Gas Exchange in Humans

A very thick cellular wall to prevent damage

A thin, one-cell thick exchange surface

A dry surface to prevent bacteria from growing

A small total surface area to concentrate gases

Goblet cells

Ciliated epithelial cells

Squamous epithelial cells

Red blood cells

To produce mucus for trapping pathogens

To facilitate the diffusion of oxygen into the blood

To prevent the airway from collapsing during pressure changes

To contract and push air into the lungs during inspiration

Diaphragm relaxes and moves up; external intercostals relax

Diaphragm contracts and moves down; external intercostals contract

Diaphragm contracts and moves down; external intercostals relax

Diaphragm relaxes and moves up; external intercostals contract

A thin layer of moisture on the surface

A wall that is only one cell thick

A dense network of blood capillaries

A large total surface area

Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli

Bronchi $\rightarrow$ Trachea $\rightarrow$ Alveoli $\rightarrow$ Bronchioles

Trachea $\rightarrow$ Alveoli $\rightarrow$ Bronchioles $\rightarrow$ Bronchi

Bronchioles $\rightarrow$ Bronchi $\rightarrow$ Trachea $\rightarrow$ Alveoli