🫁 Transport of Gases
Breathing is not just about taking air in and pushing it out. The real work happens inside the body, where oxygen (O₂) must be delivered to all the cells, and carbon dioxide (CO₂) — a waste gas — must be brought back to the lungs to be removed.
Let’s break this into two parts:
- Transport of Oxygen
- Transport of Carbon Dioxide
🔷 1. Transport of Oxygen
🔹 Step 1: Oxygen Enters the Lungs
When we inhale, fresh air rich in oxygen enters the alveoli — tiny air sacs in the lungs that look like bunches of grapes.
Now, oxygen has to move into the blood from these alveoli. This happens by a process called diffusion.
✅ What is Diffusion?
Diffusion is the movement of particles (like oxygen) from an area of high concentration (more oxygen in the alveoli) to an area of low concentration (less oxygen in blood).
🧠 Real-Life Example:
When you spray perfume in a corner of a room, the scent spreads everywhere. That’s diffusion! Similarly, oxygen spreads from alveoli into blood.
🔹 Step 2: A Small Amount Dissolves in Plasma
Oxygen first dissolves in the watery part of blood — called plasma.
But plasma can only carry a little oxygen — about 3 mL per litre of blood. This is not enough to keep us alive!
🔹 Step 3: The Role of Haemoglobin – The Real Oxygen Carrier
Now comes the hero of oxygen transport — Haemoglobin.
🩸 Haemoglobin is a protein inside red blood cells (RBCs). It contains iron and has a strong attraction to oxygen.
- Haemoglobin binds to oxygen and forms a compound called Oxyhaemoglobin.
- Each haemoglobin molecule can carry four oxygen molecules.
🌟 Fun Fact: This is why blood looks bright red when it has lots of oxygen (like tomato juice) — it’s due to oxyhaemoglobin.
🔹 Step 4: Oxygen is Delivered to Tissues
As blood flows through body tissues, oxygen is released where it’s needed.
Here’s how it works:
- Oxygen is held by haemoglobin loosely so that it can be easily released when needed.
- In tissues, where oxygen concentration is low, the oxygen leaves the haemoglobin and enters cells.
- Haemoglobin without oxygen is called Deoxyhaemoglobin, and it makes blood appear dark red.