Embryo-Pharyngeal Arches Flashcards
Ecoderm germ layer contributions to pharyngeal arches
Ectoderm–> groove (external auditory meatus, cervical sinus)
Mesenchyme (NCC) and Mesoderm–> muscles, A, N
Endoderm–> pouch (organs)
Membrane: 1 cross-section encompassing all layers
Role of NCC in pharyngeal arches
form CT in head including dermis and smooth muscle of blood vessels
Types of mesoderm in pharyngeal arches
Paraxial: muscles except extra-ocular
Lateral plate: endothelium that lines blood vessels in face
Prechordal plate: extra-ocular muscles
When do the pharyngeal arches form?
Week 4
Cleft/Groove vs Membrane
cleft/groove: ectoderm surrounding the arch
membrane: basically a cross-section of an arch with a section of ectoderm and endoderm
Describe pharyngeal membranes and its derivative(s).
Membrane (ectoderm, middle arch, endoerm)
quickly infiltrated by mesenchyme (NCC)–> tympanic membrane
Derivative(s) of pharyngeal ectoderm
External acoustic meatus
grooves 2-4 are in cervical sinus–>closes off during development
common birth defects involve 2nd groove
Skeletal/cartilage derivatives of PA 1 mesoderm
Meckel's cartilage (degenerates--> placeholder for mandible) Malleus Incus Mandible Sphenomandibular L Anterior L of malleus
Skeletal/cartilage derivatives of PA 2 mesoderm
Reichert's cartilage
(will degenerate and
contribute to below)
Stapes
Styloid process of
temporal bone
Lesser cornu of hyoid
Stylohyoid LSkeletal/cartilage derivatives of PA 3 mesoderm
Greater cornu of hyoid
Skeletal/cartilage derivatives of PA 4 mesoderm
Laryngeal cartilage
Epiglottis
Skeletal/cartilage derivatives of PA 6 mesoderm
Laryngeal cartilage
PA 1 muscular derivatives
muscles of mastication (CN V3)
PA 2 muscular derivatives
muscles of facial expression (CN VII)
PA 3 muscular derivatives
Stylopharyngeus M (CN IX)
PA 4 muscular derivatives
Pharyngeal Constrictor Ms (CN X)
PA 6 muscular derivatives
Intrinsic muscles of larynx (CN X)
PA 1 innervation
CN V- Trigeminal
Sensory of head and neck
Motor for muscles of mastication
PA 2 innervation
CN VII- Facial
Muscles of facial expression
PA 3 innervation
CN IX- Glossopharyngeal
Stylopharyngeus M
PA 4 innervation
CN X- Vagus
Superior laryngeal N
Internal branch:
sensory above cord
External branch:
cricothyroid M
Recurrent laryngeal N
–> Pharyngeal Branch
Levator veli palatine
Pharyngeal
constrictor Ms
PA 6 innervation
CN X- Vagus
Recurrent laryngeal N
Inferior laryngeal N
Intrinsic muscles of
larynx, sensory
below cord
PA 1 Endodermal derivative(s)
tympanic cavity
mastoid antrum
Eustachian tube
tympanic membrane via 1st membrane derivative
PA 2 Endodermal derivative(s)
tonsillar sinus
tonsillar lympoid tissue
PA 3 Endodermal derivative(s)
inferior parathyroid gland
thymus
BOTH MOVE SOUTH
PA 4/6 Endodermal derivative(s)
superior parathyroid gland
ultimobranchial body–> thyroid gland
Tonsils Development
PA 2 endoderm proliferation–> tonsillar epithelium–> mesenchyme differentiation–> lymphoid nodules and tonsillar sinus
Thyroid Development
PA 4 endoderm–> ultimobranchial body–> thyroid gland
Thyroid primordium (24 days) descends in neck with tongue growth, connected by thyroglossal duct–> degenerate–> patent airway
Parathyroid Development
PA 4 dorsal endoderm----> superior parathyroid glands
ultimobranchial body
fuses with thryoid
gland to make
parafollicular cells
PA 3 dorsal endoderm—-> inferior parathyroid glands
Thymus Development
PA 3 ventral endoderm–> thymic primordium
Grow into surrounding mesenchyme to make thymic lobules
lobules arranged around central point–> thymic corpuscles
Form reticulum for housing lymphocytes
Not complete at birth, replaced with adipose tissue in adult
First Pharyngeal Arch Syndrome
Abnormal development:
Malformation of eyes, ears, mandible, palate
–>insufficient migration of NCC during 4th week
Treacher-Collins Syndrome
Mandibulofacial dysostosis
Malar hypoplasia–> down-slanting features, defects of lower eyelids, deformed ears
AD mutation in TCOF1, increased apoptosis of NCC
Pierre Robin
De novo
Hypoplasia of mandible and cleft palate
Defects of eyes and ears
micrognathia (small mandible)–> posterior displacement of tongue—> obstruction of closure of palate–> BL cleft palate
DiGeorge Syndrome
Breakdown of signaling form PA endoderm to NCC
Agenesis of thymus and parathyroid
Congenital hypoparathyroidism
Shortened upper lip, low set and notched ears
Nasal cleft
Thyroid hypoplasia
Cardiac abnormalities
COMMON, VARYING SEVERITIES
Agenesis of thyroid gland
Congenital abnormality d/t abnormal migration of NCC or failure of thyroid primordium to form
Cervical cyst
Remnant of cervical sinus (ectoderm) or 2nd pharyngeal groove
—>covered with skin but not completely closed inside
Slow to enlarge inferior to angle of mandible
Fluid cellular debris pile up, painless
Cervical sinus congenital abnormality
Failure to close or 2nd pharyngeal groove to degenerate (partial closing)
Discharge of mucus BL, commonly associated with auricular sinuses
Infection risk
Cervical fistula
Abnormal canal into tonsillar sinus that extends out of neck
—> persistence of 2nd pharyngeal groove and pouch
Open from pharynx to skin, leaks mucus from oral cavity out to skin
