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
