Embryology: The End

Front 1

neuroectoderm

Back 1

1. retina
2. optic nerve

Front 2

surface ectoderm

Back 2

1. lens
2. lacrimal gland
3. corneal epithelium
4. conjunctival epithelium

Front 3

mesoderm

Back 3

remaining structures

Front 4

optic vesicles

Back 4

- from developing forebrain (diencephalon) as a lateral outgrowth

Front 5

lens placodes

Back 5

- optic vesicle makes contact with the overlying ectoderm, inducing it to form lens placodes
- later invaginated, becomes detached and rounds off into a lens vesicle which occupies the mouth of the optic cup

Front 6

optic cup

Back 6

- invagination of optic vesicle
- develops choroid fissure for the passage of the hyloid artery

Front 7

retina

Back 7

pigmented and sensory layers of the retina develop from the two walls of the optic cup

Front 8

optic stock

Back 8

- connects the optic cup to the forebrain
- becomes the optic nerve

Front 9

corneal epithelium

Back 9

- surface ectoderm which is reconstituted after the detachment of the lens vesicle

Front 10

fibrous and vascular coats

Back 10

- fibrous (sclera) and vascular (choroid) coats develops by local condensation of the mesoderm

Front 11

smooth m of iris

Back 11

- from ectoderm at the margin of the optic cup

Front 12

occular mm

Back 12

from paraxial mesoderm

Front 13

palpebrae

Back 13

develops as a skin fold above and below the eye

Front 14

coloboma

Back 14

failure of the choroidal fissure to close

Front 15

micro-opthalamia

Back 15

- small eye
- may result from intra-uterine infections: toxoplasmosis

Front 16

anopthalamia

Back 16

absence of eye
- resulting from exposure of mother to toxic chemical during pregnancy

Front 17

congenital cataracts

Back 17

cloudiness of lens

Front 18

ectoderm

Back 18

pharyngeal or branchial cleft

Front 19

mesoderm + neural crest

Back 19

pharyngeal arches

Front 20

pharyngeal pouches

Back 20

- bilateral outpocketings of endoderm
- along lateral wall of the most cranial part of the gut
- extend from the buccopharyngeal membrane to the commencement of the esophagus

Front 21

branchial arches

Back 21

dorso-ventrally thickened masses
- from pharyngeal pouches causing adjacent mesenchymal tissues to become partially segregated
- each supplied by an aortic arch and specific cranial nerve

Front 22

branchial groove/ cleft

Back 22

series of grooves in the surface ectoderm between the branchial arches

Front 23

derivatives of pharyngeal pouch I

Back 23

1. tympanic cavity
2. tonsilar fossa

Front 24

derivative of pharyngeal pouch II

Back 24

tonsillar fossa

Front 25

derivatives of pharyngeal pouch III and IV

Back 25

1. parathyroid
2. thymus

Front 26

derivatives of pharyngeal pouch V

Back 26

ultimobranchial body: gives rise to the parafollicular cells

Front 27

thyroid bud

Back 27

median endodermal downgrowth from the floor of the pharynx

Front 28

thyroglossal duct

Back 28

from thyroid bud growing ventrally and caudally, becoming canalized

Front 29

foramen cecum of the tongue

Back 29

- thyroglossal duct detaches its connection and migrates to the neck
- after the thyroglossal duct disapppears, this is the recognizable point of origin from the floor of the pharynx

Front 30

cells of thyroid follicles

Back 30

endodermal

Front 31

CT components of thyroid

Back 31

derived from the invasion of the surrounding mesoderm

Front 32

pharygeal clefts

Back 32

-series of grooves which demarcate the arches externally

Front 33

external acoustic meatus

Back 33

first pharyngeal cleft

Front 34

cervical sinus

Back 34

- from pharyngeal cleft II, III and IV
- normally regresses and disappears

Front 35

first pharyngeal arch

Back 35

-mandibular:
1. mandible (part), malleus, incus
2. muscles of mastication, digasticus (part)
3. mandibular division of trigeminal n

Front 36

second pharyngeal arch

Back 36

-hyoid:
1. hyoid apparatus (part), stapes
2. muscles of facial expression, digasticus (part), stapedius
3. facial n

Front 37

third pharyngeal arch

Back 37

1. hyoid apparatus: part
2. pharyngeal mm (part)
3. glossopharyngeal n

Front 38

fourth pharyngeal arch

Back 38

1. most laryngeal cartilages
2. pharyngeal and laryngeal mm
3. nerves: vagus, medullary part of accesory

Front 39

rostral 2/3 of tongue

Back 39

1. ventral part of the first pharyngeal arches
2. paired lateral swelling
3. median tuberculum impar

Front 40

caudal 1/3 of tongue

Back 40

1. pharyngeal arches 2, 3, and 4
2. hypobranchial eminense (copula)
3. forms the root of the tongue

Front 41

body of the tongue

Back 41

- rostral part
- grows and projects into the developing mouth
- lined by stromodeal ectoderm
- separated from the caudal part by the terminal sulcus
- caudal part lined by endoderm

Front 42

striated mm of tongue

Back 42

occipital somites

Front 43

innervation of the tongue

Back 43

1. trigeminal
2. facial
3.glossopharyngeal
4. hypoglossal

Front 44

dental lamina

Back 44

- thickened ridge of the oral ectoderm
along the length of the upper and lower jaw

Front 45

dental buds

Back 45

- from lamina
- deep surface invaginates, forming the enamel cup:
1. outer and inner dental epithelium
2. central core: stellate reticulum

Front 46

dental papilla

Back 46

mesenchyme of neural crest origin

Front 47

enamel

Back 47

- from amelioblasts of inner enamel epithelium
- produce prisms of enamel which become calcified

Front 48

dentine

Back 48

- laid down by odontoblasts: specialized cells of dental papilla

Front 49

pulp

Back 49

remaining cells of dental papilla

Front 50

cementum

Back 50

- from cementoblasts: differentiated mesenchymal cells located outside the tooth in contact with the root

Front 51

periodontal ligament

Back 51

- from mesenchyme outside the cementum layer

Front 52

auricle

Back 52

of external ear
- from swellings in the dorsal region of pharyngeal arches 1 &2

Front 53

external acoustic meatus

Back 53

first pharyngeal cleft
- of external ear

Front 54

auditory tube and tympanic cavity

Back 54

- of middle ear
- from first pharyngeal cavity

Front 55

tympanic membrane

Back 55

- of middle ear
1. ectoderm of the first cleft
2. endoderm of the first pouch

Front 56

malleus and incus

Back 56

- of middle ear
- from first pharyngeal arch

Front 57

stapes

Back 57

- of middle ear
- from second pharyngeal arch

Front 58

otic placode

Back 58

- of internal ear
- thickening of the surface ectoderm at the level on the rhombencephalon

Front 59

otic vesicle or otocyst

Back 59

- of inner ear
- formed when otic placode invaginates and detaches from the surface ectoderm

Front 60

membranous labyrinth

Back 60

- of inner ear
- from otic vesicle
1. utericle
2. saccule
3. endolymphatic duct
4. semilcircular duct
5. cochlear duct

Front 61

bony labyrinth

Back 61

- of inner ear
- chondrification and ossification of the surrounding mesoderm

Front 62

face

Back 62

develops around the stromodeum

Front 63

frontal process

Back 63

- dorsally appears as a result of growth of the mesenchymal cells around the forebrain

Front 64

maxillary and mandibular process

Back 64

- from division of mandibular arch

Front 65

nasal placode

Back 65

- two local ectodermal thickenings
appearing in the covering ectoderm bounding the oral depression

Front 66

nasal pit

Back 66

- invaginations of each nasal placode
- excavates the mesoderm ventrally
- communicates with stomodeum

Front 67

medial and lateral nasal processes

Back 67

- proliferating regions on either side of the nasal pits

Front 68

mandibular processes

Back 68

grow and develop into lower jaws

Front 69

maxilla

Back 69

maxillary process fused with the medial nasal processes

Front 70

cheek

Back 70

fusion of the mandibular and maxillary process at the corner of the mouth

Front 71

lacrimal duct

Back 71

groove between the lateral nasal and maxillary process

Front 72

microstomia and macrostomia

Back 72

abnormalities of fusion of the maxillary and mandibular process

Front 73

genetic teratology

Back 73

-mutation or inheritance of dominant or recessive genes
- may be caused by inbreeding

Front 74

physical teratogens

Back 74

x rays

Front 75

chemical teratogens

Back 75

vitamin A deficiency: micropthalmia in pigs

Front 76

drug teratogens

Back 76

thalidomide: pups

Front 77

infectious teratogens

Back 77

panleukopenia virus in kittens

Front 78

proportional causes of teratology

Back 78

1. 50-60%: idiopathic
2. 20-25%: multifactorial inheritance
3. 7-10%: environmental agents
4. 7-8% teratogens
5. 6-7%: chromosomal abnormalities

Front 79

susceptability to teratology

Back 79

1. maximum sensitivity to abnormal development during embryonic period
2. fetal period
3. pre-differentiation