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Development of the respiratory system
Last reviewed: 23.04.2024
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The development of the external nose and nasal cavity is associated with the formation of the visceral skeleton of the head, oral cavity and olfactory organs. The development of the larynx, trachea and bronchi occurs in connection with the transformation of the primary gut of the embryo. On the ventral wall of the primary intestine, in the region of the pharyngeal and trunk intestine, a saccular protrusion is formed. It grows in the ventral-caudal direction in the form of a duct (a laryngeal-tracheal projection). The upper, head end of the tube communicates with the future pharynx. The lower end of the laryngeal-tracheal protrusion at the 4th week of embryogenesis is divided into right and left protrusions - the future bronchi of the right and left lungs. The proximal part of the laryngeal-tracheal prominence gives rise to the development of the epithelial cover and glands of the mucous membrane of the larynx. The distal part of this unpaired protrusion is transformed into the epithelium and the gland of the trachea. Right and left protrusions give rise to the epithelial cover and glands of the bronchi and lungs. With the development of the larynx, close connections are established between the derivatives of the endoderm (the primary gut) and the mesenchyme. The mesenchyme surrounding the endoderm is gradually transformed into connective tissues, cartilage, musculature, blood and lymphatic vessels. Bookmarks of future cartilage and laryngeal muscles appear on the 4th week of embryogenesis. The source of the development of cartilage of the larynx is the second and third gill arches. From the general muscular sphincter, located outside of the pharynx, laryngeal muscles are formed. The rudiments of the lobar bronchi appear at the 5th week of embryogenesis. They are subdivided into secondary bud-like protrusions - future segmental bronchi, which also divide, forming a bronchial tree.
From the 4th to the 6th month of embryogenesis, bronchioles are laid, from the 6th to the 9th month - alveolar courses and alveolar sacs. By the birth of a child, both the bronchial and the alveolar tree have about 18 orders of branching. After birth, the bronchial tree and alveolar tree continue to grow (up to 23 orders), their structure is complicated, differentiated.
The source of development of the visceral pleura is the splanchnopleura, the parietal pleura develops from the somatopleura. Between the visceral and parietal pleura, the pleural cavity is formed.
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