Embryo Exam 3

Front 1

1. Pharyngeal (branchial arches)

Back 1

Are composed of mesoderm and neural crest cells.

They are formed by migration of neural crest cells around cores of mesoderm covered externally by ectoderm and internally by endoderm.

Each arch has its own cartilaginous, muscular, vascular and nervous components.

Front 2

2. Pharyngeal arch 1

Back 2

Forms the Meckel's cartilage which develops:
1. Malleus
2. Incus
3. Maxilla
4. Zygomatic and temporal squamous bones
5. Mandible

Forms CN V (V2 and V3), which supply muscles of mastication and mylohyoid, digastric anterior belly, tensor veli palatini, and tensor tympani muscles.

Front 3

3. Pharyngeal arch 2

Back 3

Forms the Reichert's cartilage, whch develops:
1. Stapes
2. Styloid process
3. Lesser horn and upper half of the hyoid bone

Forms CN XII, which innervates muscles of facial expression and the digastric posterior belly, stylohyoid, and stapedius muscle.

Front 4

4. Pharyngeal arch 3

Back 4

Forms the third arch cartilage which forms:
1. Greater horn and lower half of the hyoid bone

Forms CN IX, which innervates the stylopharyngeus muscle

Front 5

5. Pharyngeal arch 4

Back 5

Forms the fourth arch cartilage, which forms the laryngeal cartilages.

Forms CN X (superior laryngeal branch), which innervates the muscles of the soft palate (except the tensor veli palatini), muscles of the pharynx (except stylopharyngeus), and the cricopharyngeus muscle.

Front 6

6. Pharyngeal arch 6

Back 6

Forms the sixth arch cartilage, which forms laryngeal cartilages

Forms CN X (recurrent laryngeal branch), which innervates the intrinsic muscles of the larynx (except cricothyroid), and the upper muscles of the esophagus

Front 7

7. Pharyngeal pouches

Back 7

Are evaginations of the foregut endoderm.

Front 8

8. Pharyngeal pouch 1

Back 8

Forms the epithelium of the auditory tube (pharyngotympanic tube) and the middle ear cavity

Front 9

9. Pharyngeal pouch 2

Back 9

Forms the epithelium and crypts of the palatine tonsil

Front 10

10. Pharyngeal pouch 3

Back 10

Forms the inferior parathyroid gland and thymus

Front 11

11. Pharyngeal pouch 4

Back 11

Forms the superior parathyroid gland and the ultimobranchial (ultimopharyngeal) body

Front 12

12. Pharyngeal grooves (or clefts)

Back 12

Are four invaginations of the surface ectoderm between adjacent arches

Front 13

13. Pharyngeal groove 1

Grooves 2, 3, and 4

Back 13

Gives rise to the epithelium of the external auditory meatus and skin over the tympanic membrane

Other grooves (2, 3, and 4) are obliterated

Front 14

14. Pharyngeal membranes

Back 14

Are located at the junction of each pharyngeal groove and pouch

Front 15

15. Pharyngeal membrane 1

Membranes 2, 3, and 4

Back 15

Pharyngeal membrane 1 gives rise to the tympanic membrane

Membranes 2, 3, and 4 are obliterated

Front 16

16. Development of the thyroid gland

Back 16

1. The gland derives from median endodermal thickenings on the floor of the pharynx and is closely associated w/ the development of the tongue.
2. The thyroid descends from the pharynx to the neck and remains connected to the tongue via a thyroglossal duct.
3. The superior opening of the thyroglossal duct remains open as a small pit on the dorsum of the tongue
- This pit is the foramen cecum

Front 17

17. Branchial cysts/fistulas

Back 17

Occur when the second pharyngeal arch fails to grow caudally over the third and fourth arches, leaving remnants of the second, third and fourth grooves in contact with the surface by a narrow canal.

Such a defect results in a lateral cervical cyst directly anterior to the SCM muscle below the jaw.

Fistulas have openings on the lateral aspect of the neck.

Front 18

18. Branchial vestiges

Back 18

Normally, pharyngeal cartilages disappear; remnants of cartilage or bone elements under the skin anterior to the inferior 1/3 of the SCM muscle.

Front 19

19. Ectopic thyroid tissue

Back 19

The thyroid gland undergoes a migration from the oral cavity to the neck region.

It is common for remnants of thyroid tissue to remain along the course of migration.

The parathyroids also undergo a migration and are highly variable in the their location.

Front 20

20. Thyroglossal cysts and sinuses

Back 20

Thyroglossal cysts lie in the midline of the neck and are tubular remnants of the thyroglossal duct.

Are usually located close to or just inferior to the body of the hyoid bone.

Sometimes they are connected to the outside by a fistulous canal, a thyroglossal fistula (sinus)

Front 21

21. Treacher Collins syndrome

Back 21

Is a genetic defect involving the first arch

Characterized by:
1. Malar hypoplasia
2. Mandibular hypoplasia
3. Down-slanting palpebral fissures
4. Lower eyelid colobomas
5. Malformed external ears
6. Faulty dentition

Front 22

22. Pierre Robin sequence

Back 22

Also involves the first arch.

Characterized by:
1. Micrognathia (small jaw)
2. Cleft palate
3. Glossoptosis (post. placed tongue)
4. External ear defects

Front 23

23. DiGeorge anomaly

Back 23

Involves abnormalities with the heart, parathyroid glands, face, and thymus gland.

Affected individuals will have:
1. Congenital heart disease
2. Unusual facial features
3. Low set ears
4. Jawbone that recedes
5. Wide set eyes
6. Born w/o parathyroid glands

Front 24

24. Goldenhar syndrome

Back 24

Includes a number of craniofacial abnormalities that usually involve the maxillary, temporal, and zygomatic bones, which are small and flat.
Defects in:
1. Ear (anotia, microtia)
2. Eye (tumors and dermoids in eyeball)
3. Vertebral (fused and hemivertebrae, spina bifida)
4. Cardiac abnormalities (tetrology of fallot and ventricular septal defects)

Front 25

25. Anterior 2/3's of the tongue

Back 25

Develop from one median lingual swelling (tongue bud) and two lateral lingual swellings in the pharyngeal arch 1.

Lateral swellings grow over the median tongue bud and fuse and form the anterior 2/3's of the tongue

Front 26

26. Posterior 1/3 of tongue

Back 26

Develops behind the foramen cecum from the copula ( from pharyngeal arch 2) and the hypopharyngeal eminence (from the mesoderm of the pharyngeal arches 3 and 4.

Terminal sulcus marks the division of the anterior 2/3 and posterior 1/3 of tongue.

Front 27

27. Muscles of the tongue

Back 27

Most of the tongue muscles are derived from myoblasts athat migrate to the tongue region from occipital somites.

These somites are accompanied by the hypoglossal nerve (CN XII).

Front 28

28. Tongue tie (ankyloglossia)

Back 28

The tongue is not freed from the floor of the mouth.

Normally, extensive cell degeneration occurs and the frenulum is the only tissue that anchors the tongue to the floor of the mouth.

In the most common form of ankyloglossia, the frenulum extends to the tip of the tongue.

Front 29

29. Development of the cranial base (cartilaginous neurocranium)

Back 29

Develops mainly by endochondral ossification

Contains cartilages:
1. Prechordial (mostly up front)
2. Parachordal (around back)
3. Hypophyseal (in center)

Front 30

30. Development of the flat bones of skull (membranous neurocranium)

Back 30

Derives from neural crest cells

Formed by intermembranous ossification at the sides and top of the brain (calvaria)

Has the significance of six fontanelles at birth

Front 31

31. Development of the facial skeleton (membranous viscerocranium)

Back 31

Arises from the first arch (maxillary prominence) and neural crest cells

Forms mainly by intramembranous ossification so not from the cartilage of the first arch.

Front 32

32. Summary of development of skull:

Back 32

Cranial base develops mainly from endochondral ossification

Cranial vault and facial skeleton develops mainly by intramembranous ossification

Sutures are important sites of growth and allow bones to overlap during birth

Front 33

33. Primary palate

Back 33

During the 6th week the primary palate forms from the intermaxillary segment (medial nasal prominences)

Is triangular in shape and forms the premaxillary part of the maxilla and holds the incisor teeth.

Front 34

34. Secondary palate

Back 34

Also develops in the 6th week

Formed by fusion of the lateral palatine processes (palatal shelves) that develop from the maxillary prominences to form the hard palate

Bone ceases to form in the secondary palate leaving a bone free soft palate and uvula

Front 35

35. Acrania or anencephaly

Back 35

No calvaria, failure of cephalic part of neural tube to close.

As a result, the vault of the skull does not form, leaving the malformed brain exposed.

Later this tissue degenerates, leaving a mass of necrotic tissue called anencephaly, although the brainstem remains intact.

Front 36

36. Craniosynostosis

Back 36

Premature closing of the sutures; results in a skull w/peculiar shapes

Front 37

37. Scaphocephaly

Back 37

Sagittal suture closes

Skull is long and narrow

Front 38

38. Oxycephaly

Back 38

Coronal suture closes

Skull is tall

Front 39

39. Clover leaf skull

Back 39

Sagittal, coronal, and lambdoid sutures closed

Only squamous suture is still open between the temporal and parietal bones

Skull is trilobate: one frontal protrusion and two postero-lateral protrusions

Front 40

40. Microcephaly

Back 40

Cranial vault is smaller than normal. Fontanelles close early and sutures close during the first year.

Since the size of the cranium depends of the growth of the brain, underlying defects is in brain development.

Often accompanied by severe mental retardation

Front 41

41. Causes of microcephaly

Back 41

Fetal infection by toxoplasmosis may result in cerebral calcification, mental retardation, hydrocephalus, or microcephaly

Front 42

42. Causes of exancephaly, anencephaly, or acrania

Back 42

Brain develops outside of skull

Exposure to radiation during the early stages of development or hyperthermial by maternal infection or by sauna baths may cause spina bifida and exancephaly.

Front 43

43. Microstomia

Back 43

Small mouth due to excessive merging of maxillary and mandibular prominences

Front 44

44. Clefts anterior to the incisive foramen (anterior clefts)

Back 44

1. Lateral cleft lip
2. Cleft upper jaw
3. Clefts between primary and secondary palates

Due to a partial or complete lack of fusion of the maxillary prominence and intermaxillary segment (medial nasal prominence)

Front 45

45. Clefts posterior to the incisive foramen (posterior clefts)

Back 45

1. Cleft (secondary palate)
2. Cleft uvula

Cleft palate results from a lack of fusion of the palatine shelves; defective development of the secondary palate

Cleft palates usually occurs in females and freq occur with other deformities, unlike cleft lip

Front 46

46. Cleft lip

Back 46

Involves only the lip and may be bilateral; occurs in various degrees

1/1000; 80% of cases are male

Front 47

47. Median (midline) cleft lip

Back 47

Rare; failure of the medial nasal prominences to merge and form intermaxillary segments

Usually accompanied by a deep groove between the right and left sides of the nose.

Lost of midline structures may be so extensive that the lateral ventricles fuse (holoprosencephaly).

Characteristic of Mohr syndrome

Front 48

48. Oblique facial clefts

Back 48

produced by failure of the maxillary prominence to merge with its corresponding lateral nasal prominence.

When this occurs, the nasolacrimal duct is usually exposed to the surface

Front 49

49. Positional plagiocephaly

Back 49

Flat head syndrome

Due to assymetric closure from physical deformations (car seat position)

The skull becomes twisted

Front 50

50. Development of external ear

Back 50

1. Pharyngeal groove 1 forms the external auditory meatus and tympanic membrane

2. Auricular hillocks form the auricle

Front 51

51. Development of the middle ear.

Back 51

1. Pharyngeal arch 1 forms the incus, malleus, tensor tympani muscle and trigeminal nerve (CN V)

2. Pharyngeal arch 2 forms the stapes, stapedius muscle and facial nerve (CN VII)

3. Pharyngeal pouch 1 forms the auditory tube and middle ear cavity

4. Pharyngeal membrane 1 forms the tympanic membrane

Front 52

52. Development of the internal ear

Back 52

Develops from the otic placodes (thickening of embryonic ectoderm), which invaginates to form the otic pit and otic vesicle (vesicle forms the otic capsule)

Front 53

53. Otic vesicle

Back 53

Gives rise to the membranous labyrinth and develops:
1. Utriclar portion
2. Saccular portion
3. Vestibular pouch
4. Cochlear pouch

Front 54

54. Utricular portion

Back 54

Forms:

1. Utricle
2. Semicircular ducts
3. Vestibular ganglion on CN VIII

Front 55

55. Saccular portion

Back 55

Forms:

1. Saccule
2. Cochlear duct
3. Spiral ganglion of CN VIII

Front 56

56. Vestibular pouch

Back 56

Forms:

1. Semicircular canals
2. Utricle
3. Endolymphatic duct

Front 57

57. Cochlear pouch

Back 57

Forms:

1. Saccule, which forms a diverticulum, that in turn, forms the cochlear duct

Front 58

58. Otic capsule

Back 58

Develops from mesenchyme around the otic vesicle and forms:

1. Perilymphatic space (develops into the scala tympani and scala vestibule)
2. The cartilaginous part ossifies to form the bony labyrinth

Front 59

59. Derivation of the tympanic membrane

Back 59

Derived from all three germ layers

Front 60

60. Minor deformities of the external ear

Back 60

The top of the ear should be in the same horizontal level as the corner of the eye.

Common; they are often associated with other anomalies

Front 61

61. Auricular appendages

Back 61

Caused by the persistence of extra auricular hillocks

Front 62

62. Microtia

Back 62

Results from the absence of auricular hillocks and is characterized by the absence of the auricle; this defect is often associated w/other defects

Front 63

63. Preauricular pits or sinuses

Back 63

Small depression located anterior to the auricle.

Results from the abnormal closure of the first pharyngeal groove.

Can become infected

Front 64

64. Atresia of external auditory meatus

Back 64

During development of the external ear, there is a plug of cells situated in front of the tympanic membrane

These cells normally regress but if they fail to die, atresia occurs

Front 65

65. Congenital deafness

Back 65

Caused by abnormal development of the membranous and bony labyrinths or by malformations of the auditory ossicles and eardrum.

Can be caused by:
1. Genetics
2. Rubella virus
3. Poliomyelitis
4. Erythroblastosis fetalis
5. Diabetes
6. Hypothyroidism
7. Toxoplasmosis

Front 66

66. Development of the eye (neuroectoderm)

Back 66

Neuroectoderm from diencephalon evaginates to form the optic vesicle, which invaginates to form the optic cup and optic stalk.

This induces the ectoderm to thicken and form the lens placode.

Front 67

67. Optic cup

Back 67

Forms:
1. Retina
2. Iris
3. Ciliary body

Front 68

68. Optic stalk

Back 68

Forms the optic nerve

Front 69

69. Development of the eye (surface ectoderm)

Back 69

Invaginates to form the lens placode which forms the lens and anterior epithelium of the cornea

Front 70

70. Development of the eye (mesoderm)

Back 70

Forms:

1. Sclera
2. Portions of the cornea
3. Vitreous body
4. Extraocular muscles (from prechordal plate mesoderm or preotic somites)
5. Fibrous and vascular coats

Front 71

71. Development of the eye (neural crest cells)

Back 71

Forms:

1. Choriods
2. Sphincter pupillae muscle
3. Dilator pupillae muscle
4. Ciliary muscle

Front 72

72. Development of the eye (hyaloid artery and vein)

Back 72

Forms the central artery and vein of the retina

Front 73

73. Congenital retinal detachment

Back 73

The two layers of the retina (pigmented and neural) are separated by an intraretinal space

Normally, there is some degree of fusion between the two layer but if they fail to fuse during development the defect is congenital

Can also be caused by a blow to the eye in which case fluid can accumulate and vision can be impaired

Front 74

74. Coloboma

Back 74

This defect involves an improper closing of the choriod fissure resulting in a gap in the iris only (coloboma iridis) or in both the retina and iris.

May occur w/other eye defects or be present as a part of the renal coloboma syndrome (renal defects)

Front 75

75. Persistent iridopupillary membrane

Back 75

The iridopupillary membrane may persist instead of being resorbed during the formation of the anterior chamber

Front 76

76. Cyclopia and synophthalmia

Back 76

Single eye (cyclopia) and fused eyes (synophthalmia) are due to a loss of midline tissue that may occur with an underdevelopment of the forebrain and frontonasal prominence.

Associated with cranial defects such as holoprosencephaly.

Commonly occur with a midline proboscis superior to the fused eyes

Front 77

77. Micophtalmia

Back 77

Indicated by a small, normal appearing eye or an eye that was arrested at some point during normal development.

May lack a lens

Front 78

78. Anopthalmia

Back 78

Congenital absence of an eye or eye tissue.

Can only involve the optic stalk and may involve development of the forebrain which is usually accompanied by severe cranial abnormalities

Front 79

79. Congenital glaucoma (cataracts)

Back 79

The lens becomes opaque during intrauterine life and results in an increased intraocular pressure.

Occurs due to a congenital defect in the draining mechanism (the scleral venous sinus)

May arise in relation to a rubella infection during pregnancy

Front 80

80. Congenital aphakia and aniridia

Back 80

Aphakia (absence of the lens) and aniridia (absence of the iris) are rare anomalies that are due to disturbances in induction and formation of tissues responsible for these structures.