Embryology of head and neck Flashcards
3 regions of mesoderm
Paraxial mesoderm
Lateral plate mesoderm
Intermediate mesoderm
What is paraxial mesoderm
Thicked plate of tissue either side of midline
What is lateral plate mesoderm
divdes into two layers
Somatic/partietal mesoderm
Splanchin/visceral mesoderm
Line the intaembryonic cavity
What is intermediate mesoderm
Connects the paraxial and lateral plate mesoderm
What is a somite
Ball of mesoderm
WHat do somites begin as and where do they appear
First known as somitomeres
Appear in the cephalic region of embryo then develop cephalo-caudally
How many somites should be present at the end of 5th week
42-44 paris
Which somites disappears
first occipital somite
last 5-7 coccygeal somite
What somites are left and what do they do
3 occipital 8 cervical 12 thoracic 5lumbar 5 sacral 3-5 coccygeal
Go on to form axial skelton
How does the sclerotome form
Somites (contain fibroblasts-like cells)
They then arrange themselves in a donut shape around a small lumen and become epithelial cells
Cells in the ventromedial wall of somite lose epithelial characteristics
Change their position to surround the neural tube and notochord
forming the sclerotome
What does scelerotome eventually form
Vertebrae and ribs
How does the myotome form
Cells in the dorsomedial and ventrolateral walls of somite form the myotome
What is the myotome
Precursor for muscle cells
Some muscle precursors cells migrate into the parietal later of lateral plate mesoderm to form body wall muscles
How does the dermatome form
Cells in between the muscle precursor cells fo the somite form the dermatome
What is the dermomyotome
Myotome cells migrate beneath the dermatome to form a dermomyotome
How is the dermis layer of the back formed
Dermatome cells become migratory and migrate beneath the surface ectoderm, forming the dermis of the back
How is the dermis layer of the back formed
Dermatome cells become migratory and migrate beneath the surface ectoderm, forming the dermis of the back
How are the myotome and dermatome innervated
Retains innervation from its segment of origin
What does the intermediate mesoderm form
Forms urogenital structures
Forms future nephortomes
More caudally forms the nephrogenic cord
What does the lateral plate mesoderm go on to form
Lines the intraembryonic cavity
Lines the organs and gut tube
Goes on to form the serous membranes of future peritoneal, plural and pericardial cavities
What does parietal LPM form
lateral body wall folds
form the dermis of skin in body wall and limbs
Form muscles of limbs, body wall and costal cartilages along with sclerotome and muscles cells from somites
What does the visceral LPM form
With the endoderm forms the wall fo the gut tube
What does the intraembryonic cavity form
Thoracic and abdominopelvic cavities
What does the paraxial mesoderm from regarding head and neck
Somiters and somitomeres
LArge portion of membranous and cartilaginous parts of skull
All voluntary muscles of craniofacial region
Dermis
Connective tissue of dorsal head
Meninges caudal to prosencephalon
What does the LPM do regarding head and neck
Laryngeal cartilages
Connective tissue of laryngeal region
How do thickened regions of ectoderm assist in development of head and neck
With NCC, form neurons of the 5th, 7th, 9th and 10th cranial sensory ganglia
What do pharyngeal arches contain
Consists of a core of mesenchymal tissue derived from mesoderm
Covered externally by ectoderm
COnvered internally by endorderm
What components do each pharyngeal arch have
Muscular component
SKeletal/cartilaginous component
cranial nerve
arterial component
Which cranial nerves contribute to the pharygeal arches
CN V
CN VII
CN IX
CN V
What happens at the end of 4th week of development regarding face development
Centre of face is formed by the stomedeum
closed by the oropharyngeal membrane
surrounded by the first pair of pharyngeal arches
What two parts is the first pharyngeal arch made up of
Maxaially part - latyeral to stomedeum
Mandibular part - caudal to stomodeum
What is the stomodeum
Future oral cavity
What dies maxiallary process of 1st pharyngeal arch go on to form
Future maxilla, zygomatic bone and part of the temporal bone
What dies mandibulary process of 1st pharyngeal arch go on to form
Contains Mercel’s cartilage
Mesenchyme surround Meckel’s cartilage will become future mandible
What muscles are associated with the 1st PA
muscles of mastication
Anterior belly of digastric, mylohyoid, tensor tympani, tensor palatini
What nerve components are associated with the 1st PA
The mandibular branch of CN V supplies all the muscles
All 3 branches of CN V provide innervation to the skin of the face
What catilagionous component dfoes the 2nd PA contain
Reichert’s cartilage
What does reichert’s cartilage go on ot form
Stapes
Styloid process of temporal bone
Stylohyoid ligament
Parts of the hyoid bone
Muslces involved with 2nd PA
Stapedius, stylohyoid, posterior belly of digastric, auricular muscles, and muscle fo facial expression
What nerve is involved with 2nd PA
CN VII
The CArtilage of 3rd PA function
Produces parts of the hyoid bone
The mesenchyme of which PA forms most of the external ear
2nd PA
MSucles associated with the 3rd PA
Styloharyngeus muslce
NErve ivolved with 3rd PA
CN IX
Cartilagious componentn of 4th and 6th PA function
Fuse to form laryngeal cartialges which form the thyroid, cricoid, arytenoid, corniculate and cuneiform
Muslces of 4th PA
Cricothyroid, lavator veli palatini, constrictors of the pharynx
Muslces of 6th arch
Intrinsic muscles of larynx
Nerve fo 4th PA
Superior laryngeal rbanch of CN X
nerve of 6th PA
Recurrent laryngeal branch of CN X
Which PA contributes to the bones of middle ear, part of the external ear and the EAM
1st arch
What is the aortic sac
Distal part of the truncus arteriosus
What happens to the first AA
mostly regresses, with small portion forming the maxilalry artery
What happens to he 2nd aortic arch
Disappers
What happens to the 3rd aortic arch
Forms common carotid artery and the proximal part of the ICA
Gives rise to the ECA
What happens to te 4th aortic arch
Left side forms part of the aortic arch between the left common carotid and left subclavian
Right forms the right subclavian artery
What happens to the 6th aortic arch
Pulmonary arch
Proximal part of the right pulmonary artery
Let side it forms the ductus arteriosus and left pulmonary artery
What happens to the right forsal aorta and the connection between 3rd and 4h arch
Regresses
What happens to the right dorsal aorta and the connection between 3rd and 4h arch
Regresses
What does Pharyngeal pouch 1 form
Distal end forms tympanic cavity
Proximal end forms auditory tube
What does Pharyngeal pouch 2 form
Palatine tonsil and the tonsilar fossa
What does Pharyngeal pouch 3 form
Inferior parathyroid glands
Thymus
How does thymus migrate
Both inferior parathyroid gland and thymus lose their connection to wall of the pharynx
Thymus migrates towards mediastinum, pulling the inferior parathyroid gland with it
Thymus fuses with its counterpart from the other side
What does Pharyngeal pouch 4 form
Superior parathyroid glands
What is the ultimopharyngeal body
Becomes embedded in the thyroid gland as parafollicular cells
These cells secrete calcitonin
How does tongue form
Initially from 3 swellings
Two lateral lingual swellings
One medial selling
Both originate from the 1st pharyngeal arch
Another swelling then forms called the copula
Epiglottis then forms from the another swelling from the 4th arch
From where does the copula form
Swelling formed from the mesoderm of the 2nd, 3rd and 4th arches
What is immediately behind the epiglottis swelling
Laryngeal orifice
What forms the anterior 2/3 of the tongue
Lateral lingual swelling and medial swelling increase in size and merge
What performs the general sensory innervation of the anterior part of the tongue
CN V3
What si the posteiror part of tongue derived from
Arches 2-4
What provides sensory innervation of the posteror aprt of tonue
CN IX
How does the thyroid gland develop
Develops from the epithelial proliferation situated at a point called the foramen caecum
Develops as a diverticulum
Descends anterior to the pharynx
Connected via the thyroglossal duct to the tongue (should regress)
Reaches final position ventral to the trachea
What does the face form from
Facial prominences which are derived from the first PA
What are the facial prominences
Maxillary prominence - lateral to stomodeum
Mandibular prominence - caudal to stomodeum
Frontonasal prominence - upper border of stomodeum
Bilateral thickening of surface ectoderm appear - nasal placodes
How do nasal pits form
Invagination of nasal placodes
What happens after week 5 regarding the maxillary prominence
Increase in size and grow medially
compress the medial nasal prominences
towards midline, which fuse
Gap between medial nasal prominence and maxillary prominence is lost forming upper lip
How is upper lip formed
Fusion of the maxillary and medial nasal prominence
How does lower lip and mandible form
Mandibular prominence grows towards one another and fuse in the midline
How does intermaxillary segment form
Two nasal prominences merge together
What is the main part of the palate formed from
maxillary prominence
What acts as the landmark between the primary and secondary palates
Incisive foramen
What are anterior cleft deformities
lateral cleft lip
Cleft upper jaw
Cleft between the primary and secondary palate
These are due to partial or complete failure of the fusion of the maxillary and medial nasal prominence
What are posterior cleft deformities
Cleft palate - palatine shelves do not fuse
Cleft uvula
What are palatine shelves
a medially directed outgrowth of the embryonic maxilla; when fused with its opposite number it forms the secondary palate
What does the labial component form
Philtrum of the upper lip
What does the upper jaw component form
4 incisor teeth
What does the Palatal component form
Primary palate
What are the pharyngeal clefts lined with
ectoderm
What was previously thought to form the EAM and what actually forms it
Previosly thoguth to be formed by the 1st pharyngeal cleft
Actually arised from the 1st PA
What causes PC 1 to disappear
PA2 expands in size
Also extends caudally overlapping cleft 2 and 3
How do cleft 2,3 and 4 lose contact with outside
What happens to them after
PA 2 meets another bulk of tissue called epicardial ridge and they merge
cleft 2,3 and 4 form a cavity called the cervical sinus that will disappear
What is branchial fistula
Remnants of the 2nd, 3rd and 4th pharyngeal clefts
Cysts can be remains of the cervical sinus that should regress
