01-11-21 - Early Embryonic Development Flashcards
how do we get from one cell to a human
Cell growth and division
Cell differentiation (e.g. transcription factors by signals)
Cell migration / shape changes / cell adhesion
Cell death / apoptosis (e.g. webbing)
Invasion (e.g. implantation)
Cell-cell communication
what’s the structure spermatozoon?
where are secondary oocytes found? what is their cytoplasm surrounded by?
Mature, motile male sex cell (gamete)
Has a head, mid-piece and tail.
Head contains the nucleus and an acrosome, which contains enzymes required for the penetration of the zona pellucida of the oocyte
Secondary oocytes are found in the ovary, arrested in metaphase II of meiosis I
Cytoplasm of ovulated secondary oocyte is surrounded by plasma membrane, zona pellucida and corona radiata
what is ovulation?
what happens?
when is meiosis II completed?
how is oocyte brought into ampulla?
Discharge of usually a single secondary oocyte from the ovary as a result of increase in luteinizing hormone (LH)
Granulosa + ECM cells form the corona radiata and are needed to capture oocyte
When secondary oocyte is fertilized, meiosis II is completed
The ends of the uterine tubes come into close contact with the ovary during ovulation.
Fimbriae of uterine tubes “sweep” the ovulated secondary oocyte (ovum) into the uterine tube.
Peristaltic waves of uterine tube musculature + cilia bring the secondary oocyte into the ampulla of the uterine tube
what happens during fertilization?
what must spermatozoa undergo?
what are the 3 stages in which spermatozoon penetrates the oocyte?
Fertilization is the fusion of haploid sperm and haploid oocyte to form a diploid Zygote
Fertilization takes place usually in the ampulla, but can take place in any part of the uterine tube
Spermatozoa must undergo capacitation and the acrosome reaction to acquire fertilization capability
Spermatozoon penetrates the oocyte in 3 phases
Phase 1: Capacitation (~7 hours) Passing through the corona radiata
Phase 2: Acrosome reaction Penetration of the zona pellucida
Phase 3: Penetration of the oocyte membrane by one spermatozoon, which loses its own plasma membrane.
Penetration of corona radiata (by hyaluronidase)
Interaction with ZP3 receptor
Acrosome reaction (digests zona pellucida with lysosomal enzymes)
Membrane fusion
Completion of oocyte meiosis
Release of the contents of the cortical granules
Degradation of ZP3 to prevent second penetration
what is clevage? what does it occur after and what does it transform?
how does a cell go from a zygote to a morula?
how long does it take?
process of mitotic cell divisions that occurs after fertilization, which transforms a single-celled zygote into a multicellular embryo
Once the zygote has reached the two-cell stage, it undergoes a series of mitotic divisions, increasing the numbers of cells.
These cells, which become smaller with each cleavage division, are known as blastomeres
72 hours
how does a morula become a blastocyst?
Morula has an inner cell mass (Embryoblast Embryo), surrounded by the outer cell mass (Trophoblast will contribute to the Placenta)
Fluid-filled cavities form within the inner cell mass, between blastomeres
Cavities merge into a single blastocyst cavity, which will later become the primitive yolk sac
Morula becomes Blastocyst
implantation of blastocyst
Morula/blastocyst travels down the uterine tube
On day 6-7, the blastocyst reaches the uterine cavity
Trophoblast cells over the embryoblast begin to implant into the uterus
Host-versus-graft and graft-versus-host reactions are normally suppressed
what does the embryoblast differenciate into and under what influence at early blastocyst stage?
what is the new name of the inner cell mass?
Under the influence of fibroblast growth factors (FGFs) at the early blastocyst stage, cells in the embryoblast differentiate into epiblast and hypoblast cells
Scattered cells segregate Bilaminar disc
what happens during implantation? = day 8
1. partial implantation
2. total
On day 8, the blastocyst is partially embedded in the endometrium of the uterus.
In the area next to the embryoblast, the trophoblast differentiates into the inner layer of cytotrophoblast, and an outer zone of syncytiotrophoblast (secretes beta-HCG)
A small cavity appears within the epiblast called amniotic cavity
Blastocyst is completely embedded
Cells of the syncytiotrophoblast penetrate deeper
Maternal blood enters the trophoblastic lacunar system
Uteroplacental circulation
what happens around day 15?
where does it appear and what does it do?
Around day 15, Primitive streak appears as a thick structure on the epiblast
Near the caudal region of the bilaminar embryonic disc
In the midline
Defines the body axes
what is the primitive streak and node?
Cranial end of primitive streak is expanded and called the primitive node, which contains primitive pit
Primitive streak has a groove called primitive groove
what happens around day 16? where do the epiblast cells go?
what are new layers called ?
Cells of the epiblast migrate through the primitive streak, detach from the epiblast, displace hypoblast and create a third layer (invagination)
Previous hypoblast becomes definitive endoderm
Remaining epiblast cells are called ectoderm
Cells between ectoderm and definitive endoderm is called mesoderm
what is the notochordal process?
what are the steps from notochordal process to notochord?
towards what region is it formed?
what does notochord activate?
~Day 16, cells migrating through the primitive node begin to form a hollow structure called notochordal process
~Day 18, notochordal process fuses with endoderm becomes notochordal plate
Two edges of notochordal plate come together and fuse and become notochord
Because these events occur in a cranial-to-caudal sequence, notochord is first formed near the cranial region
Notochord activates a signaling pathway involved in tissue differentiation and development
what does each layer of trilaminar disc become?
paraxial mesoderm
lateral plate mesoderm
intermediate
what is an ectopic pregnancy?
what are the most common?
what can they lead to?
what increases from 2 to 5th months?
Implantation of the blastocyst in an abnormal location
In the ovary or anywhere along the path of migration into the uterine cavity
Placenta can form on most tissues or structures
Tubal pregnancies (95%) are the most common ectopic pregnancies
Can lead to spontaneous tubal abortion or …
Can lead to maternal mortality if undetected after intraperitoneal rupture of the uterine tube and its vessels
The likelihood of tubal rupture and haemorrhage increases from the second through the fifth months
