02 Unit Chapters 3 - 6
Chapter 3
ANIMAL PHYSIOLOGY
BREATHING & GAS EXCHANGE
Structure of the Respiratory System
ACTIVITY : Label the parts.
Structure Function
1. Nasal Cavity Filters, warms, and moistens air
2. Trachea Air passage; lined with mucus and cilia to trap dust and microbes
3. Bronchi Two main tubes leading from trachea to lungs
4. Bronchioles Smaller branches of bronchi that lead to alveoli
5. Alveoli Site of gas exchange; surrounded by capillaries
6. Diaphragm Muscle that contracts and flattens during inhalation
7. Intercostal Muscles Muscles between ribs; help move the ribcage during breathing
8. Ribcage Protects lungs and aids in breathing movement
Page 1 BRIGHTWAY ACADEMY Miss. Manthila Fernando
,What is Breathing?
Breathing is the movement of air in and out of the lungs. It allows oxygen to enter the body and carbon
dioxide to be removed.
The Respiratory System
The human respiratory system includes the organs labelled in the previous page. Let us discuss the way how
the above parts will cooperate to facilitate breathing.
The Process of Breathing (Ventilation)
Inhalation Exhalation
Diaphragm contracts and flattens Diaphragm relaxes and domes
External intercostal muscles contract External intercostal muscles relax
Ribcage moves up and out Ribcage moves down and in
Thoracic volume increases Thoracic volume decreases
Lung pressure decreases Lung pressure increases
Air moves into lungs Air is forced out of lungs
Composition of Inhaled and Exhaled Air
Gas Inhaled Air Exhaled Air
Oxygen ~21% ~16%
Carbon dioxide ~0.04% ~4%
Nitrogen ~78% ~78%
Water vapour Variable (low) High (saturated)
Page 2 BRIGHTWAY ACADEMY Miss. Manthila Fernando
, Detailed Notes – Human Respiratory System
1. Nasal Cavity
Located at the entrance of the respiratory tract.
Lined with mucus membranes and tiny hairs (cilia).
Functions:
Warms the air (blood vessels heat the air).
Moistens the air (prevents dryness in alveoli).
Filters dust and microbes using mucus and cilia.
Traps pathogens and sends them to the throat to be swallowed and killed in the stomach.
2. Pharynx and Larynx
Pharynx: The throat – common to both food and air.
Larynx: Voice box – contains vocal cords. Air passes through here
and vibrates vocal cords to produce sound.
3. Trachea (Windpipe)
A wide, hollow tube supported by C-shaped rings of cartilage.
Function:
Carries air from the throat to the bronchi.
The cartilage rings keep it open and prevent collapse.
Lined with cilia and mucus:
Cilia: Tiny hair-like structures that beat to move mucus upwards.
Mucus: Traps dust, bacteria, and other particles.
4. Bronchi and Bronchioles
Bronchi (singular: bronchus): The trachea divides into two bronchi
– one to each lung.
Bronchioles: The bronchi branch into smaller and smaller tubes inside
the lungs.
Function:
Transport air to and from the alveoli.
Bronchi have cartilage, bronchioles do not.
Lined with mucus and cilia (especially larger bronchioles).
5. Lungs
Two large, spongy organs located in the thoracic (chest) cavity.
Function:
Contain the alveoli, where gas exchange occurs.
Protected by the ribcage.
Size: Left lung is slightly smaller than the right lung
to make space for the heart.
Each lung contains millions of alveoli – tiny sacs where
oxygen and carbon dioxide are exchanged.
Page 3 BRIGHTWAY ACADEMY Miss. Manthila Fernando
Chapter 3
ANIMAL PHYSIOLOGY
BREATHING & GAS EXCHANGE
Structure of the Respiratory System
ACTIVITY : Label the parts.
Structure Function
1. Nasal Cavity Filters, warms, and moistens air
2. Trachea Air passage; lined with mucus and cilia to trap dust and microbes
3. Bronchi Two main tubes leading from trachea to lungs
4. Bronchioles Smaller branches of bronchi that lead to alveoli
5. Alveoli Site of gas exchange; surrounded by capillaries
6. Diaphragm Muscle that contracts and flattens during inhalation
7. Intercostal Muscles Muscles between ribs; help move the ribcage during breathing
8. Ribcage Protects lungs and aids in breathing movement
Page 1 BRIGHTWAY ACADEMY Miss. Manthila Fernando
,What is Breathing?
Breathing is the movement of air in and out of the lungs. It allows oxygen to enter the body and carbon
dioxide to be removed.
The Respiratory System
The human respiratory system includes the organs labelled in the previous page. Let us discuss the way how
the above parts will cooperate to facilitate breathing.
The Process of Breathing (Ventilation)
Inhalation Exhalation
Diaphragm contracts and flattens Diaphragm relaxes and domes
External intercostal muscles contract External intercostal muscles relax
Ribcage moves up and out Ribcage moves down and in
Thoracic volume increases Thoracic volume decreases
Lung pressure decreases Lung pressure increases
Air moves into lungs Air is forced out of lungs
Composition of Inhaled and Exhaled Air
Gas Inhaled Air Exhaled Air
Oxygen ~21% ~16%
Carbon dioxide ~0.04% ~4%
Nitrogen ~78% ~78%
Water vapour Variable (low) High (saturated)
Page 2 BRIGHTWAY ACADEMY Miss. Manthila Fernando
, Detailed Notes – Human Respiratory System
1. Nasal Cavity
Located at the entrance of the respiratory tract.
Lined with mucus membranes and tiny hairs (cilia).
Functions:
Warms the air (blood vessels heat the air).
Moistens the air (prevents dryness in alveoli).
Filters dust and microbes using mucus and cilia.
Traps pathogens and sends them to the throat to be swallowed and killed in the stomach.
2. Pharynx and Larynx
Pharynx: The throat – common to both food and air.
Larynx: Voice box – contains vocal cords. Air passes through here
and vibrates vocal cords to produce sound.
3. Trachea (Windpipe)
A wide, hollow tube supported by C-shaped rings of cartilage.
Function:
Carries air from the throat to the bronchi.
The cartilage rings keep it open and prevent collapse.
Lined with cilia and mucus:
Cilia: Tiny hair-like structures that beat to move mucus upwards.
Mucus: Traps dust, bacteria, and other particles.
4. Bronchi and Bronchioles
Bronchi (singular: bronchus): The trachea divides into two bronchi
– one to each lung.
Bronchioles: The bronchi branch into smaller and smaller tubes inside
the lungs.
Function:
Transport air to and from the alveoli.
Bronchi have cartilage, bronchioles do not.
Lined with mucus and cilia (especially larger bronchioles).
5. Lungs
Two large, spongy organs located in the thoracic (chest) cavity.
Function:
Contain the alveoli, where gas exchange occurs.
Protected by the ribcage.
Size: Left lung is slightly smaller than the right lung
to make space for the heart.
Each lung contains millions of alveoli – tiny sacs where
oxygen and carbon dioxide are exchanged.
Page 3 BRIGHTWAY ACADEMY Miss. Manthila Fernando
