13.3 : 呼吸和气体交换

During respiration, gaseous exchange takes place through a process called diffusion.

Gas molecules move from an area of higher partial pressure to a lower partial pressure.

Partial pressure is the independent force exerted by each distinct gas in a mixture of gasses.

The greater the partial pressure, the more gas dissolves into a liquid.

External respiration is associated with both the internal and external environment.

During external respiration, oxygen diffuses from the lungs' alveoli into blood in the pulmonary capillaries.

Conversely, carbon dioxide diffuses across the respiratory membranes from the blood into the alveolar air.

The partial pressure of oxygen is high in the alveoli and low in the pulmonary capillaries, whereas carbon dioxide is high in the pulmonary capillaries and low in the alveoli.

Internal respiration is associated with only the internal environment.

During internal respiration, oxygen moves out of the blood into the tissues, and carbon dioxide diffuses out of the tissue into the blood.

As a result, the partial pressure of oxygen is low, and carbon dioxide is high in the tissues.