3.1 Air Passage Way

Introduction

Respiration is the process by which cells obtain energy from glucose. Oxygen is needed for this process, and carbon dioxide is produced as a waste product. The respiratory system is responsible for taking in oxygen from the environment and removing carbon dioxide from the body. The air passageway is the path through which air travels from the outside environment to the lungs. This topic explains the structure and function of the air passageway and lungs.

Definition

The air passageway is the series of organs and tubes through which air travels from the external environment to the lungs. It consists of:

• Nose
• Pharynx
• Larynx
• Trachea
• Bronchi
• Bronchioles

The lungs are the main organs of respiration where gas exchange occurs.

Main Idea

The organs responsible for gas exchange in man are the two lungs and the air passages which lead to the lungs.

Respiration vs. Breathing:

• Breathing is the movement of air into and out of the lungs.
• Respiration is the chemical reaction inside the cell that releases energy.

The respiratory system moves oxygen from outside the environment into the body. It also removes carbon dioxide from the body.

Core Concept

Parts of the Air Passageway

Detailed Explanation

1. Nose

The nose is an elevated structure. It is divided into two parts.

Structure:

• The external openings of the nose are nostrils having hairs.
• The nostrils lead into a nasal cavity.
• The top of the nasal cavity has a lining of nerve cells, which are responsible for the sense of smell.
• The walls and the base of the nasal passage are lined with cilia.
• Between the ciliated epithelial cells are goblet cells, which produce sticky fluid called mucus.

Functions of the nasal cavity:

The nasal cavity performs important functions:

• Warming: The air entering the respiratory system must be warmed.
• Moistening: The air must be moistened.
• Filtering: The air must be filtered to keep the lung tissue healthy.

How it works:

• The hairs lining the entrance to the nasal cavity trap large dust particles.
• The thin layer of mucus moistens the air and also traps particles of dust or smoke.
• The cilia sweep the trapped particles and mucus towards the pharynx.
• These are either swallowed or spit out.
• By the time air reaches the lungs, it is relatively dust-free, germ-free, warm, and moist.

Simple explanation: The nose is like an air conditioner and filter. It warms, moistens, and cleans the air before it reaches the lungs.

Do You Know?

All the cilia in the respiratory system beat toward the back of the throat, up from the lungs and down from the nose. Cilia may beat 1,000 times a minute.

2. Pharynx

What it is: Air is drawn out of the nasal passages into a channel called the pharynx, at the back of the mouth.

Structure:

• There are several openings in the pharynx.
• The air is channelized from the pharynx into the larynx.

Function:

- The pharynx is a common passage for food and air.

Simple explanation: The pharynx is like a crossroads where the paths for food and air meet.

3. Larynx

What it is: Larynx or voice box is a cartilaginous structure.

Structure:

• It surrounds the upper end of the trachea.
• The cavity of the larynx is called the glottis.
• Epiglottis is a cartilaginous structure that prevents food from entering the glottis during swallowing.

Function:

• Produces sound (voice).
• Passage for air.

Simple explanation: The larynx is the voice box. It contains the vocal cords that produce sound. The epiglottis acts like a lid to prevent food from entering the airway.

4. Trachea

What it is: The trachea is a tube running from the pharynx to the lungs.

Structure:

• It is held permanently open by C-shaped rings of cartilage in its walls.
• The cartilage rings also keep the trachea open when it develops a low internal air pressure during every intake of breath.

Function:

- Conducts air from the larynx to the bronchi.

Simple explanation: The trachea is the windpipe. The C-shaped cartilage rings prevent it from collapsing.

Why C-shaped rings?

• The C-shape allows the oesophagus (which is behind the trachea) to expand when swallowing food.
• The open part of the C faces the oesophagus.

5. Bronchi

What it is: The trachea divides into two bronchi (singular: bronchus), one leading to each lung.

Structure:

- Bronchi have irregularly shaped plates of cartilage, which keep the tubes permanently open.

Function:

- Conduct air from the trachea to each lung.

Simple explanation: The bronchi are like two large branches that carry air into each lung.

6. Bronchioles

What it is: Inside the lungs, each bronchus divides again and again to form a mass of very fine branches called bronchioles.

Structure:

• Bronchioles are fine tubes.
• They branch into many short tubes of equal diameter called alveolar ducts.

Function:

- Conduct air from the bronchi to the alveoli.

Simple explanation: Bronchioles are like tiny twigs at the end of branches. They carry air deep into the lungs.

7. Alveoli

What they are: The alveolar ducts end in tiny hollow bags called air sacs. The air sacs have many bubble-like pockets in their walls called alveoli.

Structure:

• Alveoli are tiny air sacs.
• They look like bunches of grapes.
• Each alveolus is surrounded by a network of capillaries.
• The inner surface of the alveoli has moisture.

Function:

• The alveoli are the respiratory surface of a mammal.
• Gas exchange occurs here: oxygen diffuses into the blood, and carbon dioxide diffuses out.

Simple explanation: Alveoli are like tiny balloons where oxygen enters the blood and carbon dioxide leaves the blood.

Why alveoli are important:

• They provide a large surface area for gas exchange.
• The arrangement of bubble-like alveoli gives the lungs a far greater surface area.
• The thin walls and rich blood supply allow efficient gas exchange.

Intermediate Level

The air passageway consists of:

Key features:

• Nasal cavity has cilia and goblet cells.
• Trachea has C-shaped cartilage rings.
• Bronchi have irregular cartilage plates.
• Alveoli are surrounded by capillaries.
• Gas exchange occurs by diffusion.

Important Points

• - The air passageway consists of nose, pharynx, larynx, trachea, bronchi, and bronchioles.
• - The nose is an elevated structure with nostrils.
• - The nasal cavity warms, moistens, and filters air.
• - The nasal cavity has cilia and goblet cells.
• - The pharynx is a common passage for food and air.
• - The larynx is the voice box.
• - The cavity of the larynx is called the glottis.
• - The epiglottis prevents food from entering the glottis.
• - The trachea is held open by C-shaped rings of cartilage.
• - The trachea divides into two bronchi.
• - Bronchi have irregularly shaped plates of cartilage.
• - Bronchioles branch into alveolar ducts.
• - Alveolar ducts end in air sacs.
• - Air sacs have alveoli.
• - Alveoli are the respiratory surface of a mammal.
• - The lungs are protected by ribs and intercostal muscles.
• - Each lung is surrounded by a membrane called pleura.
• - The lungs are spongy due to the presence of alveoli.
• - Gas exchange occurs by diffusion across the thin membrane of an alveolus and a capillary.

Remember

• - Air passageway = nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
• - Nose = warms, moistens, filters air
• - Pharynx = common passage for food and air
• - Larynx = voice box
• - Glottis = opening of larynx
• - Epiglottis = prevents food from entering glottis
• - Trachea = C-shaped cartilage rings
• - Bronchi = two divisions of trachea
• - Bronchioles = fine branches
• - Alveoli = site of gas exchange
• - Lungs = protected by ribs and pleura
• - Gas exchange = by diffusion

Common Mistakes

• 1. Thinking breathing and respiration are the same.
• - Breathing = movement of air into and out of the lungs.
• - Respiration = chemical reaction inside cells.
• 2. Confusing the glottis and epiglottis.
• - Glottis = opening of the larynx.
• - Epiglottis = flap that covers the glottis during swallowing.
• 3. Thinking the trachea has complete rings of cartilage.
• - The trachea has C-shaped rings of cartilage, not complete rings.
• 4. Forgetting the role of cilia and goblet cells.
• - Cilia sweep mucus and trapped particles towards the pharynx.
• - Goblet cells produce mucus.
• 5. Mixing up bronchi and bronchioles.
• - Bronchi = two main divisions of the trachea.
• - Bronchioles = fine branches inside the lungs.
• 6. Thinking gas exchange occurs in the bronchi.
• - Gas exchange occurs in the alveoli.
• 7. Believing the lungs are solid organs.
• - The lungs are spongy due to the presence of millions of alveoli.

Quick Revision

60-Second Revision

• Air passageway = nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
• Nose = warms, moistens, filters air
• Pharynx = common passage for food and air
• **Larynx** = voice box
• Glottis = opening of larynx
• Epiglottis = prevents food from entering glottis
• Trachea = C-shaped cartilage rings
• Bronchi = two divisions of trachea
• Bronchioles = fine branches
• Alveoli = site of gas exchange
• Lungs = protected by ribs and pleura
• **Gas exchange** = by diffusion
• Warning: Do not confuse breathing (movement of air) with respiration (chemical reaction in cells).