Embryology Chapter 4
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when does the development of the face take place?
begins in the 4th week in the embryonic period.
what is the order of the embryonic layers involved in facial development?
- ectoderm on the outside
- mesoderm in the middle
- endoderm on the inside
facial development depends on 5 facial processes. Name those.
- single frontonasal process
- paired maxillary processes
- paired mandibular processes
explain how most facial tissues are developed.
by the fusion of swellings, or tissues on the same surface of the embryo
what is initially located between adjacent swellings or tissues in facial development?
a cleft or groove
during fusion of tissues on the same surface of the embryo, how are the clefts or grooves usually eliminated?
by underlying mesenchymal tissues migrating into the groove, making the embryonic surface smooth
describe the fusion in palatal fusion.
allows the fusion of swellings or tissue from different surfaces of the embryo
what is the stomodeum? and how does it initially appear on the surface of the embryo?
- it is the primative mouth
- appears as a shallow depression in the embryonic suface ectoderm at the cephalic end
In the beginning of the 4th week what is limiting the depth of the stomodeum?
oropharyngeal membrane -temporary membrane consistin of external ectoderm overying endoderm formed during the 3rd week of prenatal development
the oropharyngeal membrane also separates the stomodeum from the ____________.
what is the first event in the development of the face during the 4th week of prenatal development?
disintegration of the oralpharyngeal membrane
what happens with the disintegration of the oralpharyngeal membrane?
the primitive mouth increased in depth enlarging it
what is the first process to form after the stomodeum? and where does it form in relation to it?
- the mandibular processes
- form inferior to the stomodeum
how is the mandibular arch formed?
by the fusion of the mandibular processes in the middle
what is the mandibular symphisis?
a faint line where the 2 mandibular processes fused
what is considered to be the 1st branchial arch?
the mandibular arch
what cells do all branchial arches depend on to form?
what is Meckel's carilage? and what will it give rise to?
- cartilage that forms within each side of the mandibular arch
- will give rise to Malleus and Incus
what structure gives rise to the temporomandibular ligaments?
the perichondrium surrouning Meckel's cartilage
Describe the frontonasal process
a bulge of tissue in the upper facial area at the most cephalic end of the embryo and is the cranial boundary of the stomodeum.
what are placeodes? and where are they located on the embryo?
- rounded areas of specialized, thickened ectoderm
- located on the outer surface of the embryo, and at the location of developing special sense organs
Name the 3 types of placodes and what they will become
- lens placodes: eventually migrate medially, and form the eyes and related tissues
- otic placodes: located more laterally and posteriorly than the lens placodes, and are the future ears andrelated tissues
- nasal placodes: form in the anterior portion of the frontonasal process just superior to the stomodeom and are the future nose and olfactory cells
how are the nasal pits formed? and what will they later become?
- the nasal placodes become submerged forming a depression in the center of each placode
- develops into the nasal cavity
As the nasal placodes continue to deepen into the nasal cavity, what structures are developing on the lateral walls of the nasal cavity?
the superior, middle, and inferior nasal conchae
what are the medial nasal processes?
bilateral crescent shaped tissues between the 2 nasal pits.
the medial nasal processes fuse externally to form_________________________and fuse internally to form____________________.
- middle portion of nose
- intermaxillary segment
What are the lateral nasal processes?
bilateral crescent shaped tissues lateral to each nasal cavity
what will the lateral nasal processes fuse to become?
the alae of the nose, or the nostrils
How does the maxillary process begin to form?
as an adjacent swelling from increased growth of the mandibular arch, it grows superiorly and anteriorly on each side of the stomodeum.
what happens to cause upper lip formation during the 4th week of prenatal development?
each maxillary process fuses with each medial nasal process
what happens to cause the labial commissures to form in the 4th week of prenatal development?
fusion of the maxillary processes with the mandibular processes
what does fusion of the maxillary processes with the lateral nasal processes form? And what does it give rise to?
- nasolacrimal groove
- nasolacrimal duct
what are branchial arches?
6 pairs of U-shaped bars witha core of mesenchyme formed by neuro crest cells that migrate to the neck region
What is the first branchial arch?
the mandibular arch
what is the second branchial arch?
the hyoid arch
what is the cartilage that forms within each side of the hyoid arch called?
What is the name of the cartilage in association with the third branchial arch?
it is unnamed
How many branchial arches are there?
6, but the fifth arch is so rudimentary that it is included with the 4th branchial arch
what are pharyngeal pouches? And how many are there?
- the develop as ballon like structures between the branchial arches and give rise to many tissues of the face and neck
- there are 4, but the 3rd and 4th are combined
what is the branchial groove?
the 'wedgie' between the first branchial arch and the second branchial arch the give rise to the eardrum
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