Respiratory system

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 bloodvessels 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 02 for tissue metabolism occurs via four mechanisms. Ventilation – the transport of air from the environment to the gas exchange surface in the alveoli. 02 diffusion from the alveolar air space across the alveolar-capillary membranes to the blood.

Transport of 02 by the blood to the tissues: 02 diffusion from the blood to the tissues.

Removal of C02 produced by tissue metabolism occurs via four mechanisms. C02 diffusion from the tissues to the blood.

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

C02 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 m²). It consists of alveolar epithelium, basement membrane interstitium, and capillary endothelium.