Fertilization Flashcards
What is the antrum of the primary follicle?
A cavity filled with fluid the firms in the primary follicular phase. It forms within / between the granulosa cells
What is the cumulus mass?
The bulge of granulosa cells closest to the oocyte, around the zona pellucida. It borders the antrum
What separates the granulosa cells from the theca cells?
The basal lamina
What is the theca interna?
Steroidogenic layer outside of granulosa cells of follicle. They are stimulated by LH from anterior pituitary to secrete testosterone
What is the function of granulosa cells?
Convert testosterone from theca cells into estrogen via aromatase.
What triggers the production of aromatase in granulosa cells?
FSH from pituitary
What is the function of estrogen produced by granulosa cells?
Stimulates granulosa proliferation, oocyte maturation, endometrial proliferation, and production of LH from pituitary (leads to LH surge prior to ovulation)
What is the theca externa?
Elastic connective tissue that can expand as the antrum gets bigger
What is the corona radiata?
Innermost cumulus mass cells (granulosa) which have microvilli to form gap junctions with the oocyte surface.
What is the function of oocyte - corona radiata gap junctions?
They extend through the zona pellucida and transport cAMP to hold the oocyte in meiotic arrest
When does Meiosis 1 proceed from Prophase 1? (What stage?)
In the Graafian follicle, occurs about 12 hours before ovulation. Arrested at metaphase 2 about 6 hours before ovulation
What are the follicular stages of the cortex?
Primordial, primary, antral (with antrum), and Graafian (largest)
What triggers meiosis 1 to resume?
Granulosa retract from oocyte, stopping cAMP delivery. The polar body sits in the perivitelline space and the secondary oocyte arrests in metaphase II.
What causes ovulation and what complex is released?
LH surge from E2 feedback loop causes the late Graafian follicle to have the Theca externa stretched and rupture, releasing Cumulus-oocyte complex into the peritoneal cavity
How does the cumulus-oocyte complex enter the uterine tube?
Hyaluronic acid secreted by the cumulus (granulosa) cells helps it stick to the fimbriae. Ciliated epithelia move the mass into the infundibulum (beginning portion of the tube) and transport it to the ampulla
What is the function of hyaluronidase in sperm?
Facilitates dispersal of cumulus mass around the oocyte.
What forms the corpus luteum?
Empty follicle of Graafian follicle. Its primary function is to secrete progesterone, but it does secrete some estrogen. There are more granulosa cells than theca cells. These both produce progesterone but only theca cells produce testosterone, so minimal estrogen can be produced (made in granulosa cells from testosterone)
What eventually shuts down the corpus luteum?
When it is functioning, the luteinized (sensitized to LH) granulosa cells rapidly convert cholesterol (LDL) to progesterone. This progesterone causes negative feedback for LH, which ends the LH surge. Loss of LH stops production of LH, which causes degradation of corpus luteum
How is the cervical mucus different during ovulation?
It is thinner, for optimal sperm penetration
How is semen moved to the ampulla of the oviduct?
Ciliary movement and muscular contractions. Happens within minutes of coitus. Typically only a few hundred sperm make it
How long are eggs and sperm viable?
Sperm 2-4 days
Eggs - less then 24 hours. Sperm can wait, eggs can’t. Best to have sex 0-2 days before ovulation
What is capacitation?
Biochemical changes necessary for sperm to be able to bind to the zona pellucida and undergo the acrosome reaction. Can be achieved in vitro by washing away seminal plasma
How is the sperm changed by capacitation?
Change in lateral head movements to allow access to ZP, and membrane / metabolic changes
What is the acrosome reaction?
Outer acrosome membrane fuses with sperm plasma membrane, releasing the contents of the acrosome by exocytosis. Inner acrosomal membrane becomes the apical surface. Happens all through the female reproductive tract
What are three spots where the acrosome reaction occurs?
- Contacting epithelial cells of uterine tube or uterus. 2. Contacting cumulus mass. 3. Contacting zona pellucida
What is the zona pellucida?
A structure consisting of 4 glycoproteins, ZP1-4, synthesized during primary follicular stage. Induces acrosome reaction allowing capacitated sperm to penetrate its structure. It is a porous, spongy ECM, with pores large enough for sperm to pass through
What are the functions of hyaluronidase and acrosin?
Released in acrosome reaction. Hyaluronidase - breaks up hyaluronic acid in cumulus-oocyte complex. Acrosin is a protease which remains bound to inner acrosomal membrane and digests zona pellucida.
How is the acrosome reaction at zona pellucida triggered?
Likely mechanosensory - smaller pores in study triggered acrosome reaction (AR)
What is Izumo1?
Transmembrane protein of inner acrosomal membrane on sperm and that is essential for male fertility. Connects with Juno protein of egg
What is Juno?
Transmembrane protein of egg essential for female fertility, connects to Juno. On the microvilli of the egg
What event marks fertilization?
Sperm entering the perivitelline space, sperm and egg plasma membranes fuse and sperm nucleus starts to decondense. Polyspermy blocks activate. Postacrosomal region which still has plasma membrane starts the fertilization, and the entire sperm will enter.
What is the initial block to polyspermy?
Membrane depolarization - happens within a second, Na+ / H+ exchange across plasma membrane, shocking other sperm about to fuse
What is the Ca+2 wave?
Calcium influx from the endoplasmic reticulum caused by phospholipase C activation. PLC generates IP3, which releases sequestered calcium from ER. Triggers cortical reaction
What is the cortical reaction and what triggers it?
Triggered within the first minute by calcium influx, it causes cortical granules to exocytose their contents which modify ZP and egg surface
What is Juno shedding?
Another prevention to polyspermy, blebs of egg membrane containing juno are released. These bind and neutralize Izumo1 of other sperm, and prevents other sperm from binding the surface.
What is the function of the intracellular pH rise?
Intracellular pH rise occurs in minutes, and activates proteins which restart meiosis
When is the second polar body produced?
When the female pronucleus is formed, right after the intracellular pH rise released the egg from metaphase 2 following fertilization.
What do the pronuclei do?
Male and female pronuceli remain separate for 24 hours, approaching but never actually fusing. They do not actually associate until 24 hours after fertilization, during first cleavage (mitosis)
What are the cleavage stages?
2 to 8-cell embryo, occuring the uterine tube. Occurs every 12 hours after the 2-cell stage, which each happening within a 30-60 minute spam. Divides cytoplasm into smaller and smaller blastomeres with little increase in diameter. Cells are totipotent in this stage and can form entire blastocysts.
What is Embryonic Genome Activation?
For the first few cleavages, mRNA and proteins produced by the egg are used for the embryo development. EGA is an event that occurs around the 8 cell stage for humans, when new transcripts produced by the embryonic genome are made and used for remainder of development
What is the morula?
The compacted embryo, after the third cleavage (8-cell stage). Blastomeres adhere tightly to eachother and individual blastomeres are no longer visible
What is cavitation?
Formation of blastocyst cavity (blastocoel) following compaction / morulation. Tight junctions seal outer cells, osmotic gradient forms by inward sodium pumping, single large cavity is formed.
What is trophoectoderm differentiation?
First transport epithelium. They are the outside cells of morula responsible for cavitation, and will become the trophoblast.
What is the blastocyst?
Embryo that enters the uterus around day 4. Contains inner cell mass (ICM) and trophoblast
What is the inner cell layer of the blastocyst?
Also called the embryoblast, they are pluripotent and can form all fetal cell types (germ layers). They can be isoluated to produce embryonic stem cells
What is the outer cell layer of the blastocyst?
The trophoblast, mediates implantation into the uterine wall. They transport between maternal and embryonic tissues, and differentiate into cells which invade the uterus. They form the placenta and chorionic membranes in conjunction with extraembryonic mesoderm
