Extra embryonic membrane: chorion
Developed from cells of inner cell mass and cytotrophoblast
Villous chorion: contains chorionic villi that anchor to the decidua basalis
Smooth chorion: extends from placenta and surrounds all other extra embryonic membranes and embryo
Inner cell mass:
Some cells merge with CYTOTROPHOBLAST to form chorion
EPIBLAST: some cells form amnion rest undergo gastrulation
HYPOBLAST: yolk sac and Allantois
Extra embryonic membranes: Allantois
Formed from a pocketing of the yolk sac
Extraembryonic membrane: amnion
Developed from cells of EPIBLAST
Surround embryo providing protection, homeostatic thermoregulation, and allow movement
Derived from maternal blood initially, as foetus grows mainly foetal urine
Gastrulation:
- primitive streak forms on dorsal aspect of epiblast
- cells fall through to form cells on endoderm
- more cells follow to form mesoderm
- remaining cells are epiderm
TRILAMINAR DISK
Structures that form from endoderm:
Epithelial lining and glands of digestive and respiratory tracts
Structures forming from mesoderm
Everything else
Structures of ectoderm cells
- Epidermis, hair, nails, glands of skin
- brain and spinal cord
- neural crest
- structures of the head
Organogenesis
Formation of organs and organ systems day 16 - week 8
Critical periods and teratogens
Time during which embryo and specific organs are most susceptible to teratogens: any agent that interferes with or interrupts development causing an abnormality Physical Chemical Nutritional Metabolic Environmental
Critical periods:
Nervous system: 3-36wk Heart: 3-6wk Upper limbs: 4-5wk Eyes: 4-8wk Lower limbs: 4-5wk Teeth: 6-8wk Palate: 7-8wk External genitalia: 4-9wk
Neuralation
Differentiation of ectoderm in to neural tubes and crests
Takes a few days and is crucial to embryo survival
Begins ~17 days
Process of Neuralation
- Ectoderm thickens forming neural plate
- neural plate folds along long axis
- as grove deepens prominent neural folds develop
- folds move towards each other forming neural crest
- folds reach each other and fuse forming neural tube
FORMED BY DAY 22
Nervous system development (tube and crest)
- Neural tube is pinched off from ectodermal layer and becomes covered by surface ectoderm & differentiates in to brain and spinal cords
- neural crests develop in to most peripheral nervous system structures
Head and neck development
But 4th week pharyngeal arches are developed from all three germ layers. Will develop and contain artery, cartilage rod, nerve and muscular component
5 primordial of face development
Frontonasal prominence
2 x mandibular prominence
2 x maxillary prominence
