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Flashcards in Development Of The Pharynx Deck (33)
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1

Describe the structure of a pharyngeal arch.

-consists of core of mesenchyme

-outside is covered with ectoderm

-inside is lined with endoderm

-separated from other arches by a groove on the outside and a pouch on the inside

-intervening tissues between groove and pouch consists of endoderm and ectoderm and is subject to perforation

2

What are the pharyngeal arch components?

-artery

-cranial nerve

-skeletal component

3

What is the main organizer for pharyngeal arch development?

-foregut endoderm

4

What is the craniocaudal segmentation determined by?

-Hox genes

5

Outline the processes used for pharyngeal arch formation.

Pharyngeal endoderm Tbx-1 -> FGF-8 -> pharyngeal arch formation

6

How many pharyngeal arches are there?

-primitively there are 6 pairs

-in humans there are 4 pairs of arches and 4 grooves that separate from each other

7

What are the derivatives of the first arch?

-mandibular arch

-Meckel's cartilage
+main component of embryonic lower jaw
+distal part is reabsorbed via apoptosis
+sphenomandibular ligament
+malleus
+incus

8

What is the nerve associated with the first arch?

Trigeminal nerve

9

How does the first arch develop?

-neural crest derived from rhombomeres 1-2 and midbrain

-differentiation associated with Otx-2

10

What are the derivatives of the second arch?

-hyoid arch

-Reichert's cartilage
+body and lesser horn of hyoid
+stapes
+styloid process and stylohyoid ligament

-muscles of facial expression

11

What nerve is associated with second arch?

-facial nerve

12

How is the second arch developed?

-influenced by Hoxa2

13

What nerves are associated with the third and fourth arches?

-glossopharyngeal and vagus nerves

14

What are the derivatives of the third and fourth arches?

-part of hyoid bone and upper pharynx (3rd)
+greater horn of hyoid

-stylopharyngeus muscle (3rd)

-muscles and cartilages of larynx and lower pharynx (4th)

15

What is the derivative of the 1st groove?

-external auditory meatus

16

What is the derivative of the 2nd and 3rd grooves?

-cervical sinus

17

What are the derivatives of the first pouch?

-tympanic cavity of middle ear

-auditory tube

18

What are the derivatives of the second pouch?

-fossa of palatine tonsils

19

What are the derivatives of the third pouch?

-inferior parathyroids -> high conc Shh

-thymus -> high conc of BMP-4

20

What are the derivatives of the fourth pouch?

-superior parathyroids

-postbrachial (ultimobrachial) bod
+become incorporated into thyroid as parafollicular cells which secrete calcitonin

21

What does the thyroid begin as?

-begins as a node (anlage) of cells located on the ventral surface of the pharynx between the first and second pairs of pharyngeal arches

22

How is the anlage signaled?

-induced via signals from the underlying mesenchyme

-the cells express transcription factors Hhex, Nkx2-1, Pax8, adn Foxe-1

23

How does the thyroid anlage grow?

-grows down into the underlying mesenchyme as the thyroid diverticulum

-diverticulum remains connected temporarily to the floor of the pharynx via the thyroglossal duct

-the opening of this duct persists as a small pit at the base of the tongue called the foramen cecum

24

What is the infundibular process and what does it form?

-ventral downgrowth from floor of diencephalon

-forms neurohypophysis (posterior pituitary)

25

What is Rathke's pouch and what does it form?

-midline upgrowth from roof of stomodeum

-stimulated by BMP-4 followed by FGF-8 from floor of diencephalon

-forms a cup like extension distally that attaches to the infundibular process
+inner layer adheres to neurohypophysis and forms pars intermedia

+outer layer is separated from pars intermedia by narrow lumen called the residual lumen

+outer cup will form the anterior pituitary

26

Where are the lateral lingual swellings? When do they form?

-5 weeks

-located in ventral areas of first pair of pharyngeal arches
+located between sarcolemma and basal lamina

27

Where does the tuberculum impar form? When?

-5 weeks

-ventral swelling between first and second pairs of arches

28

Where does the cupula form? When?

-5 weeks

-ventral swelling between second and third pairs of arches

29

Where is the foramen cecum located?

-between the tuberculum impar and the copula

30

What is micrognathia?

-condition in which the jaw is undersized

31

What is agnathia?

-absence of a portion or the entirety of one or both jaws

32

What is Treacher Collins syndrome?

-autosomal dominant disorder characterized by craniofacial deformities such as absent cheekbones

33

What is ankyloglossia?

-aka tongue tie

-unusually short, thick lingual frenulum