Embryology Exam 3

• Mandibular Arch
• Nerve: CN V, Mandibular and Maxillary
• Muscles: Mastication, mylohyoid, anterior digastric, tensor palatine, tensor tympani
• Skeleton: Premaxilla, maxilla, temporal zygomatic, mandible, malleus, incus

• Nerve: CN VII Facial
• Muscles: Facial expression, post. digastric, stylohyoid, stapedius
• Bones: Stapes, styloid process, part of hyoid

• Nerve: CN IX
• Muscles: Stylopharyngeus
• Bones: Part of hyoid bone

• Nerve: CN X, superior laryngeal (IV), recurrent laryngeal (VI)
• Muscles: Cricothyroid, levator palatine, pharyngeal constrictors, intrinsic muscles of larynx
• Bones: Laryngeal cartilages (IV is thyroid cartilage, VI is cricoid cartilage)

• Auto-dom mutation on Chr. 5
• Affects all Arch I structures
• Downward slanting eyes, small lower jaw, malformed or missing ears

• Affects Arches I & II
• Affects Pouches I, II, III, IV, V
• CATCH-22 (22 chromosome)
• C- Cardiac Defects
• A- Abnormal facies
• T- Thymic aplasia
• C- Cleft Palate
• H- Hypoparathyroidism

• Also called Goldenhar Syndrome (Oculo-Auriculo-vertebral syndrome)
• Not heritable
• 1st and 2nd arch defect
• maxillary, temporal and zygomatic bones small
• small mandible
• anotia
• microtia
• tetrology of fallot

• Cleft I - external auditory meatus
• Cleft II, III, IV - form cervical sinus (degenerates)
• Persistent sinus can form a cist, or a fistula if it has an external opening

• Starts at base of tongue and migrates inferior to laryngeal prominence
• Thyroid forms as a part of a blind pouch, the thyroglossal duct, may persist as pyramidal lobe of the thyroid
• Remnant is the foramen cecum of tongue
• C-cells come from the 4th pharyngeal pouch

Migrates to posterior surface of thyroid, inferior pair is III pouch, superior pair is IV pouch

Arises from 4th pouch, incorporates into thyroid gland as parafollicular cells (C) cells

• Migrates from 3rd left and right pouch to anterior mediastinum
• Ectopic Thymus: often misdiagnosed as tumor or cyst

• Tympanic cavity (middle ear cavity)
• Auditory tube

• Palatine tonsils
• Tonsillar fossa

Inferior parathyroid, thymus

Superior parathyroid glands, parafollicular cells (ultimobranchial body) of thyroid

• May lie anywhere in midline along migratory path of thyroid
• Most common is inferior to hyoid bone
• Treatment with antibiotics

• Develops from 2 lateral and 1 medial swelling (tuberculum impar)- Arch I
• Second swelling (copula) forms from Arches II-IV
• Third swelling forms from posterior IVth arch
• Lateral swellings grow and form anterior 2/3rds of tongue, CN V innervation
• Posterior 1/3 of tongue formed from arches II-IV receives sensory innervation from CN IX to arch III

Short frenulum of tongue

Lateral lingual swellings fail to fuse

Big ass tongue

• Frontal: Neural Crest
• Parietal: Paraxial mesoderm
• Laryngeals: Lateral plate mesoderm

Thickenings of neural crest-like cells that remain in surface of ectoderm to form neuroepithelium.

• 1. Nasal placode forms elevated nasal prominence
• 2. Nasal pit forms in the center of prominence
• 3. Line drawn through pit creates medial and lateral regions
• 4. Nasolacrimal groove forms between maxillary and nasal prominence (gives rise to nasolacrimal duct and lacrimal sac)
• 5. Right and left medial nasal prominence fuses to form upper lip

Forms forehead and bridge of nose

Forms cheeks and lateral portion of upper lip

Forms philtrum of upper lip, crest and tip of nose

Forms Alae of nose

Forms lower lip

• All trigeminal nerve
• V1 (Ophthalmic) - Scalp, upper eyelid, conjunctiva and cornea of eye, bridge of nose
• V2 (maxillary) - lower eyelid, cheeks, upper lip and alae of nose
• V3 (mandibular) - lower lip and lower jaw

• 1.  Nasal pit invaginates to form nasal cavity, stomodeum forms oral cavity, oronasal membrane separates cavities
• 2.  Oronasal membrane disappears, medial nasal prominence forms primary palate
• 3.  Maxillary prominence grows to form secondary palate
• 4.  Neural crest cells form nasal placode

Forms from medial ingrowth of nasal prominences

• Two palatine shelves grow from maxillary prominences
• Initially lateral to tongue and project obliquely downward
• Secondary palate important for baby sucking
• Tongue moves downward and palatine shelves project horizontally and meet at midline to form secondary palate
• Incisive foramen is the midline landmark for junction of primary and secondary palates
• Nasal septum grows inferiorly to contact superior surface of secondary palate

• Anterior Defects: anterior to incisive foramen
• Posterior Defects: posterior to incisive foramen
• Median cleft of lower lip: mandibular prominences don't fuse
• Median cleft of upper lip: left and right medial nasal prominences fail to fuse
• Complete unilateral cleft of upper lip and unilateral cleft of primary palate: failure of maxillary and medial nasal prominences to fuse
• Bilateral cleft of secondary palate: failure of left and right palatine shelves to fuse
• Bilateral oblique facial cleft with complete bilateral cleft lip and exposed nasolacrimal duct: failure of maxillary prominences to fuse to medial and lateral nasal prominences

Mouth extends far laterally, failure of maxillary and mandibular prominences to fuse

Small mouth, excessive fusion of maxillary and mandibular prominences

I2 C2 P2 M3

• -Oral ectoderm invaginates to form dental lamina which develops into cup shaped structure
• -Ectomesenchyme condenses adjacent to ectoderm
• -Enameloblasts secrete enamel
• -Odontoblasts secrete dentin
• -kid tooth forms first, permanent tooth froms from a bud in the dental lamina
• -dental lamina will degenerate

Enameloblasts: enamel

Odontoblasts (dentin) and Pulp

-Opening of root of tooth where nerves and blood vessels enter pulp

Mesenchymal cells in contact with dentin of tooth differentiate to cementoblasts which secrete cementum, anchored in bony sockets called alveoli.

• Layer of connective tissue attaches cementum to alveolar bone
• Sharpey's fibers attach the periodontal ligament to both cementum and alveolar bone
• When tooth erupts, ameloblasts undergo apoptosis leaving the enamel exposed to the exterior
• Periodontal ligament anchors tooth to underlying bonem allows tooth to move a little bit, to flow and change position

hypocalcification of enamel

leads to brown bands of enamel in teeth

fluorosis results in mottled enamel in children

• Toxoplasmosis
• Rubella
• CMV
• Herpes

CNS malformations, microtia, cardiac defects, thymic hypoplasia

Reduced fetal growth, polycythemia

Vascular disruptive events, cerebral infarction, urogenital anomalies, limb reduction defects

Midface hypoplasia, spina bifida, cardiac defects

Sick newborns

Pregnant women and their fetuses

number of weeks of a pregnancy from the first day of the mother's last menstrual period to the date of birth

Birth before 37 weeks gestation

Birth after 42 weeks gestation

Infant between 0-28 days of birth

• High - Neural Tube defects, multiple gestations
• Low - Trisomies 18/21 and intrauterine growth restriction

• AFP (alpha fetoprotein)
• Unconjugated estriol
• Beta HCG

Low AFP, Low unconjugated estriol, high HCG

Low AFP, low unconjugated estriol, low HCG

• Lens placode invaginates to form lens vesicle
• Optic cup forms around lens vesicle, forming retinal fissure
• Lens is initially hollow, but fills in later

Become ganglion cells of the retina

• Become the retinal artery/vein
• Retinal fissure begins to close, trapping the hyaloid vessels
• Axons of the ganglion cells surround central artery and vein, forming optic nerve
• As optic stalk matures, distal portions of hyaloid vessels degenerate, but proximal portions persist as central artery and vein of retina

• Missing structures of the eye: iris, retina, choroid, or optic nerve
• Occurs if a fissure doesn't close properly
• If the retinal/choroid fissure persists, a cleft in the iris forms called a coloboma iridis.

Can be linked to Renal Disease (Renal coloboma syndrome thorugh mutation in PAX2)

Ciliary processes produce aqueous humor that flows from posterior chamber of the eye to anterior chamber, drains into scleral venous sinus (chamber of schlemm).  Blockage results in Glaucoma

• Pressure the eye
• 1. Closed angle: angle between cornea and iris becomes too narrow
• 2. Open angle: canal of schlemm blocked so you don't get drainage

Mesenchyme surrounding eye produces most of remaining structures

• Forms from mesenchyme posterior to the anterior chamber
• Degenerates to form opening of the pupil
• Persistant iridopupillary membrane

• Avascular, outer cornea is simple squamous non-keratinized epithelium
• Epithelium of cornea forms from surface ectoderm
• Dense CT of cornea forms from mesenchyme anterior to anterior chamber

• Corneal: Results from congenital glaucoma due to abnormal formation of scleral venous sinus, rubella infection, or mutation in CYP1B1
• Lens: can be caused by rubella, radiation, congenital galactosemia

• Fusion of eyes due to underdeveloped frontonasal prominence
• Associated with holoprosencephaly
• Can be caused by maternal diabetes, alcohol

Outer and inner layer of optic up (neuroectoderm)

Outer and inner layer of optic cup (neuroectoderm)

Mesenchyme

Mesenchyme

Mesenchyme

Surface Ectoderm

Surface Ectoderm

Mesenchyme

Mesenchyme

Surface ectoderm with core of mesenchyme

Surface Ectoderm (otic placode)

• Filled with endolymph
• Inside temporal bone
• Inside Bony labyrinth
• Formed from otic placode
• Mesenchyme surrounding the labyrinth will vacuolize to form scala vestibuli and scala tympani

• Filled with perilymph
• Surrounds membranous labyrinth

• Invaginates to form otic vesicle
• Superior portion of vesicle: utricle and endolymphatic duct (cochlea)
• Inferior portion of vesicle: saccule
• Otic vesicle gives rise to organ of corti, basilar membrane and vestibular membrane

Linear acceleration, gravity, tilt of head

Linear acceleration, gravity, tilt of head

• Angular acceleration
• Form by flattening 3 parts of utricle, eventually the walls undergo apoptosis forming 3 circular canals

Audition

Curving growth of narrow process of saccule

• Ep. Cells of cochlear duct form 2 ridges separated by groove.
• Outer Ridge: forms row of inner hair cells and 3-4 layers of outer hair cells (tips of hair cells embedded in tectorial membrane)
• Impulses travel by cranial nerve VIII

Drains into subarachnoid space

Drains into endolymphatic duct, which drains into venous sinuses of cranial dura

• Functional layer of endometrium that is shed during birth
• Consists of: Basalis, capsularis, and parietalis

• 1. Chorionic Frondiosum (fetal part from chorion)
• 2. Decidua Basalis (maternal part from endometrium)

Bacteria, Heparin, IgS, IgM

umbilicus wrapped around abdomen, head in wrong orientation

Covers internal os

Placenta grows up to myometrium

Placenta grows into myometrium

Placenta grows into perimetrium

Placenta separates from uterine wall

• Lung development
• Fluid and electrolyte homeostasis
• Shock absorber
• Barrier to infection
• Maintains temperature

Before 11 weeks, swalled by fetus and wastes pass from fetus by skin, respiration or GI tract

After 11 weeks, fetus excretes urine into amniotic fluid

• Excessive fluid due to imbalance/hemolysis of fetal red blood cells by maternal antibodies
• Distends abdomen due to accumulation of ascites in peritoneal cavity

• Polyhydroamnios: Excess fluid in sac
• Oligo: too little amniotic fluid

• Fetus is entangled with strands of amniotic bands that are fibrous and string-like
• It is a disruption

Growth of one twin compresses a second mummified twin against the uterus

Monochorionic/diamniotic - arterial blood from one twin shunted to other twin

Fetal hypothalamus secretes corticotropic releasing hormone, stimulating release of cortisol from fetal adrenal cortex, increases estrogen production, which releases prostaglandins and oxytocin that increase intensity of contraction of uterine smooth muscle.