Fertilisation, Cleavage and Implantation Flashcards
What is an oocyte?
An immature egg
What stage is the oocyte in, in ovulation?
The oocyte is in metaphase of the second meiotic division and is surrounded by the zona pellucida and some granulosa cells
What is the most outer layer of the oocyte?
The corona radiata
What is the second most outer layer of the oocyte and what does it cover?
Zona pellucida and it covers the plasma membrane
What is a significant feature of the epithelial cells of the fallopian tubes?
They are highly cilliated
How does the ovulated ovum get into the oviduct (fallopian tubes)?
The ends of the oviduct come into close contact with the ovary during ovulation and the fimbriae sweep the ovulated ovum into the oviduct
How does the ovum travel down the fallopian tube and where does it travel to in the oviduct?
Peristalic waves of fallopian tube musculature bring the ovum to the ampulla of the fallopian tube
What are the stages of the development of the follicle?
Starts with a primary follcile beginning to grow but only one reaches full maturity and one oocyte is discharged at ovulation
How long before the oocyte passes into the uterus?
80 hours
What is the structure at the top of the sperm head called and what is its role?
Acrosome and it releases enzymes
What obstacles do the sprermatozoa experience?
Vaginal pH- sperm is slightly basic and vagina is acidic
Response of the immune system- foreign body
Cervical mucous
Physical barriers
What is fertilisation?
Process by which the male and female gametes fuse to form a zygote
What is capacitation?
A glycoprotein coat and seminal plasma protein are removed from the spermatozoon.
What is the significance of capicitation?
Only sperm cells that are capacitated can pass through the corona cella and undero the acrosome reaction
What is the first stage of fertilisation?
Penetration of corona radiata
Capacitated sperm pass freely though the corona cells
Aided by flagella action and release of enzymes from acrosome
What is the second stage of fertilisation?
Penetration of the Zona Pellucida
What is the zona pelluicda?
A glycoprotein shell surrounding the egg that facilitates and maintains sperm binding and induces the acrosome reaction
What is ZP3
Zona pellucida 3 a protein that mediates the binding and acrosome reactions
What is the third stage of fertiliation?
Cortical and Zona reactions
What is the cortical reaction?
Release of cortical vesicles from oocyte plasma membrane
forms the fertilisation membrane
What is fertilisation membranes function?
To prevent polyspermy so the zona pellucida crisps up
if polyspermy occurs the fetus will abort
What is the fourth stage of fertilisation?
Fusion of membranes and resumption of second meiotic division
What is oogenesis?
Maturation of the ovum
What is the fifth stage of fertilisation?
Formation of the male and female pronuclei.
the membranes of the pronuclei will break down and the chromosones will become arranged for mitotic division
What is a pronuclei?
nucleus of one of either gamete before the fusion leads to the formation of the zygote
What are the three results of fertilisation?
Restoration of the diploid number of chromosomes
Determination of the sex of the new individual
Initiation of cleavage - without fertilisation - the oocyte will degenerate
What is cleavage?
A series of mitotic divisions the resulting cells (blastomeres) become smaller with each division.
What happens after 3 divisions during cleavage?
Blastomeres undergo compaction- compact blastomeres form a 16 cell morula
What is a blastocyst and how does it form?
Stage after morula
Cavity will appear on morula after 3/4 days when morula entersuterus
What is the embryoblast?
Inner cell massn formed at time of compaction and develops into the embryo proper at one pole of blsaocyst
What is the trophoblast?
Outer cell mass which surrounds the inner cells and the blastocyst cavity will form the trophoblast
Where do stem cells originate?
Derived from pre- implantation embryo
What are the three embryonic germ layers that are derived from embyonic stem cells?
Ectoderm eg- neuron
Mesoderm- eg blood cell
Endoderm- eg liver cell
How are human embryonic stem cells derived?
IVF-totipotent cells - blastocyst- cultured pluripotent cells
What does totipotent mean?
Capable of giving rise to any type of cell in the human body
What does multipotent mean?
Can only differentiate in their specific type of layer
What does pluripotent mean?
ability to differentiate into all three different types of germ layers but not extra- embryonic tissue
What stage is the uterus in at the time of implantation?
Secretory phase- the blastocyst implants in the endometrium along the anterior or posterior wall
What happens if fertilisation does not occur?
The menstrual cycle will begin and the spongy and compact endometrial layers are shed.
Basal layer will remain to regenerate the other layers during the next cycle
What are the two types of trophoblasts?
Outer synctiotrophblast
Inner cytotrophoblast
Where are the cytotrophoblasts and what happens here?
inner irregular layer of ovoid, single- nuculeus cells
intensive mitotic activity takes place here
Where are the syncytiotrophoblasts
Cross the basal lamina and penetrates into the stroma that lies below, eroding the wall of the capillaries.
ST will completely surround the embryo when its embedded in the endometrium
How does circulatory arise?
Extracellular vacuoles appear in the ST
Join together for a while forming the lacunae-filled with tissue fluid and uterine secretions
Erosion of mothers capillaries and blood fills the lacunae that later develops further into intervillous spaces
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What are the two layers of the embryo called?
Floor of amniotic cavity formed by epiblast
Roof of the unbilical vesicle by the hypoblast
What does the embroynic bud consist of?
Two hemisphere cavities -amniotic cavity (dorsal) umbilical vesicle (ventral)
What are the six stages of IVF and embryo transfer?
Ovulation induction Egg retrival Insemination and fertilisation Embryo transfer Luteal phase Embryo freezing
