Embryology Flashcards
Germinal Stage is from week ___ to ___
Germinal stage– week 1 to 2
The zygote (diploid) will multiply to form the _________
Morula– ball of about 8 cells
Morula becomes the ________
Blastula– bundle of cells containing an inner cavity known as the blastocoel
Implantation
Blastula fuses with the uterine wall (endometrium)
Blastula develops into the ________ and __________ after implantation
Embryoblast
- inner cell mast which will form the majority of the EMBRYO
Trophoblast
- outer cell mass that will mainly become the PLACENTA
During week 2, the embryoblast forms a _________ _____
Bilaminar disc
2 parts:
- epiblast: becomes 3 major germ layers
- hypoblast: little importance, mostly disappears
Amniotic Cavity and Yolk Sac Cavity
Visible in week 2
Amniotic cavity encases the fetus as it develops
Yolk sac cavity is responsible for nutrient and gas exchange before the placenta is developed enough to do this
Caudal Midline
Can be identified on dorsal aspect of embryo by locating the primitive node and primitive streak
Gastrulation
Week 3
3 distinct germ layers can be seen– ectoderm, mesoderm, and endoderm
Ectoderm
Forms epidermis, facial skeleton, nervous system
Forms teeth
- enamel derived from surface ectoderm
- majority of tooth derived from neural crest cells
Mesoderm
Forms “structural components” of the body like the skeletal system, muscular system, and connective tissue
Endoderm
Forms the lining of the foregut, midgut, and hindgut
Neurulation
Week 4
Neural plate folds in on itself and forms the neural tube
Notochord
Derived from mesoderm, signals the start of neurulation
Forms the vertebral column
Neural plate
Ectodermal tissue
Folds into the neural groove
Neural fold
Joining of the neural plates on either side of the neural plate
Neural groove
inner pouch that forms as the neural plate pinches in
Neural tube
Tube-like structure that sits below the remaining ectodermal layer (soon to be epidermis)
Neural crest
Former ends of the neural fold
Neural crest cells migrate throughout the embryo and form various specialized structures (ex. glia, melanocytes)
As neurulation ends, _______ ______, ________ ________, and __________ begin to form cranially to caudally.
aortic arches
pharyngeal arches
somites
Buccopharyngeal membrane
opens cranially
Forms stomodeum: primitive oral cavity
Blastopore
primitive anus, located caudally
Optic placode
Primitive eye
Otic placode
Primitive ear
Pharyngeal Arches
Visible outpouchings that are precursors to various head and neck structures
There are 6 arches total, but arch 5 does not derive any structures
6th arch is located deep within the embryo and is not visible
Distinct anatomical features
- endodermal pouch
- mesenchymal core (mesoderm, neural crest, artery, nerve, muscle, cartilage)
- external ectodermal cleft
Pharyngeal Arch I (Mandibular)
Many structures are associated with the mandible and anterior ear
Pharyngeal Arch II (Hyoid)
Many structures associated with posterior ear and regions on an axis moving anteroinferiorly
Pharyngeal Arch III
Pharyngeal Arch IV
“Adams Apple cartilage”
CN X muscles of deep pharyngeal region
Pharyngeal Arch VI
Most Inferior cartilage before trachea
Pharyngeal clefts
Grooves on the ectodermal side between adjacent pharyngeal arches
Any issues in pharyngeal cleft formation results in brachial cyst
Pharyngeal Pouches
Grooves found on the endodermal side between pharyngeal arches
If pharyngeal pouches fail to develop correctly, brachial fistulas may result
Arch I placode, cleft and pouch
placode: trigeminal ganglion (CN V)
cleft: external auditory meatus
pouch: Eustachian tube and tympanic cavity
Arch 2 placode, cleft, and pouch
placode: geniculate ganglion (CN VII)
cleft: cervical sinus
pouch: palatine tonsil
Arch 3 placode, cleft, and pouch
placode: inferior sensory ganglion (CN IX)
cleft: cervical sinus
pouch: thymus and inferior parathyroids
pouch derivatives eventually migrate inferiorly by the lungs
Arch 4 placode, cleft, and pouch
placode: inferior sensory ganglion (CN X)
cleft: cervical sinus
pouch: superior parathyroids and ultimobranchial body (parafollicular cells)
pouch derivatives eventually migrate inferiorly by the lungs but remain superior to arch 3 pouch
Pituitary Gland Derivation
Roof of oral cavity (stomodeum) forms an invagination superiorly– Rathke’s Pouch
- forms ANTERIOR pituitary
- oral ectodermal origin
Floor of forebrain (diencephalon) evaginates inferiorly
- forms POSTERIOR pituitary gland
- neural ectodermal origin
Thyroid Derivation
Derived from tissues at the tongues base, specifically a depression known as the foramen cecum
Thyroglossal duct allows for temporary connection of the foramen cecum of the tongue and the thyroid gland
LINGUAL THYROID– may be present at base of patient’s tongue if the thyroid did not descend properly during development
Lip Derivation
Nasal pits surrounded by lateral nasal prominence and medial nasal prominence
Maxillary prominence is lateral and inferior, and moves ventrally and medially
- forms cheeks and lateral upper lip
- medial nasal prominences fuse together– form crest and tip of nose and philtrum
Mandibular prominence contributes to the jaw and lower lip
CLEFT LIP– failure of the medial nasal prominence and maxillary prominence to fuse
Palate Derivation
Primary palate = philtrum of lip, forms via fusion of 2 medial nasal prominences… 4 maxillary incisors grow here
Palatine shelves– move caudally and medially
Week 7– tongue moves inferiorly into oral cavity through palatine shelves
- now the palatine shelves can move horizontally and medially to fuse at midline (fuse cranial-to-caudal)
Secondary palate– fusion of the palatine shelves
Incisive foramen = fusion of primary and secondary palates at the midline
INCOMPLETE CLEFT PALATE= failure of palatal shelves to fuse
COMPLETE CLEFT PALATE= failure of primary palate to fuse with palatal shelves
DiGeorge Syndrome
Developmental disorder (genetic or environmental)
AKA third and fourth pouch syndrome
Affects neural crest cells, 3rd and 4th pharyngeal pouches (thymus and parathyroid gland development severely impacted)
“CATCH 22”
- Cardiac abnormalities
- Abnormal facies (hypertelorism, short philtrum, small mandible)
- Thymus aplasia
- Cleft palate
- Hypocalcemia (lack of PTH via parathyroid)
- 22q11 deletion
