22 - Reproduction Flashcards
Describe the formation of a zygote
- sperm arrive at the oocyte in the oviduct and become capacitated –> swim more vigurously
- sperm penetrates the corona radiata
- many sperm contact the glycoprotein of the zona pellucida and the acrosome reaction occurs –> digesting the ZP
- One sperm contacts the plasma membrane of the oocyte
- the cell membrane of the oocyte depolarizes and cannot bind further sperm and the cortical reaction occurs
- fast block to polyspermy - ZP hardens
- second block to polyspermy - 2nd polar body is formed and meiosis 2 is finally compelted
- haploid male and female pronuclei are formed - female and male pronuclei fuse resulting in the zygote
What happens in the first week of development
- oviduct gets close to the ovary
- fimbriae of oviduct captures released oocyte
- fertilization @ amuplla
- cleavage of zygote
- develops brand new cells - Forms morula (cell mass)
- Blastocyte froms after fertilization (out of ZP)
- Developing blastocyte undergoes implantation 6 days after fertilization
What happens at the second week of development
- plasticist impalnts into endometrium
- gets covered and looks for blood vessels
- becomes placenta!!!
- trophoblast makes hCG - Implantation/nidation complete
- trophoblast invades maternal blood vessels – results in an implantation bleed - extraembryonic mesoderm and trophoblast form the chorion (fetal part of the placenta)
What are the embryonic layers of the embryo
ectoderm: skin and NS
mesoderm: blood, bones, muscles
endoderm: GI, U, Repro, Resp
What are the parts fo the embryo
amniotic cavity: eventually surrounds the fetus
umbilical vesicle/yolk sac: early source of nutrients and blood cells – will not develop
allantois: collects early wastes - forms parts of bladder
connecting stalk: future umbilical cord
How is the head fold and tail fold formed in the embryo
amniotic cavity and neuronal tube formed at much faster rate than the rest of the embryo
What structures have developed at 28 days
mesoderm: primitive heart
endoderm:
- foregut (pharynx to duodenum)
- mid gut
- hind gut (distal colon to rectum)
At what week does the embryo enter fetal stage
week 9
What happens at the pre-embryonic phase
cenceptus about 1.5 mm length
poorly differentiated
tiny trophoblast (the beginning of the placenta)
much of the earlier parts of this phase the zona pellucida is still present and the embryo is isolated from the maternal environment
What happens at the embryonic phase
all major organs are assembled – period of organogenesis
embryo grows to about 2.8cm or just over one inch
placenta is much larger than the embryo at this point and there is complete access to materials in maternal circulation
What happens at the fetal phase
organs grow during this period – called histogenesis phase
What are problems that could occur in the embryonic phase
sensitive to exposure to environmental toxins and can result in dysgenesis of organ systems
phocomelia –> thalidomide (anti-emetic)
spina bifida –> valproic acid (anti-seizure medication)
What are problems that could occur in the fetal stage
can lead to incomplete or abnormal development in organ systems
microtia
lenticular cataracts –> rubella infection
What is placentation
development of the placenta
- the site of nutrient and waste exchange between fetal and maternal circulation
- produces hormones necessary to maintain the pregnancy
What are the layers of the placenta
fetal portion –> chorionic villi of the chorion
maternal portion –> basal layer of the endometrium (decidua)
