Embryonic development Flashcards
Define embryology
The branch of medicine concerned with the study of embryos and their development
What does development involve?
- the division and differentiation of cells
- the changes that produce and modify anatomical structures
What periods can embryonic development be divided into?
- pre-embryonic (0-2 weeks)
- embryonic (3-8 weeks)
- foetal period (8 weeks - 9 months)
What is the pre-embryonic period?
- 1-2 weeks
- Early cell division and implantation
- formation of a bilaminar
What is the embryonic period?
- 3-8 weeks
- trilaminar structure forms
- rudiments of most organs and tissues develop
What is the foetal period?
- 8 weeks - 9 months
- rudiments grow and mature
What kind of cell is a fertilised ovum?
totipotent stem cell
What is cleavage?
a series of cell divisions thet subdivide the cytoplasm of the zygote
What is a morula?
A ball of 16 cells in pre-embryonic development
How many cells does a blastocyst have?
70-100
What is the order of the pre-embryonic stage?
- ovum
- zygote
- morula
- blastocyst
How is the bilaminar disk formed?
- after implantation, some cells in the inner cell mass differentiate into a new type of cell layer
- new layer is the hypoblast
- original layer is epiblast
What is is the hypoblast?
The new layer of cells formed by the blastocyst to create the bilaminar disk
What is the epiblast?
The original layer of cells that remains as part of the bilaminar disk
What are the important changes at the start of week 3?
- gastrulation
- neurulation
What is gastrulation?
The process by which the three germ layers are formed
What are the stages of gastrulation?
- epiblast cells form a primitive streak
- they move down into the hypoblast layer and displace it
- this forms the endoderm layer
- some epiblast cells move inbetween the epiblast and endoderm to form the mesoderm
- the epiblast becomes known as the ectoderm
When does gastrulation occur?
day 14-20
What are the three germ layers?
- ectoderm
- mesoderm
- endoderm
What type of cells are the germ layers?
multipotent stem cells
What is the three germ layer structure known as?
the embryo
What process forms the organs?
Organogenesis
What forms the notochord?
A central tube of mesoderm cells
What will the notochord become?
the vertebral discs
What does the notochord stimulate?
stimulates the ectoderm to thicken, which forms a neural plate made of neuroectoderm cells
What does the neural plate do?
- forms 2 ridges
- fuse to form neural tube
What are the cells on the neural crest called?
Neural crest cells
What will the neural tube eventually become?
the brain and spinal cord
What forms over the neural tube?
Ecotoderm layer, which will form the outer skin of the developing embryo
What does the ectoderm give rise to?
- nervous system
- skin
- lens and cornea
What happens by day 25?
the neural tube closes at the cranial end (brain) and the caudal end (spinal cord)
What happens if the neural tube does not close?
- spina bifida if caudal neuropore doesn’t close
- anencephaly if cranial neuropore
Where do neural crest cells migrate to?
the mesoderm, where they differentiate into different cell types
What do neural crest cells differentiate into?
craniofacial cartilages and bones
What is ectomesenchyme
The neural crest cells which have migrated into the mesoderm
What happens at the start of week 4?
the pharyngeal arches arise
What will the endoderm develop into?
- epithelial lining of GI and digestive tract
- lining of urethra, bladder, and reproductive system
- pancreas
What will the mesoderm form?
- circulatory system
- muscular layer of stomach and intestines
- musculoskeletal system
- vertebral discs of spinal cord
