Gas exchange in humans

How is the lungs structured?

1. Trachea

2. Trachea splits into two bronchi 

3. Bronchus branches off into smaller tubes called bronchioles 

4. They end in small sacs called alveoli

How do we breath?

1. External intercostal muscles contract, pushes rib cage upwards and outwards

2. Diaphragm contracts and flattens

3. Increases volume of the thoracic cavity

4. As volume increases, pressure decreases

5. Air flows down a pressure gradient to stabilise conditions

Does inspiration require energy?

Yes

How do we breathe out?

1. External intercostal muscles relax, brings rib cage downwards and inwards

2. Diaphragm relaxes and curves

3. Volume of thoracic cavity decreases 

4. Pressure increases

5. Air is forced out down the pressure gradient and out of the lungs

Does it require energy?

No but when it is forced expiration, it requires energy 

How does forced expiration occur?

1. External intercostal muscles relax, and internal intercostal muscles contract

2. Ribcage is further pulled down

3. They are said to be antagonistic 

How does oxygen diffuse into the blood?

It crosses the alveolar epithelium and the capillary endothelium

How is the alveoli adapted?

1. A thin exchange surface area- it's one cell thick which means there is a short diffusion path

2. A large surface area-  means there is large surface area for gas exchange 

3. Steep concentration gradient- gradient between oxygen and carbon dioxide, increases rate of diffusion. It is maintained by the flow of blood and ventilation.