UNIT 1 - Embryology

What are the main periods of embryology ?

• Pre-embryonic

• Embryonic

• Fetal

When does pre-embryonic period take place ?

0-3 weeks

When does embryonic period take place ?

4-8 weeks

When does fetal period take place ?

9-38 weeks

What happens during 1st week ?

the zygote develops into what is called a blastocyst/blastocoel

What happens during 2nd week ?

zygote becomes bilaminar disc

What happens during 3rd week ?

bilaminar disc becomes trilaminar disc (gastrula), whose germ layers contain the origin of all cells, tissues and organs

What are the different germ layers ?

• Ectoderm

• Mesoderm

• Endoderm

What is happening to ectoderm ?

Gives rise to two layers :

• neural crest

• neuroectordem

What is happening to endoderm ?

• oroopharyngeal membrane

• cloacal membrane

in contact with ectoderm

What is happening to mesoderm during embryonic period?

Divided into :

• paraxial mesoderm

• intermediate mesoderm

• lateral plate of mesoderm

What are the different divisions of paraxial mesoderm ?

• Myotomes : head muscles

• Dermatomes : CT of the skin

• Sclerotomes : bones & cartilages of the head

What is derived from Ectoderm ?

• Parts of the oral cavity

• ENAMEL

• Parotid gland

• Neurocranium

• CNS & PNS

What is derived from Endoderm ?

• Parts of the oral cavity

• Submaxillary/submandibular and sublingual glands

• Tongue

• Pharynx

• Larynx

• Parathyroid glands

• Thyroid glands

What is derived from Mesoderm ?

• Smooth & striated muscles

• Connective tissue

• Cartilage

• Cranial bones

• Blood

Where do the head and neck derive from ?

• Paraxial mesoderm

• Lateral plate of mesoderm

• Neural crest

• Ectodermal placodes