The respiratory system is structurally and functionally adapt ed for the efficient transfer of gases between the ambient air and the bloodstream as well as between the bloodstream and the tissues. The major functional components of the res piratory system are: the airways, alveoli, and blood vessels of the lungs; the tissues of the chest wall and diaphragm; the systemic blood vessels; red blood cells and plasma; and respi ratory control neurons in the brainstem and their sensory and motor connections. LUNG FUNCTION: provision of O 2 for tissue metabolism occurs via four mechanisms. Ventilation – the transport of air from the environment to the gas exchange surface in the alveoli. O 2 diffusion from the alveolar air space across the alveolar—capillary membranes to the blood.

Transport of O 2 by the blood to the tissues: O 2 diffusion from the blood to the tissues.

Removal of CO 2 produced by tissue metabolism occurs via four mechanisms. CO 2 diffusion from the tissues to the blood.

Transport by the blood to the pulmonary capillary—alveolar membrane.

CO 2 diffusion across the capillary—alveolar membrane to the air spaces of the alveoli. Ventilation – the transport of alveolar gas to the air. Functional components: Conducting airways (conducting zone; anatomical dead space).

These airways are concerned only with the transport of gas, not with gas exchange with the blood.

They are thick—walled, branching, cylindrical structures with ciliated epithelial cells, goblet cells, smooth muscle cells. Clara cells, mucous glands, and (sometimes) cartilage.

Alveoli and alveolar septa (respiratory zone; lung parenchyma).

These are the sites of gas exchange.

Cell types include: Type I and II epithelial cells, alveolar macrophages.

The blood—gas barrier (pulmonary capillary—alveolar membrane) is ideal for gas exchange because it is very thin (< 0,5 mm) and has a very large surface area (50 —100 m 2). It consists of alveolar epithelium, basement membrane in—terstitium, and capillary endothelium.

New words

respiratory – дыхательный

air – воздух

bloodstream – кровоток

airways – воздушные пути

alveoli – альвеолы

blood vessels – кровеносные сосуды

lungs – легкие

chest – грудь

diaphragm – диафрагма

the systemic blood vessels – системные кровеносные сосуды

red blood cells – красные кровяные клетки

plasma – плазма

respi ratory control neurons – дыхательные нейроны контроля

brainstem – ствол мозга

sensory – сенсорный

motor connections – моторные связи

ventilation – вентиляция

transport – транспортировка

environment exchange – окружающая среда

surface – поверхность