Review of Embryology (Oral Bio)

Growth — definition

Physical increase in size or number; differential process in which some parts grow more rapidly than others.

Development — definition

Increase in degree of organization and/or functional complexity; a physiologic and behavioral process.

Craniofacial morphogenesis — critical period

Weeks 4-14 of intrauterine life are the critical period for formation of the face and oral cavity. (MKE 414)

Proliferative period

Weeks 0-2: fertilization, implantation, and embryonic disk formation.

Embryonic period

Weeks 2-8: tissues and organ systems develop; weeks 3-8 are most susceptible to serious malformations.

Fetal period

Week 8-birth: tissues enlarge, differentiate, and function; susceptibility to major malformations declines.

Week 1 — what happens to embryonic disc

Bilaminar disc forms from cells of the zygote: differentiation of ectoderm + endoderm.

Ectoderm — key idea

Outer structures; skin/hair and nervous-system development.

Endoderm — key idea

Forms GI tract epithelial linings and associated glands.

Week 2 — gastrulation

Gastrulation (process of forming 3rd layer) forms mesoderm and produces a trilaminar disc: ectoderm, mesoderm, endoderm.

What important system does the ectoderm develop into?

Nervous system

What sensory epithelium does the ectoderm include?

Sensory epithelium of eye, ear, and nose

What type of skin structures does the ectoderm give rise to?

Epidermis, hair, and nails

What glands are derived from the ectoderm?

Mammary, intraoral and cutaneous (skin) glands

What cavities are formed from the ectoderm?

Oral and nasal cavities, epithelium of the sinuses

What dental structure is developed from the ectoderm?

Tooth enamel

What are the 3 M's when it comes to mesoderm?

Muscles, middle, mesoderm

What are the connective tissue derivatives of the mesoderm?

Bone, cartilage, blood, dentin, pulp, cementum, periodontal ligaments

After week 2, the trilaminar disc becomes the...

embryo

Weeks 0-2 (proliferative period) — environmental susceptibility

Least susceptible to environmental factors and acquired defect formation.

"p"roliferative = "p"rotected

Weeks 3-8 (embryonic period) — environmental susceptibility

Most critical for serious malformations because structures are developing and highly susceptible.

What happens during week 3?

neural folds appear, neural tube closes, primary brain vesicles (brain, spinal cord) form

Week 8-birth — susceptibility

Declining susceptibility to malformations; defects tend to be minor.

By week 4

Heart begins to beat.

heart 4 you

Weeks 4-7

Formation of the face and oral structures.

Weeks 8-14

Face takes on a more human appearance. Fetal period begins at week 8.

What happens during neurulation?

Week 3. Neural folds appear and form the neural tube; this initiates CNS formation.

Neural groove development

Deepens between rising neural crests. Where CNS forms

What are NCC (neural crest cells)?

Differential cells around neural grooves that migrate laterally/ventrally to form diverse structures in the future face. Contribute to sensory nerves and teeth.

What structures does the newly formed CNS make in week 3?

Primary brain vesicles; forebrain, midbrain, and hindbrain; cerebral hemispheres also form.

What makes up the forebrain?

frontal, temporal, and occipital lobes, other brain matter

Weeks 4-5 — cranial nerves

Cranial nerves begin development and grow into the tissues they innervate.

What stage does Fetal alcohol syndrome affect?

Affects Stage 1 which is the initial organization of germ layers.

Fetal alcohol syndrome — brain impact

First three ventricles of the brain fail to separate.

Fetal alcohol syndrome — face deformations (7 key features)

Saddle nose (low nasal bridge), minor ear abnormalities, epicanthal folds (folds within eye lids), indistinct philtrum (no two lines from nose to mouth), micrognathia (less developed jaw), flat midface and short nose, thin upper lip

Gut tube — foregut becomes:

Upper digestive tube from throat to duodenum.

Gut tube — midgut derivatives:

Small intestine, cecum, ascending colon, and most of the transverse colon.

Gut tube — hindgut derivatives

Sigmoid colon and rectum.

Buccopharyngeal membrane

Between cardiac bulge and forehead, opening to oral cavity

Week 4 — facial development

Pharyngeal arches appear and facial development begins.

Orange Box in image (develops in to)

Front Nasal Passage

Purple Box in Image (develops in to)

Nostrils

Teal box in image (develops in to)

Mandible

Pink box in image develops in to

Buccopharyngeal membrane

Black box develops in to

Nose

Frontal prominence (week 4)

Becomes the forehead area.

Stomodeum (week 4)

The oral pit; becomes the oral cavity.

Maxillary process (week 4)

A facial prominence that grows toward the oral cavity and contributes to facial structures/cheeks.

Mandibular process (contributes to? what week do they form?)

Contributes to the developing mandible/lower face.

week 4

What are Nasal pits and what week do they start to form

Beginning of the nasal cavity.

week 4

Ncc contribute to tooth and periodontium formation by..

and why is this an exception

Migrating to oral ectoderm

ectoderm is usually for outer parts of the body but it also refers to the front of the oral cavity.

What are some complex processes of NCC's

NCC's migrate to epithelial areas with specific homeobox genes in high concentrations

also help with cell signaling

What can happen when NCC's don't work properly

Missing teeth, or supernumerary teeth

What is the orange box (middle black gray area)

Stomodeum (oral pit) and rupturing buccopharyngeal membrane

What does the lighter gray area (purple box) develop

Maxillary process (first arch)

Blue box

medial nasal process

Black box

lateral nasal process

Pink box, what does the maxillary process develop

shelves that are sent out to form palate

When does the oral pit first appear and what is it

Week 4

Develops between brain and heart buldge, becomes oral cavity, or stomodeum

What day does a heart start beating

day 21

Light blue box

where does it emerge

Maxillary process

emerges from arch

Teal (bottom) box

first branchial groove

three black boxes (in parenthesis is arch it orignates from)

1. Mandibular arch

2. Hyoid arch

3. Third branchial arch

Week 5 — oropharyngeal membrane

Ruptures, opening the oral cavity to the tubular foregut and establishing the oropharynx.

In week 5, ____ grows ___(direction)__ to oral pit and will develop in to the _____ which forms the cheeks.

a. mandibular arch

b. laterally

c. maxillary process

What direction do maxillary processes grow

Ventromedially (towards the surface and towards the middle)

What face parts develop during week 5-6?

nose and nostrils develop, eyes and external ears become for evident

What is ossification of the mandible and when does it happen?

Mandible begins ossification (boney calcification next to cartilage) during the late sixth week

During weeks 5-6, the maxillary processes grow _____ toward the oral cavity and meet the _____ and lower extent of the _____.

ventromedially

lateral nasal prominences

medial nasal processes

What happens to the mandible during late week 6

Mandible begins ossification.

What nose and nostril feature develops from the nasal placodes

Develop into nasal pits, with medial and lateral nasal prominences forming around them.

What is the nasolacrimal groove

this region runs between eye and maxillary prominence

Weeks 6-9 — facial development updates?

Facial processes continue fusion and maturation; facial contours become increasingly recognizable.

Weeks 10-14 — facial development updates? What region becomes more recognizable

The face continues to take on a more human appearance; the intermaxillary/philtrum region becomes recognizable

What are the 3 components of the pharyngeal apparatus from outside the inside

Groove -> arch -> Pouch

What is the importance of pharyngeal arches

Also called branchial arches; contribute greatly to formation of the head and neck.

Pharyngeal arches - when do malformations happen

Many major craniofacial malformations originate during transformation of the branchial apparatus into adult derivatives.

Each pharyngeal arch contains...

Cartilage, an artery, a cranial nerve, and mesodermal tissue.

What are pharyngeal grooves/clefts?

Develop around week 5

vertical indentations between the arches outside (groovy outside) (cleft= went outside)

they develop around week 5

Pharyngeal pouches

Internal structures that separate the arches within the pharynx and correspond with external grooves.

(pouch is inside something)

Arch 1 — name and cartilage

Mandibular arch

meckels cartilage (bilateral)

Arch 1- development time

develop in week 4 and disappear in week 5

Arch 1 — cranial nerve

CN V (Trigeminal)

Arch 1 — muscles (name and when they develop)

Muscles of mastication; also anterior belly of digastric, mylohyoid, tensor veli palatini, and tensor tympani.

Develop in week 5 and spread into muscle origin in weeks 6/7

Arch 1 — skeletal/bone derivatives

Melleus and incus

Arch 1 lined by

ectoderm (both internally and externally)

Arch 2 — name and cartilage

Hyoid arch

Reicherts cartilage (rod shaped)

Arch 2-5 development time and lining (AND EXCEPTION)

weeks 4-7

ectoderm externally and endoderm internally

EXCEPT anterior area behind arch 2

Arch 2 — cranial nerve

CN VII (Facial).

Arch 2 — muscles (5 answers)

Muscles of facial expression, posterior belly of digastric, stylohyoid, and stapedius.

Arch 2 — skeletal/bone derivatives (5 answers)

stapes, styloid process, stylohyoid ligament, upper body of hyoid and lesser cornu.

Arch 3 — cranial nerve

CN IX (Glossopharyngeal).

Arch 3 — muscles (1)

Stylopharyngeus; (from styloid process to pharynx)

Arch 4 muscles

inferior pharyngeal constrictor muscles

Arch 3 vessels become prominent, becoming the ____ and suply the ____p

common carotid arteries

supply neck face and brain

During week 7, 3rd arch vessels switch from the ____ to the ___ to face and neck. ___[first blank]___ supplies the brain

1. internal carotid

2. external carotid

3. internal carotid

Arch 3 — skeletal derivatives

Greater cornu and lower body of the hyoid

Arch 4/5 — cranial nerve

CN X (Vagus).

Arch 4 becomes the ...

Dorsal aorta (descending aorta)

Week 7 — carotid supply

External carotids supply the face/neck; internal carotid supplies the brain.