Introductory Embryology, Oral-Facial Development and Associated Developmental Abnormalities Flashcards
What are the stages of human development?
-Proliferation period (0-3 weeks)
-embryonic period (3-8 weeks)
-fetal development period (9 weeks to term)
What forms after an ovum is fertilized?
zygote
What does mitotic cleavage of a zygote form?
blastomere
What is the stage of >32 blastomeres called?
morula
What happens at the 64 cell stage?
morula develops an internal blastocytstic cavity and becomes a blastocyst
What is a cyst?
a mass lined with usually epithelial tissue with a hollow cavity
(can be fluid filled)
What is an embryoblast ?
cell stage in development after the blastocyst develops an inner cell mass
When does implantation of embryoblast occur?
starting at day 4 and usually done by day 10
What are syncytiotrophoblasts?
finger like projections that help the embryoblast implant into the wall of the uterus
What is the bilaminar embryonic disc?
two layers of cells that form in the inner cell mass
When does the bilaminar embryonic disc form?
when the embryoblast starts getting engulfed into the uterine wall
What does the outer cell mass become?
cytotrophoblast and syntrophoblast layers
(precursors to the placenta)
What does the epiblast layer of the bilaminar embryonic disc become?
ectoderm and mesoderm
What does the hypoblast layer of the bliaminar disc become?
endoderm
What is the Heuser’s membrane?
the internal lining of the blastocyst cavity
What is the blastocyst cavity become?
yolk sac
What is the third cavity that forms during development?
chorionic cavity
What are the three distinct embryonic germ layers?
endoderm
mesoderm
ectoderm
What is formed during the 3rd week of development from the bilaminar embryonic disc?
primitive streak
notochord
neural tube
How is the notochord formed?
pre-notochordal cells invaginate within the primitive node and migrate toward the cephalad until the reach the prechordal plate
-they detach themselves from the ectodermal layer to line within the mesoderm forming the notochord
What is the order of steps to make the notochord?
primitive node -> notochordal process -> notochord
What is the function of the notochord?
functions as a primitive skeletal support of the embryo around which the axial skeleton forms later
What does the notochord induce the formation of?
the somites
-precursors of the vertebral column, ribs, associated back muscles, and overlying dermis
What are the three types of mesoderm?
-paraxial
-intermediate
-lateral plate
What are the two types of lateral plate mesoderm?
-parietal
-visceral
What does the paraxial mesoderm form?
somites
What does the intermediate mesoderm form?
the urogenital system
What does the parietal segment of the lateral plate mesoderm form?
mesothelial (serous) membranes that cover the peritoneal, pleural, and pericardial cavities
What does the visceral segment of the lateral plate mesoderm form?
the thin serous membranes that cover individual organs, stomach, pancreas, spleen, and other organs
What are the derivatives of ectoderm?
-epidermis, hair, and nails
-epithelium of the oral and nasal cavities and paranasal sinuses
-salivary and endocrine glands
-nervous system
-tooth enamel
What are the derivatives of the endoderm?
GI tract epithelium and associated glands
What is spina bifida?
developmental defect that occurs when the neural tube does not close properly
-due to folic acid deficiency
What is meningocele?
extrusion of dura and arachnoid mater
What is meningomyelocele?
extrusion of neural tissue plus all three meninges
What is meningoencephalocele?
extrusion of a ventricular cistern plus neural tissue
What is anencephaly?
fatal defect characteristics by lack of development of the cranium and brain
What are other names for neural crest cells?
ectomesenchyme and neuroectoderm
What are some of the things that cranial neural crest cells form ?
-odontoblasts
-truncocoronal septum
-pharnygeal arch and cartilage
-dermis and epidermis of the head and neck
What are some things that spinal neural crest cells form?
-preaortic ganglia
-adrenal medulla
-dorsal root ganglia
-chain ganglia
What are some things that are formed from both cranial and spinal neural crest cells?
-schwann cells
-glial cells
-arachnoid and pia mater
-enteric ganglia
When do the pharyngeal arches begin forming?
day 28 of development
What are associated with each level of pharyngeal arches?
blood vessel, cranial nerves, and cartilage
What does the 1st branchial groove form?
external auditory canal
What does the 1st branchial pouch form?
eustachian tube
What does the 2nd branchial pouch form?
palatine tonsils
What does the 3rd branchial pouch form?
inferior parathyroids/thymus
What does the 4th branchial pouch form?
superior parathyroids/ultimobranchial body
What happens to the relative size of the fetal head during development?
the head stays around the same size but the body gets larger
-means the percentage of the fetus that is head gets smaller
What are the four processes of the face that start lateral and move toward the medial to form the face?
-mandibular process
-maxillary process
-lateral nasal process
-median nasal process
What is the remanent of the face of the lateral processes coming together?
the filtrum of the lip
What can happen if the processes do not meet properly?
cleft lip or palate
When does fusion of the maxillary and medial nasal processes usually occur?
5-6 weeks gestation
when does fusion of the palatine shelves occur?
begin during the 8th week and is completed in the 12th week
What percentage of clefts are combined cleft lip/palate?
45%
What percentage of clefts are just cleft palate?
30%
What percentage of clefts are just cleft lip?
25%
Incidence of cleft lip/palate in Chinese, Japanese, and Native American populations
1 in 500
Incidence of cleft lip/palate in Caucasian populations
1 in 700
Incidence of cleft lip/palate in African American populations
1 in 500
Incidence of cleft lip/palate in all populations
1 in 2500
Is there a genetic aspect of cleft lip/palate?
yes sort of
-if you have one child with cleft lip/palate, there is a 40% chance of having a second child with it
What are some drugs that can cause cleft lip/palate ?
ethanol, tetracycline, dilantin, lithium, methotrexate, warfarin, thalidomide, androgens, progesterone, and retinoic acid
What are some chemicals that can cause cleft lip/palate?
methylmercrury, polychlorinated biphenyls
Can radiation cause cleft lip/palate?
yes
Where can a nasopalatine duct cyst form?
at the fusion between palatine shelves and primary plate
Where do lateral cervical cyst/branchial fistuals form?
along the line of the sternocleidomastiod muscle
What pharyngeal arches help to form the tongue?
1- forms the anterior part of the tongue and contributes CN 5
2- provides some innervation
3 and 4- both help to form the posterior tongue
What is the intermediate and adult structure the come form the branchial arch 1?
intermediate
-median tongue bud
-foramen cecum
-lateral lingual swellings
adult
-overgrown my lateral lingual swellings
-origin of the thyroid ectoderm
-anterior 2/3 of tongue
What is the intermediate and adult structure the come form the branchial arch 2?
intermediate
-copula/tuberculim impar
adult
-overgrown by the hypobranchial eminence
What is the intermediate and adult structure the come form the branchial arch 3?
intermediate
-hypobranchial eminence
adult
-posterior 1/3 of tongue
What is the intermediate and adult structure the come form the branchial arch 4?
intermediate
-minor contributions to the hypobranchial eminence
adult
-none
What cranial nerve innervates branchial arch 1?
CN V (trigeminal)
What cranial nerve innervates branchial arch 2?
CN VII (facial)
What cranial nerve innervates branchial arch 3?
CN IX (glossopharyngeal)
What cranial nerve innervates branchial arch 4?
CNX (vagus)
What cranial nerve innervates branchial arch 6?
CN XII (hypoglossal)
What does the trigeminal nerve do for the tongue?
sensory to the anterior 2/3
What does the facial nerve do for the tongue?
special sensory (taste) to anterior 2/3 via the chorda tympani branch
What does the glossopharyngeal nerve do for the tongue?
sensory to the posterior 1/3
What does the vagus nerve do for the tongue?
sensory to the extreme posterior 1/3 via the superior laryngeal branch
What does the hypoglossal nerve do for the tongue?
motor to all of the tongue muscles
What is the median rhomboid glottitis?
was thought to present a portion of the tuberculum impar (branchial arch II) that persists, but is now considered to be a result of a fungal infection
How does a thyroglossal duct cyst form?
failure of thyroglossal duct to involute
Where does the thyroid start forming?
near the foramen cecum of the tongue
-must move inferiorly past the epiglottis, hyoid bone, thyroid cartilage, and the cricoid cartilage to make it to the correct place
What is a ectopic lingual thyroid?
when the thyroid does not move inferiorly and remains on the posterior part of the tongue
What cartilages forms from the first pharyngeal arch?
Meckel’s cartilage
Mandible
maleus
incus
What cartilage and bone forms from the second pharyngeal arch?
reichart’s cartilage
stapes
styloid process
stylohyoid ligament
lesser horn of hyoid
What cartilage and bone forms from the third pharyngeal arch?
greater horn of hyoid
What cartilage and bone forms from the fourth pharyngeal arch?
thyroid cartilage
What are the segments that are combined to form the ear?
there are 6 auricular hillocks that come together to form the ear
-sometimes there are more than 6 or less than 6 depending on formation
