Fertilization thru Wk 2 Flashcards
Where in the fallopian tube (AKA uterine tube) does fertilization typically occur?
In the ampulla of the tube
What is the uterine tube peristalsis stimulated by?
A hormone-like lipid compound called SEMINAL FLUID PROSTAGLANDINS
What is the difference b/w emission and ejaculation?
When is semen produced?
Emission: Sperm are shifted from epididymus to prostatic urethra via the ductus deferens and ejaculatory duct. Semen is produced during this process.
Ejaculation: sperm travels through penile urethra to be deposited to the vaginal fornix
How much sperm is released during ejaculation?
How many sperm reach the ampulla?
2-6mL of semen, approx. 200-600 million sperms;
Usually only 200 sperms
What 3 muscles work together during ejactulation?
Closure of the INTERNAL URETHRALSPHINCTER
and contraction of the URETHRAL ISCHIOCAVERNOSUS and BULBOSPONGIOSUS muscles occur.
What prevents the backflow of sperm into the vagina?
Vesiculase, an enzyme produced by the seminal glands, forms a uterine canal plug
What type of pH is favored for more rapid sperm movement?
How does the cervical fluid affect sperm motility?
alkaline pH;
During ovulation, the cervical fluid is less viscous.
What are the 2 phases of sperm maturation and where do they occur?
What 2 enzymes regulate them?
Capacitation (lasts approx. 7 hrs) occurs in the uterus and uterine tubes, and Acrosomal reaction occurs during the fertilization process.
They appear to be regulated by a TYROSINE KINASE and SRC KINASE
What happens during capacitation of sperm?
A glycoprotein coat and seminal proteins are removed from the acrosome. NO morphological changes occur to the sperm.
NOTE: Capacitation permits the acrosomal rxn
What happens in acrosomal rxn?
Sperm penetrate the zona pellucida as the result of the release of enzymes from the acrosomal membrane
What concentration of sperm is considered for a man to be sterile?
10 million sperm/mL of semen
For fertility, what % of sperm sould be motile after 2 hours?
50%
What are the 6 stages of fertilization?
1) Corona Radiata Penetration
2) Penetration of Zona Pellucida
3) Fusion of Oocyte and Sperm Membranes
4) Completion of 2nd Meiotic division and formation of female pronucleus
5) Formation of the male pronucleus
6) Formation of the Zygote
During Corona Radiata penetration (during fertilization), the breakdown of the acrosomal membrane results in the release of what enzyme?
Hyaluronidase
What is the purpose of the Zona Pellucida during fertilization and how does it achieve that?
Pupose: To facilitate sperm binding & induce the acrosome rxn.
The Acrosome rxn is elicited when a sperm binds to the “glycoprotein sperm receptor molecule” ZP3
What is the acrosome reaction?
It is the exocytosis of acrosome enzymes to digest the Zona Pellucida during fertilization.
The enzymes are: Esterases, acrosin, and neuraminidase
What happens once the sperm penetrates the Zona Pellucida?
Cortical granules from beneath the oocyte’s cell membrane are released (this is called the CORTICAL RXN). These cortical granules alter the ZP recepter proteins, which cause the ZONA RXN, which causes the ZP to become impermeable to other sperm.
At what point is the female pronucleus produced?
After the penetration of the oocyte, meiosis II (halted at metaphase II) is completed, producing the mature oocyte plus a 2nd polar body. The maternal chromosomes condense and the female pronucleus is formed.
What is an ootid?
It is the oocyte, containing 2 haploid pronuclei (male and female)
What happens when the male and female pronuclei fuse during fertilization?
They form a single diploid aggregate of chromosomes called a zygote. The chromosomes condense, eventually cross over, and prepare for cleavage of the zygote.
Define: 1)Blastomere
2) Morula
3) Blastocyst cavity
4) Trophoblast/embryoblast
5) Blastocyst
1) Embryonic cells that divide my mitosis
2) 12-32 blastomeres that form a spherical ball of cells, at Day 3 the morula enters the uterus
3) At 4 days post-fert., it is a fluid-filled space that appears inside the morula, fluid comes from uterus thru ZP
4) As fluid in cavity inc., the blastomeres seperate into 2 parts: 1.Trophoblast: thin outer cell layer, 2.Embryoblast: Inner cell mass
5) Happens at day 4 after tropho/embryoblasts have formed
What happens day 5 post fert?
Day 6?
Day 5: The Zona Pellucida (ZP) degenerates and the BLASTOCYST “hatches”
Day 6: The blastocyst attaches to endometial epith. which triggers proliferation of the trophoblast, which differentiates into 2 layers:
- Cytotrophoblast (inner layer)
- Syncytiotrophoblast (outer layer)
What is the syncytiotrophoblast?
It is a multinucleated invasive mass that sends projections through the endothelium into the connective tissue of the uterus, superficially implanting itself.
NOTE: this happens around day 7
After fert. when does the hypoblast appear? What is it?
At end of first week, it is a layer on the surface of the embryoblast facing the blastocyst cavity
How can there be no increase in size in the developing embryo prior to day 5 post fert?
While cleavage inc. the # of blastomeres, each daughter cell is smaller than its parent. Thus no inc. in embryonic size until day 5, when the ZP degenerates.
Where is the most common spot for implantation of the embryo?
If implantation occurs outside of the endometrium of the uterus what is this called?
The superior portion of the body of the uterus, toward the posterior wall.
Ectopic.
Describe 3 ways to diagnose pregnancy
1) Early Pregnancy Factor: The zygote stimulates the ovary to release EPF which shifts to the trophoblast at implantation. It suppresses mothers immune system preventing it from attacking the fetus. EPF appears in maternal serum w/in 24-48 hrs
2) Human Chorionic Gonadotropin (hCG): is a glycoprotein hormone produced by syncytiotrophoblast. It’s needed (for 1st 2 months) to support corpus luteum which provides continued secretion of progesterone ad estrogens. It does this until placenta takes over
3) Ultra sound cand be done around 3 wks after conception
When do Human Chorionic Gonadotropin levels peak?
hCG levels double every 2 days for 1st 6 wks of pregnancy, PEAKING AT 8-10 WKS of gestation.
NOTE: After that levels drop rapidly for the rest of gestation
What are the differences b/w totipotentiality, pluripotentiality, and multipotentiality in cells?
Totipotentiality: ability of a single cell to divide and produce all the differentiated cells in an organism
Pluripotentiality: can produce all cells of an organism EXCEPT EXTRAEMBRYONIC TISSUES (eg trophoblast cells)
Multipotentiality: Tissue specific stem cells (ie can produce specific cells)
What do embryoblasts and trophoblasts differentiate into?
Embryoblasts: hypoblasts and epiblasts (the first cavity AKA amniotic cavity develops w/in epiblast in day 8 post fert)
Trophoblast: Cytotrophoblast and syncytiotrophoblast
What kind of cells are the epiblast and hypoblast made of? What type of membrane do the hypoblasts form?
Epiblast: Tall columnar cells
Hypoblast: cuboidal cells; They migrate to form the exocoelomic membrane that surrounds the blastocyst cavity AKA exoceolomic cavity
By what day is the cenceptus fully embedded in the UTERUS and what is this marked by?
What day is it fully embedded in the endometrium?
Day 9, marked by a coagulation plug at the point of implantation.
Day 10
Describe the progressing names of the blastocyst cavity and what days post fert they change.
Day 4:Blastocyst cavity
Day 9:Exocoelomic cavity
Day 10: Umbilical vessel or Yolk Sac
What is the extraembryonic mesoderm and what day post fert does it first appear?
It is a connective tissue layer that develops from the ubilical vessel/yolk sac and surrounds it along with the amnion.
This develops at the end of day 9 and beginning of day 10
What is the lacunar network?
Spaces that develop w/in the synciotrophoblast and become filled w/ a mixture of maternal blood and secretions from uterine glands. The fluid is called EMBRYOTROPH and diffuses to the embryo to provide early nutrients.
(NOTE: Lacunar networks BEGIN developing on day 9-10)
Describe the 3 main events that occur days 11/12 post fert.
1) The regenerated epithelium of the endometrium covers the plug
2) As the syncyiotrophoblast penetrates deeper, maternal capillaries are eroded, and become continuous with the lacunae establishing an early uteroplacental circulation
3) A 3rd cavity appears W/IN the extraembryonic mesoderm that begins w/ several cavities until they become confluent, forming the EXTRAEMBRYONIC COELOM (AKA chorionic cavity)
The extraembryonic mesoderm differentiates into what 2 layers?
What day does this happen at?
1) Extraembryonic SOMATIC mesoderm: lines trophoblast and covers amnion
2) Extraembryonic SPLANCHNIC mesoderm: Surrounds yolk sac
This happens day 13 post fert
What is the prechordal plate?
A localized circular area of hypoblast cells that become columnar, indicating the future site of the mouth. This happens at day 14
