The respiratory system originates as a its connection with the pharynx through foregut diverticulum, which is known as the slit-like laryngeal orifice. At its distal tracheobronchial diverticulum (also end the laryngotracheal tube bifur-called respiratory diverticulum or lung cates to form two bronchial buds, bud). Consequently, the lining epithelium of the larynx, trachea, bronchi and Development Of Larynx lungs is endodermal in origin. However, As mentioned above, the epithe-the connective tissue, cartilage and lial lining of the larynx develops from smooth muscle of the trachea and the endoderm of the most proximal part lungs are derived from the splanchnic of the laryngotracheal tube. However, mesenchyme that surrounds the fore- the cartilages and muscles of the lar-gut. ynx are derived from the mesenchyme
The respiratory diverticulum be- of the 4th and 6th pharyngeal arches, comes separated from the esophageal The pharyngeal arch mesen-part of the foregut by the development chyme at the proximal end of the laryn-of a septum called tracheoesophageal gotracheal tube proliferates rapidly to septum. After separation from the form a pair of arytenoid swellings which esophagus the respiratory diverticulum flank the laryngeal orifice. These swell-is called laryngotracheal tube. This ings grow toward the tongue and con-tube is the primordium of larynx, tra- vert the laryngeal orifice from a sagittal chea, bronchi and lungs. At its proximal slit to T-shaped laryngeal inlet. The lar-end, the laryngotracheal tube maintains ynx assumes its characteristic shape
when the arytenoid; thyroid and cricoid cartilages develop from the mesen-chyme of the 4th and 6th pharyngeal arches. The epiglottis develops from the caudal part of the hypobranchial eminence. As described in the devel-. opment of tohgu6, this swelling is produced by the proliferation of mesen-chyme in the ventral ends of the 3rd and 4th pairs of pharyngeal arches (the cranial part of the hypobranchial eminence forms the pharyngeal part of the tongue).
The laryngeal muscles develop from the myoblasts originating in the mesenchyme of the 4th and 6th pharyngeal aches. Hence, these muscles are innervated by the superior laryngeal and recurrent laryngeal branches of the vagus nerve.
During the 7th and 8th weeks the endodermal epithelium of the larynx pro-liferates rapidly and temporarily occludes the laryngeal lumen completely. Later on, the cells filling the laryngeal lumen break down and recanalization of the larynx occurs by the 10th week of development, so that laryngeal lumen is restored once again. Recanalization also results in the formation of a pair of lateral recesses of larynx, which are also called laryngeal ventricles. The laryngeal ventricles are bounded by folds of laryngeal mucous membrane: vestibular folds lying superiorly and vocal folds lying inferiorly.