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Development of the respiratory system
Last reviewed: 07.07.2025
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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 gut, in the area of the border of the pharyngeal and trunk intestines, a saccular protrusion is formed. It grows in the ventral-caudal direction in the form of a tube (laryngeal-tracheal protrusion). The upper, head end of the tube communicates with the future pharynx. The lower end of the laryngeal-tracheal protrusion on the 4th week of embryogenesis is divided into the right and left protrusions - the future bronchi of the right and left lungs. The proximal part of the laryngeal-tracheal protrusion 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 glands of the trachea. The right and left protrusions give rise to the epithelial covering and glands of the bronchi and lungs. During the development of the larynx, close connections are established between the derivatives of the endoderm (primary intestine) and the mesenchyme. The mesenchyme surrounding the endoderm is gradually transformed into connective tissue formations, cartilage, muscles, blood and lymphatic vessels. The rudiments of the future cartilages and muscles of the larynx appear in the 4th week of embryogenesis. The source of development of the laryngeal cartilages are the second and third branchial arches. The muscles of the larynx are formed from the common muscular sphincter, located outside the pharyngeal intestine. The rudiments of the lobar bronchi appear in the 5th week of embryogenesis. They are subdivided into secondary kidney-shaped protrusions - future segmental bronchi, which also divide, forming the bronchial tree.
From the 4th to the 6th month of embryogenesis, bronchioles are laid down, from the 6th to the 9th month - alveolar passages and alveolar sacs. By the time a child is born, both the bronchial and 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 becomes more complex and differentiated.
The source of development of the visceral pleura is the splanchnopleura, the parietal pleura develops from the somatopleura. The pleural cavity is formed between the visceral and parietal pleura.
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