🔸 2. BRONCHI, BRONCHIOLES, AND ALVEOLI

🟩 Bronchi (Singular: Bronchus)

• The trachea splits into two bronchi — one goes to the right lung, the other to the left lung.
• These are called primary bronchi.
• Inside the lungs, these bronchi branch into smaller secondary bronchi.

📌 Difference between left and right lungs:

• Right lung: 3 secondary bronchi (more space).
• Left lung: 2 secondary bronchi (less space, because of the heart).

The C-shaped cartilage rings of trachea become cartilage plates in bronchi to keep the airways strong.

🟨 Bronchioles

• The secondary bronchi branch into even smaller tertiary bronchi, and then into bronchioles.
• Bronchioles are tiny airways — like narrow roads leading deep into the lungs.
• No cartilage in bronchioles — so they are more flexible but can collapse easily.

🔄 Bronchioles branch many times and end in the terminal bronchioles.

🟧 Alveoli (Singular: Alveolus)

• Terminal bronchioles open into alveolar ducts.
• These ducts end in alveolar sacs, made of many tiny alveoli.

📦 Think of a bunch of grapes — the alveoli are like the grapes.

🔬 Each alveolus is extremely small:

• Wall is only 0.1 micrometre thick.
• Made of moist epithelial cells to allow gas exchange.

📌 Each cluster contains 20–30 alveoli, and total alveoli in both lungs = 700 million. That’s a huge surface area for gas exchange — about the size of a tennis court!

🔸 3. LUNGS – Our Breathing Organs

✅ Structure of Lungs

• Two large, soft organs on either side of the chest.
• Made of millions of alveoli and blood vessels.
• Covered by two protective membranes:

Membrane	Covers what?
Visceral pleura	Covers the lungs
Parietal pleura	Lines the chest cavity (rib cage)

✅ Pleural Cavity and Fluid

• The space between these membranes is called the pleural cavity.
• It contains pleural fluid.

📌 Function of pleural fluid:

• Works like oil in an engine — reduces friction between lungs and chest wall.
• Allows the lungs to expand and contract smoothly during breathing.

✅ Lobes of the Lungs

Lung	Lobes	Reason
Right Lung	3	It is wider and larger
Left Lung	2	Smaller to make room for the heart

💡 The heart sits slightly to the left, so the left lung adjusts to give it space.

🔸 Gas Exchange in Alveoli – The Main Purpose