Effects of Aging on the Respiratory System

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Chapter: Anatomy and Physiology for Health Professionals: Respiratory System

Human embryos develop in a head-to-tail (cephalo-caudal) direction. Therefore, upper respiratory structures develop first.


Effects of Aging on the Respiratory System

Human embryos develop in a head-to-tail (cephalo-caudal) direction. Therefore, upper respiratory structures develop first. By week four of development, two thickened ectodermal plates called olfactory placodes are present on the head’s anterior aspect. These quickly form the olfactory pits, from which the nasal cavity develops. The pits extend posteriorly, connecting with the early pharynx, which simultaneously forms, from the endodermal germ layer. The lower ­respiratory organ ­epithelia develop as outpockets of the foregut­ endoderm, eventually becoming the pharyngeal mucosa. This protruding laryngotracheal bud is pres-ent by week five of development. Its proximal section forms the lining of the tracheal. Its distal end splits to form the bronchial mucosae and eventually the alveoli. These linings are covered by mesoderm, which forms the respiratory passage walls and lung stroma.

By week 28, the respiratory system is developed enough to allow a premature baby to breathe by itself. Infants born before week 28 usually have IRDS due to inadequate surfactant production. During fetal development, the lungs are filled with fluid and ­respiratory exchange is handled by the placenta. The lungs are mostly bypassed by vascular shunting of circulating blood. At birth, the respiratory passages become filled with air. The partial pressure of CO2 rises in the blood, exciting the respiratory centers. This causes the first breath to be taken by the baby. The alveoli inflate and begin gas exchange. However,­ it will take almost two weeks until the lungs are fully inflated.

Aging causes the lungs to lose elasticity, lower-ing their VC. The ribs play a role in affecting breath-ing because they may become arthritic and the costal cartilages may become less flexible. Respira-tory volume is therefore impaired, resulting in the inability to exercise as long or as hard compared with earlier in life. Emphysema risk is much higher in smokers than in nonsmokers, but some evidence of the disease is present in most people over age 50 regardless of their history of smoking. Although aging affects the respiratory system of every adult, smokers ­experience greatly increased problems as aging continues.

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