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The lungs and tracheobronchial structures undergo few but significant changes over the course of the lifespan. From moments after birth to near the end of life the lungs function continuously and consistently, bringing air into the body to deliver oxygen to the blood and carrying air out of the body to eliminate carbon dioxide and other gaseous metabolic wastes from the body. The entire respiratory process breathing and oxygenation-takes place under the regulation of the brainstem, without conscious awareness or control.
Pulmonary changes of aging
Before birth, though the lungs go through the movements of breathing they do not oxygenate the fetus’s blood. Rather, the fetus draws its oxygen from the mother’s blood through the placenta where oxygen molecules migrate across the capillary membranes from the mother’s blood supply to the fetus’s blood supply. Differences in the cardiovascular system of the fetus further support this mechanism of oxygenation.
In the unborn child the heart shunts blood from the right atrium to the left atrium through an opening in the atrial septum (wall of muscle that separates the right atrium and the left atrium) called the foramen ovale. Blood also passes from the pulmonary arteries to the aorta through an opening called the ductus arteriosus, bypassing the lungs.
The newborn’s first breath fills the lungs with air, setting in motion a sequence of events that results in the closure of these openings in the heart and the rerouting of blood flow from the right side of the heart to the lungs and from the lungs to the left side of the heart. As the lungs fully expand after a few breaths, they take over complete responsibility for oxygenating the body.
The lung tissue produces a chemical called surfactant, a fluid that coats the inner layer of the lung surfaces to maintain appropriate surface tension to keep the alveoli from collapsing with each exhaled breath, much in the same fashion moisture inside a balloon keeps the walls of the balloon from sticking together when the balloon deflates. These changes may lag in an infant born prematurely, giving rise to breathing and oxygenation difficulties until the lungs can more fully develop.
The lungs continue to function in the same responsibility for the remainder of life, with few changes beyond growing as the body grows. Lung capacity (the ability of the lungs to hold air) and diffusing capacity (the ability of the lungs to transfer oxygen to the blood) peak in the early 20s, after which both slowly but steadily decline until by about age 75 they are roughly half what they were at age 25.
Beginning at age 35, lung capacity diminishes about 5 percent every 10 years. In the 50s the muscles of breathing begin to stiffen and lose resilience, though in counterbalance changes within the lungs and airways occur to reduce the resistance air encounters during inhalation. Regular aerobic conditioning throughout life can offset many of the functional implications of these changes, allowing strong pulmonary performance well into the 70s or beyond.
The health conditions affecting the lungs before age 30 tend to be acute (of sudden onset and contained duration), often infection such as viral or bacterial bronchitis, pleuritis, and pneumonia. Chronic (ongoing) health conditions affecting the lungs become increasingly common with advancing age, in part because the natural changes in the lungs may precipitate them and in part because other health situations or environmental factors begin to have cumulative consequences.
Cardiovascular disease (cvd), which becomes more common in middle age and beyond among both men and women, can have as much effect on the structures and functioning of the pulmonary system as do conditions of the lungs. Heart failure, in which the heart cannot pump enough blood to meet the body’s oxygen needs, allows fluid to back up into the lungs. The resulting circumstances, pulmonary congestion and pulmonary edema, flood the alveoli and prevent them from conducting the oxygen-carbon dioxide exchange.
Chronic hypertension (high blood pressure) diminishes the elasticity of all arteries in the body, including the pulmonary arteries. The resulting stiffness and inflexibility of the arteries can contribute to or exacerbate cardiovascular conditions such as heart failure. Other forms of cardiovascular disease may result in pulmonary hypertension, increased pressure within the pulmonary arteries that damages the smaller arteries within the lungs.
Cigarette smoking and risks
External factors also influence pulmonary health throughout life. Cigarette smoking is the single-most destructive exposure the lungs typically face, causing an extremely high risk for progressive disorders such as chronic obstructive pulmonary disease (copd) and especially for lung cancer. Cigarette smoking accounts for 85 percent of lung cancer in the United States. Over time breathing exposes the respiratory tract to numerous insults from substances such as environmental pollution, viruses, bacteria, pollens, dust, and other materials.
These exposures may injure or damage the lungs, resulting in conditions such as asthma, pneumonitis, bronchitis, and pneumonia, as well as infections such as tuberculosis and influenza. Such pulmonary conditions can contribute to deteriorating lung functions, particularly in people who have not maintained adequate aerobic fitness.
Maintaining a steady level of aerobic fitness through regular physical activity keeps the pulmonary system as healthy as possible for as long as possible, helping offset the changes of advancing age. Aerobic fitness enables the lungs to efficiently extract oxygen from the air and conduct it into the bloodstream. As well, the lungs fill more fully with air on each inhalation, keeping the alveoli open and functioning. This helps keep fluid from accumulating within the alveoli.
See also AGING, CARDIOVASCULAR CHANGES THAT OCCUR WITH; AGING, CHANGES IN THE BLOOD AND LYMPH THAT OCCUR WITH; ASPIRATION; CONGENITAL HEART DISEASE; PLEURISY; SMOKING AND HEALTH.
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