Embryology

Question 1

Embryo 4th week - general anatomy?

Answer 1

Stomatodeum
-  future mouth 
Buccopharyngeal membrane:
- ruptures at day 26
Cardiac bulge:
- migrate later
Head and neck not developed yet

Question 2

Pharyngeal vs branchial?

Answer 2

Pharyngeal - human and developing in relation to the primordial pharynx
Branchial - fish and develops into the gill

Question 3

Neural crest cells? Origin? Undergo process? Contributor to? Role?

Answer 3

Origin:
- neuroectoderm
Undergo an epithet to mesenchymal transition
Major contribution to mesenchyme in head and neck region
Role:
- crucial to development of arch formation

Question 4

Neural crest derivatives - names?

Answer 4

• CT and bones of face and skull
• Cranial nerve ganglion
• C cells of thyroid gland
• Odontoblasts
• Dermis in face and neck
• Forebrain (meninges)

Question 5

Pharyngeal apparatus - types? Derivatives? Formation of?

Answer 5

Pharyngeal arches
- core of mesenchyme/mesoderm
Pharyngeal pouches
- endodermal extensions
Pharyngeal grooves
- ectoderm
Pharyngeal membranes 
- fused ectoderm and endoderm
Formation of:
- the future face and neck

Question 6

Pharyngeal arches - what are they? #? Disappear? Names? Components?

Answer 6

What are they:
- rod like thickening of mesoderm in wall of gut
#:
- 6 arches
Disappear:
- fifth pair
Names:
1. Lens placide
2. Pharyngeal arches 
3. Otic placode
4. Heart bulge
5. Limb ridges 
6. Somites 
Components:
- skeletal; cartilagenous to begin with, may remain to develop into bone or disappear
- muscle: carry nerve during mig
- artery: arterial arches lies in each arch
- nerve; derived from neuroectoderm

Question 7

Pharyngeal arches - 4th week - timeline (first arch, 3 pairs? Arches covered by?

Answer 7

Timeline:
- first arch acter day 24
- by day 26 there are 3 pairs 
Covered by:
- externally by surface ectoderm and inside by endoderm

Question 8

Pharyngeal arches - first arch (mandibular arch) - 2 prominence? Induced by? Nerve supply? Muscles present? Cartilage formation type? Bone formation? Syndromes?

Answer 8

2 prominences:
- maxillary and mandibular
Induces by:
- mig of neural crest cells
Nerve:
- trigeminal (mand and max div)
Muscles:
- masticatory, mylohyoid, ant belly of digastric, tensor tympani and tensor palatini
Cartilage:
- Meckel’s cartilage (ear bones malleis and incus)
Bome formation:
- premaxilla, maxilla, zygomatic bone, part temporal, mandible and malleis and incus
Syndromes:
- caused by insufficient neural crest cells
- Treacher Collins; autosomal dom, underdeveloped zygomatic bone, defective eyelids and ears
- Pierre Robin; underdeveloped mandible, cleft palate, defects of eye and ear

Question 9

Pharyngeal arches - second arch (hyoid arch) - nerve? Muscles? Cartilage?

Answer 9

Nerve
- facial
Muscles
- facial exp, stapedius, stylogyoid and post belly of digastric
Cartilage: Reichert’s
- staples, styloid process, smaller corn of hyoid bone and superior part of body of hyoid

Question 10

Pharyngeal arches - third arch - nerve and muscles?

Answer 10

Nerve
- glossopharyngeal
Muscles
- stylopharyngeus

Question 11

Pharyngeal arches - fourth and sixth arch - nerves and muscles?

Answer 11

Nerve
- superior laryngeal and recurrent laryngeal (vagal branch)
Muscles
- levator veli palatini, intrinsic muscles of larynx, constrictor of pharynx and cricothyroid

Question 12

Aortic arches - #? Names?

Answer 12

6 surrounding the right and left dorsal aorta
Names:
1. Maxillary
2. Stapedial
3. Common and interal carotid
4. Part of arch of aorta and right subclavian
6. Pulmonary artery

Question 13

Pharyngeal pouches - what is it? #? Absent? Location of 1st pouch? Role?

Answer 13

What is it:
- balloon like diberticula of endoderm lining of interal aspect of the arches
#
- 4 well defined pairs of pouches
Absent:
- 5th
Location:
- between 1st and 2nd arch
Role:
- form important organs in the head and neck region

Question 14

1st pharyngeal pouch - expand to form? Contact with? Forms a? Connection with?

Answer 14

Expand to form"
- tubotympanic recess
Contacts 
- with first cleft/groove
Forms a
- cavity of tubotymapnic traces form tympanic cavity and mastic antrum 
Connection
- pharynx elongated confirm pharyngotympanic tube (auditory tibe)

Question 15

And pharyngeal pouch - what is it? Together form the? Part of pouch becomes?

Answer 15

It is
- epithelial lining ofnthe porch invade surrounding mesenchyme 
Together
- form the primordium of palatine tonsil
Part
- remains as tonsillar sinus or fossa

Question 16

Third pharyngeal pouch - dorsal bulbar part becomes? Form of thymus? Migration of?

Answer 16

Dorsal bulbar
- form inferior parathyroid
From of thymus
- bilateral primordial of thums come together in median plane form
Migration of
- primodria of thymus and parathyroid lose connection with pharynx and mig to ant mediastinum

Question 17

Fourth pharyngeal pouch - expands to form? First part becomes? Ventral part develops to?

Answer 17

Expand
- form dorsal and ventral parts
Dorsal
- contribute for superior parathyroid
Ventral
- develops into ultimopharyngeal body (fuses with the thyroid gland and contribute for parafollular cells or c cells of thyroid gland)

Question 18

Pharyngeal grooves - #? 1 pair contribution? Other grooves become?

Answer 18

#:
- four grooves develop
1 pair contribute:
- first pair persists as external acoustic meatus 
Other
- lie in cervical sinus and disappear

Question 19

Pharyngeal membranes - first membrane?

Answer 19

First membrane becomes the tympanic membrane

Question 20

Development of thyroid gland - day 24? Develop from? Thyroglossal duct? Parafollocular derived from?

Answer 20

Day 24:
- first endocrine gland forms
Develops from
- median endodermal thickening in floor of primordial pharynx
Thyroglossal:
- formed from thickening of epith in floor of pharynx
Parafollocular cells:
- derived from causal pharyngeal complex (from pouches 4 and 5)

Question 21

Anamolies of thyroid

Answer 21

Shape and osition

Question 22

Development of tongue- ant 2/3?

Answer 22

• Apperance of median tongue bud (tuberculum impar) in floor of primordial pharynx
• Distal tongue buds (lateral lingual swelling) develops on each side of median
• prolif of mesenchyme from first arches
• distal tongue buds increase in size, merge together and overgrowth the median bud to form ant 2/3 of tongue
• median tongue bud does not form any part of adult tongue

Question 23

Development of tongue - post 1/3?

Answer 23

• apperance of copula (bond or tie) due to fusion of ventromedial part of 2nd pair of arches
• hypopharyngeal eminence appear die to prolif of mesenchyme from 3rd and 4th arch
• copula is overgrown by hypopharyngeal eminence
• post 1/3 develops from rostral part of hypobranchial eminence
• tongue muscles derived from myoblasts
• CT and vasc of tongue derived from arch mesenchyme

Question 24

Development of tongue - papilla and taste buds?

Answer 24

• appear at end of week 8

- taste buds develop during week 11-14 by inductive interaction between epithelial cells and invading gustatory nerves

Question 25

Head and neck abnormalities?

Answer 25

During transform of pharyngeal arches to adult structures

• branchisl cysts/sinuses or fistula
• accessory thymic tissue
• ectopic parathyroid glands