how long does pregnancy last
9 months, 38-40 weeks, 3 trimesters
what period are weeks 0-3
conceptus/embryo
what period are weeks 3-8
embryonic period
what period are weeks 9-40
foetal period
what are the 6 phases of embryogenesis (in order)
- gametogenesis
- fertilisation
- cleavage
- gastrulation
- formation of a body plan
- organogenesis
gamete
cell with a chromosome complement of 23 (haploid)
spermatogenesis
formation of male gametes
when does spermatogenesis occur
at puberty and continues throughout life
how long is once cycle of spermatogenesis
~64 days
production of sperm (increases/decreases) with age
decreases
sperm contain how many chromosomes and what sex chromosome(s)
22 X/Y
oogenesis
formation of female gametes
when does oogenesis occur
starts in development (arrests in prophase of meiosis) and begins again in puberty, stopping in menopause
when is female reproductive life span determined
in foetal life
fertilisation
fusion of female and male gametes to form zygote
zygote
diploid cell with full chromosome complement
cleavage
rapid mitotic cell division with NO increase in size (stays in same area as original zygote)
the zygote forms a _ then _
morula, blastocyst
morula
16+ cells
blastocyst
days 1-4
gastrulation
formation of germ layers and boxy axes established
germ layers
ectoderm (external), mesoderm (middle) and endoderm (internal)
formation of body plan
embryonic folding
organogenesis
formation of organs and organ systems
when are the basis of all organs and systems in place
end of embryonic period (develops throughout foetal period)
what happens in the foetal period (5)
- weight gain (3rd trimester) and growth (2nd trimester)
- tissues mature and become functional
- sexual differentiation
- bone laid down
- connections made in CNS
what are the 6 primary processes
- cell division
- differentiation
- apoptosis
- cell migration
- induction
- cell attachment
cell attachments
physical/functional linkages, formation of tissues
induction
ability of one cell to cause another to differentiate
name the 2 secondary processes
- axis formation/polarity
- folding/rotation
axis formation/polarity
which way is which - cells know where they are in relation to others and the embryo
folding/rotation
entire embryo and strictures fold allowing formation of complex organ structures and giving the embryo its 3D structure
what 3 factors control development of the embryo
- genetic
- epigenetic
- environmental
epigenetic
preferential expression of either maternal or paternal genes
