In this essay I am going to talk about the lungs and the stages of their embryonic development. I chose the lungs because they are one of the most important organs for survival -they supply oxygen to cells and release carbon dioxide to the atmosphere. This essay will mostly focus on the different stages of the lung development- the embryonic, the pseudoglandular, the canalicular, the terminal sac, and the postnatal stage.
The successful maturation of the lungs requires the completion of both biochemical and physical processes. The physical one is required for the structure and the biochemical one is required for maintaining such large surface area (surfactant). These two requirements are greatly related and the incomplete development of any of these processes will lead to insufficiency and compromise of the newborn. In the picture below you can see the all the stages summarized:
We know that the human lung starts as a primitive lung bud in the early fetal life and then undergoes many different morphological processes that also continue in the postnatal life. Genetic, hormonal, physical, and environmental factors, as tightly regulated events, together with lung liquid, and fetal breathing movements form a complex that contributes to each stage. The 5 stages of structural lung development occur at progressive times during gestation. The timing of the phases is not exact set since we have disparity between fetuses.
First is the Embryonic Stage (Weeks 4 to 7). This embryonic stage includes the initial formation of the respiratory diverticulum up to the formation of the all the key bronchopulmonary segments. The lung develops as an outgrowth of the ventral wall of the primitive foregut the laryngotracheal groove. Foregut’s endodermic epithelial cells invade the mesenchyme forming the trachea which then branches to the left and right bronchi (main) and afterward into the lobar and segmental ones. Lobar and segmental ones appear about the fifth week. The foregut is divided between the trachea and the esophagus by the esophagealtracheal septum. Here it Is important to mention that the formation of the trachea and the lung buds are independent events (according to experiments FGD 10 null mice develop a trachea but no buds of lungs. The veins together with the pulmonary arteries grow as a lone non-vascular bud from the sixth aortic arch and go one with grow by vasculogenesis in the region of the airways buds. Close to the end of the embryonic phase mesenchymal cells begin to hollow the early formed trachea and starts differentiate into cartilage precursor. However the cartilage formation keeps until the end of the canalicular stage where is also completed around even the smallest bronchi.
The same time lung buds expand in a caudolateral direction into a fluid filled body cavity between the intestines and the body wall of some higher metazoans (lined with mesodermal epithelium). Each pericardioperitoneal canal will be progressively...