Okay so we know that air enters the body through the nose and mouth. As it enters, it passes down the trachea and divides through the bronchioles eventually ending at these small sacks called Alveoli.
Its here where the majority of gasses exchange occurs.
Observe the diagram to the right. The alveoli look like bunches of grapes coming off a vine.
The capillaries wrap around the alveoli, allowing for simple gas diffusion.
The animation to the left shows how carbon dioxide diffuses off the red blood cells and oxygen in.
Scroll over the image to see the animation.
Although the atmosphere is only 21% oxygen, 78% nitrogen and 1% other gases, our red blood cells act as sponges only for oxygen. This is due to the haemoglobin protein found in red blood cells.
The air we inhale is around 21% oxygen, 78% nitrogen and 0.04 % carbon dioxide.
While the air we exhale is 16% oxygen, 4% carbon dioxide and 78% nitrogen.
Specific cells throughout the respiratory system secrete mucus which trap foreign pathogens or dust. However if a pathogen gets through and reaches the alveoli it could cause serious damage.
This is why, within the alveoli are white blood cells called alveolar macrophages.
These Macrophages patrol very close to the surface of the alveolus and enter its thin walls when an invader is detected. The macrophage quickly engulfs and digests the intruder.
The surface of these alveoli have specific properties to allow for efficient diffusion of gasses across the membrane.
Thin - Gases have a short distance
Large SA - More molecules diffusing in less time
Moist - keeps the cell alive
Ventilated - concentration gradients for O2 and CO2 are kept up.
Close to the blood supply - gasses can be carried to organs that need them.
Try some questions bellow
1. Draw the diagram in your book and label
Capillary
Alveolus
Oxygen in
Oxygenated blood
Deoxygenated blood
Carbon dioxide out
Deoxygenated blood
Short diffusion distance
2. The concentration of oxygen in the atmosphere is?
3. After participating in strenuous exercises the air expelled contains mostly?
4. Define the concentration gradient and explain how we ensure it within our lungs (2 marks)
5. What are four adaptations of alveoli to ensure efficient gas exchange (4 marks)
6. Explain the purpose of Red blood cells (RBC) and explain how they assist in the respiratory system (2 marks)
