2.3 Gaseous Exchange

Scientific word for breathing

Ventilation

Gas exchange

Oxygen is inhaled, enters the alveoli and diffuses into the blood.
Carbon dioxide diffuses out of the blood and into the alveoli, to be exhaled.

The site of gas exchange

Alveoli

The process gas exchange relies on

Diffusion

Diffusion

Movement of gases or liquids from an area of high concentration to an area of low concentration.

The two concentration areas

Alveoli and the blood

The concentration areas of oxygen

• High Concentration Area: The alveoli, because we are constantly breathing it in, which enters the alveoli.

• Low Concentration Area: The blood, because the arriving blood has returned from the body and is depleted of oxygen.

The concentration areas of carbon dioxide

• High Concentration Area: The blood, because it is carrying waste (CO₂) collected from the body's tissues.

• Low Concentration Area: The alveoli, because inhaled air contains very little carbon dioxide.

Does diffusion happen with energy

No

Will diffusion occur if there is no diffusion gradient

No

Diffussion gradient

A difference in concentration between two areas

The key factors diffusion gradients are affected by

• Concentration difference

• Distance

• Surface area

• Ventilation and blood flow

How concentration difference affects diffusion gradients

The bigger the difference between the two areas of concentration, the faster the diffusion happens

How distance affects diffusion gradients

A shorter distance increases the rate of diffusion

An example of a shorter distance that increases the rate of diffusion

Thin walls of alveoli

How surface area affects diffusion gradients

A larger surface area allows more particles to diffuse at the same time

How ventilation and blood flow affects diffusion gradients

Constant movement of air and blood maintains the gradient by keeping the concentrations of the two areas different, making diffusion continue efficiently.

How ventilation and blood flow keeps the concentrations of the two areas different.

• Ventilation keeps oxygen high in alveoli

• Blood flow removes oxygen and brings carbon dioxide