Respiratory System

The human respiratory system, working in conjunction with the circulatory system, supplies oxygen and removes carbon dioxide. The respiratory system conducts air to the respiratory surfaces of lung units. There, the blood in the lung capillaries readily absorbs oxygen, and gives off carbon dioxide gathered from the body cells. The circulatory system transports oxygen-laden blood to the body cells and picks up carbon dioxide. The term respiration describes the exchange of gases across cell membranes both in the lungs (external respiration) and in the body tissues (internal respiration). Pulmonary ventilation, or breathing, exchanges volumes of air with the external environment.