CTB 8 – Early development of the human head and face

Question 1

What occurs with phase 1 (0-3 weeks) i.u?

Answer 1

Cell proliferation and migration

Question 2

What occurs with phase 2 (3-8 weeks) i.u?

Answer 2

Morphogenesis and differentiation

Formation of organs and body structures

Question 3

What are teratogens?

Answer 3

Substances that introduce birth defects

Question 4

How many weeks i.u. do craniofacial defects can develop?

Answer 4

4-8 weeks

Question 5

How does anencephaly develop?

Answer 5

Absence of brain tissue as neural tube fails to close

Question 6

How can anencephaly develop?

Answer 6

Folic acid deficiency or high retinoic acid (vit A) levels can interfere with the Hox gene expression

Question 7

How many days i.u. does the embryo head folding begin?

Answer 7

21 days

Question 8

What organ develops at 16 days i.u?

Answer 8

Heart

Question 9

What is the function of the yolk sac in an embryo?

Answer 9

Provides nutrients

Question 10

What is formed from the neural plate in an embryo?

Answer 10

Brain

Question 11

What organ develops at 18 days i.u?

Answer 11

• Oropharyngeal membrane develops, separating the future mouth from the pharynx
• This membrane acts as a transient cell signalling centre to oral cavity

Question 12

What is the biological term for mouth?

Answer 12

Stomodeum

Question 13

What organ occurs at 22 days i.u?

Answer 13

Formation of the stomodeum

Heart rotates

Question 14

What length is an embryo at 30 days?

Answer 14

4mm

Question 15

What happens at 30 days i.u?

Answer 15

• Rudiments (anlagen) of most organs are established
• Oropharyngeal membrane starts to breakdown
• Pharyngeal arches (PA) 1,2,3 become prominent

Question 16

What cells are outcompeted by other cells in the PA, in the face?

Answer 16

Neural crest cells can out compete the mesodermal cells in the face

Question 17

What cells from the pharyngeal arches form muscles and bones?

Answer 17

Mesodermal cells

Question 18

What is the formation of neural crest cells?

Answer 18

• Cells are induced between neuroectoderm and epidermis induced by a morphogenic gradient
• Neural plate invaginates – forming neural folds and then an open tube
• Neural folds fuse forming the neural tube – neural crest cells migrate along predetermined pathways
• Migration continues and become specialised cell types

Question 19

What is the function of the Hox gene in PA1?

Answer 19

There is a lack of Hox gene, therefore cranial neural crest cell are specified by Hox gene code

Question 20

What type of bone is the hyoid bone?

Answer 20

Composite bone

Question 21

What is eagles syndrome? And the symptoms?

Answer 21

Calcified/elongated styloid process

Causing pain and difficulty swallowing

Question 22

What is the facial development at 4-5 weeks?

Answer 22

• Formation and growth of an unpaired frontonasal prominence – mesenchymal cells in the frontonasal prominence
• Nasolateral and nasomedial processes form the nasal pit
• Mandibular processes form grows and merge and the same for the maxillary processes

Question 23

How is the nasal placode formed?

Answer 23

Thickening of the overlying ectoderm

Question 24

What is the facial development at 5.5-6 weeks?

Answer 24

• Frontonasal prominence recedes as nasomedial processes grow strongly
• Nasolateral processes and maxillary processes grow – fusing to form the nasolacrimal duct, cheek and alar base of the nose

Question 25

What is the facial development at 7-8 weeks?

Answer 25

- Merging of nasomedial processes - Further growth of the maxillary processes - Forming – central part of the nose, upper lip and primary palate - Upper lip formed from the maxillary processes laterally and in the midline from the nasomedial processes (PHILTRUM)

Question 26

How is the philtrum formed?

Answer 26

Fusion between the maxillary processes

Question 27

Define merging.

Answer 27

- Elimination of a furrow between 2 processes – by mesenchymal cell proliferation - Always been connected

Question 28

Define fusion.

Answer 28

- 2 processes are separate to begin with - Contact between epithelial cells of the process’s triggers fusion of the epithelial cell sheets and then elimination of epithelial cells

Question 29

What does the maxillary process contribute to the facial structures?

Answer 29

- Maxilla | - Upper lateral lip

Question 30

What does the mandibular process contribute to the facial structures?

Answer 30

- Mandible | - Lower lip

Question 31

What does the medial nasal processes contribute to the facial structures?

Answer 31

- Medial part of the nose - Upper medial lip - Primary palate

Question 32

What does the lateral nasal processes contribute to the facial structures?

Answer 32

Lateral part of the nose

Question 33

What processes fail to come together in a median cleft lip?

Answer 33

Failure of merging of med nasal processes

Question 34

What processes fail to come together in a bilateral cleft lip?

Answer 34

Failure of fusion between maxillary processes and med nasal processes

Question 35

What is the most common cleft lip?

Answer 35

Bilateral cleft lip

Question 36

What processes fail to come together in an oblique cleft lip?

Answer 36

Failure between maxillary and lateral nasal processes

Question 37

What processes fail to come together in a lateral cleft lip?

Answer 37

Failure merger between mandibular and maxillary process

Question 38

What is micrognathia?

Answer 38

Small mandible

Question 39

What is agnathia?

Answer 39

No mandible

Question 40

What is Pierre Robin Sequence presented in?

Answer 40

Micrognathia, cleft lip and glossoptosis

Question 41

What is glossoptosis?

Answer 41

Medical condition and abnormality which involves the downward displacement or retraction of the tongue. It may cause non-fusion of the hard palate, causing cleft palate

Question 42

What are the symptoms of teacher collins syndrome?

Answer 42

- Hypoplasia (under development) of mandible (macrostomia) and facial bones (e.g. cheek) - Ear malformations - Cleft palate - Abnormal dentition - Slanting of palpebral fissures - Eyelid coloboma

Question 43

How does treacher collins syndrome develop i.u?

Answer 43

Failure of neural crest cells to migrate into craniofacial region – cells apoptose

Question 44

What is the mutation in treacher collins syndrome?

Answer 44

Heterozygous mut in Tcof1 in ribosome biogenesis