Respiratory System Works

How the Respiratory System Works
The respiratory system has the following basic functions:
• Movement of air in and out of the lungs
• Exchange of oxygen and carbon dioxide
• Helping maintain acid-base balance
Ventilation moves air in (inspiration) and out (expiration) of the lungs. Dur-
ing inspiration, air flows in through the nose and passes into the nasopharynx.
Air is then drawn through the pharynx, larynx, trachea, and bronchi. The bronchi
branches (bifurcates) right and left into smaller tubes called bronchioles that ter-
minate in alveoli. The airways are lined with mucous membranes to add moisture
to the inhaled air. There is a thin layer of mucous in the airways that helps to trap
foreign particles, such as dust, pollen, or bacteria. Cilia—small, hair-like projec-
tions—help to move the mucous with the foreign material upward so it can be
coughed out.
Alveoli are air-filled sacs containing membranes coated with surfactant. The
surfactant helps the alveoli to expand evenly on inspiration and prevents collapse
on exhalation. Carbon dioxide and oxygen are exchanged; a higher concentration
of gas moves to the lower area of concentration. A higher concentration of carbon
dioxide in the hemoglobin moves across the membrane into the alveoli and is
expired by the lung. Higher concentration of oxygen in the alveoli crosses the
membrane and attaches to the hemoglobin which is then distributed by the circu-
latory system throughout the body.
Lungs are contained within a pleural sac in the thoracic cavity and operate on
negative pressure. The visceral pleura is close to the lungs and the parietal pleura
is close to the chest wall. There is a pleural space between these two layers that
contains a small amount of fluid to prevent friction with chest movement on inspi-
ration and expiration.