Human Embryonic Development Flashcards
What are the two main periods of human development?
Embryonic period
- up to 8 weeks
- most of organogenesis occurs
Feral period
- remaining time in uterus
- involves growth and remodelling
In what period can defects cause congenital malformations?
Defects during embryogenesis
What are the mechanisms of development from egg to adult?
- Fertilisation
- Cleavage
- Gastrulation
- Neurulation and somitogenesis
- Organogenesis
What is it called when the mitosis division of fertilisation reaches 12-16 cells?
Morula
How is a morula converted to a blastocyst?
Through compaction
When does a blastocyst form?
4/5 days after fertilisation
How many cells is a blastocyst made of?
32-64 cells
What are the two structural compartments of a blastocyst?
Blastocoele - fluid filled space
Inner cell mass - group of cells
What structures are visible in the blastocyst at full implantation?
Bilamina germ disk
- Epiblast (from inner cell mass) - forms the lining of the amniotic fluid cavity
- Hypoblast - forms lining of blastocoele
What is gastrulation?
Blastocyst goes From 2 to 3 layers
Hypoblast is displaced by involuting cells (epiblast)
New mesoderm and endoderm forms (along side endoderm)
What are the first steps in neurulation?
- At 15 days the primitive streak extends along the epiblast (gastrulation occurs as this takes place)
- At 18 days notochordal process instruct the ectoderm on top of it to become neural tissue + neural plate starts being established
- At 19 days prechordal plate forms and primitive streak regresses
- At 20-21 days notochord elogated, neural folds rise out of the plane of the disk - neural folds meet and fuse to form a neural tube
- At 22 days surface ectoderm covers tube (formation of anterior Neuropore and posterior neuropore)
Why is the folding of the embryo called a closed purse model?
- Open with chord around margins
- Folding to form purse neck
What is the result of folding?
Formation of the umbilical chord
What occurs during organogenesis?
Differentiation of somatic derivatives
- bones, muscles, tendons
Development of sensory organs
- ears,eyes, olfactory bulb
Limb formation
- forelimbs first, hindlimbs next
- establishment of pattern in the limbs
Formation of face structures
- jaws,nose,toungue, palate
Formation of genital structures
When will malformation cause serious damage to a returns?
The first two weeks - death
Embryonic period - major malformations effecting whole systems and whole organs
