Lesson 2 Flashcards
Describe facial development
- The face and its associated tissue begin to form during the fourth week of prenatal development, within the embryonic period.
- Completed in the 12th week (fetal period)
- Also developing is the brain, face, and heart
Describe the Stomodeum and
Oral Cavity Formation (wk 4)
- During this time, the rapidly growing brain of the embryo bulges over the stomodeum (which has a membrane over it called the oropharyngeal membrane)
- Disintegration (infolding)of the oropharyngeal membrane (ectoderm) over the stomodeum
- Enlarges the primitive mouth
- Allowing access to the primitive pharynx(endoderm)
- Formation of the Oropharynx
- The primitive pharynx is the cranial part of the foregut
- The beginning of the future digestive tract.
What germ cell layer(s) are involved in facial development?
All three embryonic germ cell layers are involved in facial development: ectoderm, mesoderm, and endoderm.
What does facial development depend on?
- the 5 facial processes (prominences) surround the embryo’s primitive mouth:
- fronto(nasal) process
- maxillary processes
- mandibular processes.
How do most facial tissues develop?
- Most of the facial tissues develop by fusion of swellings or tissue on the same surface of the embryo.
- A cleft or furrow is initially located between these adjacent swellings due to proliferation, differentiation, and morphogenesis.
Describe facial fusion
- Furrows are usually eliminated as the underlying mesenchyme migrates into the furrow making the embryonic facial surface smooth.
- This migration takes place because adjacent mesenchyme grows and merges beneath the external ectoderm during the maturation of the structure.
- E.g. hillocks of the ear
Describe the principles of development of the face
- Overall growth of face is in an INFERIOR and ANTERIOR direction in relationship to the cranial base
- Growth upper face initially most rapid keeping pace with developing brain
- Growth of forehead ceases around 12 years
- Growth of the middle and lower portions of the face grow more slowly
- Growth ceases late into puberty
- Eruption of permanent third molars marks end of major growth: lower 2/3 of face
- FACIAL bones developing at this same time
__________ forms as a bulge of tissue in the upper facial area. This process is at the most cephalic end of the embryo and is the cranial boundary of the stomodeum.
Frontonasal process
What does the frontonasal process develop into?
- Forehead
- Bridge of the nose
- Primary palate
- Nasal septum
- Philtrum of the upper lip (Structures related to the medial nasal process)
Describe the maxillary process (middle face formation)
Maxillary arch gives rise to the lower face, including the: Maxillary (upper lip), Maxilla, Maxillary teeth & associated tissues
Describe the Mandibular Arch and lower face formation
- The processes inferior to the stomodeum: Mandibular Processes (1st branchial arch)
- Core of mesenchyme - initiated by neural crest cells that migrate to the facial region
- External – ectoderm
- Internal - endoderm
- The mandibular processes fuse at the midline, forming the mandibular arch inferior to the enlarged stomodeum
- After fusion, the mandibular arch extends as a band of tissue inferior to the stomodeum and between the developing brain and heart.
What does the mandibular arch give rise to?
- Mandibular (lower lip)
- Mandible
- Mandibular teeth & associated tissues
Describe placodes
- Areas of specialized, thickened ectoderm from neural crest cells
- Develop special sense organs
Describe the types of placodes
- Lens placodes - which are initially located on each side of the frontonasal process
- Nasal Placodes – superior to the stomodeum
- Otic Placodes - laterally and posteriorly to the stomodeum
What do lens placodes develop into?
future eyes and related tissues
What do nasal placodes develop into?
olfactory cells for the sensation of smell
What do otic placodes develop into?
future internal ear and related tissues
Describe nose formation in the 4th week
- Nasal placodes on the frontonasal process are the Center for the development of the nasal region and the nose.
- Depression in the center of each placode - Called the nasal pits
- Central area of frontonasal process migrates inferiorly
- there are medial and lateral nasal processes
Describe the medial nasal process
Medial nasal processes fuse together (week 6)to form: root-apex of nose, philtrum of the lip, tubercle of the upper lip
Describe the lateral nasal processes
- The lateral nasal processes form the alae of the nose
- Fusion of the lateral nasal, maxillary, and medial nasal processes forms the nares (nostrils)
The embryonic nose remains visually flat, until _________, when facial development is completed and it has its more mature elevated appearance.
the fetal period
Describe the development of paranasal sinuses
- Begin development in the embryonic stage, continue into fetal stage and after birth
- All form as outgrowths of the walls of the nasal cavities: air filled extensions of nasal cavities in adjacent bones
- Original openings of outgrowths persist as orifices of the adult sinuses
Describe upper lip formation
- Upper lip is formed when bilaterally maxillary process fuses with each medial nasal process
- Due to the underlying growth of the mesenchyme.
- During week 6 - Fusion of the sides of the developing oral cavity: maxillary processes & mandibular arch, forming the Labial commissures
- Upper lip - medial nasal process/maxillary processes
- Lower lip - Mandibular process
- Labial Commissure - Mandibular & Maxillary process
Describe the development of the nasolacrimal duct
- Maxillary process fuses with lateral nasal process along the nasolacrimal groove
- Ectodermal groove which canalizes (cell degeneration) to become the nasolacrimal duct
- Draining tears of the eye
Describe a cleft lip
Failure of fusion of the maxillary process with the medial nasal process can result in cleft lip, with varying degrees of disfigurement and disability.
Describe Commissural Lip Pits
- Epithelium-lined blind tracts located at the labial commissure
- May be shallow or several millimeters deep.
- Congenital lip pits may also be observed near the midline of the vermilion border.
- Treatment: none
The development of the neck parallels the development of the ________ in time span, beginning during the fourth week of prenatal development, within the embryonic period, and completed during the fetal period. The neck and its associated tissues develop from the _________ and the _________
- face
- primitive pharynx
- branchial apparatus
Describe the development of Branchial Arches (or pharyngeal arches)
Fourth week bilateral swellings of tissue appear inferior to the oral pit (stomodeum) and superior/adjacent to the heart bulge
Describe the Branchial Arches (or pharyngeal arches)
- Five pairs of u-shaped tissue with mesenchyme (mesodermal) core
- Ectoderm covering, lined by endoderm
- Give rise to important structures of the face and neck
- Each paired arch has its own developing - Cartilage, Nerve components, Vascular components, & Muscular components within each mesodermal core
What is the first Branchial Groove to develop during the 4th week?
External auditory canal
Describe the Branchial Pouches
- Endodermal lining
- First Branchial pouch: middle ear and eustachian tube
- Second Branchial pouch: palatine tonsils
- Third Branchial pouch: thymus & parathyroid gland
What is the first branchial membrane?
Tympanic membrane
Describe vascular development (week 4)
- Each branchial arch contains a right and left aortic arch vessel
- Aortic vessels from Heart transverse through arches to face, brain, neck
Describe vascular development (week 5)
- 3rd arch vessel becomes: common carotid artery
- External carotid artery: face, neck and brain
- Internal carotid artery: eyes, brain, coverings of brain
Describe Muscular & Neural development (week 5)
- Muscle cells (myoblasts) migrate from the myotome
- Differentiate into elongated muscle cells (myofibers)
- 1st branchial arch muscle cells begin to develop within the 1st branchial arch (called: mandibular arch) : muscles of mastication
- Nerves develop in conjunction with the developing muscle fibers
Muscles of Mastication begin to form from the 1st branchial arch during weeks ___________
5 – 7
Describe Muscular development (week 7)
2nd arch muscles begin to form the muscles of the face (facial muscles)
Muscles of facial expression
2nd arch muscles grow to form the facial muscles beginning in the weeks __________
7-8
Describe Neural Development (week 7)
- Cranial Nerves - Parasympathetic & Sympathetic NS: originate from basal plate of the neural tube and the neural crest cells
Describe the innervation of trigeminal nerve (cranial nerve V)
- Innervates the 1st branchial arch derivatives
- innervates developing muscles of mastication
- innervates sensory for face and mouth
Describe the innervation of facial nerve (cranial nerve VII)
- innervates the 2nd branchial arch derivatives
- innervate the developing muscles of facial expression
- innervate secretion of tears, saliva & taste anterior 2/3 of the tongue
Describe the innervation of glossopharyngeal nerve (cranial nerve IX)
- Innervates the 3rd branchial arch derivatives
- posterior tongue: general & taste
- Upper pharyngeal constrictor muscles
- parotid gland
Describe the innervation of vagus nerve (cranial nerve X)
- Innervates the 4th branchial arch derivatives
- larynx
- pharynx
- epiglottis taste
Describe Cartilaginous Skeletal Development
Initial skeleton of the pharyngeal arches develop as cartilaginous bars of tissue
What is Meckel’s cartilage?
First iteration of the mandible during development
Describe the Primitive temporomandibular joint
- Meckel’s cartilage with terminal malleus articulates with cartilaginous incus & stapes
- Primitive articulation of lower jaw
Describe mandible development at week 7
- Mandibular bone beginning to form from Intramembranous ossification (bone formation directly from connective tissue)
- lateral and posterior to Meckel’s cartilage
- Body of mandible and cartilaginous condyle replace Meckel’s cartilage
- Fusing with other (intra)membranous bones due to muscular response and development of teeth (alveolar process)
Describe mandible development at 5 months
- 2nd (adult) temporomandibular joint: articulation of the condyle and temporal fossae
- Growth continues into puberty: acts as growth center for the temporomandibular joint
Describe the bones of the face
- Protective covering of the brain(skull): intra membranous ( Frontal, parietal, temporal, interoccipital)
- Facial bones: intra membranous (develop overlying the nasal capsule) - Premaxillary, maxillary, zygomatic, temporal
- Maxillary bones grow medially into the palate
What are sutures?
- Fibrous joints opposing surfaces are closely associated
- Sutures named for two or more bones with which they articulate
- Positioned in direction of facial growth - Forward away from the brain; Downward to facilitate lengthening of face
- Growth sites allow for associated bones to expand and maintain orientation by fibrous attachment
- When facial growth complete all sutures become inactive
- Boundaries are always defined
