Breathing and Exchange of Gases
Lung Volumes and Capacities
Let’s explore how much air your lungs can hold! 🫁
- Residual Volume (RV): Air remaining in lungs after you forcefully exhale.
👉 Average: 1100-1200 mL - Inspiratory Capacity (IC): Max air you can breathe in after normal exhale.
✨ Formula: IC = Tidal Volume + Inspiratory Reserve Volume - Expiratory Capacity (EC): Max air you can breathe out after normal inhale.
✨ Formula: EC = Tidal Volume + Expiratory Reserve Volume - Functional Residual Capacity (FRC): Air left in lungs after normal exhale.
✨ Formula: FRC = Expiratory Reserve Volume + Residual Volume - Vital Capacity (VC): Max air you can breathe in after forced exhale (or max air breathed out after forced inhale).
✨ Formula: VC = ERV + TV + IRV - Total Lung Capacity (TLC): Total air in lungs after forced inhale.
✨ Formula: TLC = Vital Capacity + Residual Volume
How Gas Exchange Works
Gas swapping happens in tiny air sacs called alveoli 🎈 and between blood & tissues! Two key players:
- Oxygen (O2) moves into blood
- Carbon dioxide (CO2) moves out of blood
This happens through simple diffusion – gases flow from areas of high concentration to low concentration like water sliding downhill! 🌊 Three factors affect this:
- ✅ Pressure/concentration gradient
- ✅ Solubility of the gas
- ✅ Thickness of membranes
Partial Pressure: The Driving Force
The pressure from a single gas in a mix is called partial pressure (written as pO2 for oxygen, pCO2 for CO2). Check out these numbers:
| Gas | Atmosphere | Alveoli | Deoxygenated Blood | Oxygenated Blood | Tissues |
|---|---|---|---|---|---|
| O2 (mmHg) | 159 | 104 | 40 | 95 | 40 |
| CO2 (mmHg) | 0.3 | 40 | 45 | 40 | 45 |
What this tells us:
- 🧪 O2 gradient: Alveoli (104) → Blood (40) → Tissues (40)
- ♻️ CO2 gradient: Tissues (45) → Blood (45/40) → Alveoli (40) (flows opposite to O2!)
Fun fact: CO2 diffuses 20-25× faster than O2 because it dissolves more easily in water! 💧
Gas Diffusion Membrane
The “gate” where gases cross has 3 super-thin layers (total thickness < 1 mm!):
- 👆 Alveolar epithelium (single-cell-thick lining of air sacs)
- 👇 Capillary endothelium (wall of blood vessels)
- 🖐️ Basement substance (glue-like layer in between)
This thin setup makes gas exchange super efficient! ⚡
Key NEET Concepts 🔑
- Partial pressure gradients for O2 and CO2 (memorize the table!)
- Vital Capacity vs. Residual Volume (how they relate to Total Lung Capacity)
- CO2 solubility advantage (why it diffuses faster than O2)
- Structure of diffusion membrane (the 3 layers)
- Direction of gas movement (O2: alveoli→blood→tissues; CO2: tissues→blood→alveoli)
You’ve got this! 💪 Remember: gradients are your friends, and thin membranes make happy lungs! 😊
