✅ EMBRIOLOGÍA de la CABEZA y el CUELLO (Parte 2°) 🦷🙇🏻

Hello! Welcome to my channel Today we are going to talk about Head and Neck Embryology Second part I tried to be as updated as possible so my video is built based on the 14th edition Langman Embryology book Hope this can help you Taking up where we had stayed let's start talking about THE PHARYNGEAL BAGS The human embryo has 4 pairs of pharyngeal bags; the 5th is rudimentary The 1st pharyngeal pouch forms a diverticulum called recess tube-tympanic that comes into contact with the epithelial lining of the 1st Pharyngeal Cleft The distal portion of the diverticulum widens to create a sack-like structure which is called Primitive Tympanic Cavity or Middle Ear while its proximal segment remains narrow and constitutes the Eustachian Tube (or Pharyngotympanic) Tympanic Cavity Coating later participates in the Tympanic Membrane or Eardrum formation You can see this in my Ear Embryology video In the 2nd Pharyngeal Bag its epithelial lining proliferates and forms buds that penetrate to the surrounding mesenchyme These buds undergo a secondary invasion by mesodermal tissue, to constitute the primordium of the Palatine Tonsils The 3rd and 4th Bags they are characterized at their distal end by a dorsal and a ventral wing In the 5th week, the epithelium of the dorsal region of the 3rd pouch it differs in the Lower Parathyroid Gland, meanwhile, in the ventral region it forms the Thymus The two glandular primordia lose their connection to the pharyngeal wall, and the thymus then migrates in the caudal and medial direction, taking with him the Lower Parathyroid The epithelium of the dorsal region of the 4th pharyngeal pouch forms the Superior Parathyroid Glands When the Parathyroid Gland loses contact with the pharynx wall attaches to the dorsal surface of the Thyroid Gland that is in caudal migration, to constitute the Superior Parathyroid Glands. The ventral region of the 4th bag gives rise to the Ultimobranchial Body, later incorporated into the Thyroid Gland Regarding PHARYNGEAL CLEARS The 5-week embryo is characterized by the presence of 4 pharyngeal clefts HERE COMES THE DIFFERENCE WITH OTHER EDITIONS The External Auditory Canal (CAE) was thought to was formed from the 1st Pharyngeal Cleft, but this has been ruled out and it is now known that the CAE develops from invagination of superficial ectoderm of the 1st Pharyngeal Arch The overgrowth of the 2nd Arc while making up the majority of the outer ear, makes 1st Cleft disappear.

Active proliferation of the mesenchymal tissue of the 2nd Arch leads you to overlap the 3rd and 4th And finally, it fuses with the epicardial border in the lower neck region and the 2nd, 3rd and 4th Clefts lose contact with the outside The clefts form a cavity covered by ectodermal epithelium, which is called the Cervical Sinus and then it disappears at a later stage of development LANGUAGE appears in embryos around the 4th week as two lateral lingual bumps and a medial bulge called Odd Tuber These three bumps originate from the 1st Pharyngeal Arch A 2nd medial bulge called the Dome or Hypobranchial Eminence, is formed by mesoderm of the 2nd, 3rd and part of the 4th Arc Finally, a 3rd medial protuberance marks the development of the Epiglottis Just behind this bulge The Laryngeal Orifice is located, flanked by arytenoid bumps As the lateral lingual bumps grow, pass the odd tubercle and merge, to give origin to the previous 2/3, o Body of the Tongue The body of the tongue is separated from the posterior third by a V-shaped groove called Terminal Groove The posterior portion or Root of the Tongue originates from the 2nd, 3rd and certain portions of the 4th Pharyngeal Arch The Epiglottis and the posterior end of the tongue develops from the 4th Arc Some of the tongue muscles perhaps they differ in situ, but mostly derived from myoblasts that originate in the occipital somites THE THYROID GLAND appears as epithelial proliferation on the floor of the pharynx, between the Odd Tuber and the Dome in a place that later will be indicated by the Blind Foramen Subsequently, the Thyroid descends past the Pharyngeal Intestine like a bilobed diverticulum During this migration the Thyroid remains connected to the tongue through the Thyroglossal Duct and then it disappears As development progresses, the thyroid gland descends in front of the hyoid bone and the laryngeal cartilages Reach its final position in front of the Trachea in the 7th week By this time, a small midline isthmus and two lateral lobes have been developed. Now let's talk about THE FORMATION OF THE FACE At the end of the 4th week facial prominences appear, consisting mainly of mesenchyme derived from the Neural Crest and formed primarily by the 1st pair of Pharyngeal Arches Maxillary Prominences can be identified in lateral position to Stomodeo, while the Mandibular Prominences they are observed in a caudal position to this structure The Frontonasal Prominence, integrated from proliferation from the ventral mesenchyme to the Brain Vesicles, constitutes the upper edge of the Stomodeus On both sides of the Frontonasal Prominence localized thickenings of superficial ectoderm called Nasal or Olfactory Placodes originate, under the inductive influence of the ventral portion of the forebrain During the 5th week the Nasal Placodes invaginate to give rise to the nostrils In doing so they form the tissue crest around each pit and nasal prominences During the following 2 weeks, Maxillary Prominences continue to grow in the medial direction simultaneously, so they compress the Medial Nasal Prominences Towards the Midline Subsequently the Cleft located between Medial Nasal Prominence and Maxillary prominence is lost and the two merge Thus, the Upper Lip is formed. from the 2 Medial Nasal Prominences and the 2 Maxillary Prominences The Lateral Nasal Prominences do not participate in the formation of the upper lip Lower lip and jaw are integrated from the Mandibular Prominences that merge into the middle line At the beginning the Maxillary Prominences and the Lateral Nasal Prominences are separated by a deep groove, known as the Nasolacrimal Groove The ectoderm of the floor of this groove forms a solid epithelial cord that emerges from the overlying ectoderm After channeling the cord gives rise to the Nasolacrimal Duct its upper end widens and ends it generates the Lacrimal Sac After the detachment of the cord, Maxillary Prominences and Lateral Nasal Prominences fuse with each other The Nasolacrimal Duct is directed like this from the medial angle of the eye to the inferior meatus of the nasal cavity and the Maxillary Prominences grow to constitute the cheeks and upper jaws Nose is formed from 5 prominences or facial processes: The Frontonasal Prominence that gives rise to the bridge The medial nasal prominences that fused they form the back and the tip and the Lateral Nasal Prominences that will form the wings As a consequence of medial growth of the Maxillary Prominences, the 2 medial nasal prominences merge not only on the surface, but also on a deeper level The structure formed by this merger is the Intermaxillary Segment And this one is made up of: 1- A Lip Component which forms the Filtrum of the upper lip; 2- A Superior Maxillary Component, containing the 4 incisor teeth; 3- A Palatine Component, that forms the Triangular Primary Palate The Intermaxillary Segment is going to keep continuity with the rostral portion of the Nasal Septum formed from Frontal Prominence Although the Primary Palate derives from the Intermaxillary Segment, the main segment of the Definitive Palate integrates from 2 similar evaginations to ledges of the Maxillary Prominences.

These evaginations they receive the name of Palatine Crests appear in the 6th week of development, and they grow oblique and down on either side of the tongue However, during the 7th week the palatine ridges rise to adopt a horizontal position above the tongue and merge, with which the Secondary Palate is formed In the previous region the Crests merge with the Triangular Primary Palate and the incisor foramen is the landmark between the Primary and Secondary Palate At the same time they merge the Palatine Crests, Nasal Septum grows down and joins the cephalic face of the newly formed Palate THE NOSTRILS During the 6th week, they deepen to a considerable degree, partly due to the effect of growth of the surrounding Nasal Prominences and also for its penetration towards the underlying mesenchyme At the beginning the Oronasal Membrane separates the pits from the primitive oral cavity through the newly formed holes which are the Primitive Coanas These Coanas are located one on each side of the midline and just behind the Primary Palate Later, with the Formation of the Secondary Palate and further development of the Primitive Nostrils, the Definitive Coanas end up locating at the junction of the Nasal Cavity and Pharynx The Paranasal Sinuses develop as diverticula of the lateral nasal wall and extend into the maxillary bone, ethmoid, frontal and sphenoid They reach their maximum dimension during puberty and contribute to the final configuration of the face The shape of the face depends not only on expansion of the paranasal sinuses, but also of growth jaw and maxilla to house the teeth TEETH originate from an epitheliomesenchymal interaction between the overlying oral epithelium and the underlying mesenchyme derived from neural crest cells Around the 6th week of development, The basal layer of the epithelial covering of the oral cavity forms a letter C structure which is called Dental Sheet and that is located throughout maxilla and mandible This sheet, in turn, gives rise to several dental buds 10 in the maxilla and 10 in the jaw, which form the outlines of the ectodermal components of the teeth Shortly after the deep face from the buds invagina which gives way to the Cap Stage of teeth development This cap is made up of: an outer layer called the External Dental Epithelium; an inner layer, which is the Internal Dental Epithelium, and a central core of loose tissue which is called the Starry Reticle The mesenchyme inside the indentation of the bud, forms the Dental Papilla As the dental cap grows and his indentation deepens, the tooth takes on a bell-like appearance called the Bell Stage Papillary mesenchyme cells adjacent to the inner dental layer they differ in Odontoblasts, that later produce dentin With the thickening of the dentin layer, odontoblasts retract into the dental papilla leaving the dental process in the dentin The odontoblast layer persists throughout the life of the tooth and provides predentin continuously The rest of the cells of the dental papilla constitute the pulp of the tooth Meanwhile, the epithelial cells of the internal dental epithelium they differ in Ameloblasts These cells produce elongated enamel prisms that are deposited on the dentin. Furthermore, a group of these cells in the internal dental epithelium integrates the Enamel Knot that regulates the early development of teeth. Tooth root formation begins when the layers of the dental epithelium penetrate the underlying mesenchyme and they form the Epithelial Radicular Sheath Dental papilla cells deposit a layer of dentin which is continued with that of the crown As more dentin is deposited, the pulp chamber narrows and finally constitutes a canal that contains the blood vessels and nerves of the tooth Mesenchymal cells on the outside of the tooth that are in contact with the root dentin they differ in Cementoblasts These cells produce a thin layer of specialized bone called Cement.