intro to embryology Flashcards
weeks 0-3
conceptus/embryo
weeks 3-8
embryonic period. critical time most problems occur also the most development
weeks 9-40
foetal period. growth rather than development
phases of embryogenesis
- Gametogenesis
- Fertilisation
- Cleavage
- Gastrulation
- Formation of a body plan
- Organogenesis
what is gametogenesis
formation of a gamete. consisting of mitosis and meiosis leading to genetic variation
what is a gamete
- A gamete is a cell with a complement of 23 chromosomes (half of a typical somatic cell)
- Haploid (23 chromosomes)
what id oogenesis
formation of female gamete
when does oogenesis take place
- Starts in development (of embryo) and ends at menopause.
- By week 28-30: Primary oocytes begin meiosis but arrest in prophase until puberty.
- Reproductive life span determined in fetal life (already has all eggs from birth)
spermatogenesis
- Formation of male gametes
- Occurs at puberty and continues throughout life - Each cycle takes ~64-74 days
production rate of spermatogenesis
- Production rate: ~6.5 million sperm per gram of testicular tissue/day. Decreases with age
who determines sex of baby
males. * Outcome 22+X or 22+Y
trisomy 21
additional copy of chromosome 21. typically caused by nondisjunction
when does nondisjunction typically occur
75% of nondisjunction occurs during oocyte formation
fertilisation
union of gametes. fusion of sperm and oocyte
cleavage
- Period of rapid mitotic cell division
- No increase in size
- Formation of Morula then Blastocyst (blastocyte splits into 2 parts 1 forming the placenta the other forming the embryo)
what is a blastomere
an individual cell
what is a morula
multiple blastomeres
gastrulation
formation of germ layers (week 3). body axes established
what 3 layers are formed during gastrulation
Ectoderm (outer, forms skin and other) , Mesoderm (forms muscles nd skeleton), Endoderm (inner, forms GI tract ect)
how does the formation of a body plan happen
embryonic folding (tube within a tube)
organogenesis
- Formation of Organs and Organ Systems
- Basis of these all-in place by end of embryonic period
- Will continue to develop through foetal period
foetal period
growth and weight gain. grows in 2nd trimester. weight gain in 3rd. overt sexual differentiation. bones laid down and connections made in CNS
orientation of foetus
top = cranial. back = dorsal. front - ventral. bottom = caudal
primary processes. zygote to human
cell division. differentiation. cell attachment. apoptosis. induction. cell migration
