Organ Systems

Organ Systems

Organ systems must continue to grow and mature after de­livery. Many are at a minimal level of functioning at birth. This often places the infant at risk for health problems.

Respiratory System. Onset of respiration must begin at birth for survival. By the late fetal period, the lungs are capable of respiration because the alveolar capillary membrane is sufficiently thin to allow for gas exchange.

Characteristically, mature alveoli do not form until after birth. Before birth, the primordial alveoli appear as small ridges on the walls of the respiratory bronchioles and ter­minal saccules. After birth, the primordial alveoli enlarge as the lungs expand, but the most important increase in the size of the lungs results from an increase in the num­ber of alveoli and growth of the airways. Infants are obli­gatory nose breathers until 3 to 4 months of age; any upper airway obstruction may cause respiratory distress.⁷ The tra­chea is small and close to the bronchi, and the bronchi's branching structures enable infectious agents to be easily transmitted throughout the lungs. The softness of the sup­porting cartilage in the trachea, along with its small di­ameter, places the infant at risk for airway obstruction. The auditory (eustachian) tube is short and straight and closely communicates with the ear, putting the infant at risk for middle ear infections (see Chapter 55).