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Prenatal lung development is made up of stages that continue on after the baby is born. The three stages that take place during fetal development are pseudoglandular, canaliclular and saccular. The lungs don't have to be fully developed at birth in order for a baby to be able to breathe; however, these three stages must take place prior to delivery. During these stages, cells differentiate into individual structures within the lungs, and the bronchial airways are formed.
The pseudoglandular stage takes place during the first three to four months of gestation. During this time, the conducting airways are being formed inside what looks like a glandlike structure. Tall columnar epithelium cells grow inside these airways and form a lining. Tubular branching continues to develop throughout this stage. As early as two months into the pseudoglandular stage, all of the bronchi segments are present.
The canalicular stage of fetal lung development starts at the 16th week of gestation and lasts until the 24th week. At this point, individual chambers inside the left and right ventricles have been formed by the bronchial segments that resulted from the prior stage. Layers of epithelium linings grow throughout these chambers. The capillaries that will later on allow for future gas exchange form, while the surrounding lung muscles begin to take shape. Respiratory structures called bronchioles begin to grow inside the bronchi segments. These structures contain sacs that will later become the lungs' alveoli.
The saccular stage starts at the 24th week and lasts until the foetus comes to term. Airway development begins to spread out and form airspaces, or saccules, within the chambers. The airspace expands as saccules continue to form. The bronchiole formations that appeared in the previous stage begin to grown into alveoli and develop into a cluster of airways throughout each chamber. A fourth developmental stage, called the alveolar period, occurs after the foetus is born and will continue into the fourth year of childhood.
Lung development during the prenatal stages is an intricate process that is highly susceptible to complications in the presence of outside toxic agents. Environmental tobacco smoke (ETS) is one such agent that specifically impedes the development of the epithelial cell layers during fetal lung growth. The overall effect stunts cell layer maturity and reduces cell layer growth. Childhood asthma, chronic coughing, wheezing and chronic mucous production are possible conditions that arise as a result of ETS.
The use of steroid medications can also work to hamper lung development in the foetus. Steroids also target epithelial cell layer growth; however, the effect is the opposite of that from ETS. Growth rate accelerates cell maturity, causing a reduced number of cells and thinner layer formations to form. One other factor that greatly affects lung development in the foetus is the nutritional intake provided by the mother.
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