Fertilisation and luteal phase Flashcards
What is the state of ejaculated semen?
Ejaculated semen is coagulated
What does seminal fluid comprise of?
Prostatic and seminal vesicle secretions comprise seminal fluid which coagulates-prevents loss, later liquefies
What does movement through cervical mucus remove?
Movement through cervical mucus removes seminal fluid, abnormally morphological sperm and cellular debris
When sperm passes into cervix What quality of cervical mucus allows it to pass and why?
Cervical mucus is less viscous in the absence of progesterone allowing sperm to pass
What can sperm inhabit when they pass into the cervix?
Sperm can inhabit cervical crypts which may form a reservoir
What may attract the sperm to the egg?
-Chemoattractants released from the oocyte cumulus complex may attract the sperm
What can happen to the sperm during its journey to the egg?
Sperm can become hyperactivated with forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via catsper channels
What is sperm capacitation?
It is the biochemical arrangement of the surface of glycoprotein and changes in membrane composition which must occur before the acrosome reaction takes place
How can sperm capacitation be partly achieved?
Is partly achieved by removing the sperm from seminal fluid
What may promote sperm capacitation?
Uterine or tubal fluid may may contain factors which promote capacitation
Where does the acrosome reaction occur?
Occurs in contact with the zona cumulus complex
What happens in the acrosome reaction?
- The acrosomal membrane on the sperm head fuses releasing enzymes that cut through the complex
- Acrosin bound to the inner acrosomal membrane digests the zona pellucida so the sperm can enter
What does progesterone make during the luteal phase?
Makes the endometrium secretory and receptive to implantation
What does progesterone suppress in the luteal phase?
Supressess cilia in uterine tubes once oocyte has already passed
What does progesterone make viscous again in the luteal phase?
Makes cervical mucus viscous again to prevent further sperm penetration
What does oestrogen help in the luteal phase?
Helps to maintain endometrium in luteal phase
What does the cumulus oophorus do and what is it derived from?
Protects egg and is derived from granulosa cells
What is the corona radiata and what is in contact with?
It is the innermost layer of cumulus cells in contact with the zona pellucida
What is the corona radiata formed by?
Formed by granulosa cells
What does the corona radiata adhere to before it leaves the ovarian follicle?
Adheres to the oocyte before it leaves the ovarian follicle
What is the zona pellucida secreted by?
Secreted by the egg
What happens to the zona pellucida after the cortical reaction?
Becomes impenetrable after the cortical reaction
Where does fertilisation usually occur?
Usually occurs in the ampulla of the uterine tubes
What are the steps involved in sperm binding and penetration?
- The acrosome reaction occurs in contact with the zona cumulus complex. The sperm penetrate the cumulus and bind to the zona pellucida
- Sperm enzymes cut through the zona pellucida and sperm fuses with plasma membrane
- Sperm taken in by phagocytosis. Phosphate zeta activated by basal Ca2+ inside egg. PIP2 –> DAG + IP3 causes the release of intracellular Ca2+ leading to a large Ca2+ spike
- Cortical reaction as wave of Ca2+ sweeps around egg; release of proteases, peroxides and hyaline prevents polyspermy
What are the steps involved syngamy?
- After the sperm enters, Ca2+ causes completion of meiosis 2 expelling the second polar body and initiates the cortical reaction
- The sperm nuclear membrane breaks down, the chromatin decondenses and chromosomes separate
- 4-7 hours after fusion, the 2 sets of haploid chromosomes become surrounded by distinct membranes forming pronuclei. These haploid structures synthesise DNA in preparation for the first mitotic division
- The pronuclei fuse and the mitotic metaphase spindle forms with the chromosomes assuming their position at its equator
- Mitosis is completed and the one cell zygote becomes a 2 cell embryo
