Fertilization and implantation Flashcards
What happens to sperm after it enters the vagina?
The seminal and prostatic fluids mix and cause coagulation, which adheres the sperm to the female reproductive tract. The vagina is acidic but the seminal fluid buffers it to around pH 7.2.
The sperm needs to get through the cervix into the uterus. The cervical mucus can prevent sperm entry. During ovulation the mucus is watery, and contain spinnbarkeit.
The sperm tails move along the spinnbarkeit causing them to vibrate in rhythm. Sperm that can’t do this can’t get into the uterus.
Some sperm remain in he crypts of the cervix. Others travel from the uterus to the utero-tubal junction (30 mins).
What happens if sperm enter the fallopian tube prior to ovulation?
The sperm can slow their motility and wait for 48 hours for ovulation.
Where does fertilization usually take place?
At the ampulla isthmus junction
How do you get rid of excess sperm?
By an innate immune system. Neutrophils and macrophages. Sperm may tolerate the mother to the featus.
What is capacitation?
When sperm is ejaculated it does not have the ability to swim and they cannot do the acrosome reaction.
Capacitation happens in the vagina and involves a removal of capicitation inhibitory factors.
Once it has occurred the sperm become hyperactivated and the tail bends more and the head swings more to assist moving through tortuous fold.
Describe the acrosome reaction.
The acrosome is a pouch filled with proteinases and enzymes.
The acrosomal and plasma membrane of the sperm fuse.
The reaction is triggered by Ca influx. It cn be triggered by several things including protein of the zona pellucida (ZP3) or progesterone. 10% of sperm perform this away from the oocyte - no fertilization.
How does a sperm fertilize the egg?
It must first penetrate the cumulus cells. As the sperm is approaching the egg it gets stimulated by progesterone which stimulates the acosomal reaction (starts it) and the acrosomal protein hyaluronidase, which degrades the the connection between the cells allowing the sperm to squeeze between the cumulus cells.
This is only a partial release of the acrosome Next it must pass through the corona radiata, a layer of tightly packed cells, and the connections between these cells must also be degraded to get to the zona pellucida.
ZP3 then causes the acrosomal reaction. This exposes receptors that can bind to the oocyte
The sperm then enter through the zona pellucida to the perivitaline space.
It then fuses with the oolemmal membrane, the sperm and oolemmal membranes fuse and the sperm nucleus enters the ovum.
What is the cortical reaction?
Once the sperm has entered the ovum it causes a Ca2+ release in the oocyte. This is followed by regular spikes of Ca2+. This causes the final phases of meiosis to occur by destabilizing the proteins holding chromosmes in metaphase. It also causes the zona to harden. Other sperm now cannot enter.
How many polar bodies does the ovum generate?
2
What happens to the zygote after fertilzation?
It makes it’s way down the tube to uerus while undergoing cleavage. The blastomeres divide symmetrically.
Continued doubling gives rise to the morula at 6-18 cell stage. The cells of the morula become tightly cohesive and packed.
What is the name of the embryo at 8-16 cell stage?
Continued doubling gives rise to the morula at 8-16 cell stage. The cells of the morula become tightly cohesive and packed.
What is the blastocyst?
The embryo at the 60 cell stage. It has two types of cells, the trophoectoderm (forms the placental trophoblast) and the inner cell mass which forms the embryo proper.
Blastocele cavity is filled with blastocele fluid
Remains in the uterus free floating before it hatches from the zona. This must occur before it can interact with the uterine epithelium
What is nidation?
When the hatched blastocyst comes into contact with the receptive decidua via receptors.
How long does it take for sperm to get to the ampulla after entering the cervix and how long in total?
30 mins after going through the cervix and 2-7 hours total
