D) High CO₂

3. Which statement about haemoglobin is correct?

   • A) It binds only one O₂ molecule.

   • B) It binds irreversibly.

   • C) One Hb binds four O₂ molecules.

   • D) It is present in plasma.
     ✅ Answer: C) One Hb binds four O₂ molecules.

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🧠 Summary

Process	Key Concept
External Respiration	O₂ enters blood, CO₂ leaves into alveoli
Internal Respiration	O₂ enters tissues, CO₂ enters blood
Oxygen Transport	Mainly via oxyhaemoglobin
Bohr Effect	High CO₂ promotes O₂ release at tissues

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📘 Keep learning with us at:

• biologyatease1.blogspot.com

• neetpyqall.blogspot.com

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