Germinal Period Flashcards
What’s the duration of the germinal period?
The first 3 weeks
What is the duration of the embryonic period?
The end of the 3rd week to the end of the 8th week
What is the duration of the fetal period?
The beginning of the 3rd month to the end of pregnancy
Where does fertilization occur?
In the ampullary region of the uterine tube
What must happen before the oocyte can be fertilized?
Capacitation
Acrosome reaction
What is capacitation?
Period of conditioning in the female reproductive tract that lasts approximately 7 hours
What is acrosome reaction and when does it happen?
Occurs after binding to the Zona pellucida and induced by Zona proteins
The release of enzymes needed to penetrate the zona pellucida, including acrosin and trypsin like-substances
what is phase 1 of fertilisation ?
penetration of the corona radiata
what is phase 2 of fertilisation ?
penetration of the zona pellucida
what is the zona ?
Zona is a glycoprotein shell that
facilitates & maintains sperm binding
& induces the acrosome reaction.
what does acrosin do ?
allows sperm to penetrate the zona & contacts plasma
membrane of the oocyte which result in release of lysosomal enzymes from the oocyte.
what is phase 3 of fertilisation?
fusion of the oocyte & sperm cell membranes.
what happens after the sperm enters the cytoplasm of the ovum ?
Cortical & zona reaction
Resumption of 2nd meiotic division
Male nucleus becomes swollen and come in contact with the nucleus of the definitive oocyte
what is the Cortical & zona reaction?
The oocyte release lysosomal enzymes from cortical
granules that prevent polyspermy, through:
- The oocyte membrane becomes impenetrable to other
spermatozoa.
- The zona pellucida alters its structure & composition to
prevent sperm binding & penetration.
what is the Resumption of 2nd meiotic division ?
-The secondary oocyte finishes its 2nd meiotic division immediately after entry of the spermatozoon.
-This result in formation of the definitive oocyte (22+X),
& the second polar body .
what is the name given to swollen nuclei?
pronuclei
what are the main results of fertilisation?
Formation of the zygote.
Restoration of diploid number of chromosomes
Determination of the sex of the new individual
Initiation of cleavage & migration of the zygote to the
site of implantation.
how many days after fertalisation does the blastocyst develop ?
4th day
what is the morula?
the 16 cell stage, 3 days after fertilisation
on what day does the zona pellucida start to degenerate?
the 4th day
what happens on the 5th day after fertilisation ?
The blastocyst reaches the uterine
cavity and begins to penetrate between the epithelial cells of the uterine mucosa (implantation) about the 6th day of fertilisation
what are the cells of the outer cell mass of the blastocyst called ?
trophoblast
what are the cells of the inner cell mass of the blastocyst called ?
embryoblast
what cells will form the fetal membrane and the placenta ?
trophoblast
what is the Blastocele?
the cavity of the blastocyst
what is the Embryonic pole?
the side of blastocyst
that corresponds the embryoblast.
what is the Abembryonic pole?
is the opposite side of the embryonic pole of the blastocyst.
what is implantation and when does it occur?
It is the process by which the blastocyst becomes embedded in the superficial compact layer of the endometrium. • It starts at the 6th-7th day & is completed about the 11th- 12th day after fertilisation.
describe what happens during the implantation stage
The trophoblast begin to erode epithelium of endometrium forming a penetration defect. • The blastocyst enters the endometrium through the defect & become implanted into it. • After complete embedding, penetration defect is closed by a fibrin clot
what are examples of contraceptive methods?
Barrier techniques - male and female condoms The contraceptive pill Depo-Provera A male “pill” The intrauterine device (IUD) Vasectomy & tubal ligation
what happens with regards to implantation on the 8th day of development?
the blastocyst is partially embedded in the
endometrium.
what happens with regards to implantation on the 9th and 10th day of development?
the blastocyst become larger & more deeply implanted & the penetration defect becomes closed by a fibrin clot.
what happens with regards to implantation on the 11th and 12th day of development?
the blastocyst is completely embedded & the defect is covered by epithelium.
what happens with regards to implantation on the 13th day of development?
is complete with closure of the penetration defect by
epithelium.
what happens with regards to the Embryoblast on the 8th day of development?
The cells become organized to form a bilaminar germ disc formed of 2 layers: - Hypoblast layer: small cuboidal cells adjacent to the blastocyst cavity. - Epiblast layer: high columnar cells adjacent to the amniotic cavity.
what happens with regards to the Embryoblast on the 9th and 10th day of development?
no marked changes.
what happens with regards to the Embryoblast on the 11th and 12th day of development?
no marked changes.
what happens with regards to the Embryoblast on the 13th day of development?
no marked changes.
what happens with regards to the Trophoblast on the 8th day of development?
The part of the trophoblast lying over the embryonic pole become differentiated into 2 layers:
• Outer zone: syncytiotrophoblast.
• Inner zone: cytotrophoblast.
what happens with regards to the Trophoblast on the 9th and 10th day of development?
Trophoblast: the whole cells become
differentiated into cyto. & syncytiotrophoblast.
• Small spaces called vacuoles appear in trophoblast at the embryonic pole.
• These vacuoles fuse, forming large lacunae & this phase of trophoblast development is the lacunar stage.
what happens with regards to the Trophoblast on the 11th and 12th day of development?
(this answer is very long)
- Syncytiotrophoblast:
• The lacunar spaces form an intercommunicating network.
• The cells penetrate deeper & erode the endothelial lining of the maternal capillaries (sinusoids).
• The lacunae become continuous with the sinusoids & maternal blood enters the lacunar system. - Cytotrophoblast:
Formation of extraembryonic mesoderm:
• Cells of the inner surface of the cytotrophoblast forms a very loose tissue called extraembryonic mesoderm between the inner surface of the cytotrophoblast & the outer surface of the primitive yolk sac cavity.
• The trophoblast will be called the chorion & the blastocyst is now called chorionic vesicle. - Formation of the extraembryonic coelom:
• Large cavities develop in the extraembryonic mesoderm forming a new space known as the extraembryonic coelom, or chorionic cavity.
• The chorionic cavity: divides the extraembryonic mesoderm into:
• Extraembryonic somatopleuric mesoderm lining the cytotrophoblast & amnion.
• Extraembryonic splanchnopleuric mesoderm covering the yolk sac.
what happens with regards to the Trophoblast on the 13th day of development?
characterised by appearance of villous structures.
• Cells of the cytotrophoblast proliferate locally & penetrate into the syncytiotrophoblast, forming cellular
columns known as (Primary chorionic villi), which are surrounded by trophoblastic lacunae.
what happens with regards to the cavities on the 8th day of development?
the amniotic cavity starts to be formed within the epiblast.
• Epiblast cells adjacent to the cytotrophoblast are called
amnioblasts.
what happens with regards to the cavities on the 9th and 10th day of development?
(long answer)
The amniotic cavity become larger.
• The primitive yolk sac cavity
(exocoelomic cavity) starts to be formed as follows:
- Cells from the hypoblast grow down to line the inner surface of the cytotrophoblast forming a thin membrane called Hauser’s membrane (exocoelomic membrane).
- The primitive yolk sac cavity replaces the cavity of the blastocele.
what happens with regards to the cavities on the 11th and 11th day of development?
(long answer)
The amniotic cavity becomes larger.
• The yolk sac shows no definite changes.
• The extraembryonic coelom, or chorionic cavity develops.
- Growth of the bilaminar disc is relatively slow compared
with the trophoblast.
- Cells of the endometrium, meanwhile, become
polyhedral & loaded with glycogen & lipids; intercellular
spaces are filled with extravasate & the tissue is edematous.
-These changes, known as the decidua reaction.
what happens with regards to the cavities on the 13th day of development?
(long answer)
Amniotic cavity: no major changes.
- New generation of cells fromhypoblast line the primary yolk sac to form the secondary or definitive sac yolk sac.
- Pinching off a large part of the secondary yolk sac with marked reduction in its size.
-The extraembryonic coelom expands & forms a large cavity, the chorionic cavity.
The only place where extraembryonic mesoderm
traverses the chorionic cavity is in the connecting stalk.
- With development of blood vessels, the stalk becomes
the umbilical cord.
-The extraembryonic mesoderm lining the inside of the
cytotrophoblast is then known as the chorionic plate.
why does occasional bleeding happen on around the 13th day ?
bleeding at the implantation site caused by increased blood flow into lacunar spaces.
what is Gastrulation and during which week does it happen ?
the process that establishes the three germ layers (ectoderm, mesoderm, & endoderm)
it happens in the third week
what is the Notochord formation during which week does it happen ?
it is the temporary axial skeleton of the embryonic disc.
it happens in the third week
what 2 things happen during the third week ?
Development of the embryonic disc
Development of the trophoblast (Chorion)
what happens during gastrulation ?
formation of the primitive streak & primitive node on the surface of the epiblast.
what is the primitive streak ?
a narrow groove with slightly bulging regions on either side formed in the midline of the embryonic disc
what is the primitive node?
a round bulge located at cephalic end of the streak, with middle depression known as the primitive pit.
what is Invagination?
Cells of the epiblast migrate toward the groove of the streak & they detach from epiblast & slip beneath it toward the hypoblast, to form:
- Endodermal layer that replace the hypoblast.
• Intraembryonic mesoderm which form the middle layer in the disc.
• Ectoderm layer formed by the remaining cell in the epiblast.
• Thus, the epiblast is the source of all of the germ layers.
what is the Cloacal membrane?
a small area of fusion between ectoderm & endoderm (no mesoderm).
The cloacal membrane during future development becomes divided into Urogenital membrane & anal membrane.
what is the buccopharyngeal membrane?
it consists of a small region of tightly adherent ectoderm & endoderm cells (no mesoderm) that represents the future opening of the oral cavity.
what is the Notochord?
is the temporary axial skeleton of the embryonic disc.
how is the notochord formed?
it is formed by invagination of solid cord of cells from primitive pit, this process extend cranially in the midline between the ectoderm & endoderm till the
buccopharyngeal membrane.
what is the Notochordal canal?
primitive pit extends into the process transforming it into a canal.
what is Neurenteric canal?
It serves as a temporary connection between amniotic cavity & yolk sac cavity.
what is the Definitive notochord?
notochordal plate becomes folded upon itself forming a solid cord
why Is the notochord important?
- Is the temporary axial skeleton of the embryonic disc.
- During folding its firmness limits the head fold.
- Vertebral column is formed around the notochord.
what happens to the primitive streak in the 4th week ?
shows regressive changes, rapidly shrinks & soon disappears.
the teratogenic insult is highly sensitive at which week ?
the beginning of the 3rd week of development
what is the chorion?
the wall of the chorionic cavity which is formed at the 12th day of gestation.
what are the parts of the chorion?
Chorion frondosum
Chorion laeve
what is the Chorion laeve?
the part that carries degenerating tertiary villi covered
with decidua capsularis.
what is the Chorion frondosum?
the part that carries well developed tertiary villi that face the decidua basalis, it share in the formation of the placenta.
