Anatomy - Week 5 PP

Question 1

What is embryology?

Answer 1

Study of the embryo
◦ “Embryo-” relates to the early development stages of an animal
◦ “-ology” a science or branch of knowledge

Question 2

• Understanding normal development allows us to:

Answer 2

Differentiate normal vs. abnormal appearances
◦ Plan for the best possible treatment(s)

Question 3

development disturbances / malformations

Answer 3

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

Question 4

Embryo vs Fetus

Answer 4

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

Question 5

Embryonic Germ Layers - in week 3

Answer 5

Endoderm - inside tube, primitive gut

Mesoderm - middle

Ectoderm - outside tube

Question 6

Endoderm

Answer 6

the most internal germ layer, forms
the lining of the stomach, pharynx and other internal organs

Question 7

Mesoderm

Answer 7

the middle germ layer, forms muscle, the skeletal system, the circulatory system, and the dentin, pulp and cementum

Question 8

Ectoderm

Answer 8

the most exterior germ layer, forms
skin, lining of oral cavity, tooth enamel, the nervous system, and other external tissues

Question 9

Opening at both ends of the tubes…

Answer 9

1. Mouth - cephalic/head
2. Anus - caudal/tail

Question 10

Overview of Facial Development

Answer 10

• 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.

Question 11

Stomodeum

Answer 11

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

Question 12

Primitive Pharynx

Answer 12

is the primitive throat

Question 13

Foregut

Answer 13

is the endodermal canal which gives rise to the pharynx, tongue, esophagus, stomach, liver, pancreas, and thyroid

Question 14

Frontal Process

Answer 14

-Above stomodeum
◦ Future forehead, nasal septum, and anterior roof of mouth

Question 15

1st Branchial Arch

Answer 15

Below the stomodeum
◦ Future lower lip, lower face and mandible

Question 16

Mandibular Process

Answer 16

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

Question 17

Maxillary Processes

Answer 17

• 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

Question 18

Frontonasal Processes

Answer 18

• Upper face
  ◦ Forehead
  ◦ Bridge of the nose
  ◦ Primary palate (anterior portion)
  ◦ Nasal septum
  ◦ All structures associated with the medial nasal processes

Question 19

Upper face formation: nasal region

Answer 19

• 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

Question 20

Nasal Pits

Answer 20

• 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

Question 21

Nasal Septum

Answer 21

A separation of the two nasal cavities
* Downward extension of median nasal process (intermaxillary segament) towards center of hard palate forms the nasal septum

Question 22

Palate formation - 3 processes coming together

Answer 22

• 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

Question 23

When does anterior portion of palate start forming??

Answer 23

forms between 5th - 6th week

Question 24

When does the palate finish formation?

Answer 24

the 12th week

Question 25

Upper & Lower Lip Formation

Answer 25

• 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

Question 26

Cleft Lip

Answer 26

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

Question 27

Cleft Palate

Answer 27

• 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

Question 28

Neck development

Answer 28

• 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.

Question 29

Tongue formation

Answer 29

Formed from the first 4 branchial arches

body of tongue - 1st arch
base - 2nd, 3rd, and 4th brachial arches

Question 30

Summary of Development - Frontal Process

Answer 30

Median Nasal Process
-Center of nose
-Philtrum

• Intermaxillary segment
  -Nasal Septum
• Premaxilla

Lateral Nasal Processes
- Sides of nose

Question 31

Summary of Development - Branchial Arches

Answer 31

• 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

Question 32

Epithelial Rests

Answer 32

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

Question 33

Odontoma

Answer 33

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)

Question 34

Brachial Cleft Cyst

Answer 34

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

Question 35

Nasolabial Cyst - soft tissue

Answer 35

A cyst in soft tissue where the upper lip meets the nasal ala.

Benin