Intro to embryo development Flashcards
Fertilisation -> implantation chronologic events occurring…
Fertilisation -> 1st cleavage (zona pelucida) -> 2 cell stage -> 4 cell stage -> 8 cell stage -> morula -> blastocyst -> implantation
Define the events involved in embryonic cleavage…
a series of rapid (mitotic) divisions following fertilisation
- cell size gets smaller from that of the zygote
- absence of cell growth between
Cells resulting from the cleavage process?
blastomeres
Outline the events of cleavage…where does it occur? how long? secretions?
Occurs in isthmus
contraction propels embryo forward
4-5 days in most domestics to uterus
secretions from epithelial lining - provide nutrients & proteins for dev
What is a morula?
solid ball of cells (16 - 64 blastomeres)
Formed near the end of cleavage processes
Surrounded by the zona pellucida
mammalian and non-mammalian cleavage are not the same. What are some differences?
mammalian:
- small no. of oocytes produced at ovu.
- small in size
- occur inside organism
- primary cleavage controlled by embryo genome
non-mammalian:
- large no. of oocytes produced at ovu.
- large in size
- Occurs outside the organism
- Primary cleavage events controlled by maternal genome
For implantation to occur, what must happen?
blastocyst must shed the zona pellucida
What happens at implantation?
process of apposition, adhesion and attachment of the embryo to the uterine lining
What are some factors that aid the ‘sticking’ of the blastocyst to the extracellular matrix?
collagen, laminin, fibronectin, hyaluronic acid
Timing of implantation & onset of placentation varies between species. Give an example of 2 species where it is varied.
Entry to uterus: - sheep: 3 - 4 - horse: 6 Placentation begins: - sheep: 15 - 20 - horse: 35 - 40
How is implantation classified?
according to relationship between blastocyst and uterine lumen
Define central implantation…spp eg?
blastocyst remains within uterine lumen eg. carnivores
Define eccentric implantation…spp eg?
blastocyst lies within uterine crypt or recess eg. mouse/rat
Define interstitial implantation…spp eg?
conceptus invades the uterine wall eg. man & chimps (fastest process)
The main roles of foetal/extraembryonic membranes…
protection, nutritional & excretory requirements for dev. embryo. Has 4 major membranes: yolk sac, amnion, chorion and allantois
Describe the yolk sac… function? origins?
1st membrane formed
involved with early haemtopoiesis & angiogenesis
houses nutrients for embryo
originates from extraembryonic endoderm
Describe the amnion… function? origins?
fluid-filled sac that surrounds the foetus.
1st layer of protection for embryo
secretions from GI & resp. tract
originates from ectoderm
Why is the amnionic fluid important?
…cushions the foetus
- allows unrestricted movement
- prevents pressure-related growth abnormalities
- acts as lubricant when ruptured at birth
Describe the chorion… function? origins?
- surrounds all other embryonic membranes and foetus
- mid layer of protection
- Participates in formation of foetal component of placenta
- originates from extraembryonic mesoderm
Describe the allantois… function? origins? spp variation, maybe focus on birds…
- stores urinary waste
- very large
- mediates gas exchange & Ca+ transport
Outline what happens in abnormal allantoic development… gene involved…
- Fox 01 essential for allantois & CV morphogenesis
- Fox 01 (-/-) may cause pericardial oedema & death
What is the placenta? functions?
Organ of metabolic interchange between mother and foetus Large surface area for: - nutrition - excretion - immune defences - endocrine
What is placentation?
the structural organisation and mode of attachment of the placenta
What are the components of the placenta? maternal? foetal?
Maternal: - endothelial lining - connective tissue - epithelial lining of uterine lumen Foetal: - trophoblastic outer layer of chorionic sac - connective tissue - endothelial lining the allantoic capillaries
