Healthy lung tissue provides the exchange surface for blood and the gases in alveoli. The alveoli are the final structures enabling the transfer of gases between lung tissue and blood. When lung tissue is damaged from chronic obstructive pulmonary disease---a collection of lung diseases including emphysema, chronic bronchitis and asthma---lungs lose the ability to extract oxygen and carbon dioxide.
Lobes
Lungs are divided into two halves, the right lung and the left lung. Each lung is further divided into lobes. The left lung has two lobes, the superior and the inferior lobes. The right lung has three lobes, the superior, inferior and middle lobes. An average-sized adult's lungs weigh about 2.2 pounds. Lung tissue is about 10 percent solid tissue with the remainder composed of air and blood.
Bronchi
The air breathed in flows from the trachea into the bronchi, two large tubes serving as the initial airway into each lung. Inflammation of the lining of the bronchi is called bronchitis. Untreated, acute bronchitis can lead to chronic bronchitis in which the swollen membranes increase mucous production, eventually obstructing the airway. Chronic bronchitis is a typical symptom of smoking.
Bronchioles
Each bronchi subdivides into many bronchioles. Asthma is a condition in which the lining of the bronchioles swell and secrete thick mucosa into the bronchioles. Asthma also results in the obstruction of bronchioles not only from mucous, but also from muscle spasms.
Alveoli
The lungs contain over 600 million alveoli. Alveoli are tiny air-sacs with elastic, thin walls where gas exchange between the lungs and blood take place. Healthy alveoli are about 0.3mm in diameter, the sac walls completely available for gas exchange. With emphysema, alveoli are abnormally and permanently enlarged. The sac walls are inflamed, trapping air in the sacs and preventing normal gas exchange between the lungs and the blood.
Blood Supply
The pulmonary artery brings deoxygenated blood from the right side of the heart to the lungs. This artery further divides into pulmonary arterioles supplying deoxygenated blood to alveoli. Alveoli transfer oxygen from air inhaled into the incoming blood. Alveoli also remove carbon dioxide from the incoming blood. Once the gases have been exchanged, oxygen-rich blood flows from alveoli capillaries into pulmonary venules then into the pulmonary vein. From the pulmonary vein, oxygen rich blood flows into the left side of the heart to be pumped into the body.
Control of Breathing
Breathing is controlled by a complex communication system between the brain, nerves, muscles, body temperature, blood, arteries and receptors in the lungs. Signals from the medulla in the brain stimulate the nerves in the diaphragm and the muscles between ribs to inflate the lungs, controlling the volume of air inhaled and exhaled. Sensory receptors in the lungs also receive signals to initiate a cough reflex when the airways are irritated from fumes, debris or cigarette smoke.
References
- American College of Sports Medicine: Exercise for Persons with Chronic Obstructive Pulmonary Disease
- "Exercise Physiology, Energy, Nutrition and Human Performance"; William D. McArdle, Frank I. Katch and Victor L. Katch; 2007
