🌬️ Chapter 15: Breathing and Exchange of Gases – Part 1

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🫁 Introduction

Every cell in our body needs oxygen to carry out cellular respiration, and it produces carbon dioxide as a waste. The process by which oxygen is taken in and carbon dioxide is expelled out is called breathing, and the overall exchange and transport of gases in the body is termed respiration.

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🔍 Types of Respiration

1. Aerobic respiration – Uses oxygen to release energy from glucose.

2. Anaerobic respiration – Does not require oxygen (e.g., in some microorganisms and muscle cells temporarily).

In humans, we perform aerobic respiration, and our respiratory system supports this vital function.

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🏗️ Human Respiratory System – Structure

Let’s go step-by-step through the parts of the human respiratory system:

📌 1. External Nares (Nostrils)

• Openings through which air enters the body.

📌 2. Nasal Passage

• Warms, moistens, and filters air.

• Lined with mucus and cilia.

📌 3. Pharynx

• Common passage for food and air.

• Divided into:

  • Nasopharynx

  • Oropharynx

  • Laryngopharynx

📌 4. Larynx (Voice Box)

• Contains the vocal cords.

• Prevents entry of food into the trachea via epiglottis.

📌 5. Trachea (Windpipe)

• Supported by C-shaped cartilaginous rings.

• Conducts air into the bronchi.

📌 6. Bronchi and Bronchioles

• Trachea divides into:

  • Right and left primary bronchi

  • Further divides into secondary and tertiary bronchi.

  • Ends in bronchioles.

📌 7. Alveoli

• Tiny air sacs where gaseous exchange takes place.

• Richly supplied with blood capillaries.

• Large surface area, moist lining, and thin walls make them ideal for diffusion.

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📦 Lungs – The Main Organs

• Right lung has 3 lobes, left lung has 2 lobes.

• Enclosed in a double-layered pleural membrane with pleural fluid to reduce friction.

• Located in the thoracic cavity.

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💨 Breathing: Inspiration and Expiration

Breathing involves two main processes:

➕ Inspiration (Inhalation)

• Diaphragm contracts (flattens).

• External intercostal muscles contract, lifting the rib cage.

• Volume of thoracic cavity increases → intrapulmonary pressure decreases.

• Air rushes into the lungs.

➖ Expiration (Exhalation)

• Diaphragm relaxes (curves up).

• Intercostal muscles relax, rib cage drops.

• Volume of thoracic cavity decreases → pressure increases.

• Air is forced out of the lungs.

🧠 Controlled By:

• Medulla oblongata and pons in the brain regulate the rhythm of breathing.

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🧪 NEET PYQs – Respiratory System Basics

1. In humans, the exchange of gases takes place in:

   • A) Bronchi

   • B) Alveoli

   • C) Trachea

   • D) Bronchioles
     ✅ Answer: B) Alveoli

2. Which structure prevents food from entering the trachea?

   • A) Epiglottis

   • B) Glottis

   • C) Pharynx

   • D) Uvula
     ✅ Answer: A) Epiglottis

3. The number of lobes in the right and left lung is respectively:

   • A) 2, 3

   • B) 3, 2

   • C) 3, 3

   • D) 2, 2
     ✅ Answer: B) 3, 2

4. C-shaped cartilage rings are found in:

   • A) Esophagus

   • B) Bronchioles

   • C) Trachea

   • D) Alveoli
     ✅ Answer: C) Trachea

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🧠 Summary

Process	Mechanism Involved
Inspiration	Diaphragm contracts, lungs expand, air enters
Expiration	Diaphragm relaxes, lungs contract, air exits
Gaseous Exchange	Occurs in alveoli via diffusion
Brain Control	Respiratory centers in medulla and pons

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📘 Keep exploring more NEET content at:

• biologyatease1.blogspot.com

• neetpyqall.blogspot.com

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