Introductory Embryology, Oral-Facial Development And Associated Developmental Anomalies Flashcards
Stages of human development: (3)
Proliferation Period (0-3 weeks)
Embryonic Period (3-8 weeks)
Fetal Development Period
(9 weeks to term)
Fertilization of ovum yields —
zygote
mitotic cleavage of zygote forms —
blastomeres
more than 32 blastomeres is called a —
morula
The 64 cell stage morula develops an internal blastocystic cavity and thereafter is referred to as a
blastocyst
The blastocyst also develops an inner cell mass at days 6-7
and thereafter is referred to as the
embryoblast
Implantation of the embryoblast in the uterine wall begins
at day - and is complete at day -
4, 10
The inner cell mass of the embryoblast transitions into the
bilaminar embryonic disc
two layers
Outer cell mass becomes the (2)layers which are precursor to the placenta
cytotrophoblast & syntrophoblast
Epiblast Layer (2)
Ectoderm
Mesoderm
Hypoblast Layer (1)
Endoderm
Structures associated with the bilaminar embryonic disc (6)
- Epiblast Layer
- Hypoblast Layer
- Amniotic Cavity
- Blastocyst Cavity
- Syntrophoblasts
- Cytotrophobasts
Enlargement of the amniotic cavity and migration of cells out of the hypoblast to form
Heuser’s membrane
Heuser’s membrane will form the internal lining of the blastocyst cavity – now called the
yolk sac
Cell layers (3)
Epiblast
Embryonic mesoderm
Hypoblast
Embryonic cavities (3)
Amniotic
Yolk sac
Chorionic
During the 3rd week of development, the bilaminar
embryonic disc is characterized by formation of the: (3)
Primitive Streak
Notochord
Neural Tube
And the three distinct embryonic germ layers: (3)
Ectoderm (formerly the epiblast layer)
Mesoderm
Endoderm (formerly the hypoblast layer)
Primitive Streak (3)
Pit
Node
Groove
steps in formation of the notochord
Primitive node → Notochordal Process → Notochord
— cells invaginate within the — and migrate towards the cephalad until the reach the —. They detach themselves from the ectodermal layer to line within the mesoderm forming the —
Pre-notochordal
primitive node
prechordal plate
notochord
The notochord functions as a
primitive skeletal support of the
embryo around which the axial skeleton later forms
The notochord also induces formation of —, the precursors
of the vertebral column, ribs, associated back muscles and
overlying dermis.
somites
formed from ectodermal cells derived from the —. The cells then migrate within the mesodermal layer to their appropriate midline position. The notochord functions as a primitive axial skeleton for the embryo, establishing symmetry and polarity of development and induction of the —
primitive node
somites
Lateral Plate Mesoderm (2)
Parietal
Visceral
Derivatives of Mesoderm: • Paraxial mesoderm → • Intermediate mesoderm → • Lateral plate mesoderm: Parietal mesoderm → Visceral mesoderm →
somites
urogenital system
mesothelial (serous) membranes that cover the peritoneal, pleural and pericardial cavities.
forms the thin serous membranes that cover individual organs,
e.g., stomach, pancreas, spleen, etc.
Derivatives of Ectoderm: (5)
• Epidermis, hair and nails • Epithelium of the oral and nasal cavities and paranasal sinuses • Salivary and endocrine glands • Nervous system • Tooth enamel
Derivatives of Endoderm: (1)
• GI tract epithelium and associated glands
Spina Bifida
folic acid deficiency
Meningocele
extrusion of dura and arachnoid mater
Meningomyelocele
extrusion of neural tissue plus all three meninges
Meningoencephalocele
extrustion of a ventricular cistern plus neural tissue
Anencephaly
fatal defect characterized by lack of development of
the cranium and brain
The clinical consequences of a defect in neural tube closure
ranges from mild to fatal. — and — are examples of a mild defect. A slightly more severe defect is the —. Still more severe is the —. — is a fatal defect.
Spina bifida meningocele meningomyelocele meningohydroencephalocele Anencephaly
Neural Crest Cells
a.k.a. (2)
Ectomesenchyme
Neuroectoderm
1st branchial groove ⇒
external auditory canal
1st branchial pouch ⇒
eustachian tube
2nd branchial pouch ⇒
palatine tonsils
3rd branchial pouch ⇒
inferior parathyroids/thymus
4th branchial pouch ⇒
superior parathyroids/ultimobranchial body
Development of the Face: (4) processes
- Mandibular Process
- Maxillary Process
- Lateral Nasal Process
- Median Nasal Process
Defective fusion of the medial nasal process with the maxillary
process results in —. Fusion of these processes normally
occurs at — of gestation.
cleft lip
5-6 weeks
Defective fusion of the palatine shelves results in —.
Fusion of the palatine shelves normally begins during the 8th
week of gestation and is completed by the —
cleft palate
12th week
–% of all clefts are combined cleft lip/cleft palate.
45
–% of cases are isolated cleft palate.
30
—% of cases are isolated cleft lip.
25
The incidence of cleft lip/cleft palate is:
• — in Chinese, Japanese and NativeAmerican populations
• — in Caucasian populations
• — in Afro-American populations
1 in 500 births
1 in 700 births
1 in 500 births
The incidence of cleft palate alone is 1 in — births.
2,500
If one child is born with cleft lip, there is a —% chance of a second child exhibiting the same defect.
40
Known Teratogens Involved in Congenital Malformations
Drugs:
Chemicals:
Radiation:
Ethanol, Tetracycline, Dilantin, Lithium, Methotrexate, Warfarin, Thalidomide, Androgens, Progesterone, Retinoic Acid
Methylmercury, polychlorinated biphenyls
High levels of ionizing radiation
Nasopalatine Duct Cyst develops at the line of fusion between
palatine shelves and primary plate
cervical sinus remains past
7th week
Embryonic Precursor: Branchial Arch #1
Intermediate Structure:
Adult Structure:
Median Tongue Bud
Foramen Cecum
Lateral Lingual Swellings
Overgrown by lateral lingual swellings
Origin of the thyroid ectoderm
Anterior 2/3 of the tongue
Embryonic Precursor: Branchial Arch #2
Intermediate Structure:
Adult Structure:
Copula/Tuberculum Impar
Overgrown by the hypobranchial eminence
Embryonic Precursor: Branchial Arch #3
Intermediate Structure:
Adult Structure:
Hypobranchial Eminence
Posterior 1/3 of the tongue
Embryonic Precursor: Branchial Arch #4
Intermediate Structure:
Adult Structure:
Minor contributions to the hypobranchial eminence
None
Branchial Arch: 1
Cranial Nerve:
Tongue Structure:
Trigeminal (C-V)
Sensory to the anterior 2/3
Branchial Arch: 2
Cranial Nerve:
Tongue Structure:
Facial (C-VII)
Special sensory (taste) to anterior 2/3 via
the chorda tympani branch
Branchial Arch: 3
Cranial Nerve:
Tongue Structure:
Glossopharyngeal (C-IX)
Sensory to the posterior 1/3
Branchial Arch: 4
Cranial Nerve:
Tongue Structure:
Vegas (C-X)
Sensory to the extreme posterior 1/3 via the superior laryngeal branch
Branchial Arch: 6
Cranial Nerve:
Tongue Structure:
Hypoglossal (C-XII)
Motor to all tongue muscles
Median Rhomboid Glossitis: Was thought to represent a portion of the
tuberculum impar (branchial arch II) that persists, but now it is considered to be a result of a fungal infection.
Branchial Arch Cartilage (4)
I: (Meckel’s Cartilage) Mandible, Maleus, Incus II: (Reichart’s Cartilage) Stapes, Styloid Process, Stylohyoid Ligament, Lesser Horn of Hyoid III: Greater Horn of Hyoid IV: Thyroid Cartilage