Face and Neck Development Notes PDF

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Notes regarding the development of the face and neck. ...

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DEVELOPMENT OF THE FACE AND NECK (CHAPTER TWO) 9/29/2016 FOURTH WEEK (Continued from Prenatal Development PPT)  Tail and head folding  Embryo creates a tube within a tube toward the midline o Creates cavities 1. Coelom 2. Gut 

The trilaminar disc is beginning to fold into the embryo as a result of extensive growth of the ectoderm. The endoderm is thus inside the ectoderm, with the mesoderm filling in the areas between these two tissue types, except at the two embryonic membranes. Note the developing brain, heart, and digestive tract.

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Getting morphogenesis Getting cytodifferentiation Getting histodifferentiation Extensive proliferation (growth) o Major factor* o Brain is rapidly expanding  Prosencephalon (forebrain)—Telencephalon (cerebrum, cerebral hemisphere) & Diencephalon (thalamus, epithalamus, hypothalamus)

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Mesencephalon (midbrain)—Mesencephalon (Corpora quadrigemina, tegmentum, cerebral peduncles)

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Rhombencephalon (hindbrain)—Metencephalon (pons, cerebellum) & Myelencephalon (Medulla oblongata)

Amnion is all around the embryo Connecting stalk = umbilical cord Pharyngeal arches are bilateral o Start as swellings of pharynx (all three germ layers and neural crest cells) Limb buds are forming o Nubs on side Developing heart is covered in ectoderm o Stomodeum = opening to the mouth (primitive mouth)  Covered in ectoderm  Entrance to pharynx is thru the stomodeum into the buccalpharyngeal membrane Somites = future musculature Cloacal membrane = caudal

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DOMINANT FACTOR IN FOURTH WEEK: MORPHOGENESIS

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 22-28 days: the heart starts beating Vessels are starting to interact with the heart as well Stomodeum is access to the foregut KNOW SOMATOPLUR AND SPLANCLOPLUR Right column: splancloplur (visera, gut) then somatoplur (outside, body)

***Video is lateral folding KNOW SLIDE 50

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Neural crest cells produce the jaw and muscles that move the jaw Paraxial mesoderm: mostly skeletal muscles o Is mesoderm, closest to notochord, next to long axis Intermediate mesoderm: urogenital system (gonads, ducts and accessory glands) o Mesoderm, inbetween paraxial and lateral Lateral mesoderm: visceral wall (body wall) o Outermost Ectoderm: epidermis, nervous system (neuroectoderm), neural crest cells (peripheral nerves, ganglia), pharyngeal arch cartilages and bone, head mesenchyme and connective tissue, ENAMEL Endoderm: respiratory system, epithelium of GI tract and several other organs, glands (especially from pharynx) Neural crest cells of the pharyngeal arches create connective tissue, bone, dentin, periodontium, muscles o Specialization of neural crest cells

DEVELOPMENT OF PHARYNX  Placode: thickening of ectoderm o Create teeth o Bump that looks like an eye (lens placode)  Foregut gives rise to the primitive pharynx o Forms oropharynx  Where the faucial pillars are is the buccalpharyngeal membrane  Mouth is lined with ectoderm (stratified squamous epithelium)  Gut is lined with endoderm

Maxilla Mandible (Filled with mesenchyme (ectoderm on surface)) ONE ARCH

There are 1,2,3,4,6 pharyngeal arches 5th was obliterated SUMMARY SLIDE 52  Heart starts to beat @ day 22  By day 24, two arches are visible  By day 26, 3 pharyngeal arches are visible  By this time, most organ primordia are present and the structure of the body is established…by the end of the embryonic period all essential external and internal structures are formed  The 5th and 6th weeks are dominated by the development of the pharyngeal arches  Neural crest development (pharyngeal arches begin)  Primordia of the diaphragm first discernable Pharyngeal Arches & Innervations 1st arch: mandible and maxilla - Innervated by Trigeminal 2nd arch: hyoid - Innervated by Facial rd 3 : tongue -Innervated by Glossopharyngeal n Embryonic Period is the most critical period of prenatal development!

TREACHER COLLINS SYNDROME  Neural crest cells are important in the formation of the cranium

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Bones of the face are too small

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Creates sagging Small zygomatic and mandible

FETAL ALCOHOL SYDROME

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Alcohol (ethanol) and nicotine cross into the placenta Small in cranium Skull is small Wide spaced eyes Bridge of the nose is underdeveloped Lacks prominent sutures at the midline

RUBELLA

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Affects the fetus Example of an infective teratogen Can result in Cardiac defects, Cataracts and deafness in the first 12 weeks

Embryo becomes a fetus at Week 9 Fetal Period: beginning of week 9 (third month) to the end of the ninth month  This process involves not only the physiological process of maturation of the individual tissue types and organs but also proliferation, differentiation, and morphogenesis, as discussed before with the embryo.  Congenital malformations can occur during the fetal period as well o Diagnostic test: Amniocetesis  Amniotic fluid is sampled during the 14th week to the 16th week after the last missed menstrual period  Used to see if anything is wrong with the fetus  Can tell gender this way Antibiotic Exposure o Tetracycline staining  Interferes with the dentin  Intrinsic yellow to brown discoloration of the teeth  Can interfere with the child’s primary teeth that are developing at this time  Antibiotic becomes chemically bound to the dentin for the life of the tooth

DEVELOPMENT OF THE FACE AND NECK PPT FACIAL DEVELOPMENT  Forms during the 4th week of the embryonic period

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Not completed until the 12th week Growing brain bulges over the oropharyngeal membrane and developing heart Eyes and nose are considered placodes o “Thickening of ectoderm”

Arches 1,2,3,4  

Otic means “related to the ear” First arch is called the Mandibular Arch o Also creates the Maxilla

Facial Development includes the primitive mouth, mandibular arch, maxillary process, frontonasal process and nose 

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Facial development comes from 5 processes & some subcategories 1. Frontonasal (1)  Nose, septum, palate 2. Maxillary (2) 3. Mandibular (2) Facial and Neck development involves all three germ layers (ecto, meso, endoderm) Doesn’t finish development until 17-21 years old (at least) Direction of growth is anterior and inferior KNOW CHART ON SLIDE 4

MERGING AND FUSION OF TISSUES  Two independent structures that are coming together at the midline, FUSE together o Mandibular processes  Cells migrate to these areas and fill in = MERGE o Smoothing the surface o Mesenchyme migrates into the furrow o This migration takes place because adjacent mesenchyme grows and merges beneath the external ectoderm during the maturation of the structure

*** The stomodeum and oral cavity formation are results of folding and development of branchial arches*** Branchial means“gill” Pharyngeal Clef  In between each arch  One cleft is left in the adult  Cleft 1 becomes the External Auditory Meatus  Inside of clefts = pouches Pharyngeal or Branchial Arches = pharynx, “foregut”  Formed by neural crest cells that migrate to the neck region  Inside the arch = mesoderm, neural crest cells  Exterior of the arch and clefts = ectoderm  Each paired arch has its own developing cartilage, nerve, vascular and muscular components within each mesodermal core  Arches 1 & 2 develop into the greatest extent of all the arches o Are also the only ones specifically named  Mandibular Arch and Hyoid Arch  Rhombomeres = segmentation of the brainstem  Arches 1 & 2 surround the primitive mouth (stomodeum)  Swellings in the middle of the arches are the future tongue

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Clefts and Pouches are opposite of each other o Cleft 1 becomes the External Aucoustic Meatus Arches have both mesenchyme or mesoderm proper Ectomesenchyme: mesenchyme like cell group o Comes from ectoderm or neural tube o Mesenchyme is a primordia of connective tissue (will make all)

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Arch One: muscles of mastication Arch Two: muscles of facial expression Arch Three: muscles with glossopharyngeal Arch Four: anything associated with Vagus Nerve Arch Six: larynx Preotic mesoderm: eye muscles Tongue muscles come from Occipital Myotomes, NOT pharyngeal arches o Both intrinsic and extrinsic muscles

Pharyngeal Third Arch  Forms parts of the Hyoid Bone  Stapes comes from Arch Two NOT Arch Three

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Arches Four and Six = strictly Vagus Nerve CN XI innervates trapezius

MANDIBULAR ARCH AND LOWER FACE FORMATION  We have five growth centers (5 processes)  MX and MD swellings are from Arch 1  Arch 2 obliterates external view of arches

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Little horseshoes are medial and lateral nasal processes!

Formation of the face

FUSE AND MERGE Groove separating the maxillary process and lateral nasal process = NASOLACRIMAL GROOVE Groove separating the maxillary process and medial nasal process = BUCCONASAL GROOVE PRIMARY PALATE+UPPER LIPS  Where the medial nasal processes meet = philtrum o Can get a cleft here!  The two maxillary processes contribute to the sides of the upper lip  Intermaxillary Segment or Globular Segment o Forms the primary palate (technically not a part of the maxilla) o Maxilla doesn’t fully fuse o Has a wedge in between o Where Philtrum is

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Differential Cell Growth and Proliferation are the key components of this formation/development!

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Placode: thickening of ectoderm o On the external surface of the embryo o Rounded areas of specialized, thickened ectoderm o Found at the location of developing special sense organs (eyes, ears, nose) o Facial area has two lens placodes  Located fish like on opposing sides of the head o The two otic (meaning connected to the ear) placodes are even more laterally and posteriorly placed and form pits that create the future internal ear and associated tissue as they appear to rise to their mature position as a result of their relative growth. Parts of the nearby branchial apparatus of the embryonic neck later form the external and middle ear o The two nasal placodes form in the anterior part of the frontonasal process, just superior to the stomodeum, during the fourth week

LENS PLACODE (OPTIC)

Maxillary Processes fused and merged The Median Nasal Processes merge NASAL AND PALATE FORMATION  Tissue around the nasal placodes on the frontonasal process starts to grow o Initiates development of the nasal region and the nose  The union of the medial nasal swellings forms the intermaxillary process of the maxillary arch. o The intermaxillary process produces the philtrum of the lip  The segment of the maxilla bearing the incisor teeth, and the primary palate.

INTERMAXILLARY SEGMENT

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Intermaxillary Segment comes from the median nasal process (fusion), which is a sub category of frontonasal process Primary palate is intermaxillary segment! Secondary palate is the maxilla! o Arises from shelf-like extensions In embryogenesis, Rathke's pouch (ECTODERM) is an evagination at the roof of the developing mouth in front of the buccopharyngeal membrane. o Gives rise to the anterior pituitary (adenohypophysis), a part of the endocrine system. Rathke's pouch, and therefore the anterior pituitary, is derived from ectoderm

CLEFT LIP  Failure of fusion of the maxillary process with the medial nasal process o BUCCONASAL GROOVE  Clef Palate: failure of fusion of the palatal shelves with the primary palate  Nasolacrimal: failure of fusion of the lateral nasal processes and maxillary process  1 in 1000 cases  Failure of mesenchyme growing beneath the ectoderm to obliterate any grooves between these processes  Can be caused by genetics (hereditary) or environmental factors  Can be isolated or with other developmental abnormalities

A = Maxillary Process B = Mandibular Process C = Medial Nasal Process D = Lateral Nasal Process (Where Philtrum is = Intermaxillary Segment) BRANCHIAL GROOVE AND MEMBRANE FORMATION  Pouch is an endodermal product o There are four of them  Arch includes endoderm, ectoderm and mesoderm. As well as Neural crest cell derivatives  Clef/Groove is located between each arch o Ectodermal o One cleft produces External Acoustic Meatus!  Groove between 1st and 2nd arches o THAT’S IT! The others are pinched off!  Arch 2 grows over the rest!  Only the first branchial groove, which is located between the first and second branchial arches at approximately the same level as the first pharyngeal pouches, gives rise to a definitive mature structure of the head and neck…the external auditory meatus and the tympanic membrane  Creates the Cervical Sinus

PHARYNGEAL POUCH FORMATION  Four well-defined pairs of pharyngeal pouches develop as endodermal evaginations from the lateral walls lining the pharynx.

Pattern of the branchial arches. I-IV branchial arches, 1-4 branchial pouches (inside) and/or pharyngeal grooves (outside) a Tuberculum laterale b Tuberculum impar c Foramen cecum (“blind hole”) d Ductus thyreoglossus e Sinus cervicalis

- Sup. And Inf. Parathyroid cross. - Inferior descends further even though it comes from the 3rd arch - Ultimobrachial body comes from the 5th pouch that was obliterated - Calcitonin cells (calcium homeostasis) - POUCHES MAKE GLANDS - The Thyroid gland comes form the border of the first and second arches

- 1st Pouch: Ear ossicles come from arches 1 & 2 o They used to be a part of the jaw (mandible and maxilla come from arch 1) nd - 2 Pouch = Palatine tonsils - 3rd Pouch = Thymus gland, Inferior Parathyroid (3rd arch)

- 4th Pouch = Superior Parathyroid (4th) (Passes with Inf. Parathyroid in the night) - 5th Pouch = Ultimalbrachial (parafalicular cells, calcium hormones—calcium homeostasis)...