Breathing and respiration—two words often used interchangeably, but scientifically, they represent two distinct yet interconnected processes vital for life. Breathing is the physical process of taking in oxygen and releasing carbon dioxide. Respiration is the biochemical process where cells break down glucose to produce energy (ATP). In this chapter, we explore how humans and animals manage respiration, the mechanism behind breathing, the complex process of gas exchange, transport, and common respiratory disorders—all in a NEET-centric format.
Breathing and Respiration – Complete NEET 2026 Notes
🧬 Respiratory Organs in Animals (Recall Only)
Different animals have evolved various organs to perform respiration:
| Animal Group | Respiratory Organs |
|---|---|
| Porifera & Coelenterates | Diffusion through body surface |
| Insects | Tracheal system |
| Earthworm | Moist skin |
| Fishes (Pisces) | Gills |
| Amphibians | Skin + Lungs + Buccal Cavity |
| Reptiles, Birds, Mammals | Lungs |
🧠 Key NEET Tip: Match the respiratory organs with animal groups for quick MCQ scoring!
🫁 Human Respiratory System – Structure & Organs
Main Organs:
- Nostrils → Nasal cavity: Filters, moistens, and warms the air.
- Pharynx: Common passage for food and air.
- Larynx (Voice box): Produces sound; prevents food entry into the windpipe.
- Trachea: Supported by C-shaped cartilage rings; conducts air to bronchi
- Bronchi & Bronchioles: Branches into each lung
- Lungs: Contain alveoli – sites of gas exchange.
Mechanism of Breathing in Humans
- Breathing = Inhalation (Inspiration) + Exhalation (Expiration)
- It is regulated by the diaphragm, external intercostal muscles, and the respiratory center in the brain (medulla oblongata and pons).
Inhalation (Active Process):
- Diaphragm contracts → moves downward.
- Intercostal muscles contract → rib cage expands.
- Thoracic volume increases → pressure decreases → air flows in.
Exhalation (Passive Process):
- Diaphragm relaxes → moves upward.
- Intercostal muscles relax → rib cage falls.
- Thoracic volume decreases → pressure increases → air pushed out.
Exchange of Gases
| Location | Oxygen Movement | Carbon Dioxide Movement |
|---|---|---|
| Lungs | Alveoli → Blood | Blood → Alveoli |
| Tissues | Blood → Cells | Cells → Blood |
🧠 Partial pressure (pO₂ & pCO₂), solubility, and surface area are key factors in gas exchange.
Transport of Gases
Oxygen Transport:
- 98.5% as Oxyhemoglobin (HbO₂)
- 1.5% dissolved in plasma
- Hb + O₂ ⇌ HbO₂ (Reversible reaction depending on pO₂)
Carbon Dioxide Transport:
- 70% as Bicarbonate ion (HCO₃⁻) in plasma
- 20–25% as Carbaminohemoglobin (HbCO₂)
- 7–10% dissolved in plasma
🧠 Enzyme carbonic anhydrase plays a vital role in CO₂ transport.
Regulation of Respiration
Controlled by:
- Respiratory Rhythm Center (Medulla) – basic breathing rate
- Pneumotaxic Center (Pons) – moderates the rhythm
- Chemoreceptors – sensitive to CO₂ concentration, regulate respiratory rate
🧠 Higher CO₂ = faster breathing. Oxygen plays a minor regulatory role.
Respiratory Volumes & Capacities
| Term | Definition | Normal Value (approx.) |
|---|---|---|
| Tidal Volume (TV) | Air inhaled/exhaled during normal breathing | 500 mL |
| Inspiratory Reserve (IRV) | Extra air inhaled beyond normal inspiration | 2500–3000 mL |
| Expiratory Reserve (ERV) | Extra air exhaled beyond normal expiration | 1000–1100 mL |
| Residual Volume (RV) | Air left in lungs after forced expiration | 1100–1200 mL |
| Vital Capacity (VC) | TV + IRV + ERV | 4000–4800 mL |
| Total Lung Capacity (TLC) | VC + RV | 6000 mL |
🧠 Vital Capacity is a key value in lung function tests.
Respiratory Disorders
1. Asthma 🫁
- Chronic inflammation of bronchioles
- Symptoms: Wheezing, shortness of breath
- Cause: Allergens, stress
- Treatment: Bronchodilators, steroids
2. Emphysema
- Destruction of alveolar walls → reduced surface area
- Cause: Smoking
- Result: Poor oxygen exchange → breathlessness
3. Occupational Respiratory Disorders
- Long-term inhalation of harmful substances in workplaces (coal, silica, asbestos)
- Leads to fibrosis, reduced lung function
- Prevention: Protective gear, ventilation systems
NEET Quick Revision Points:
- Human breathing is involuntary but can be voluntary.
- Alveoli are the main sites of gas exchange.
- Hemoglobin has high affinity for O₂ but forms carbaminohemoglobin with CO₂.
- CO₂ levels mainly control respiratory rate (not O₂).
- Residual volume ensures lungs never collapse completely.
- Smokers are at higher risk of emphysema and asthma.
Practice NEET MCQ:
Q. What percentage of CO₂ is transported in the blood as bicarbonate?
- A. 7%
- B. 20%
- C. 70%
- D. 98.5%
Answer: C. 70%
🎯 Final Thoughts
Understanding Breathing and Respiration not only helps you score well in NEET but also builds a strong base for your MBBS first-year Physiology. Remember to visualize structures (like lungs and alveoli), understand mechanisms (like gas exchange and CO₂ transport), and relate them to diseases.
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