Craniofacial Embryology; PHARYNGEAL APPARATUS, TONGUE &THYROID GLAND Peter A. Jezewski, DDS, PhD STEVEN J. ZEHREN, PH.D.
NBDE Part I • Is a comprehensive exam • 400 questions • Anatomic sciences (100): • Gross anatomy (49) • Histology (23) • Oral Histology (16) • Developmental Biology (11) • Professional Ethics/Patient Management (1) • Biochemistry-physiology (100) • Dental Anatomy (100) • Microbiology-Pathology (100)
Axial Patterning Outline of CF Development to make it all more obvious First ANTERIOR to POSTERIOR Early definition of head versus tail end. Animal pole versus vegetal pole: ORAL always at animal pole. Gastrulation (in deuterostomes): We are deuterostomes (Second mouth) Gastrulation (gut formation) = First mouth Stomation (mouth formation) = second mouth From posterior (vegetal) pole of egg towards the animal pole or future anterior end. Defines germ layers Ectoderm, mesoderm, endoderm
Axial patterning continued Gastrulation: also DORSAL to VENTRAL Asymmetric gastrulation Defines Dorsal to ventral axis, (and L and R too) Defines dorsal neural domain Eventually defines dorsal anterior (cranial) region Defines early neural crest specification; laterally to neural plate. Cranial placodes are formed just ventrally to neural crest cells. Neurulation Neural plate, CNCC, Cranial Placodes Pharyngeal stage Pharyngeal arches 1, 2 and jaw formation: Primary, Secondary palate. Tongue Thyroid gland
Deuterostomy • Primary AP axis, determined in the egg. • Mouth formation always at the Animal Pole, coincident with the Anterior. Diploblasts: Triploblasts: Ani Ant Protostomes: Deuterostomes: Veg Post
Deuterostomy • Anterior mouth, Posterior Gut: • Protostomes = Common mouth and anus • Deuterostomes = Second mouth • Gut at Posterior • Mouth at Anterior Diploblasts: Triploblasts: Ant Protostomes: Deuterostomes: Post
Gastrulation => Posterior Gut formation => Germ layers • Ectoderm • Skin, nervous system. • Endoderm • Gut, liver, lungs. • Mesoderm • Skeleton, muscles, heart, blood. • A tissue centric hypothesis focusing upon cell types.
Anterior-Posterior Axial Differentiation: Hox genes • Gene expression colinear between phyla.
Asymmetric Gastrulation => Dorsaland Ventral Tissues • Dorsal Anterior Ectoderm • Neural tissue • Dorsal Mesoderm • Notochord • Ventral Mesoderm • Blood, muscle, bone A lancelet - cephalochordate
Neurulation • Neural plate is most dorsal neural tissue • Induced by dorsal mesoderm (notochord) • Lateral to that is “less neural” tissue • Like regions that will form the neural crest, from the lateral aspects of the neural plate • Lateral to this are the regions that will induce the cranial placodes or preplacodal ectoderm Epidermis PPE NCC NCC PPE Epidermis Neural plate
Neurulation, CNCC formation Helms J A et al. Development 2005;132:851-861
Cranial Placodes • existence of a common pre-placodal region • it seems that an initial step common to all placodes involve signals from the mesendoderm, while later, more region-specific signals confer placode-specific properties. • induction of the pre-placodal domain • Endoderm or mesoderm or neural plate
Hox and Pharyngeal arches R1 R2 R3 R4 R5 R6 R7 R8 CN VII. CN V.
Comparative Embryology:Common Pharyngula Stage? • Follows the blastula, gastrula, neurula stages. • At pharyngula stage, all vertebrates show remarkable similarities: • notochord, • dorsal, hollow nerve cord, • post-anal tail, • series of paired branchial arches. Mammalian Non-mammalian frog zebrafish mouse chicken
Site of midbrain Pharyngeal(branchial) arches Lens placode Somites Max. prom. 4 3 2 1 Nasal placode Mand. prom. Stomodeum Heart A PHARYNGEAL ARCHES FORM DURING 4TH WEEK. ECTODERMAL GROOVES SEPARATE ARCHES ON OUTSIDE. Slide 10.1
STOMODEUM & OROPHARYNGEAL MEMBRANE Endoderm of pharynx Oropharyngeal membrane Ectoderm Stomodeum (primitive oral cavity)
Development of the craniofacial primordia. Helms J A et al. Development 2005;132:851-861
Frontonasal prominence Eye Maxillary prominence Entrance to stomodeum Mandibular prominence Second pharyngeal arch Umbilical vein Third pharyngeal arch Fourth pharyngeal arch Entrance to intraembryonic coelom Spinal cord SCANNING EM OF EMBRYO (5TH WEEK) Slide 10.31
Mesoderm Endoderm Ectoderm 1st pharyngeal pouch Aortic arches (1st to 4th) Midbrain Esophagus Level ofsection C Lung bud Dorsal aorta Esophagus B Thyroid diverticulum (primordium of thyroid gland) Heart Truncus arteriosus (common arterial trunk from heart) Germ Layer Derivatives ENDODERMAL PHARYNGEAL POUCHES SEPARATE ARCHES ON INSIDE Slide 10.2
Mesoderm Endoderm Ectoderm Mandibular (1st) arch 1st arch (Meckel) 1st pharyngeal (branchial) membrane Cartilages 2nd arch (Reichert) Hyoid (2nd) arch Nerve 2nd pharyngeal pouch Muscle 3rd aortic arch C 3rd pharyngeal pouch Mesodermal core of 4th arch Germ Layer Derivatives COMPONENTS OF A PHARYNGEAL ARCH Slide 10.3
NCC + and mesoderm boundary • NCC makes all anterior structures of face: including cartilage, bone, muscle. • Mesoderm makes all those posterior to the pituitary gland Pink = paraxial mesoderm derived. Blue = neural crest Cells derived.
ZYGOMATIC MAXILLA MANDIBLE SQUAMOUS TEMPORAL MEMBRANE BONES OF ARCH 1
The muscles derived from arch 1 (green) include the muscles of mastication (eg, temporalis and masseter) and the mylohyoid and anterior belly of the digastric. Also derived from arch 1 are the tensor palati m. (soft palate) and tensor tympani m. (middle ear)(not shown). All of the muscles of mastication insert into the mandible (also from arch 1). The mylohyoid and anterior belly of the digastric also attach to the mandible. The muscles derived from arch 2 (salmon) include the muscles of facial expression, stylohyoid m. and posterior belly of the digastric. Also derived from arch 2 is the stapedius m. (middle ear)(not shown). 5. The muscle derived from arch 3 (purple) is the stylopharyngeus m. The muscles derived from arch 4 (light blue) include most of the muscles of the pharynx and soft palate, as well as the cricothyroid m. The muscles derived from arch 6 (dark blue) include most of the muscles of the larynx and the striated musculature of the esophagus (not shown). • PHARYNGEAL ARCH MUSCLES: DERIVATIVES
(Arch 2) (Superior laryngeal br. and pharyngeal br. to arch 4; recurrent laryngeal br. to arch 6) (Arches 4 &6) (Arch 1) (Arch 1) (Arch 3) PHARYNGEAL ARCH NERVES
3rd, 4th, and 6th aortic arches Spinal cord Midbrain Pulmonary artery Dorsal aorta Aortic sac Yolk stalk Yolk sac C PHARYNGEAL ARCH ARTERIES (AORTIC ARCHES) Slide 14.56
6th aortic arch 3rd aortic arch 4th aortic arch Truncus arteriosus Dorsal aortae Aortic sac Left dorsal aorta External carotid artery Left dorsal aorta Internal carotid artery Right 3 3 4 Aortic sac 4 5 Aortic arches 5 6 6 Ductus arteriosus Truncus arteriosus (partly divided aortic and pulmonary arteries) Right subclavian artery Left dorsal aorta Aortic sac Pulmonary arteries Left subclavian artery 7th intersegmental artery 7 WKS 6 WKS A B TRANSFORMATION OF AORTIC ARCHES (VENTRAL VIEW) Slide 14.57
3rd aortic arch 6th aortic arch 4th aortic arch Aortic sac Dorsal aortae Truncus arteriosus Internal carotid arteries Left common carotid artery External carotid arteries Right Brachiocephalic artery Left subclavian artery Subclavian arteries Arch of aorta Ascending aorta Right pulmonary artery Ligamentum arteriosum Ductus arteriosus Left pulmonary artery Ascending aorta Descending aorta C D Pulmonary trunk 8 WKS 6 MO. INFANT TRANSFORMATION OF AORTIC ARCHES (VENTRAL VIEW) Slide 14.58
PHARYNGEAL POUCHES, GROOVES & MEMBRANES Opercular flap (becomes incorporated into the thyroid gland and forms the parafollicular cells: secretes Calcitonin) A B
Auditory tube(pharyngotympanic tube) and tympanic cavity (pouch I) Foramen cecum of tongue Tonsillar sinus and surface epitheliumof palatine tonsil(pouch II) Tongue Tract ofthyroglossal duct Larynx Pouch IV Parathyroidglands Pouch III Ultimobranchialbody (pouch IV) Thyroid gland Thymus (pouch III) 20 WEEK FETUS SHOWING DERIVATIVES OF PHARYNGEAL POUCHES Slide 10.13
Hyoid bone Undescended parathyroid gland Accessory thymic tissue Persistent thyroglossal duct Thyroid cartilage Thyroid gland Superior parathyroid glands Trachea Persistent cord of thymic tissue Manubrium of sternum Ectopic inferior parathyroid gland Retrosternal thymus Body of sternum CONGENITAL ANOMALIES OF THYROID, THYMUS & PARATHYROID GLANDS Slide 10.19
LATERAL CERVICAL CYSTS (REMNANTS OF CERVICAL SINUS) Epicardial ridge (SCM develops in it) C A B
LATERAL CERVICAL CYST. NOTE ITS POSITION ANTERIOR TO SCM MUSCLE. Sternocleidomastoidmuscle Swelling formed bybranchial cyst Tendon ofsternocleidomastoidmuscle Slide 10.16