Fertility - Har-Vardi Flashcards
What are possible causes of infertility that arise when the sperm enters the cervical mucus?
Impaired sperm movement (can’t enter pores)
Antibody interactions in mucus with sperm head
Abnormal morphology of the sperm
Cervical mucus functions as a selective barrier, up to 96% can be effective
What are the effects of hormones during the menstrual cycle on cervical mucus and fertility?
In the follicular phase/preovulation, estrogen is highest and the water content increases so sperm can move freely between glycoproteins
Progesterone turns mucus thick and less penetrable
Cervical crypts hold sperm until up to 72h after ejaculation to wait for ovum to descend
How many sperm are deposited into the vagina?
How many reach the egg?
What is the lifespan of the sperm?
Average of 200 million sperm deposited in vagina
About 100 reach proximity to egg
Fertilizable for 72 hours but remain motile for 5 days
What is the process of capacitation?
Decreased stability of membrane
Removal of epididymal proteins, seminal plasma proteins and cholesterol coating sperm
Exposure of molecules that bind zona pellucida, ability to undergo acrosome reaction, acquisition of hypermotility.
Begins when sperm moves through mucus by friction (if they continue too quickly to the egg they won’t succeed)
After binding to zp3 receptor the outer acrosomal membrane dissolves and leaves the equatorial segment and the inner acrosomial membrane
Describe the process of oogenesis and ovary transport to the uterus
In utero: Oogonia is diploid and differentiates by mitosis into primary oocytes (germinal vesicle-also diploid).
Primary oocyte goes through first meiotic division and arrests after first division
During puberty: first meiotic division completes prior to ovulation (from an LH surge) to get a secondary oocyte and the first polar body- haploid (haploid-23 chromosomes and double chromatids).
After fertilization: 2nd meiotic division is completed to create an ovum. Get 23 chromosomes (haploid) with zygote (instead of oocyte) and 3 polar bodies (assuming the first polar body divided)
Transport of the egg to ovary takes 5 days: ovum picked up by fimbria on the first day and then there is prolonged ampullatory residence.
Rapid transport through the isthmus and then uterine retention for another 2 days before implantation (7 total).
How do the granulosa cells communicate with the oocyte?
Cumulus cells are groups of granulosa cells that have processes that connect to the oocyte through gap junction with nutrients and cAMP.
LH maintains meiotic arrest by disrupting gap junctions.
cAMP maintains oocyte in arrest in meiosis I.
Block of cAMP by LH surge causes oocyte to complete the first meiotic division and arrest in metaphase of meiosis II.
Once the oocyte is mature and completes meiosis II it can only be fertilized for 24 hours
Which part of the sperm enters into the zona pellucida?
Everything except the plasma membrane and acrosome (even the tail!)
Centriole in the neck organizes the sperm’s chromosomes-necessary for creating an embryo
Neck helps cleavage of the zygote after fertilization
Mitochondria enter as well but DNA expression is blocked by the oocyte
What is the process of the sperm-egg interaction?
1- sperm penetrates through cumulus cells that surround oocyte. cumulus matrix- has hyaluronic acid, is digested by specific sperm receptor- hyaluronidase. Digests connections of cumulus cells so it can go between them.
2- sperm binds zp3 on zona pellucida- signalling for acrosomal exocytosis. Sperm penetrates zona pellucida and binds zp2 in zona pellucida. Next step is penetration through perivitallin space.
3- Fusion plasma membrane of sperm with oolemma- membrane of egg. After fusion- see penetration of sperm
After fusion with oocyte: cortical reaction: exocytosis of cortical granules. Enzyme modifies the zona pellucida to prevent other sperm penetration but in between its penetration and fusion the oocyte completes second meiosis with two polar bodies secreted. Blocks polyspermy and allows species specificity
Fertilized oocyte has 2 pronuclei (1 male, 1 female) with nucleoli inside and 2/3 polar bodies outside the oolemma.
What are the two techniques of IVF?
- Insemination (100,000 motile sperm/mL around oocyte vs natural 50)
- ICSI (Intracytoplasmic sperm injection- used in less than normal parameters):
Single sperm into oocyte cytoplasm
What preparation is done between extraction of an oocyte and fertilization in ICSI?
Must remove oolemma from corona radiata and cumulus cells using hyalurodinase
Mechanical denuding using thin pipettes to remove rest of corona cells
Assessing maturity of oocytes (look to see polar body)
Choose a sperm: make sure it moves so it isn’t dead
Polar body needs to be at 6 or 12 o’clock so that the division is as far away as possible from the injection
What is the time progression of IVF after injection of sperm?
After 16-20 hours:
No fertilization, single, two or three pronuclei.
3 pronuclei means: penetration of diploid sperm, 2 sperm, or mature oocyte didn’t complete second meiotic division and 23 chromosomes stayed in oocyte. This is NOT transferred.
After 2 days want to see 2 or 4 cells.
After 72 hours see 8 cells
After 96 hours: a morula is formed by compaction
After 5 days: blastocyst. Contains:
-inner cell mass to form the embryo itself
-trophectoderm to give rise to placenta.
After that, expanded blastocyst.
To implant: oocyte must hatch out of zona pellucida in the uterus.
Transfer 1-3 embryos (less if younger) at 2-8 days of development or 1 blastocyst (higher rate of implantation but lower rate of formation)
Receptive days of the endometrium are days 19-21 (2-3 day window if ovulation is on day 14 and menstruation begins on day 1)
What are the phases of the implantation process?
Transport - the blastocyst arrives in the uterus
Orientation - the ICM is orientated towards the endometrium
Hatching - the zona pellucida dissolves
Apposition - the blastocyst is no
Adhesion - connections are established
Invasion - thin folds of trophectodermal cells intrude between the endometrial epithelial cells
Syncytialization - some trophectodermal cells fuse to form syncytia
By day 7 blastocyst begins to implant
The trophoblast peroliferates to form the cytotrophoblast cells which divide to form the invasive syncytiotrophoblast to invade between endometrial cells.
By day 8 the growing syncytiotrophoblast expands to cover more of the blastocyst.
By day 9 the embryo is completely implanted in the
endometrium, and the synsytiotrophoblast completely
surrounds the embryo
