1. Embryology
Definition: the study of the origin and development of an organism
Prenatal period: before birth
38 weeks from conception to birth (average) “fetal” age
Gynecologic timing has been from LMP therefore refers to 40 weeks “gestational” age
Date of conception has been difficult to time
LMP is on average two weeks before ovulation

2. HUMAN EMBRYOLOGY
Development of Face,
Neck & Limbs

3. Our goals for learning:Development of the orofacial structures
Formation of inner cell mass which gives rise to embryonic germ layers.
Formation of neural crest
Development of face
Formation of tongue
Development of mandible
Formation of palate
Congenital malformation

4. Development can be interrupted by
abnormal genetic conditions
Diseased conditions of the mother(crossing the placenta)
or environmental agents (teratogens)

5. Developmental Anatomy in human
Prenatal development ( events inside the uterus; before birth)
Includes:
1.Preimplantation period: first two week.
2.Embryonic period: nd to 8th week.
3. Fetal period : From 9th week till end of pregnancy.
Postnatal development: All the developmental events which occur after birth( Further development of some organs and structures e.g. teeth, mandible, maxilla, long bone.

6. Fertilization to Implantation
Ovary
At the time of fertile peroid

7. Week 1: 4 cell stage Late Day 2 Morula Day 3 2 cell stage Day 2
Blastocyst
Day 5
Implantation
Day 6 - 7
Fertilization
Day 1

8. Fertilization period Developmental disturbances in meiosis:
Results in chromosomal abnormalities like Down’s syndrome (triosomy 21 )
Children with Down syndrome may have increased level of periodontal diseases and abnormally shaped teeth.

9. Formation of blastocyt
Inner cell mass will differentiate to epiblast (ectoderm)
& hypoblast (endoderm).the cells of ectoderm will
Migerate to form a third layer (mesoderm).these three
Layers are the germ layer which will form embryo.

10. Morula

11. At the end of sixth week after fertilization, the embryo becomes
22-24 mm in length

12. Development during fetal period consists of growth and maturation of the structures that have already formed during embryonic period

13. Events of embryonic period
Formation of three germ layers (ectoderm, mesoderm and endoderm)
Development of CNS and neural crest
Migration of neural crest cells to their final destination
Development of branchial arches
Development of teeth
Development of mandible and maxilla
Development of tongue and palate
Development of thyroid gland and part of pituitary gland.
Development of lips and mouth cavity

17. Derivatives of germ layers
Mesoderm
Endoderm
Ectoderm
Muscles
Connective tissues in the body
Gastrointestinal tract & associated glands
Nervous system
Sensory epithelium
Epidermis, hair, nails
Mammary & cutaneous glands
Sinuses epithelium,
enamel

19. Neural Crest Cells Neural crest: “a transient band of cells
that joins the neural tube to the
epidermis.”
􀂄 migrate long distances
􀂄 give rise to a variety of cell types
􀂄 Sensory neurons, autonomic
neurons, glial cells, pigment cells,
endocrine cells, and connective and
supportive