Week 1 Development Flashcards
How does the sperm find the oocyte?
chemotaxis toward oocyte attractants help guide sperm to the secondary oocyte
Where does fertilization usually occur?
occurs in the ampulla of the oviduct
What is the length of the window of opportunity for fertilization?
up to 24hrs
Penetration of corona radiata is facilitated by what enzyme?
Hyaluronidase released from acrosome
-capacitated sperm readily move through corona radiata cells
Penetration of zona pellucida is facilitated by what enzyme?
Acrosin causes lysis of thee zona pellucida to create a path
What is the zona reaction?
- What is the outcome
Zona reaction are the changes in the zona pellucida after the first sperm penetrates
- makes zona pellucida impenetrable by additional sperm
What of sperm enters oocyte during the fusion of sperm and secondary oocyte plasma membranes?
sperm contents
What happens when secondary oocyte completes meiosis II?
- mature ovum and secondary polar body form
- ovum nuclear material decondenses somewhat to become the female pronucleus
How does the male pronucleus form?
forms as the sperm nucleus enlarges somewhat
How is the male pronucleus distinguishable from the female pronucleus?
They are morphologically indistinguishable
After the formation of the male pronucleus, what happens to thee rest of the sperm?
the other sperm contents degenerate
What is an Ootid?
An Ootid is the cell at the point containing the 2 pronuclei
What happens to the DNA in both pronuclei?
It is duplicated to form double-strand chromosomes
What happens when the male and female pronuclei fuse?
creation of a zygote
what is the ploidy number of the zygote?
4N
What is the chromosomal content of the zygote?
Genotypical sex is established as 46 XX, or 46XY
How are the follicles stimulated to grow in In Vitro fertilization?
development of multiple mature ovarian follicles is stimulated chemically
How are the oocytes harvested in in vitro fert.?
Mature secondary oocytes are harvested laparoscopically just prior to ovulation
- Or by ultrasound guided needle aspiration via the vaginal canal
Mature secondary oocytes are mixed with what after being harvested?
They are mixed with capacitated sperm in a Petri dish
How long does the development progress in vitro?
fertilization and early zygote cleavage are monitored microscopically for 3-5 days
How many embryos are typically transferred?
1-2 embryos are transferred by catheter into uterine lumen
In what position is the patient told to remain in to allow for implantation?
Supine for several hours
What happens to the rest of the embryos in in vitro fert.?
remaining viable embryos are cryopreserved in liquid nitrogen for later use
Gamete intrafallopian transfer involves what?
Placing harvested oocytes and capacitated sperm in the ampulla of the oviduct
What is done in surrogacy?
Placing in vitro fertilized oocytes of one woman into uterus of a different woman
What occurs in intracytoplasmic sperm injection?
single sperm injected directly into cytoplasm of mature oocyte
- used if male sperm count is low
When does the first division of the zygote occur?
30hrs after fertilization
Where is the zygote during the repeated mitotic divisions?
occurs as zygote is moving through oviduct towards uterus
- still surrounded by thick zona pellucida
What are blastomeres?
embryonic cells formed by zygote cleavage
- get progressively smaller with each mitotic division
How does the zygote change in size?
Gets progressively smaller with each mitotic division (forming blastomeres)
What is the process of compaction?
- occurs after the 8-cell stage
- Increases cell contact and is mediated by cell surface adhesion glycoproteins
Why is compaction a necessary step?
its a necessary step prior to forming certain cells that will become embyro
What is the composition and appearance of a morula?
many mitotically divided cells (12-32 blastomeres) in the inside and zona pellucida on the outside
When does a morula form?
Forms ~3 days after fertilization
Which blastomeres of the morula will form the:
1) embryo 2) embryonic part of the placenta
1) internal cells will become the embryo
2) outer cells will become the embryonic part of the placenta
What is the chromosomal condition referred to as mosaic?
results from nondisjunction in early mitotic cleavage of zygote
What are the results of mosaic?
results in 2+ cell lines with different chromosomal complements
Is Mosaic a permanent condition?
These may be a lost or persist as development continues
Where is the morula on day 4?
enters the uterine cavity
How does the blastocyst differ from the morula?
Blastocyst is the next stage of development in which the morula has developed a fluid-filled cavity
What is the blastocoele?
The fluid filled cavity of the blastocyst
Where does the fluid in the blastocyst come from?
Fluid diffuses through the zona pellucida into the blastocoele from the uterine cavity
What is the trophoblast?
thin outershell of blastomeres
What are the 2 groups that the blastomeres are separated into?
1) Trophoblast
2) Embryoblast
What will the Trophoblast develop into?
Develops into the embryonic portion of placenta
What is the embryoblast? Embryonic pole?
- Embryoblast is a cluster of cells located on inner surface in one region of trophoblast (will develop into embryo)
- The region of blastocyst containing the embryoblast is the embryonic pole
When does the zona pellucida disappear?
Day 5
What happens to the zygote after Day 5
The blastocyst will finally start increasing in size
Will the blastocyst implant immediately?
The blastocyst will float freely in the uterine cavity for up to 2 days
How do monozygotic twins develop?
from one zygote
how common are monozygotic twins?
~25% of all twins
When does twinning like monozygotic occur?
twinning usually occurs in week 1 with division of the embryoblast in blastocyst
What is the genotype and phenotype of the monozygotic twins?
same sex, genetically identical, very similar physical appearance
How many physical differences in monozygotic twins occur?
Physical differences may result from varied placental blood supply
How do dizygotic twins develop?
Develop from 2 ova fertilized by 2 sperm in the same cycle
How common do dizygotic twins occur?
~75% of all twins
When does twinning like dizygotic occur?
hereditary tendency - recurrence in families is approx 3x the general population
What is the phenotype and genotype of dizygotic twins?
may be same sex or different sex (fraternal twins)
- no more genetically similar than other brothers/sisters
How do Conjoined monozygotic twins develop?
due to incomplete separation of the embryonic disk
What is craniopagus?
joined at the head
What is thoracopagus?
joined at the anterior thorax
How are the unions structured in conjoined monozygotic twins?
Unions may be skin only or involve other tissues as well
How are embryonic stem cells harvested?
Derived from embryoblast cells
What are embryonic stem cells potential?
pluripotent - can form virtually any cell or tissue type
What are the ethical considerations for stem cells?
obtained from embryos produced by in vitro fertilization
- limit the availability of cells from these sources
What are adult stem cells?
multipotent - restricted in their availability to form only certain cells or tissue types
What are the disadvantages to working with adult stem cells?
difficult to isolate and they have a low mitotic index
Therapeutic cloning is also known as?
somatic cell nuclear transfer
How does therapeutic cloning work?
- insert nucleus of adult skin cell into an enucleated oocyte
- oocyte is stimulated to differentiate into a blastocyst to provide embryonic stem cells
What are the advantages of therapeutic cloning?
stem cells are genetically identical to recipient and no fertilization is involved
