Chapter 17: Head and Neck

Question 1

Mesenchyme for formation of the head region is derived from ______ and ______, ______, and thickened regions of ______ known as ______.

Answer 1

paraxial, lateral plate mesoderm, neural crest, ectoderm, ectodermal placodes

Question 2

Paraxial mesoderm (______ and ______) forms a large portion of the ______ and ______ components of the ______ (______), all ______ muscles of the ______ region, the ______ and ______ tissues in the ______ region of the head, and the ______ caudal to the ______. Lateral plate mesoderm forms the ______ (______ and ______) and ______ tissue in this region.

Answer 2

somites, somitomeres, membranous, cartilaginous, neurocranium, skull, voluntary, craniofacial, dermis, connective, dorsal, meninges, prosencephalon, laryngeal cartilages, arytenoid, cricoid, connective

Question 3

Neural crest cells originate in the ______ of ______, ______, and ______ regions and migrate ______ into the ______ and ______ around the ______ and ______ into the facial region.

Answer 3

neuroectoderm, forebrain, midbrain, hindbrain, ventrally, pharyngeal arches, rostrally, forebrain, optic cup

Question 4

In these locations, they form the entire ______ (______) and parts of the ______ and ______ regions of the ______ (______). They also form all other tissues in these regions, including ______, ______, ______, ______, ______, ______ and ______, sensory ______, and glandular ______ tissue.

Answer 4

viscerocranium, face, membranous, cartilaginous, neurocranium, skull, cartilage, bone, dentin, tendon, dermis, pia, arachnoid, neurons, connective

Question 5

Cells from ectodermal placodes (______), together with ______, form neurons of the ______, ______, ______, and ______ cranial sensory ganglia.

Answer 5

epipharyngeal placodes, neural crest, 5th, 7th, 9th, 10th

Question 6

The most distinctive feature in development of the head and neck is the presence of ______ (the old term for these structures is ______ because they somewhat resemble the gills [branchia] of a fish). These arches appear in the ______ and ______ weeks of development and contribute to the characteristic external appearance of the ______. Initially, they consist of bars of ______ tissue separated by deep clefts known as ______.

Answer 6

pharyngeal arches, branchial arches, fourth, fifth, embryo, mesenchymal, pharyngeal clefts

Question 7

Simultaneously, with development of the arches and clefts, a number of outpocketings, the ______, appear along the ______ walls of the ______, the most ______ part of the ______.

Answer 7

pharyngeal pouches, lateral, pharynx, cranial, foregut

Question 8

The pouches penetrate the surrounding ______ but do not establish an open communication with the external ______. Hence, although development of pharyngeal arches, clefts, and pouches resembles formation of ______ in fishes and amphibians, in the human embryo, real ______ are never formed.

Answer 8

mesenchyme, clefts, gills, gills

Question 9

Therefore, the term ______ (arches, clefts, and pouches) has been adopted for the human embryo.

Answer 9

pharyngeal

Question 10

Pharyngeal arches not only contribute to formation of the ______ but also play an important role in formation of the ______.

Answer 10

neck, face

Question 11

At the end of the ______ week, the center of the face is formed by the ______, surrounded by the first pair of ______.

Answer 11

fourth, stomodeum, pharyngeal arches

Question 12

When the embryo is ______ days old, five mesenchymal prominences can be recognized: the ______ (first pharyngeal arch), ______ to the ______, the ______ (dorsal portion of the first pharyngeal arch), ______ to the ______, and the ______, a slightly rounded elevation ______ to the ______.

Answer 12

42, paired mandibular prominences, caudal, stomodeum, paired maxillary prominences, lateral, stomodeum, frontonasal prominence, cranial, stomodeum

Question 13

Development of the face is later complemented by formation of the ______. In all cases, differentiation of structures derived from arches, pouches, clefts, and prominences is dependent on ______.

Answer 13

nasal prominences, epithelial–mesenchymal interactions

Question 14

PHARYNGEAL ARCHES

Each pharyngeal arch consists of a ______ of ______ covered on the outside by surface ______ and on the inside by ______ of ______ origin.

Answer 14

core, mesenchymal tissue, ectoderm, epithelium, endodermal

Question 15

PHARYNGEAL ARCHES

In addition to mesenchyme derived from ______ and ______ plate mesoderm, the ______ of each arch receives substantial numbers of ______, which migrate into the ______ to contribute to ______ components of the face.

Answer 15

paraxial, lateral, core, neural crest cells, arches, skeletal

Question 16

PHARYNGEAL ARCHES

The original mesoderm of the arches gives rise to the musculature of the ______ and ______. Thus, each ______ is characterized by its own ______ components.

Answer 16

face, neck, pharyngeal arch, muscular

Question 17

PHARYNGEAL ARCHES

The muscular components of each arch have their own ______, and wherever the ______ cells migrate, they carry their ______ component with them.

Answer 17

cranial nerve, muscle, nerve

Question 18

PHARYNGEAL ARCHES

In addition, each arch has its own ______ component.

Answer 18

arterial

Question 19

First Pharyngeal Arch

The ______ consists of a ______ portion, the ______, which extends forward beneath the region of the ______, and ______ portion, the ______, which contains ______.

Answer 19

first pharyngeal arch, dorsal, maxillary process, eye, aventral, mandibular process, Meckel cartilage

Question 20

First Pharyngeal Arch

During further development, ______ disappears except for ______ small portions at its ______ end that persist and form the ______ and ______.

Answer 20

Meckel cartilage, two, dorsal, incus, malleus

Question 21

First Pharyngeal Arch

Mesenchyme of the maxillary process gives rise to the ______, ______, ______, and part of the ______ through ______.

Answer 21

premaxilla, maxilla, zygomatic bone, temporal bone, membranous ossification

Question 22

First Pharyngeal Arch

The mandible is also formed by ______ of ______ surrounding ______. In addition, the ______ arch contributes to formation of the bones of the ______, part of the ______, and the ______.

Answer 22

membranous ossification, mesenchymal tissue, Meckel cartilage, first, middle ear, external ear, external auditory meatus

Question 23

First Pharyngeal Arch

Musculature of the first pharyngeal arch includes the ______ (______, ______, and ______), anterior belly of the ______, ______, ______, and ______.

Answer 23

muscles of mastication, temporalis, masseter, pterygoids, digastric, mylohyoid, tensor tympani, tensor palatini

Question 24

First Pharyngeal Arch

Hie nerve supply to the muscles of the first arch is provided by the ______ of the ______.

Answer 24

mandibular branch, trigeminal nerve

Question 25

First Pharyngeal Arch

Because mesenchyme from the first arch also contributes to the ______ of the face, sensory supply to the skin of the face is provided by ______, ______, and ______ branches of the ______.

Answer 25

dermis, ophthalmic, maxillary, mandibular, trigeminal nerve

Question 26

First Pharyngeal Arch

Muscles of the arches do not always attach to the ______ or ______ components of their own arch but sometimes ______ into surrounding regions. Nevertheless, the origin of these muscles can always be ______ because their nerve supply is derived from the ______ of ______.

Answer 26

bony, cartilaginous, migrate, traced, arch, origin

Question 27

Second Pharyngeal Arch

The cartilage of the ______ or ______ arch (______) gives rise to the ______, ______ of the ______, ______, and ______, the ______ and upper part of the body of the ______.

Answer 27

second, hyoid, Reichert cartilage, stapes, styloid process, temporal bone, stylohyoid ligament, ventrally, lesser horn, hyoid bone

Question 28

Second Pharyngeal Arch

Mesenchyme of the arch also forms most of the ______.

Answer 28

external ear

Question 29

Second Pharyngeal Arch

Muscles of the hyoid arch are the ______, ______, ______ of the ______, ______, and muscles of ______.

Answer 29

stapedius, stylohyoid, posterior belly, digastric, auricular, facial expression

Question 30

Second Pharyngeal Arch

The ______, the nerve of the second arch, supplies all of these muscles.

Answer 30

facial nerve

Question 31

Third Pharyngeal Arch

The cartilage of the ______ produces the ______ of the body and ______ of the hyoid bone.

Answer 31

third pharyngeal arch, lower part, greater horn

Question 32

Third Pharyngeal Arch

The musculature is limited to the ______. These muscles are innervated by the ______, the nerve of the third arch.

Answer 32

stylopharyngeus muscles, glossopharyngeal nerve

Question 33

Fourth and Sixth Pharyngeal Arches

______ components of the ______ and ______ pharyngeal arches fuse to form the ______, ______, ______, ______, and ______ cartilages of the ______.

Answer 33

Cartilaginous, fourth, sixth, thyroid, cricoid, arytenoid, corniculate, cuneiform, larynx

Question 34

Fourth and Sixth Pharyngeal Arches

Muscles of the ______ arch (______, ______, and constrictors of the ______) are innervated by the ______ branch of the ______, the nerve of the fourth arch.

Answer 34

fourth, cricothyroid, Levato veli palatini, pharynx, superior laryngeal, vagus

Question 35

Fourth and Sixth Pharyngeal Arches

Intrinsic muscles of the larynx are supplied by the ______ branch of the ______, the nerve of the sixth arch.

Answer 35

recurrent laryngeal, vagus

Question 36

PHARYNGEAL POUCHES

The human embryo has ______ pairs of pharyngeal pouches; the ______ is rudimentary.

Answer 36

four, fifth

Question 37

PHARYNGEAL POUCHES

Because the ______ of the pouches gives rise to a number of important organs, the fate of each pouch is discussed separately.

Answer 37

epithelial endodermal lining

Question 38

First Pharyngeal Pouch

The ______ forms a stalklike diverticulum, the ______, which comes in contact with the ______ of the ______.

Answer 38

first pharyngeal pouch, tubotympanic recess, epithelial lining, first pharyngeal cleft

Question 39

First Pharyngeal Pouch

The ______ portion of the diverticulum widens into a saclike structure, the ______ or ______, and the ______ part remains narrow, forming the ______ (______) tube.

Answer 39

distal, primitive tympanic, middle ear cavity, proximal, auditory, eustachian

Question 40

First Pharyngeal Pouch

The lining of the tympanic cavity later aids in formation of the ______ or ______.

Answer 40

tympanic membrane, eardrum

Question 41

Second Pharyngeal Pouch

The ______ of the second pharyngeal pouch proliferates and forms ______ that penetrate into the surrounding ______.

Answer 41

epithelial lining, buds, mesenchyme

Question 42

Second Pharyngeal Pouch

The buds are secondarily invaded by ______, forming the ______ of the ______.

Answer 42

mesodermal tissue, primordium, palatine tonsils

Question 43

Second Pharyngeal Pouch

During the ______ and ______ months, the tonsil is infiltrated by ______ tissue. Part of the pouch remains and is found in the adult as the ______.

Answer 43

third, fifth, lymphatic, tonsillar fossa

Question 44

Third Pharyngeal Pouch

The ______ and ______ pouches are characterized at their distal extremity by a ______ and a ______ wing.

Answer 44

third, fourth, dorsal, ventral

Question 45

Third Pharyngeal Pouch

In the ______ week, epithelium of the ______ region of the third pouch differentiates into the ______, whereas the ______ region forms the ______. Both gland ______ lose their connection with the pharyngeal wall, and the ______ then migrates in a ______ and a ______ direction, pulling the ______ with it.

Answer 45

fifth, dorsal, inferior parathyroid gland, ventral, thymus, primordia, thymus, caudal, medial, inferior parathyroid

Question 46

Third Pharyngeal Pouch

Although the main portion of the thymus moves rapidly to its final position in the ______ part of the ______ where it fuses with its counterpart from the ______ side, its ______ portion sometimes persists either embedded in the ______ or as isolated ______.

Answer 46

anterior, thorax, opposite, tail, thyroid gland, thymic nests

Question 47

Third Pharyngeal Pouch

Growth and development of the ______ continue until puberty.

Answer 47

thymus

Question 48

Third Pharyngeal Pouch

In the young child, the thymus occupies considerable space in the ______ and lies behind the ______ and ______ to the ______ and ______. In older persons, it is difficult to recognize because it is ______ and replaced by ______.

Answer 48

thorax, sternum, anterior, pericardium, great vessels, atrophied, fatty tissue

Question 49

Third Pharyngeal Pouch

The parathyroid tissue of the third pouch finally comes to rest on the ______ surface of the ______ and forms the ______.

Answer 49

atrophieddorsal, thyroid gland, inferior parathyroid gland

Question 50

Fourth Pharyngeal Pouch

Epithelium of the ______ region of the ______ forms the ______.

Answer 50

dorsal, fourth pharyngeal pouch, superior parathyroid gland

Question 51

Fourth Pharyngeal Pouch

When the parathyroid gland loses contact with the wall of the pharynx, it attaches itself to the ______ surface of the caudally migrating ______ as the ______.

Answer 51

dorsal, thyroid, superior parathyroid gland

Question 52

Fourth Pharyngeal Pouch

The ventral region of the fourth pouch gives rise to the ______, which is later incorporated into the ______.

Answer 52

ultimobranchial body, thyroid gland

Question 53

Fourth Pharyngeal Pouch

Cells of the ultimobranchial body give rise to the ______, or ______, of the ______. These cells secrete ______, a hormone involved in regulation of the ______ in the blood.

Answer 53

parafollicular cells, C cells, thyroid gland, calcitonin, calcium level

Question 54

PHARYNGEAL CLEFTS

The ______-week embryo is characterized by the presence of ______ pharyngeal clefts.

Answer 54

5, four

Question 55

PHARYNGEAL CLEFTS

Previously, it was thought that the ______ cleft contributed the ______ of the ______, but this claim has been disproved.

Answer 55

first, external auditory meatus (EAM), external ear

Question 56

PHARYNGEAL CLEFTS

Instead, the EAM forms by invagination of surface ______ from the ______.

Answer 56

ectoderm, first pharyngeal arch

Question 57

PHARYNGEAL CLEFTS

Overgrowth of the ______ arch, as it forms most of the ______, causes the ______ to disappear.

Answer 57

second, external ear, first cleft

Question 58

PHARYNGEAL CLEFTS

Active proliferation of ______ tissue in the second ______ causes it to overlap the ______ and ______ arches. Finally, it merges with the ______ in the ______ part of the ______, and the ______, ______, and ______ clefts lose contact with the ______.

Answer 58

mesenchymal, arch, third, fourth, epicardial ridge, lower, neck, second, third, fourth, outside

Question 59

PHARYNGEAL CLEFTS

The clefts form a cavity lined with ectodermal epithelium, the ______, but with further development, this sinus disappears.

Answer 59

cervical sinus

Question 60

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Neural crest cells arise from ______ adjacent to the surface ______ all along the edges of the ______.

Answer 60

neuroepithelial cells, ectoderm, neural folds

Question 61

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

______ signaling is important in establishing this edge region and then regulates ______ expression to cause prospective crest cells to undergo an ______ and begin their migration into the surrounding ______.

Answer 61

Bone morphogenetic protein (BMP), WNT1, epithelial-to-mesenchymal transition, mesenchyme

Question 62

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

In the hindbrain, crest cells originate in a specific pattern from segments called ______. There are ______ of these segments in the hindbrain (______—______), and neural crest cells from specific segments migrate to populate specific ______.

Answer 62

rhombomeres, eight, R1, R8, pharyngeal arches

Question 63

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

These crest cells migrate in ______ streams: Those from ______ and ______ migrate to the first arch along with crest cells from the caudal midbrain region, crest from ______ migrate to the second arch, and cells from ______ and ______ migrate to arches 4 to 6.

Answer 63

three, R1, R2, R4, R6, R7

Question 64

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Segregation of the three streams is assisted by the fact that very few crest cells form from ______ and ______ segments and those that do enter adjoining streams of cells to migrate.

Answer 64

R3, R5

Question 65

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Three distinct streams are important because they provide axonal guidance cues for ______ from ______ forming in the ______ and ______ region, including the ______, ______, ______, ______, and ______ ganglia. These ganglia are formed from a combination of ______ and cells from ______ in this region.

Answer 65

axons, ganglia, head, neck, trigeminal, geniculate, vestibuloacoustic, petrosal, nodose, crest cells, placodes

Question 66

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Axons from the ______ ganglion enter the hindbrain at R2, those from the ______ and ______ at R4, and those from the ______ and ______ at R6 and R7, thus accounting for three streams of crest cells.

Answer 66

trigeminal, geniculate, vestibuloacoustic, petrosal, nodose

Question 67

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

No axons project to ______ or ______.

Answer 67

R3, R5

Question 68

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Neural crest cells that populate the pharyngeal arches form the ______ components characteristic of each arch.

Answer 68

skeletal

Question 69

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Previously, it was thought that ______ regulated patterning of these skeletal elements, but now, it is clear that this process is controlled by ______.

Answer 69

neural crest cells, pharyngeal pouch endoderm

Question 70

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Formation of the pharyngeal pouches occurs prior to ______ and takes place even in the absence of ______.

Answer 70

neural crest migration, crest cells

Question 71

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Pouches are formed by migration of ______ cells ______, and this migration is stimulated by ______.

Answer 71

endoderm, laterally, fibroblast growth factors (FGFs)

Question 72

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

As pouches form, they express a very characteristic pattern of genes. ______ is expressed in the posterior endoderm of each pouch, ______ lies in the anterior endoderm, and ______ expression is restricted to the dorsalmost endoderm of each pouch.

Answer 72

BMP7, FGF8, PAX1

Question 73

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

In addition, ______ is expressed in the posterior endoderm of the ______ and ______ pouches.

Answer 73

SONIC HEDGEHOG (SHH), second, third

Question 74

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

These expression patterns then regulate diiferentiation and patterning of pharyngeal arch ______ into specific ______ structures. This process, however, is also dependent on the ______ and represents another example of an ______ interaction. In this case, the response of the mesenchyme to endodermal signals is dependent on ______ expressed in that mesenchyme.

Answer 74

mesenchyme, skeletal, mesenchyme, epithelial—mesenchymal, transcription factors

Question 75

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

These transcription factors include ______ and others carried by ______ cells into the arches. Crest cells acquire their specific gene expression patterns from the ______ of their origin.

Answer 75

HOX genes, neural crest, rhombomeres

Question 76

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

The pattern of rhombomeres itself is established by a nested code of ______ expression in the ______ that ______ carry with them when they migrate.

Answer 76

HOX gene, hindbrain, crest cells

Question 77

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

The first arch is ______ but does express ______, a homeodomain-containing transcription factor that is expressed in the midbrain; the second arch expresses ______; and arches 3 to 6 express members of the ______ paralogous group of ______ genes, ______, ______, and ______.

Answer 77

HOX-negative, OTX2, HOXA2, third, HOX, HOXA3, HOXB3, HOXD3

Question 78

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

The different expression patterns of these transcription factors allow each arch to respond differently to signals emanating from ______, such that the ______ arch forms the ______ and ______, the ______ arch, the ______ bone, etc.

Answer 78

pouch endoderm, first, maxilla, mandible, second, hyoid

Question 79

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

The remainder of the skeleton of the face, the mid and upper facial regions, also is derived from ______ that migrate into the ______. In this region, signals emanating from the surface ______ and the underlying areas of the ______ dictate the fate of the mesenchyme.

Answer 79

neural crest cells, frontonasal prominence, ectoderm, neuroepithelium

Question 80

MOLECULAR REGULATION OF FACIAL DEVELOPMENT

Again, it appears that ______ and ______ play major roles in patterning this area, but the specific genetic interactions are not known.

Answer 80

SHH, FGF8

Question 81

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Ectopic Thymic and Parathyroid Tissue

Because ______ tissue derived from the pouches undergoes migration, it is not unusual for accessory glands or remnants of tissue to persist along the pathway. This is true particularly for ______ tissue, which may remain in the ______, and for the ______. The ______ are more variable in position than the ______ ones and are sometimes found at the bifurcation of the ______.

Answer 81

glandular, thymic, neck, parathyroid glands, inferior parathyroids, superior, common carotid artery

Question 82

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

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

Answer 82

Branchial fistulas

Question 83

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Branchial FistuIas

Such a fistula, found on the lateral aspect of the neck directly anterior to the ______ muscle, usually provides drainage for a ______. These cysts, remnants of the cervical sinus, are most often just below the angle of the ______, although they may be found anywhere along the anterior border of the ______ muscle. Frequently, a ______ is not visible at birth but becomes evident as it enlarges during childhood.

Answer 83

sternocleidomastoid, lateral cervical cyst, jaw, sternocleidomastoid, lateral cervical cyst

Question 84

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Branchial FistuIas

______ are rare; they occur when the cervical sinus is connected to the lumen of the pharynx by a small canal, which usually opens in the tonsillar region. Such a fistula results from a rupture of the membrane between the ______ and ______ at some time during development.

Answer 84

Internal branchial fistulas, second pharyngeal cleft, pouch

Question 85

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ are essential for formation of much of the craniofacial region. Consequently, disruption of crest cell development results in craniofacial malformations.

Answer 85

Neural crest cells

Question 86

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

Because neural crest cells also contribute to the ______, which septate the outflow tract of the heart into pulmonary and aortic channels, many infants with craniofacial defects also have cardiac abnormalities, including persistent ______, ______, and transposition of the ______.

Answer 86

conotruncal endocardial cushions, truncus arteriosus, tetralogy of Fallot, great vessels

Question 87

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

Unfortunately, crest cells appear to be a particularly vulnerable cell population and are easily killed by compounds such as ______ and ______.

Answer 87

alcohol, retinoic acid

Question 88

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

Examples of craniofacial defects involving crest cells include the following:

Answer 88

1. Treacher Collins syndrome [mandibulofacial dysostosis]
2. Robin sequence
3. 22q11.2 Deletion syndrome
4. Hemifacial microsomia [oculoauriculovertebral spectrum or Goldenhar syndrome]

Question 89

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ is a rare autosomal dominant disorder occurring in 1/50,000 live births with 60% of cases arising as new mutations. The syndrome is characterized by hypoplasia of the maxilla, mandible, and zygomatic arches, which may be absent. Cleft palate is common as are external ear defects accompanied by atresia of the auditory canals and abnormalities of the middle ear ossicles, such that bilateral conductive hearing loss is often present. The eyes are usually involved with down-slanting palpebral fissures and lower eyelid colobomas. Mutations in the ______ gene [5q32] are responsible for most cases. The product of this gene is a nucleolar protein called ______ that appears to be necessary for preventing apoptosis and maintaining proliferation in neural crest cells but not for regulating their migration, which occurs normally. Although most cases of the syndrome are due to genetic mutations, phenocopies can be produced in laboratory animals following exposure to teratogenic doses of retinoic acid, suggesting that some cases in humans may be caused by teratogens.

Answer 89

Treacher Collins syndrome [mandibulofacial dysostosis], TCOF1, treacle

Question 90

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ may occur independently or in association with other syndromes and malformations. Like Treacher Collins syndrome, it alters first-arch structures, with development of the mandible most severely affected. Infants usually have a triad of micrognathia, cleft palate, and glossoptosis [posteriorly placed tongue].

Answer 90

Robin sequence

Question 91

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ may be due to genetic or environmental factors. It may also occur as a deformation, as for example, when the chin is compressed against the chest in cases of oligohydramnios. The primary defect includes poor growth of the mandible and, as a result, a posteriorly placed tongue that fails to drop from between the palatal shelves, preventing their fusion. This occurs in approximately1/8,500 births.

Answer 91

Robin sequence

Question 92

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ is the most common deletion syndrome in humans and has several presentations, including DiGeorge syndrome, DiGeorge anomaly, velocardiofacial syndrome, Shprintzen syndrome, conotruncal anomaly face syndrome, and congenital thymic aplasia and hypoplasia. The defects are the result of a deletion on the long arm of chromosome 22 and occur in ap- proximately1 per 4,000 births. Recent evidence shows that mutations in one of the genes in the deletion interval, TBX1 [T—box DNA binding transcription factor 1], result in the same syn- drome without a deletion. Furthermore, variability in regulation of the TBX1 gene may explain the wide range of observed phenotypes. The syndrome is characterized by a variety of malformations and degrees of severity, but infants most often present with congenital heart and aortic arch defects, mild facial dysmorphology, learning disabilities, and frequent infections due to thymic hypoplasia or aplasia that disrupts the immune system’s T cell—mediated response. Many of the infants also have seizures clue to hypocalcemia caused by abnormal development of the parathyroid glands. Later in life, these individuals are more likely to have mental illnesses, including schizophrenia and depression. In part, origin of the defects is due to disruption of neural crest cells that contribute to many of the affected structures. Even the thymus and parathyroid defects are related to neural crest cells because these cells contribute the mesenchyme into which endoderm from the pharyngeal pouches migrates. Endoderm cells from the pouches make the thymus and parathyroid cells and neural crest derived mesenchyme makes the connective tissue. Without this mesenchyme, the normal epithelial [endo-dermal]-mesenchymal interaction essential for differentiation of the glands does not occur.

Answer 92

22q11.2 Deletion syndrome

Question 93

Clinical Correlates
Birth Defects Involving the Pharyngeal Region

Neural Crest Cells and Craniofacial Defects

______ includes a number of craniofacial abnormalities that usually involve the maxillary, temporal, and zygomatic bones, which are small and flat. Ear [anotia, microtia], eye [tumors and dermoids in the eyeball], and vertebral [fused and hemivertebrae, spina bifida] defects are commonly observed in these patients. Asymmetry is present in 65% of the cases, which occur in 1/5,600 births. 0ther malformations, which occur in 50% of cases, include cardiac abnormalities, such as tetralogy of Fallot and ventricular septal defects. Causes of this are unknown.

Answer 93

Hemifacial microsomia [oculoauriculovertebral spectrum or Goldenhar syndrome]

Question 94

TONGUE

The tongue appears in embryos of approximately ______ weeks in the form of two ______ and one ______, the ______. These three swellings originate from the ______.

Answer 94

4, lateral lingual swellings, medial swelling, tuberculum impar, first pharyngeal arch

Question 95

TONGUE

A second median swelling, the ______, or ______, is formed by ______ of the ______, ______, and part of the ______ arch.

Answer 95

copula, hypobranchial eminence, mesoderm, second, third, fourth

Question 96

TONGUE

Finally, a third median swelling, formed by the ______ part of the ______ arch, marks development of the ______. Immediately behind this swelling is the ______, which is flanked by the ______.

Answer 96

posterior, fourth, epiglottis, laryngeal orifice, arytenoid swellings

Question 97

TONGUE

As the lateral lingual swellings increase in size, they overgrow the ______ and merge, forming the ______, or ______, of the tongue. Because the mucosa covering the body of the tongue originates from the ______, sensory innervation to this area is by the ______ of the ______. The body of the tongue is separated from the posterior third by a V-shaped groove, the ______.

Answer 97

tuberculum impar, anterior two-thirds, body, first pharyngeal arch, mandibular branch, trigeminal nerve, terminal sulcus

Question 98

TONGUE

The posterior part, or root, of the tongue originates from the ______, ______, and parts of the ______ pharyngeal arch. The fact that sensory innervation to this part of the tongue is supplied by the ______ indicates that tissue of the ______ arch overgrows that of the ______.

Answer 98

second, third, fourth, glossopharyngeal nerve, third, second

Question 99

TONGUE

The epiglottis and the extreme posterior part of the tongue are innervated by the ______, reflecting their development from the ______ arch. Some of the tongue muscles probably differentiate in situ, but most are derived from ______ originating in ______. Thus, tongue musculature is innervated by the ______.

Answer 99

superior laryngeal nerve, fourth, myoblasts, occipital somites, hypoglossal nerve

Question 100

TONGUE

The general sensory innervation of the tongue is easy to understand. The body is supplied by the ______, the nerve of the ______ arch; that of the root is supplied by the ______ and ______ nerves, the nerves of the ______ and ______ arches, respectively.

Answer 100

trigeminal nerve, first, glossopharyngeal, vagus, third, fourth

Question 101

TONGUE

______ (taste) to the anterior two-thirds of the tongue is provided by the ______ branch of the ______, whereas the posterior third is supplied by the ______.

Answer 101

Special sensory innervation, chorda tympani, facial nerve, glossopharyngeal nerve

Question 102

Clinical Correlates

In ______ [______], 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 this, the frenulum extends to the tip of the tongue.

Answer 102

ankyloglossia, tongue-tie

Question 103

THYROID GLAND

The thyroid gland appears as an epithelial proliferation in the floor of the ______ between the ______ and the ______ at a point later indicated by the ______. Subsequently, the thyroid descends in front of the ______ as a ______. During this migration, the thyroid remains connected to the tongue by a narrow canal, the ______. This duct later disappears.

Answer 103

pharynx, tuberculum impar, copula, foramen cecum, pharyngeal gut, bilobed diverticulum, thyroglossal duct

Question 104

THYROID GLAND

With further development, the thyroid gland descends in front of the ______ and the ______. It reaches its final position in front of the ______ in the ______ week. By then, it has acquired a small median ______ and two lateral ______.

Answer 104

hyoid bone, laryngeal cartilages, trachea, seventh, isthmus, lobes

Question 105

THYROID GLAND

The thyroid begins to function at approximately the end of the ______ month, at which time the first follicles containing ______ become visible. ______ produce the colloid that serves as a source of ______ and ______.

Answer 105

third, colloid, Follicular cells, thyroxine, triiodothyronine

Question 106

THYROID GLAND

______, or ______, derived from the ______ serve as a source of calcitonin.

Answer 106

Parafollicular cells, C cells, ultimobranchial body

Question 107

Clinical Correlates
Thyroglossal Duct and Thyroid Abnormalities

A ______ may lie at any point along the migratory pathway of the thyroid gland but is always near or in the midline of the neck. As indicated by its name, it is a cystic remnant of the thyroglossal duct. Although approximately 50% of these cysts are close to or just inferior to the body of the hyoid bone, they may also be found at the base of the tongue or close to the thyroid cartilage.

Answer 107

thyroglossal cyst

Question 108

Clinical Correlates
Thyroglossal Duct and Thyroid Abnormalities

Sometimes, a thyroglossal cyst is connected to the outside by a fistulous canal, a ______. Such a fistula usually arises secondarily after rupture of a cyst but may be present at birth.

Answer 108

thyroglossal fistula

Question 109

Clinical Correlates
Thyroglossal Duct and Thyroid Abnormalities

______ may be found anywhere along the path of descent of the thyroid gland. It is commonly found in the base of the tongue, just behind the foramen cecum, and is subject to the same diseases as the thyroid gland itself.

Answer 109

Aberrant thyroid tissue

Question 110

FACE

At the end of the ______ week, ______ consisting primarily of neural crest—derived mesenchyme and formed mainly by the first pair of pharyngeal arches appear.

Answer 110

fourth

Question 111

FACE

______ can be distinguished lateral to the stomodeum, and ______ can be distinguished caudal to this structure.

Answer 111

Maxillary prominences, mandibular prominences

Question 112

FACE

The ______, formed by proliferation of mesenchyme ventral to the brain vesicles, constitutes the upper border of the ______.

Answer 112

frontonasal prominence, stomodeum

Question 113

FACE

On both sides of the frontonasal prominence, local thickenings of the surface ectoderm, the ______, originate under inductive influence of the ventral portion of the forebrain.

Answer 113

nasal (olfactory) placodes

Question 114

FACE

During the ______ week, the nasal placodes invaginate to form ______. In so doing, they create a ridge of tissue that surrounds each pit and forms the ______. The prominences on the outer edge of the pits are the ______; those on the inner edge are the ______.

Answer 114

fifth, nasal pits, nasal prominences, lateral nasal prominences, medial nasal prominences

Question 115

FACE

During the following ______ weeks, the maxillary prominences continue to increase in ______. Simultaneously, they grow ______, compressing the ______ toward the midline.

Answer 115

2, size, medially, medial nasal prominences

Question 116

FACE

Subsequently, the cleft between the ______ and the ______ is lost, and the two fuse. Hence, the upper lip is formed by the two ______ and the two ______.

Answer 116

medial nasal prominence, maxillary prominence, medial nasal prominences, maxillary prominences

Question 117

FACE

The ______ do not participate in formation of the upper lip. The lower lip and jaw form from the ______ that merge across the midline.

Answer 117

lateral nasal prominences, mandibular prominences

Question 118

FACE

Initially, the maxillary and lateral nasal prominences are separated by a deep furrow, the ______. Ectoderm in the floor of this groove forms a solid ______ that detaches from the overlying ectoderm. After canalization, the cord forms the ______; its upper end widens to form the ______. Following detachment of the cord, the ______ and ______ nasal prominences merge with each other. The nasolacrimal duct then runs from the medial corner of the ______ to the inferior meatus of the ______, and the maxillary prominences enlarge to form the ______ and ______.

Answer 118

nasolacrimal groove, epithelial cord, nasolacrimal duct, lacrimal sac, maxillary, lateral, eye, nasal cavity, cheeks, maxillae

Question 119

FACE

The nose is formed from ______ facial prominences: the ______ prominence gives rise to the bridge, the merged ______ nasal prominences provide the crest and tip, and the ______ nasal prominences form the sides (alae).

Answer 119

five, frontonasal, medial, lateral

Question 120

INTERMAXILLARY SEGMENT

As a result of medial growth of the maxillary prominences, the two ______ nasal prominences merge not only at the surface but also at a deeper level. The structure formed by the two merged prominences is the ______. It is composed of (1) a ______ component, which forms the philtrum of the upper lip; (2) an ______ component, which carries the four incisor teeth; and (3) a ______ component, which forms the triangular primary palate.

Answer 120

medial, intermaxillary segment, labial, upper jaw, palatal

Question 121

INTERMAXILLARY SEGMENT

The intermaxillary segment is continuous with the ______ portion of the ______, which is formed by the ______.

Answer 121

rostral, nasal septum, frontal prominence

Question 122

SECONDARY PALATE

Although the primary palate is derived from the ______, the main part of the definitive palate is formed by two shelflike outgrowths from the ______. These outgrowths, the ______, appear in the ______ week of development and are directed obliquely downward on each side of the tongue.

Answer 122

intermaxillary segment, maxillary prominences, palatine shelves, sixth

Question 123

SECONDARY PALATE

In the ______ week, however, the palatine shelves ascend to attain a ______ position above the tongue and fuse, forming the ______.

Answer 123

seventh, horizontal, secondary palate

Question 124

SECONDARY PALATE

Anteriorly, the shelves fuse with the ______, and the ______ is the midline landmark between the primary and secondary palates. At the same time as the palatine shelves fuse, the ______ grows down and joins with the ______ aspect of the newly formed palate.

Answer 124

triangular primary palate, incisive foramen, nasal septum, cephalic

Question 125

NASAL CAVITIES

During the ______ week, the ______ deepen considerably, partly because of growth of the surrounding nasal prominences and partly because of their penetration into the underlying mesenchyme.

Answer 125

sixth, nasal pits

Question 126

NASAL CAVITIES

At first, the ______ separates the pits from the primitive oral cavity by way of the newly formed foramina, the ______. These choanae lie on each side of the ______ and immediately behind the ______.

Answer 126

oronasal membrane, primitive choanae, midline, primary palate

Question 127

NASAL CAVITIES

Later, with formation of the secondary palate and further development of the primitive nasal chambers, the ______ lie at the junction of the ______ and the ______.

Answer 127

definitive choanae, nasal cavity, pharynx

Question 128

NASAL CAVITIES

______ develop as diverticula of the lateral nasal wall and extend into the ______, ______, ______, and ______ bones. They reach their maximum size during ______ and contribute to the definitive shape of the face.

Answer 128

Paranasal air sinuses, maxilla, ethmoid, frontal, sphenoid, puberty

Question 129

TEETH

The shape of the face is determined not only by expansion of the ______ but also by growth of the ______ and ______ to accommodate the ______.

Answer 129

paranasal sinuses, mandible, maxilla, teeth

Question 130

TEETH

Teeth themselves arise from an ______ interaction between overlying oral epithelium and underlying mesenchyme derived from ______.

Answer 130

epithelial—mesenchymal, neural crest cells

Question 131

TEETH

By the ______ week of development, the basal layer of the epithelial lining of the oral cavity forms a C-shaped structure, the ______, along the length of the upper and lower jaws. This lamina subsequently gives rise to anumber of ______, ______ in each jaw, which form the ______ of the ______ components of the teeth.

Answer 131

sixth, dental lamina, dental buds, 10, primordia, ectodermal

Question 132

TEETH

Soon, the deep surface of the buds invaginates, resulting in the ______ of tooth development. Such a cap consists of an outer layer, the ______; an inner layer, the ______; and a central core of loosely woven tissue, the ______.

Answer 132

cap stage, outer dental epithelium, inner dental epithelium, stellate reticulum

Question 133

TEETH

The mesenchyme, which originates in the ______ in the indentation, forms the ______.

Answer 133

neural crest, dental papilla

Question 134

TEETH

As the dental cap grows and the indentation deepens, the tooth takes on the appearance of a ______ (______). Mesenchyme cells of the papilla adjacent to the inner dental layer differentiate into ______, which later produce ______.

Answer 134

bell, bell stage, odontoblasts, dentin

Question 135

TEETH

With thickening of the dentin layer, odontoblasts retreat into the ______, leaving a thin cytoplasmic process (______) behind in the ______.

Answer 135

dental papilla, dental process, dentin

Question 136

TEETH

The odontoblast layer persists throughout the life of the tooth and continuously provides ______. The remaining cells of the dental papilla form the ______ of the tooth.

Answer 136

predentin, pulp

Question 137

TEETH

In the meantime, epithelial cells of the inner dental epithelium differentiate into ______ (______). These cells produce long ______ that are deposited over the ______. Furthermore, a cluster of these cells in the inner dental epithelium forms the ______ that regulates early tooth development.

Answer 137

ameloblasts, enamel formers, enamel prisms, dentin, enamel knot

Question 138

TEETH

Enamel is first laid down at the ______ of the tooth and from here spreads toward the ______. When the enamel thickens, the ______ retreat into the ______. Here they regress, temporarily leaving a thin membrane (______) on the surface of the enamel. After ______ of the tooth, this membrane gradually sloughs off.

Answer 138

apex, neck, ameloblasts, stellate reticulum, dental cuticle, eruption

Question 139

TEETH

Formation of the root of the tooth begins when the dental epithelial layers penetrate into the underlying ______ and form the ______. Cells of the ______ lay down a layer of dentin continuous with that of the crown. As more and more ______ is deposited, the pulp chamber ______ and finally forms a canal containing ______ and ______ of the tooth.

Answer 139

mesenchyme, epithelial root sheath, dental papilla, dentin, narrows, blood vessels, nerves

Question 140

TEETH

Mesenchymal cells on the outside of the tooth and in contact with dentin of the root differentiate into ______. These cells produce a thin layer of specialized bone, the ______.

Answer 140

cementoblasts, cementum

Question 141

TEETH

Outside of the cement layer, mesenchyme gives rise to the ______, which holds the tooth firmly in position and functions as a shock absorber.

Answer 141

periodontal ligament

Question 142

TEETH

With further lengthening of the root, the ______ is gradually pushed through the overlying tissue layers into the oral cavity. The eruption of deciduous or milk teeth occurs ______ to ______ months after birth.

Answer 142

crown, 6, 24

Question 143

TEETH

Buds for the permanent teeth, which lie on the ______ aspect of the milk teeth, are formed during the ______ month of development. These buds remain dormant until approximately the ______ year of postnatal life. Then they begin to grow, pushing against the underside of the milk teeth and aiding in the shedding of them. As a permanent tooth grows, the root of the overlying deciduous tooth is resorbed by ______.

Answer 143

lingual, third, sixth, osteoclasts

Question 144

Clinical Correlates
Facial Clefts

______ and ______ are common defects that result in abnormal facial appearance and difficulties with speech.

Answer 144

Cleft lip, cleft palate

Question 145

Clinical Correlates
Facial Clefts

The ______ is considered the dividing landmark between anterior and posterior cleft deformities.

Answer 145

incisive foramen

Question 146

Clinical Correlates
Facial Clefts

Those anterior to the incisive foramen include ______, ______, and cleft between the ______ and ______ palates. Such defects are due to a partial or complete lack of fusion of the ______ with the ______ on one or both sides.

Answer 146

lateral cleft lip, cleft upper jaw, primary, secondary, maxillary prominence, medial nasal prominence

Question 147

Clinical Correlates
Facial Clefts

Those that lie posterior to the incisive foramen include ______ and ______.

Answer 147

cleft [secondary] palate, cleft uvula

Question 148

Clinical Correlates
Facial Clefts

______ results from a lack of fusion of the palatine shelves, which may be due to smallness of the shelves, failure of the shelves to elevate, inhibition of the fusion process itself, or failure of the tongue to drop from between the shelves because of micrognathia.

Answer 148

Cleft palate

Question 149

Clinical Correlates
Facial Clefts

The third category is formed by a combination of clefts lying anterior as well as posterior to the incisive foramen. Anterior clefts vary in severity from a barely visible defect in the vermilion of the ______ to extension into the ______. In severe cases, the cleft extends to a deeper level, forming a cleft of the ______, and the maxilla is split between the ______ and the ______ tooth. Frequently, such a cleft extends to the ______. Likewise, posterior clefts vary in severity from clefting of the entire ______ to clefting of the ______ only.

Answer 149

lip, nose, upperjaw, lateral incisor, canine, incisive foramen, secondary palate, uvula

Question 150

Clinical Correlates
Facial Clefts

______ is the most common syndrome associated with cleft lip with or without cleft palate. The syndrome is inherited as an autosomal dominant and is due to mutations in INTERFERON REGULATORY FACTOR 6 [IRF6; 1p32—41] that is expressed in the medial [fusing] edge of the palatal shelves. Interestingly, 88% of affected infants will have pits in their lower lip, and in 64% of these individuals, this will be the only abnormality.

Answer 150

Van der Woude syndrome

Question 151

Clinical Correlates
Facial Clefts

______ are produced by failure of the maxillary prominence to merge with its corresponding lateral nasal prominence along the line of the nasolacrimal groove. When this occurs, the nasolacrimal duct is usually exposed to the surface.

Answer 151

Oblique facial clefts

Question 152

Clinical Correlates
Facial Clefts

______, a rare abnormality, is caused by incomplete merging of the two medial nasal prominences in the midline.

Answer 152

Median [midline] cleft lip

Question 153

Clinical Correlates
Facial Clefts

Infants with midline clefts are often ______ and may have ______ abnormalities that include varying degrees of loss of midline structures. Loss of midline tissue may be so extensive that the lateral ventricles fuse [______]. These defects are induced very early in development, at the beginning of ______ [days ______ to ______] when the midline of the ______ is being established.

Answer 153

cognitively impaired, brain, holoprosencephaly, neurulation, 19, 21, forebrain

Question 154

Clinical Correlates
Facial Clefts

Most cases of cleft lip with or without cleft palate are multifactorial. These conditions are usually classified as [l] ______ with or without ______ and [2] ______ are thought to be etiologically and pathogenetically distinct.

Answer 154

cleft lip, cleft palate, cleft palate

Question 155

Clinical Correlates
Facial Clefts

Cleft lip with or without cleft palate [approximately 1/700 births] occurs more frequently in ______ [65%] than in ______, and its incidence varies among populations. ______ and ______ have some of the highest rates [3.5/1,000], whereas ______ have the lowest [1/1,000].

Answer 155

males, females, Asians, Native Americans, African Americans

Question 156

Clinical Correlates
Facial Clefts

The frequency of isolated ______ is lower than that of ______ [1/1,500 births], occurs more often in ______ [55%] than in ______. In females, the palatal shelves fuse approximately ______ week later than in males, which may be related to why isolated cleft palate occurs more frequently in females than in males.

Answer 156

cleft palate, cleft lip, females, males, 1

Question 157

Clinical Correlates
Facial Clefts

Causes of cleft lip with or without cleft palate are not well defined. Some cases are syndromic and associated with certain syndromes and genes. Others are nonsyndromic but associated with some of the same genes that cause syndromes, such as ______ [van der Woude syndrome] and ______. Still, other cases are caused by exposure to ______ compounds, such as anticonvulsant medications, particularly valproic acid. Cigarette smoking during pregnancy also increases the risk for
having a baby with orofacial clefts.

Answer 157

IRF6, MSX1, teratogenic

Question 158

MOLECULAR REGULATION OF TOOTH DEVELOPMENT

Teeth are present only in ______ and parallel the evolutionary appearance of the ______. Tooth development represents a classic example of an ______ interaction, in this case, between the overlying epithelium and underlying neural crest—derived mesenchyme.

Answer 158

vertebrates, neural crest, epithelial—mesenchymal

Question 159

MOLECULAR REGULATION OF TOOTH DEVELOPMENT

Regulation of tooth patterning from incisors to molars is generated by a combinatorial expression of ______ genes expressed in the mesenchyme. With respect to each tooth’s individual development, the epithelium governs differentiation to the ______, at which time this regulatory function is transferred to the ______.

Answer 159

HOX, bud stage, mesenchyme

Question 160

MOLECULAR REGULATION OF TOOTH DEVELOPMENT

Signals for development involve growth factors including ______, ______, and ______; the secreted factor ______;and transcription factors, such as ______ and ______, that interact in a complex pathway to produce cell differentiation and patterning for each tooth.

Answer 160

WNTs, BMPs, FGFs, SHH, MSX1, MSX2

Question 161

MOLECULAR REGULATION OF TOOTH DEVELOPMENT

Teeth also appear to have a signaling center that represents the “organizer” for tooth development much like the activity of the node during ______. This organizer region is called the ______, and it appears in a circumscribed region of the dental epithelium at the tips of the ______. It then enlarges at the ______ into a tightly packed group of cells but undergoes ______ (cell death) and disappears by the end of this stage. While it is present, it expresses ______, ______, and ______ and ______. ______ may regulate outgrowth of cusps much as it participates in limb outgrowth produced by the apical ectodermal ridge, whereas ______ may regulate the timing of apoptosis in knot cells.

Answer 161

gastrulation, enamel knot, tooth buds, cap stage, apoptosis, FGF4, SHH, BMP2, 4, FGF4, BMP4