01. pharyngeal arches (3 lectures, march 18)


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01. pharyngeal arches (3 lectures, march 18)

  1. 1. Pharyngeal arches
  2. 2. The pharyngeal (Branchial) apparatus :  It consists of : 1-pharyngeal arches. 2-pharyngeal pouches. 3-pharyngeal grooves. 4-pharyngeal membranes.  These embryonic structures contribute to the development of the head & neck regions.
  3. 3. Drawings illustrating the human pharyngeal apparatus. A, dorsal view of cranial part of an embryo. B to D, lateral views showing later development of pharyngeal arches. E to G, ventral or facial views, illustrating the relationship of the first pharyngeal arch to the stomodeum. -Maxillary prominence of 1st arch lies lateral to stomodeum. -Mandibular prominence of 1st arch lies caudal to stomodeum. H,horizontal S.of cranial part of emb. I, horizontal S. illustrating the arch components + floor of pharynx. J, sagittal S.illustrating the openings of pharyngeal pouches in the lateral wall of the primordial pharynx.
  4. 4. Pharyngeal arches They begin to develop early in the 4th week as neural crest cells migrate into the future head & neck regions. By the end of 4th week, 4 pairs of pharyngeal arches are visible externally The 5th & 6th arches are rudimentary and not visible on surface of embryo. Fronto-nasal prominence Pharyngeal arches are separated externally by fissures- the pharyngeal grooves, which numbered craniocaudally as the arches. The arches appear along lateral wall of primordial pharynx. The primordial mouth (stomodeum) is temporarily closed by oropharyngeal bilaminar membrane (ectoderm & endoderm), which ruptures at about 26 th
  5. 5. Pharyngeal arches 1st pharyngeal arch (mandibular arch), the primordium of jaws consists of : 1- A dorsal portion, the maxillary process, which gives rise to the maxilla (upper jaw), zygomatic bone, and squamous part of temporal bone. 2- A ventral portion, the mandibular process, which gives rise the mandible ( lower jaw). -1st pair of pharyngeal arches plays a major role in facial development. 2nd pharyngeal arch (hyoid arch) : contributes to the formation of hyoid bone.
  6. 6. Pharyngeal Arches A, By the end of the 4th week (28days), 4 pairs of pharyngeal arches are developed. B, Drawing showing pharyngeal pouches + aortic arches, that supplies the pharyngeal arches and arise from truncus arteriosus, then enter the dorsal aorta. The derivatives of aortic arches : are the adult arteries of head & neck. C, Horizontal section showing the floor of primordial pharynx and germ layer derivatives of the pharyngeal arch components : each arch consists of a core of mesenchyme, which is covered externally by ectoderm and internally by endoderm.
  7. 7. Pharyngeal Arch Components arch consists of a core of mesenchyme that is Each covered externally by ectoderm and internally by endoderm. A core of mesenchyme derived from the original mesenchyme - mesoderm during 3rd week + neural crest cells (neuroecto-dermal origin) during 4th week that migrate into the arches. Skeletal musculature & vascular endothelia are derived from the original mesenchyme in the arches. A typical pharyngeal arch contains : 1-an aortic arch artery : arises from truncus arteriosus of primordial heart to enter the dorsal aorta. 2-a cartilaginous rod : that forms the skeleton of arch. 3-a muscular components : to give ms. of head & neck.
  8. 8. Fate of Pharyngeal Arches A, lateral view of embryo at 5 week (32 days) showing pharyngreal arches + cervical sinus. th B, section illustrating growth of 2nd arch over 3rd & 4rth arches. C, embryo of about 33 days. D, section illustrating early closure of the cervical sinus during 5th week. E, embryo of 41 days (end of 6th w.). F, section showing the transitory cystic remnant of cervical sinus. G, drawing of 20-week fetus illustrating the area of face derived from the 1st pair of pharyngeal arches.
  9. 9. Fate of Pharyngeal Arches They contribute to the development of face, nasal cavities, mouth,larynx, pharynx, and neck. During 5th week, 2nd arch enlarges to overgrow the 3rd & 4th arches, forming ectodermal depression- the cervical sinus. B,D By the end of 7th week, 2nd to 4th pharyngeal grooves + the cervical sinus have disappeared, giving the smooth contour to the neck
  10. 10. Derivatives of Pharyngeal Arch Cartilages : A, lateral view of 4-week embryo, illustrating location of cartilages in pharyngeal arches. B, 24-week fetus illustrating adult dreivatives of arch cartilages : 1-Note development of mandible by intramembranous ossification of mesenchymal tissue surrounding the ventral part of 1st arch cartilage (Meckel’s cartilage) + development of malleus & incus (middle ear bones) dorsally + anterior ligament of malleus & sphenomandibular ligament in the middle part. 2-Note, the 2nd arch cartilage (hyoid or Reichert’s cartilage) gives rise dorsally stapes & styloid process, in the middle stylohyoid ligament, and ventrally lesser cornu + upper part of
  11. 11. Derivatives of Pharyngeal Arch Cartilages : B, 3- Note also derivatives of the 3rd arch cartilage which ossifies to form : greater cornu (horn) + inferior part of the body of hyoid bone. 4- Cartilaginous components of 4th & 6th pharyngeal arches fuse to form most of laryngeal cartilages (thyroid + cricoid + arytenoid + corniculate + cuneiform), EXCEPT the cartilage of epiglottis which develops from the mesenchyme of the caudal part of hypopharyngeal eminence lying in the floor of primordial pharynx and derived from 3rd & 4th pharyngeal arches. The 5th arch is often absent, if present it is rudimentary and has No derivatives.
  12. 12. Derivatives of Pharyngeal Arch Muscles : A, lateral view of 4-week embryo showing the muscles derived from the pharyngeal arches, the arrow showing the pathway of myoblasts from the occipital myotomes to form the muscles of tongue. B, sketch of head & neck of 20-week fetus, showing the 1st pharyngeal arch forms ms. of mastication & other ms./ 2nd arch forms ms. of facial expression, post.belly of digastric & other ms. / 3rd arch forms stylopharyngeus./ 4th arch forms cricothyroid, levator veli palatini + constrictors of pharynx. / 6th arch forms interinsic ms. of larynx + striated ms of esophagus.
  13. 13. Derivatives of Pharyngeal Arches
  14. 14. Derivatives of Pharyngeal Arch Nerves A, lateral view of head &neck and thorax of 4-week embryo showing the cranial nerves : Trigeminal N.(V), Facial N.(VII), Glossopharyngeal N.(IX), and Vagus N.(X)— supplying 1st ,2nd , 3rd & caudal (4th + 6th ) pharyngeal arches, respectively. B, sketch of head & neck of 20-week fetus showing the 2 branches of 1st arch nerve (CNV), maxillary & mandibular branches of trigeminal N C, Sagittal section of fetal head & neck showing the sensory nerves of trigeminal N., which is the principal sensory N. of head & neck supplying face, teeth & m.m. of nasal cavity, palate, mouth & tongue, and is the motor N. for ms. of mastication. C, The nerves from 2nd to 6th pharyngeal arches have little sensory nerves, however, they innervate m.m. of post.tongue, pharynx & larynx.