✅ EMBRIOLOGÍA del APARATO RESPIRATORIO 😙💨

Hi! Welcome to my channel Today we are going to talk about the Embryology of the Respiratory System The topics of this video are the formation of the lung buds, the embryological origin of the larynx, trachea, bronchi, and lungs and in the end we will divide lung maturation into four stages Let's start by talking about the formation of the lung buds When the embryo is around 4 weeks old, evagination appears from the ventral wall of the anterior intestine which is known as a respiratory diverticulum or pulmonary bud At the beginning this bud has communication with the previous intestine, however, as it expands in the caudal direction the anterior intestine is separated by means of the Tracheoesophageal Crests Subsequently, these ridges fuse and form the Tracheoesophageal Septum thus dividing the anterior intestine in a dorsal portion for the Esophagus and in a ventral portion for the Trachea The respiratory primordium maintains its communication with the pharynx through the laryngeal opening The epithelium that lines the inside of the larynx, trachea, bronchi, and lungs is entirely of endodermal origin the components of cartilage, muscle and connective tissue of the trachea and lungs derive from the visceral or splanchnic mesoderm that surrounds the anterior intestine Regarding the larynx, its internal lining originates from the endoderm instead, that of the cartilage and muscles derive from the mesenchyme of the fourth and sixth pharyngeal arches the rapid proliferation of its mesenchyme causes the laryngeal orifice to change its appearance and go from being a sagittal cleft to being a T-shaped opening As the mesenchyme of the two arches transforms into the thyroid, cricoid, and arytenoid cartilages, the laryngeal epithelium also proliferates rapidly causing temporary occlusion of its lumen, which then by vacuolization and recanalization give rise to the Laryngeal Ventricles. These gaps are limited by tissue folds that become the true and false vocal cords Because the musculature of the larynx derives from the mesenchyme of the fourth and sixth pharyngeal arches, all the muscles of the larynx are supplied by branches of the vagus nerve.

Trachea, Bronchi and Lungs The pulmonary bud when separating from the previous intestine forms the Trachea and the primary bronchial buds At the beginning of the fifth week, each of these buds widens to constitute the right and left primary bronchi The right generates three secondary bronchi, and the left two, subsequently forming three lobes in the lung on the right side and two on the left With growth in the caudal and lateral direction, the lungs expand into the body cavity The narrow spaces available to the lungs are called the Pericardioperitoneal Canals. These are located on each side of the anterior intestine and gradually from the anterior intestine and in a gradual are occupied by the growing lungs The mesoderm that covers the outside of the lung becomes the visceral pleura and the somatic mesoderm layer, which covers the inside of the body wall, becomes the parietal pleura The remaining space between the parietal and visceral pleura corresponds to the pleural cavity As development continues, the secondary bronchi divide over and over again in a dichotomous pattern. to give rise to 10 tertiary or segmental bronchi in the right lung and 8 in the left which creates the bronchopulmonary segments of the adult lung At the end of the sixth month there are about 17 generations of subdivisions, Despite this, in order for the bronchial tree to acquire its final configuration six additional divisions must occur during postnatal life And the last topic that we are going to talk about is on Maturation of the Lungs and we can divide it into 4 periods 1- Pseudo glandular period 2- Canalicular period 3- Period of terminal bags 4- Alveolar period The pseudoglandular period occurs between weeks 5 and 16 Developing lung resembles an exocrine gland The numerous endodermal tubules are lined by a simple columnar epithelium and they are surrounded by a mesoderm containing a modest capillary network Each endodermal tubule branches into 15-25 terminal bronchioles (TB) During this period, breathing is not possible and premature babies cannot survive The canalicular period occurs between 16 and 26 weeks Terminal bronchioles branch into three or more respiratory bronchioles (BR) The respiratory bronchioles subsequently branch into three to six alveolar ducts (CA) Terminal bronchioles, respiratory bronchioles, and alveolar ducts are now lined with a simple cuboidal epithelium and they are surrounded by a mesoderm containing a prominent capillary network Premature babies born before week 20 rarely survive The terminal sac period occurs between 26 weeks at birth During this period, the terminal sacs (TS) emerge from the alveolar ducts and then they dilate and expand into the surrounding mesoderm The terminal sacs are separated from each other by primary partitions The simple cuboidal epithelium within the terminal sacs differ in Type I Pneumocytes (which are part of the capillary alveolus barrier) and Type II Pneumocytes (which are the ones that produce surfactant) The terminal sacs are surrounded by a mesoderm that contains a network of capillaries.

they proliferate quickly The capillaries make intimate contact with the terminal sacs and thus establish a hematogenous barrier with type I pneumocytes Premature babies born between week 25 and week 28 can survive with intensive care The alveolar period ranges from 8 months of gestation to 8 years according to some authors.