Lecture 8- Fertilization Flashcards
Ovulated Ooctye has 3 Regions, what are they called?
- oocyte(ovum or egg)
- Zona pellucida (thick layer of glycoproteins and this is where acrosome reaction occurs)
- Cumulus oophorus(made up of granulosa cells)
To get through cumulus oophorus, we need:
Hyaluronidase, which we get from PH20. Remember epididymis gave sperm PH20.
Zona Pellucida is where the acrosome reaction takes place, how does acrosome reaction occur?
Acrosome reaction occurs because:
- High levels of progesterone increase intracellular Ca2+
- CRISP1 and ZP3 link and causes activation which increases intracellular Ca2+
- This leads to exocytosis of enzymes in the acrosome. (Enzymes being released from sperm) which degrades the zona pellucida–→ allowing sperm to get through and meet with ovum
Once sperm is past the zona pellucida and meets with the ovum membrane what happens:
Receptors on sperm head (Izumo) and receptors on the ovum (juno) bind with each other. Membranes fuse together and the contents of sperm enter the ovum.
Once sperm contents enter the ovum, there is a Ca2+ influx due to IP3 receptors. This event finishes____.
Meiosis. As a result, coritcal granules exocytose.
Prevention of polyspermy(multiple sperm trying to fertilize one ovum).
There are two ways to polyspermy, what is the first way to prevent it?
- Fast Block-Wave of depolarization, which repels sperm electrically and/or leads to the shedding of Juno
Prevention of polyspermy(multiple sperm trying to fertilize one ovum).
There are two ways to polyspermy, what is the second way to prevent it?
2.) Cortical reaction- Rising Ca2+ causes cortical vesicles to fuse with the membrane, releasing their contents(zinc and ovistacin).
It also hardens the zona pellucida so that it’s impossible for another sperm to break through.
Known as the “slow block”
Once a ovum is fertilized it becomes a zygote–→zygote eventually becoms a blastocyst as cells divide–→ Zona pellecudia hardens around blastocyst as it moves through the oviduct.
Blastocyst can not implant on endometrium until_______.
Blastocyst can not implant on endometrium until proteases from epitheleal cells degrade the ZP.
Endometrium has epitheleal cells, that release proteases once triggered by progesterone.
What is decidualization?
Process in which progesterone increases release of glycoproteins–→ increase blood flow of endometrium.
Implantation-Recognition
What signal is needed for a blastocyst to implant on the endometrium?
Glycoproteins expressed by epitheleal cells are called sLE.
Trophoblasts express L-Selectin and binds with sLE.
The binding of sLE and L-Selectin help anchor down the blastocyst.
Implantation- 2 kinds of trophoblasts:
What are the names of the 2 trophoblasts?
- Syncytial trophoblasts–→these bury themselves under the epitheleal cells and go into the endometrium.
- Cytotrophoblasts–→ these stay outside and are facing the lumen of the uterus.
Syncytial trophoblasts secrete:
- TNF alpha–→ basically tells immune cells to back off (so that immune cells don’t kill it)
- Peptidases and metalloproteinases–→helps to dig past epitheleal cells
- hCG–→ it stimulates the corpus luteum and keeps telling it to make progesterone. MUST levels must be maintained so that endometrium stays thick to provide nutrients.
hCG more in depth:
It is structured like LH so that it binds to luteal cells on the corpus leteum. Once hCG binds, corpus luteum secretes progesterone.
After blastocyst digs in deep enough in the endometrium it is now called a embryo.
While becoming a embryo, syncytial trophoblasts create pools of blood around the embryo.
What is the purpose of those pools of blood?
The purpose of the blood pools are to provide the developing embryo with oxygen and glucose.
What is the function of Cytotrophoblasts?
Main function is to work with Natural Killer cells to remodel spiral arteries to bathe embryo in blood.
