Fertilization and implantation Flashcards
When does fertilization typically occur during the menstrual cycle?
Day 15-16
About how many sperm actually reach the oviduct?
200 out of 300 million
Clinically, what sperm count per millimeter of ejaculate is considered infertile?
<20 million
What is estrogen’s effect on sperm transport in the cervix and uterus?
Cervix - production of watery mucus for aid of motile sperm
Uterus: Contraction of myometrium to help propel sperm
During capacitation of the sperm, where are the inhibitory factors of the head washed away?
Uterine and fallopian tubes
What are the 3 layers the sperm must breach during fertilization?
Corona radiata
Zona pellucida
Oocyte membrane
What do the sperm cells bind in the zona pellucida?
ZP3 glycoproteins
What is the purpose of the cortical reaction? Where is it initiated and what occurs?
Prevent polyspermy
Initiated by increased Ca2+ inside oocyte
Release enzymes that cause zona pellucida proteins to harden
What does the increase in calcium cause in the oocyte after the cortical reaction?
Completeion of 2nd meiotic division and formation of the second polar body (Haploid)
What event represents the end of fertilization and beginning of embryonic development?
Mingling of chromosomes
What day is the morula formed? How many cells?
Day 3, 16 cells
On what day does the embryo reach blastocyst stage?
Days 4, 5
What are the connections between outer cells of the morula?
Desmosomes and gap junctions
What causes formation of the blastocyst cavity within the morula?
Active transport of Na+ from trophoblast cells and osmosis of water
What is a pinopod and when does it appear?
Small-fingerlike protrusions on endometrial cells that endocytose macromolecules and uterine fluid and absorb most of the fluid in the lumen of the uterus
Day 19-21 (luteal phase)
What inhibits development of pinopods?
Estrogens
How does hCG signal to the mother’s body that she is pregnant?
Sustains function of corpus luteum => prevents menstruation and produces progesterone levels necessary to sustain pregnancy
What type of endocrine factor is hCG?
Autocrine
What hormone is closely associated with hCG?
LH
What event initiates implantation?
Contact between blastocyst and uterine wall
What is the role of syncytiotrophoblast in interstitial implantation? During what phase of implantation?
Adhesion-supported invasion and migration of syncytiotrophoblastic cells into endometrium
Breaks down extracellular matrix with matrix metalloproteases and other hydrolytic enzymes
During invasion phase
What steroid hormone does syncytiotrophoblast synthesize?
Progesterone, assists in maintaining pregnancy independent of corpus luteum
What is hatching of the blastocyst? When?
Lytic factors in endometrial cavity that dissolve the zona pellucida
6-7 days after ovulation
What are the 3 stages of implantation?
Apposition
Adhesion
Invasion
What occurs during the apposition phase of implantation? How is the blastocyst oriented?
Blastocyst makes contact with a small crypt in the endometrium
Apical side (with ICM) pointing towards endometrium
What transmembrane glycoprotein may be involved with apposition? Where is it located?
MUC1
Located on apical surface of endometrium
What occurs during the adhesion phase of implantation? Through what interactions?
Trophoblast attaches to uterine epithelium (zona compacta) through microvilli of trophoblast
Ligand-receptor interactions
During the invasion phase of implantation, the syncytiotrophoblast protrusions secrete what?
TNF-a, which inhibits cadherins and B-catenin
How far do the syncytiotrophoblast protrusions reach?
Through basement membrane of uterine epithelial cells to the uterine stroma
Uterine stromal cells transform during what phase of implantation and are then known as what?
Invasion phase
Decidual cells (become rich in lipids and glycogen)
What is decidualization?
Formation of decidua cells into an epithelial-like sheet with adhesive junctions that prevent migration of implanting embryo
