Early Development (2nd lecture) Flashcards
What is the first step of ovulation?
Oocyte starts the process of the first meoitic division when it is fully matured
What is the second step of ovulation?
The oocyte forms within a surrounding layer of cells and the zona pellucida covers the oocyte
What is the third step of ovulation?
The follicle develops a large cavity after developing
What is the 4th step of ovulation?
Cavity expands as zona pellucida pushes oocyte to one side
What is the 5th step of ovulation?
The oocyte is released from the corpus luteum and is in the metaphase of meiosis II
What is the final step of ovulation?
Meiosis II resumes and the corpus luteum releases hormones
Where do the early stages of sperm maturation occur?
Testes
What is capacitation?
The final stage of sperm maturation that enables the sperm to fertilise the egg
What part of the sperm is packed with proteins?
Acrosome
Describe phase 1 of fertilisation
Spermatozoa pass through the corona radiata by fusing together and breaking the coat surrounding the oocyte
Describe phase 2 of fertilisation
One (or more) spermatozoa penetrate the zona pellucida
Describe phase 3 of fertilisation
One spermatozoa penetrates the oocyte membrane and the fusion of the two membranes triggers the oocyte to undergo the 2nd meiotic division
Where does embryo development (week 1) occur?
Uterus
What occurs over the first 5 days of fertilisation?
New embryo travels from the uterine tube down into the uterine cavity
Where does implantation occur?
Uterine cavity
How does the penetration of the corona radiata occur?
Multiple sperm attempting to reach the oocyte by penetrating the corona radiata that breaks it down
What kind of sperm can pass freely through the corona radiata?
Capacitated sperm
What triggers the 2nd mitotic division of the oocyte?
Fusion of the oocyte and sperms membranes
Describe week one of fertilisation
Once the oocyte has fused with the sperm (12-24 hours), the new embryo travels from uterine tube into uterine cavity, where implantation occurs.
Cell division occurs as embryo moves
What is the polar axis?
Where the sperm has fused with the oocyte
Describe blastocyst hatching
The zona pellucid protects the blastocyst and restricts it from growing.
The blastocyst wants to interact with maternal structures so the protein breaks down to allow the blastocyst to leave. (Implantation can now occur)
Where is the most common implantation site?
Dorsal wall of uterus
Give examples of abnormal implantation sites
close to cervix, uterine tube, ovary or minestras of gut
What will occur if the embryo abnormally implants?
Ectopic pregnancy (these abnormal areas need blood supplies but as they are small structures, blood vessels rupture)
What will the trophoblast do once in contact with maternal tissue?
Differentiate, divide and project into uterine wall
The cells that push into the uterine form a what?
Syncytium
What does a syncytium give rise to?
Syncytiotrophoblast
What does the syncytiotrophoblast do to the blastocyst?
Pulls it into uterine wall with it and forms finger-like projections
What occurs with the epiblast in day 8?
Cell division of epiblast creates a fluid that pushes the epiblast away
What happens to the hypoblast in day 9?
It begins to divide at the edges and migrate to form the Heuser’s Membrane/Yolk sac
Implantation is not visible during day 9, but what is?
Coagulation plug
What is the trophoblastic lacuna?
Spaces within the trophoblast that fill with maternal blood
During days 10-12, what new layer is formed?
Extraembryonic mesoderm (derived from both epiblast and hypoblast)
What does the mesoderm layer separate (days 10-12)
The amnion from the amnionotic cavity
In days 12-13, what sort of cavity begins to form in the extraembryonic mesoderm?
Chorionic cavity
What does the cell division of the hypoblast result in (day 12-13)?
Cells that push away orginial yolk sac (which degenerates) and creates a definitive/secondary yolk sac
During days 14-15, a wedge forms, what is this called?
Connecting stalk
What does the wedge do?
Connects embryo to everything and allows formation of umbilical cord
What is the placenta derived from?
Trophoblast; primary villi
What cells are surrounded by maternal blood?
Cytotrophoblast (core) and syncytiotrophoblast (outer)
What occurs in the core of the mesoder, regarding the placenta?
Differentiation of blood vessels
What extends into the villus in the development of the placenta?
Blood vessels (from extraembryonic mesoderm)
How does a smaller/thinner membrane between foetal blood and maternal blood occur?
The cytotrophoblast membrane breaks down
Name the 1st villus
Syncytiotrophoblast and cytotrophoblast
Name the 2nd villus
Syncytiotrophoblast; cytotrophoblast; mesoderm
Name the 3rd villus
Syncytiotrophoblast; cytotrophoblast; mesoderm; villous capillaries
Describe end of week 3
Blood vessles of umbilical cord are created which branch up into the core of the villi; the cytotrophoblast grows past the syncytiotrophoblast creating an outer shell for the placenta
During the breakdown of the cytotrophoblast to create a thinner barrier between blood, what ends up being the barrier?
Syncytiotrophoblast
In the 2nd half of pregnancy, what surrounds the placenta?
Cytotrophoblast
What holds blood vessels that supply the villi?
Chorionic plate
What is the area where the embyro implanted called (end of 2nd month)?
Decidua basalis (interacts with chorion)
What is the decidua capsularis?
The capsule part of the uterine lining
What is destroyed at the end of the 3rd month?
Uterine cavity; chorion cavity
What surrounds the yolk sac at the end of the 2nd month?
Chorionic cavity
