Fertilization and Implantation Flashcards
What protects sperm cells form the acidity of the vaginal lumen?
High buffering capacity of the seminal fluid and the alkaline pH of cervical mucus
What occurs to semen after ejaculation into the vagina?
Coagulates in response a clotting enzyme produced by the prostate
Proteolytic enzymes and PSA liquify the coagulum over a period of about 30 minutes
How do sperm cells pass through the cervix?
Moving through the interstitial spaces created by mucin molecules
These spaces expand as mucin production and water accumulation occur in response to the mid-cycle estrogen peak
Sperm passage enhanced by uterine contractions
What changes are associated with capacitation?
Plasma membrane destabilized, making the head more fluid (acrosome)
Plasma membrane becomes more permeable to Ca
Hyperactivation - more erratic movement
What is the acrosomal reaction?
Cell surface proteins on the sperm bind with ZP3 - receptor glycoprotein in the zona pellucida
Rise in intracellular Ca in the sperm causes release of hydrolytic enzymes that digest a path through the zona pellucida
What is fast block?
Polyspermy blocking reaction
Oocyte membrane depolarizes after fusing with the sperm, preventing other sperm from fusing
What is the cortical reaction?
Depolarization from fast block illicits a wave of Ca that causes electron dense granules to fuse with the oocyte membrane
The granule contents induce a hardening of the zona pellucida, preventing further penetration
What is the role of progesterone in implantation?
Progesterone causes the endometrium to differentiate into a structure that is receptive to implantation and capable of sustaining the developing embryo
What is the blastocyst?
Hollow, fluid-filled sphere composed of an inner cell mass (develops into fetus) and outer layer of trophoblastic cells
What two cell types does the trophoblast differentiate into?
Cytotrophoblasts
Syncytiotrophoblast
What is the function of the syncytiotrophoblast?
Releases proteolytic enzymes that digest:
- the matrix proteins holding the epithelial cells of the endometrium together
- matrix proteins of the stroma
Allows blastocyst to invade the endometrium
Why is invasion beyond the stroma limited?
Presence of inhibitors of the proteolytic enzymes
What is the decidual reaction?
Transformation of endometrial stromal cells into enlarged rounded or polygonal-shaped cells that form an epithelioid-like compact layer
This compact layer limits the migration of the implanted embryo
What is the decidua?
Endometirum post-implantation
Provides nutrients to the developing embryo until the placenta is formed
What is the purpose of cytotrophoblastic invasion of the spiral arteries?
Cause the destruction of the smooth muscle layer and elastic fibers, replacing them with fibrous tissue
Creates low resistance vessels that are unresponsive to normal mediators of vascular tone, enhancing blood flow into the placenta
