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1. From the ovulation until the implantation
Terms in this set (20)
When does ovulation occur, and what event triggers it?
- Day 14 (middle of the cycle). In the days leading up to day 14 the ovarian follicle has reached the graafian stage.
- Ovulation is triggered by the LH surge
How does LH cause ovulation?
- LH stimulates collagenase, which digests collagen around the follicle
- LH stimulates prostaglandins, causing muscles in the ovarian wall to extrude the oocyte
Where does fertilization most commonly occur?
In the ampullary region of the fallopian tube
What must happen to the sperm cell before it can fertilize the egg?
It must undergo capacitation and the acrosome reaction
Describe the process of capacitation
- Spermatozoa interact with the endometrium, causing the spermatozoa to lose a glycoprotein coat and seminal plasma proteins
- Capacitation allows the spermatozoa to pass through the corona radiata
Describe the acrosome reaction
When the spermatozoa pass the corona radiata and binds to the zona pellucida enzymes is released from the acrosome
These enzymes degrade the zona pellucida at that point, allowing the spermatozoon's plasma membrane to fuse with the oocyte's plasma membrane
Describe the zona reaction
After one spermatozoon has fertilized the oocyte enzymes will be released from the plasma membrane of the oocyte
These enzymes change the properties of the zona pellucida to prevent other sperm from penetrating it
What occurs after the spermatozoon has entered the oocyte?
The pronuclei of the spermatozoon and the oocyte replicate their DNA
The pronuclei then fuse, the sister chromatids are split longitudinally, and the cell is divided into two
What is cleavage?
Cleavage is the process by which the zygote rapidly divides by mitosis
When are the two-cell and four-cell stages reached?
Two-cell stage 30 hours after fertilization
Four-cell stage 40 hours after fertilization
What is the morula, and when is it formed?
The morula is the 16-cell stage
It is separated into the inner cell mass (embryoblast) and the outer cell mass (trophoblast)
Which event marks the blastocyst stage?
The formation of a large cavity in the zygote, the blastocele
When is the zona pellucida disintegrated?
4 days after fertilization, when the zygote enters the uterine cavity
Where does implantation most commonly occur?
The anterior or posterior wall of the uterus
What is the bilaminar disc?
The bilaminar disc is the next stage of the embryoblast, which has two layers: the epiblast layer and the hypoblast layer
What will the epiblast form, and where does it lie?
- The epiblast will form the embryo itself
- It lies above the hypoblast, in contact with the trophoblast cells
What will the hypoblast form, and where does it lie?
- The hypoblast will form the yolk sac
- It lies below the epiblast, in contact with the blastocele
What is the anterior visceral endoderm, and what is its function?
The anterior visceral endoderm is a part of the hypoblast which lies at the cranial end
It will secrete antagonists to the nodal signaling pathway at the cranial end, which specifies to the cells at this end that this should develop into the cranial end
When is the dorsal-ventral axis determined?
During formation of the bilaminar disc
When is the cranio-caudal axis determined?
During formation of the anterior visceral endoderm
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