What are the characteristics of alveoli?

Options

A. Very thin, irregular walled and highly
vascularised
B. Thick and smooth membrane
C. Network of blood capillaries and thick-walled
D. Thick, regular walled and lack of blood vessels

Answer

### Step-by-Step Solution:

1. **Definition of Alveoli**: Alveoli are tiny air sacs located in the lungs where the exchange of gases (oxygen and carbon dioxide) occurs.

2. **Structure**: Alveoli are grouped together in clusters known as alveolar sacs. This arrangement increases the surface area for gas exchange.

3. **Wall Composition**: The walls of the alveoli are composed of a single layer of simple squamous epithelium. This thin layer facilitates the rapid diffusion of gases.

4. **Association with Capillaries**: Alveoli are closely associated with capillaries, which also have a thin wall made of a single layer of endothelial cells. This proximity allows for efficient gas exchange.

5. **Thickness of Membrane**: The combined thickness of the alveolar wall and the capillary wall (the diffusion membrane) is approximately 0.2 mm, making it very thin. This thinness is crucial for effective gas diffusion.

6. **Vascularization**: Alveoli are highly vascularized, meaning they have a rich supply of blood capillaries. This enhances the exchange of gases between the air in the alveoli and the blood.

7. **Innervation**: The alveoli are innervated by capillaries, which means they are supplied with nerves that help regulate the process of breathing and gas exchange.

### Summary of Characteristics of Alveoli:
- Tiny air sacs for gas exchange.
- Grouped in clusters (alveolar sacs).
- Composed of a single layer of simple squamous epithelium (thin walls).
- Closely associated with capillaries (also thin-walled).
- Very thin diffusion membrane (approximately 0.2 mm thick).
- Highly vascularized for efficient gas exchange.
- Innervated by capillaries.