Week 1 Flashcards
First week of development
At what point after copulation does the sperm reach the ovulated Oocyte?
The Sperm travel from the Vagina, through the Cervix and uterus, into the Oviducts, where they interact with the ovulated Oocyte
How do sperm associate with the Oocyte? What does this cause?
- Sperm associate via the Sperm Receptor Molecule present on the surface of the Oocyte
- Association causes the Sperm to release the Digestive enzymes present in the Acrosome, which begin degrading the Zona Pellucida
Why are more than one Sperm needed to achieve fertilization? What does this imply about a low sperm count?
- Digestive enzymes from multiple sperm are required to degrade the Zona Pellucida enough to allow one sperm in.
- If a Patient has a low sperm count, it may be difficult to conceive a child if there is not sufficient digestive enzyme present to facilitate fertilization
Once the Zona Pellucida is degraded enough to allow ONE sperm to fuse with the membrane, what occurs? Why is this important?
A. Fusion of a sperm cell with the oocyte triggers the continuation of the cell cycle from Metaphase II & the inactivation of the Sperm Receptor Molecule B. Inactivation of the SRM acts to prevent Polyspermy
What fusion event occurring post-membrane fusion, is considered Time 0
Fusion of the Male Pronucleus (N) and Female Pronucleus (N) to form the Zygote (2N).
What process must sperm undergo prior to reaching the Oviducts to achieve fertilization?
Capacitation; Modification of surface proteins *Current mechanism unknown
At which phase are Oocytes arrested in Meiosis II?
Metaphase II
What happens to the Zygote once formed?
The Zygote travels from the oviducts to the Uterus and begins undergoing Cleavage
What is Cleavage? What is special in relation to size?
Cleavage is the mitotic division of blastomeres (daughter cells) within the zygote with NO increase in size of the Zygote.
When is the embryo considered a Morula?
The Zygote is considered a Morula when the blastomere number reaches ~16-32
Approximately on day 4
What is the first event (during Cleavage) resulting in differentiation of cells into (2) distinct cell groups? What are those groups & what will they give rise to in the future?
A. Compaction; the differentiation and organization of Blastomeres B. Embryoblast (inner cell mass): Gives rise to the Embryo Proper Trophoblast (outer cell mass): Gives rise to the membranes of the placenta
Fluid absorption by the ______ during later stages of cleavage results in __________ Cavity formation
A. Morula B. Blastocyst Cavity
Formation of the Blastocyst cavity has what effect on the axis of the developing embryo?
Fluid absorption displaces the Embryoblast to one side, thereby Polarizing the embryo with the Embryonic pole and opposing Abembryonic pole.
Blastocyst Hatching occurs on Day __ and facilitates what?
- Day 5
- Blastocyst Hatches from the Zona pellucida and follicular cells allows for implantation and direct association of the embryonic pole with the endometrium
What is the “Decidual Reaction” and what causes it?
- The Decidual Reaction is the Endometrium becoming edematous, while uterine glangs englarge and it’s cells become Decidual cells (Secretory cells).
- It is caused by the association of the emrbyonic pole of the embryo with the uterine wall.
What is the major complication that can occur during week 1?
What increases the risk of it occurring?
- Ectopic Pregnancies; Occurs when the blastocyst implants in an inappropriate location
- Increased risk comes with a history of scarring due to Pelvic Inflammatory Diseases (PID), which can arise form Sexually Transmitted Diseases (STD)
How can small ectopic pregnancies be treated?
Small ectopic pregnancies can be treated using anti-tumor drugs which preferentially target rapidly dividing cells.
(i.e. Methotrexate)
How are large ectopic pregnancies treated?
Large ectopic pregnancies must be surgically removed
In general, describe the transformation of the embryo following fertilization at time 0
- Zygote
- Morula
- Blastula
- Gastrula (future)
