first week embryology Flashcards
what are the events that occur during the first week?
Fertilization, cleavage, implantation
where does capacitation occur? ( maturation of the sperm )
occurs in the uterus and the uterine tube
which layer is removed within the sperms during capacitation?
glycoproteins
does the capacitation process increase the activity of the sperms?
yes
where does the acrosome reaction of the sperms occur?
only in the ampulla of the uterine tube
what develops in the acrosome reaction?
development of multiple perforations in the acrosome of the sperms to release enzymes
what is the zona reaction?
Lysis of zona pellucida
what causes zona reaction?
caused by acrosin and zonalysin
what happens once a sperm penetrates the zona pellucida
a zona reaction occurs, resulting in change in its physical properties and making it impermeable to other sperms
what does zona reaction prevent?
prevents polyspermy ( penetration of more than one sperm into the oocyte ) to avoid the occurrence of polyploidy
what is fertilization?
is the fusion of a single sperm and secondary oocyte to form a zygote
what does the secondary oocyte convert to during fertilization?
a mature ovum
where does fertilization occur?
in the ampulla of the uterine tube
how long does fertilization last for?
24HRS
what happens if the oocyte is not fertilized?
slowly passes along the uterine tube into the cavity of the uterus where it degenerates
what are the results of fertilization?
the 2ry oocyte completes its 2nd meiotic division producing a mature ovum & 2nd polar body.
( Restoration of the diploid number of the chromosomes (46). )
what factor determines the sex of the embryo ?
*XX – Female
*XY- Male
where does the cleavage of the zygote occur?
in the uterine tube
what results into having a cleavage of the zygote?
mitotic cell divisions of the zygote ( within its zona pellucida ) resulting in a rapid increase in
the number of cells.
during the cleavage of the zygote, cells are formed what are these cells called?
are called blastomeres,
become smaller in size with each cleavage
division.
what is morula?
When there are 16 - 32 blastomeres by the
3rd day, the zygote is called a morula.
is the early morula surrounded by zona pellucida?
yes
when does the morula reach the uterine cavity?
by the 4th day after fertilization
where does the uterine fluid pass?
Uterine fluid passes through zona pellucida
and outer cells of morula
what does the accumulation of fluid convert the morula to?
Accumulation of fluid converts morula into
fluid filled cavity called the blastocystic cavity
or blastocoele.
on which day does the zona pellucida disappear?
Zona pellucida disappears by 5th day of
fertilization
Fluid increases in the blastocystic cavity, the
blastomeres are separated into 2 groups which are?
Trophoblast-outer cell mass
* Embryoblast –inner cell mass
Trophoblast: Outer cell mass
what is it structured like ?
what is its function?
Thin outer cells that forms the wall of the blastocyst.
It is the nutritive part of the blastocyst
The embryoblast (inner cell mass):
Centrally located blastomeres.
Form embryo.
Projects into the blastocystic cavity
The late blastocyst has 2 poles which are?
Embryonic pole: overlies the embryoblast & is adjacent to the
uterine endometrium.
*Abembryonic pole: away from the embryoblast &uterine endometrium
what is the endometrium of the uterus changed to?
Endometrium of the uterus is changed to decidua
on which day does the blastocyst attach himself to the uterine endometrium?
6th day
At the 7th day the trophoblast starts to proliferate rapidly & differentiate
into 2 layers which are?
- The cyto – trophoblast-:The inner original layer of cells (overlying embryoblast).
- The syncytio – trophoblast:The outer layer of a multi-nucleated fused
cells
what is implantation?
It is the process by which the blastocyst embeds itself in the
endometrium.
when does implantation occur?
This process begins at the end of the 1st week(7th day of
fertilization)& is completed by the end of 2nd week of the human
development.
what is the process of implantation?
They are finger like processes, that secrete proteolytic enzymes that erode the uterine endometrium enabling the blastocyst to burrow into the endometrium (implanted).
by the end of which week is the blastocyst superficially implanted?
by the end of the 1st week
what are the cuboidal layer of cells called that appear on the surface of the embryo blast facing the blastocystic cavity
Hypoblast cells
