Anatomy - Week 5 PP Flashcards
What is embryology?
Study of the embryo
◦ “Embryo-” relates to the early development stages of an animal
◦ “-ology” a science or branch of knowledge
- Understanding normal development allows us to:
Differentiate normal vs. abnormal appearances
◦ Plan for the best possible treatment(s)
development disturbances / malformations
This information also helps in the appreciation of any developmental considerations that may occur in these structures, especially if any disturbances occur.
* These developmental disturbances can include congenital malformations, or defects, which are evident at birth.
* Malformations can be due to:
◦ genetic factors such as chromosome abnormalities
◦ or environmental agents and factors.
* These environmental agents and factors can include infections, drugs, and radiation and are considered teratogens
Embryo vs Fetus
Similarities - developing young of an animal in womb
Differences - embryo is in the first 2-8 weeks of development - structures are not easily recognizable
Fetus is the development period after the embryo stage - structures are more easily recognizable
Embryonic Germ Layers - in week 3
Endoderm - inside tube, primitive gut
Mesoderm - middle
Ectoderm - outside tube
Endoderm
the most internal germ layer, forms
the lining of the stomach, pharynx and other internal organs
Mesoderm
the middle germ layer, forms muscle, the skeletal system, the circulatory system, and the dentin, pulp and cementum
Ectoderm
the most exterior germ layer, forms
skin, lining of oral cavity, tooth enamel, the nervous system, and other external tissues
Opening at both ends of the tubes…
- Mouth - cephalic/head
- Anus - caudal/tail
Overview of Facial Development
- During the 4th week facial development starts
- Stomodeum (primitive mouth)
- The developing brain, face, and heart are noted
- Facial development is completed in the 8th week
All three embryonic layers are involved in facial development: ectoderm, mesoderm, and endoderm.
Stomodeum
a shallow depression in the embryonic surface ectoderm at the cephalic end before the fourth week, this forms the primitive mouth
◦ At this time, the stomodeum is limited in depth by the oropharyngeal membrane: the membrane which separates the stomodeum from the primitive pharynx
Primitive Pharynx
is the primitive throat
Foregut
is the endodermal canal which gives rise to the pharynx, tongue, esophagus, stomach, liver, pancreas, and thyroid
Frontal Process
-Above stomodeum
◦ Future forehead, nasal septum, and anterior roof of mouth
1st Branchial Arch
Below the stomodeum
◦ Future lower lip, lower face and mandible
Mandibular Process
Develops from the first branchial arch
* Gives rise to the lower face, including the lower lip
* The mandibular arch will also give rise not only to the mandible, but also its mandibular teeth and associated tissues
Maxillary Processes
- During the fourth week an adjacent swelling forms from increased growth of the mandibular arch on each side of the stomodeum - the maxillary process * Each maxillary process will grow superiorly and anteriorly around the stomodeum
“forms the midface: sides of the upper lip, cheeks, and posterior part of the maxilla/palate with its canines, certain posterior teeth, and associated tissues. This tissue also forms the zygomatic bones and parts of the temporal bones
Frontonasal Processes
- Upper face
◦ Forehead
◦ Bridge of the nose
◦ Primary palate (anterior portion)
◦ Nasal septum
◦ All structures associated with the medial nasal processes
Upper face formation: nasal region
- During the fourth week, the tissue around the nasal placodes on the frontonasal process undergoes growth, thus starting the development of the nasal region and the nose
- The placodes then become
submerged, forming a depression in the center of each placode, the nasal pits
Nasal Pits
- Deepening of the nasal pits produces a nasal sac that grows internally toward the developing brain.
- The middle part of the tissue growing around the nasal placodes appears as two crescent-shaped
swellings located between the nasal pits. - These are the medial nasal processes. - Form apex of nose, philtrum
On the outer part of the nasal pits are two other crescent-shaped swellings, the lateral nasal processes. - Form ala and nares
Nasal Septum
A separation of the two nasal cavities
* Downward extension of median nasal process (intermaxillary segament) towards center of hard palate forms the nasal septum
Palate formation - 3 processes coming together
- Premaxilla
◦ Forms from intermaxillary segment (median nasal process)
◦ Anterior portion of palate
◦ Forms between 5-6th week - Lateral Palatine Process (secondary palate)
◦ Forms from maxillary process which formed from the 1st branchial arch (palatal shelves)
◦ Forms sides of the hard palate
◦ 6th to 12th week
Premaxilla + lateral palatine processes fuse in aY-shape pattern to form the palate
When does anterior portion of palate start forming??
forms between 5th - 6th week
When does the palate finish formation?
the 12th week
Upper & Lower Lip Formation
- During the sixth week, the upper lip is formed when each maxillary process fuses with each medial nasal process on both sides of the
stomodeum - the maxillary processes contribute to the sides of the upper lip, and the two medial nasal processes contribute to the philtrum
- The maxillary processes on each side of the developing face partially fuse with the mandibular arch on each side to create each labial commissure
Cleft Lip
Unfused area of the upper lip
◦ Fusion of the upper lip should occur around week 6
◦ Cause: failure to fuse one or both
maxillary processes with median nasal process
◦ Usually unilateral
◦ Appearance: absence of center and adjacent lip
-Nose often mishaped on affected side
- can be unilateral cleft lip or bilateral cleft lip
Cleft Palate
- Unfused areas of a palate
◦ Fusion should occur between week 8-12
◦ Causes
-Improper or complete failure to
fuse premaxillary area with lateral
palatine processes
Neck development
- The development of the neck parallels the development of the face 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 primitive pharynx and the 4 lower branchial arches.
Tongue formation
Formed from the first 4 branchial arches
body of tongue - 1st arch
base - 2nd, 3rd, and 4th brachial arches
Summary of Development - Frontal Process
Median Nasal Process
-Center of nose
-Philtrum
- Intermaxillary segment
-Nasal Septum - Premaxilla
Lateral Nasal Processes
- Sides of nose
Summary of Development - Branchial Arches
- Branchial Arch 1
- Mandibular Process
-Lower jaw
-Lower face
-Body of tongue - Maxillary Process
-Maxilla - Lateral palatine processes
-Sides of cheek - Branchial Arches 2.3.4
- Base of the tongue
Epithelial Rests
Misplaced groups of epithelial cells
◦ Cells from ectoderm germ layer
◦ Found between embryonic processes fusing together
◦ Causes formation of cysts
§ Group of epithelial cells divide and form a sac
§ Cysts can grow and distort tissues including teeth
Odontoma
An anomaly or tumor relating to teeth
◦ Benign
◦ Made up of all or some of the tissues that develop into teeth
◦ Two general types
§Compound (resembles a tooth)
§Complex (does not resemble a normal tooth)
Brachial Cleft Cyst
Congenital epithelial cysts, which arise on the lateral part of the neck
* A failure of the destruction of the
second branchial cleft in embryonic development
Nasolabial Cyst - soft tissue
A cyst in soft tissue where the upper lip meets the nasal ala.
Benin
