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What are the important key features of the first 17 days after fertilization?
- 2-3 days: zygote cleaves into blastomeres without ANY increase in overall size b/c the zona pellucida is STILL present
- day 3: morula forms (consists of outer cells that form the trophoblast (pre placental/extra-embryonic tissues cells) & inner cell mass (cells that will form the embryo)
- days 4-5: early blastocyst is formed as a result of further cleavages --> causes zona pellucida to SHED (hatch!) within a day or two (embryo can now implant in uterus)
- days 12-14: late blastocyst is formed (this is ~ week after implantation @ day 6-7)
- END of the second week after fertilization: implantation is COMPLETED (bilaminar embryonic disc forms)
- during the 3rd week: three germ layers form by gastrulation
When is the first time we see cell polarity?
after the zygote's 3rd mitotic division, cell division is not occurring synchronously and cells aren't all the same (polarity)
Where is the zygote at day 3, when the morula stage is taking place?
STILL in the fallopian tubes
When is the first point you see a coel?
- after morula reached the blastocyst stage, ~ day 4-5
- it's a fluid filled sack that eventually causes the zone pellucida to break
Why does the zona pellucida remain intact up until day 3 after fertilization?
it prevents the zygote from adhering to the walls of the fallopian tube and resulting in an ectopic pregnancy
What does the first division/cleavage occur after fertilization?
in the first 24 hours
by 48-60 hours, 8 blastomeres have formed without any increase in the size of the embryo
What will the ICM and trophoblast of the blastomere eventually develop into?
- these structure are necessary to establish embryo polarity
- ICM forms the embryo, amnion, yolk sac, & small parts of the placenta
- ICM is the source of embryonic stem cells (ES cells)
- trophoblast forms MOST of the placenta
What events can occur during early mitotic cleavages that produce an embryo with two or more genetically- different cell lines?
- chromosome translocation or deletion
Individuals who are MOSAICS generally have ____ severe phenotypes than those with TOTAL non-disjunction or translocation events.
LESS sever phenotypes than a total, all-encompassing event
- embryos (from the 8 cell stage) are tested for severe genetic disorders prior to selection for transfer to the uterus
- enables couples who carry lethal genetic traits to decrease or eliminate the risk of having a child with the trait
Blastocyst Formation: Days 4-5
- morula arrives in the uterus
- morula cleaves further, develops into early blastocyst
- it begins to form blastocoel cavity filled with fluid
- zona pellucida sheds as embryo expands in size b/c of fluid filling blastocoel (blastocyst hatching)
- *no overall size increase is possible unless embryo sheds the zona pellucida
Early Implantation: Days 6-7
at day 6, the blastocyst attaches to the endometrium usually adjacent to the ICM at the embryonic pole
Mid-Implantation: Days 8-12
- ICM cells differentiate into two layers of thin cells called the bilaminar disk
- this is made up of the epiblast and hypoblast
Implantation Completion: Days 12-14
- hCG in the maternal circulation ensures survival of the corpus luteum & its continued production of progesterone
- now have well differentiated inner cell mast
key points of human gastrulation:
- 1) All 3 cell layers come from the epiblast
- 2) Hypoblast layer delaminates to allow endoderm formation
- ICM -->bilaminar disk --> epiblast & hypoblast
- epiblast gives rise to all 3 embryonic germ layers
What are three major causes of first trimester spontaneous abortions?
- 1. chromosomal abnormalities (55-65%)
- 2. cleavage abnormalities (15-25%)
- 3. not enough progesterone (10-20%)
What is the silver lining of spontaneous abortions?
early losses of pregnancy keep the rate of congenital malformations at birth to 2-3%
What is the only organ that has the vasculation to handle a pregnancy?
What is infertility & how is it diagnosed?
clinics/insurance companies define infertility as the inability to achieve pregnancy after one year of unprotected intercourse (1/8 couples meet the definition)
What can cause infertility?
disruption of any of the developmental steps between gametogenesis and implantation
What is a common (sexist) misconception about infertility?
- that infertility is primarily a woman's problem
- this is incorrect b/c defects are found in males & females at similar frequencies
What are 3 defects in ovulation that can cause female infertility?
- 1. hypothalamic abnormalities that cause irregular ovulation or anovulation (eg. changes in GnRH release, tumors)
- 2. reduced secretion of FSH and LH from the anterior pituitary gland --> ovulatory disturbances
- 3. ovulation defects caused by stress, extreme athletic activity, eating disorders, hormonal imbalances
PCOS (Polycystic Ovary Syndrome)
- irregular ovulation or anovulation
- increased LH levels relative to FSH levels
- most common hormonal disturbance in women of child-bearing age
- can be treated w/ metformin (diabetes drug)
irregular ovulation or anovulation
- increased LH levels relative to FSH levels
- most common hormonal disturbance in women of child-bearing age
- high androgen levels
- can treat overall symptoms with metformin (1st line for diabetes)
What are some physical abnormalities that can interfere with gamete transport or embry/blastocyst implantation?
endometriosis, Chronic Pelvic Inflammatory Disease (CPID), tubal obstructions, uterine abnormalities (FIBROIDS)
leiomyomas (uterine fibroids)
“benign” (isolated to one region) neoplasias of uterine smooth muscle cells
congenital uterine developmental anomalies, or complete absence of the uterus
excessive scar tissue in the uterine cavity that occurs after uterine surgeries such as dilation and curettage (D&C) or myomectomy, or after lower abdominal surgery
excessive scar tissue from STIs
- scar tissue is in vaginal canal/cervix (different from Asherman’s)
- type of uterine abnormality
What do most male infertility factors cause?
- azoospermia (no sperm cells) or oligospermia (few sperm cells); low or no sperm can be caused by:
- abnormal H-P-T axis hormone levels
- high testis temperature caused by a varicocele in the scrotum (dilated internal spermatic veins)
What is the leading risk factor for infertility in the US?
- advanced maternal age (over 35)
- by 40 y/o, over HALF of ovulated oocytes are aneuploid & unable to support normal embryonic development
- in some women these losses occur earlier and cause premature ovarian failure before normal menopause @ 50 y/o
Are men over 50 at risk for producing children with compromised phenotypes?
Yes, recent data suggests men over 50 are more likely to have children with autism and certain other conditions
Approximately how many couples undergoing IVF are diagnosed with “unexplained infertility"?
What are 5 methods for treating infertility?
- 1. Surgical treatments
- 2. Fertility drugs
- 3. Intrauterine insemination (IUI)
- 4. In vitro vertilization (IVF)
- 5. Something Beyond IVF
What would women under <35 with unexplained infertility start off treatment with?
- 3 or more cycles of orally administered fertility drugs such as clomiphene citrate
- if clomiphene therapy is unsuccessful --> clomiphene citrate with intrauterine insemination (IUI)
- if clomiphene + IUI doesn't work --> injectable fertility drugs hMG, FSH + IUI
- IF THOSE 3 FAIL: IVF
- *if the woman is over 35 --> directly to IVF
- orally-administered synthetic hormone that blocks estrogen receptors in the hypothalamus, causing it to think there is a deficiency of estrogen in the blood
- used to regulate ovulation or induce ovulation in women who are anovulatory
Human Menopausal Gonadotropins (hMG)
- given by daily injection and contains both LH and FSH
- requires monitoring of follicle size by ultrasound + blood estrogen levels
- used on:
- 1) anovulatory women, no success with clomiphene
- 2) women with amenorrhea not making enough FSH and LH
Follicle Stimulating Hormone (FSH)
- administered by subcutaneous injection - stimulates ovaries to make multiple follicles & oocytes
- KEY USE is in PCOS patients (who have high LH – low FSH)
Gonadotropin releasing hormone (GnRH)
- administered at 90 minute intervals by a special drug delivery pump system (mimics pulsatile release of hypothalamic GnRH)
- KEY USE in anovulatory patients (have abnormalities in both FSH and LH release)
Human Chorionic Gonadotropin (hCG)
- administered once by subcutaneous injection at the end of ovulation induction treatment
- monitoring w/ ultrasound images and serum estrogen levels are used
- hCG mimics LH (causes rapid maturation of multiple follicles)
- KEY USE is to trigger multiple ovulations
Intrauterine Insemination (IUI)
- sperm are washed to remove surface glycoproteins and seminal proteins (mimics capacitation), concentrated, then injected into uterus after ovulation OR hCG injection
- used for couples with unexplained infertility, minimal male infertility factors, or women with cervical mucus abnormalities
In Vitro Fertilization (IVF)
- production of multiple eggs is induced by ovulation injection
- mature eggs are removed from the ovary and fertilized in vitro by incubation with sperm
- fertilization & early embryonic cleavages observed in lab for 2-3 days using a microscope
- healthy embryos w/ 8 blastomeres are placed into the uterus, unless PGD has been performed, in which case a 5-day embryo (blastocyst) is implanted
After mixing the oocytes and sperm, what will an embryologist look for that shows normal fertilization has occurred?
fertilized oocytes that have two pronuclei --> this indicates normal fertilization has occurred
How many embryos are transferred to a woman?
- if she's under 35:1 or 2 high quality ones
- over 40 and failed IVF: up to 4-5
What are a woman's options if IVF fails?
- IVF with donor eggs
What are some of the problems with infertility treatments?
- high cost, limited access to treatments
- unknown medical risks (especially for ICSI): recent data indicates increased incidence of diabetes/other medical problems in ICSI offspring
- not fully documented because of incomplete long-term outcome data
cell of the body other than egg or sperm
Somatic cell nuclear transfer (SCNT)
the transfer of a cell nucleus from a somatic cell into an egg from which the nucleus has been removed
- cells that have the ability to divide for indefinite periods, to self-renew, and to give rise to specialized cells
- self-renewing, MULTIPOTENT, can reconstitute a tissue (in vivo)
What are 3 sources of stem cells?
- 1. embryonic stem (ES) cells from the inner cell mass of the blastocyst!
- 2. fetal umbilical cord blood*
- 3. adult tissues, including induced pluripotent stem (iPS) cells
unlimited capacity to specialize into any and all cell types or tissues
capable of giving rise to most cells and tissues of an organism
capable of giving rise to several/many cell types
cells that are committed to differentiate; they are not self-renewing
an organism, colony, or group of organisms (or a colony of cells) derived from a single organism or cell by asexual reproduction, all having identical genetic constitutions
cloning to produce a pregnancy that results in the birth of a baby
cloning to produce embryonic stem cells for treatment of disease, mechanistic studies, or toxicology studies"
Somatic Cell Nuclear Transfer (SCNT)
- how a clone is made
- isolate an unfertilized egg (secondary oocyte), remove the nucleus, replace it with a donor diploid nucleus from some other cell type. grow the egg into an adult