The process of breathing and exchange of gases is one of the most vital physiological functions in animals and humans. Oxygen is essential for cellular respiration, while carbon dioxide, a metabolic waste, must be eliminated. The efficiency of this exchange directly affects energy production, metabolism, and overall survival. For NEET and other medical exams, this chapter is significant, with questions commonly focused on respiratory structures, mechanisms, and gas transport.
Introduction to Breathing
Breathing, also known as pulmonary ventilation, is the physical process of inhaling oxygen-rich air and exhaling carbon dioxide-rich air. It involves the coordinated activity of the respiratory system—including the nose, pharynx, larynx, trachea, bronchi, and lungs.
Human Respiratory System
The human respiratory system is highly specialized for efficient gas exchange.
- Nostrils & Nasal cavity – Filter, warm, and humidify air.
- Pharynx & Larynx – Conduct air and produce sound.
- Trachea – A windpipe with C-shaped cartilaginous rings.
- Bronchi & Bronchioles – Branch into smaller tubes, leading to alveoli.
- Alveoli – Tiny sac-like structures where actual gas exchange occurs.
Mechanism of Breathing
Breathing is a mechanical process regulated by pressure changes in the thoracic cavity:
- Inspiration (Inhalation) – Diaphragm contracts, thoracic cavity expands, air flows in.
- Expiration (Exhalation) – Diaphragm relaxes, thoracic cavity contracts, air flows out.
This process follows Boyle’s law—pressure and volume are inversely related.
Exchange of Gases
Gas exchange occurs in two steps:
1. External Respiration – Exchange between alveolar air and blood. Oxygen diffuses into blood, and carbon dioxide diffuses into alveoli.Transport of Gases
Oxygen Transport – About 98.5% of oxygen is carried by hemoglobin as oxyhemoglobin; the rest is dissolved in plasma.Carbon Dioxide Transport – Occurs in three forms:
- Dissolved in plasma (~7%)
- As carbaminohemoglobin (~23%)
- As bicarbonate ions (~70%) – the most significant mode
Regulation of Respiration
Respiration is regulated by the respiratory center in the medulla oblongata. Chemoreceptors sensitive to CO₂ and H⁺ levels play a key role.
- High CO₂ stimulates faster breathing.
- Oxygen levels have a minor but important role in regulation.
Disorders of the Respiratory System
Several diseases affect breathing and gas exchange:
- Asthma – Inflammation and narrowing of bronchioles.
- Emphysema – Damage to alveoli leading to reduced surface area.
- Chronic Bronchitis – Persistent mucus secretion and infection.
- Occupational Lung Diseases – e.g., silicosis, asbestosis due to dust inhalation.
Comparative Table of Gas Transport
| Gas | Transport Method | Percentage |
|---|---|---|
| Oxygen | Oxyhemoglobin (HbO₂) | ~98.5% |
| Oxygen | Dissolved in plasma | ~1.5% |
| Carbon Dioxide | Dissolved in plasma | ~7% |
| Carbon Dioxide | Carbaminohemoglobin | ~23% |
| Carbon Dioxide | Bicarbonate ions | ~70% |
Importance of Breathing and Gas Exchange in Zoology
- Survival – Provides oxygen for cellular respiration.
- Homeostasis – Maintains blood pH by regulating CO₂.
- Medical Relevance – Helps in diagnosing respiratory disorders.
- NEET Relevance – Conceptual and numerical-based questions are frequently asked.
FAQs on Breathing and Exchange of Gases
Q1. What is the difference between breathing and respiration?
Breathing is the mechanical process of inhaling and exhaling, while respiration includes cellular energy production using oxygen.
Q2. How is most oxygen transported in the blood?
Most oxygen is carried as oxyhemoglobin bound to hemoglobin.
Q3. What is the primary factor regulating breathing?
Increased levels of CO₂ in blood stimulate faster and deeper breathing.
Q4. Why does emphysema reduce gas exchange?
Emphysema damages alveoli, reducing the surface area for diffusion.
Q5. Which law explains gas exchange in alveoli?
Henry’s law and diffusion gradients explain gas exchange between alveoli and blood.