Wk8 Sperm transport & fertilisation Flashcards
What are the 5 steps to fertilisation?
- Semen deposition
- Semen transport
- Semen capacitation
- Oocyte maturation
AR and fertilisation
Where is the sight of fertilisation in female?
- The oviduct
What are the 2 phases of sperm transport to the isthmus?
- Rapid
- Minutes after mating, sperm unlikely to fertilise and quickly die
- Contractions of uterine smooth muscle
- Sustained
- Long term transport - hours after mating
- Sperm more likely to fertilise
‘trickle entry’ of motile sperm through UTJ
What is a copulatory plug
- Coagulated semen forms a plug to minimise retrograde flow (stop flow of fluid in opposite direction to the one considered to be normal)
Why does systems undergo a protective immune response (neutrophils phagocytosing sperm)
- Post mating inflammation important as semen can introduce pathogens as well, either by carrying pathogens itself or by introducing external pathogens into the system itself.
Seminal plasma has important immunomodulatory roles (fewer neutrophils will bind to it if exposed to seminal plasma)
Physical barriers to sperm transport: what is the purpose of the female physical barriers in relation to sperm?
- Retrograde flow of mucous in cervix
- UTJ (uterotubal junction, before uterine horns)q
- Limit the number f sperm gaining access to the isthmus
Also keeps pathogens out of the tract as well.
Privileged pathways of sperm in the cervix - what is this?
- Sperm traverse the cervix by swimming through the bottom part of the cervical crypts, where low viscosity mucous favours transport
Sperm capacitation process: key steps involved in capacitation and what is results in
- Loss and rearrangement of proteins in the membrane
- Loss of cholesterol from sperm membrane important for changing sperm structure
- Increased intracellular calcium (can measure in vitro to see whether sperm has capacitated)
- Sperm have to complete capacitation to be released from oviductal reservoirs
Capacitation takes several hours (usually about 3) and you can reverse a lot of these changes by exposing the sperm to seminal plasma
What are the steps involved in the fertilisation process
- Sperm and oocyte will meet in the ampulla, and the fertilisation process will begin
- Ampulla = one of 4 segments of the fallopian tube, connects to infundibulum (final segment)
○ Interstitial, isthmus, ampulla and infundibulum.
- Ampulla = one of 4 segments of the fallopian tube, connects to infundibulum (final segment)
- Hyperactivated motility
- Zona pellucida binding
- Acrosome reaction
- ZP penetration
- Sperm-oocyte membrane fusion
Decondensation of sperm nucleus
Zona pellucida binding and the AR
- Capacitation is a pre requisite for acrosome reaction*
- The sperm then secretes hyaluronidase to help sperm get through the cumulus cells
- AR leads to:
- release of enzymes to help ZP penetration
- fusion of outer and inner acrosomal membranes
Exposure of fusion proteins on sperm head
Why is there a biological mechanism regulating the number of sperm that enter the ampulla around the time of ovulation?
- If we get too many sperm that enter the ampulla, we can run into trouble.
- Polyspermy: when oocyte is penetrated by more than one sperm
- 2 polyspermy blocks:
- Depolarisation of oocyte membrane
- Cortical reaction (ZP hardening)
Cortical granules are released to harden the zona pellucida
Timing of oocyte survival (important):
Post ovulatory aging
- Oocytes need to be fertilisation within 10-12 hours post ovulation
- Post ovulatory ageing causes oocyte quality to drop sharply after this time
- Sperm also need several hours for capacitation
- Ideally sperm will be in reservoir prior to ovulation..
Ensure capacitated viable sperm are available when the oocyte enters the ampulla for fertilisation to occur in 10-12hours.
- Ideally sperm will be in reservoir prior to ovulation..
When do we inseminate- before or after ovulation?
Always before ovulation so that sperm is ready for when oocyte is released into the ampulla (only have 10-12hours of oocyte survival)
MCQ: A sperm is undergoing the acrosome reaction. Which process has NOT yet occurred?
- Release from the oviductal reservoir
- Syngamy
- Capacitation
- Hyperactivated motility
Secretion of hyaluronidase
- Syngamy: fusion of male and female nuclei
- The rest have already occurred
E.g. secretion of hyaluronidase (break through the oocyte cells)
What are the 2 polyspermy blocks? (when oocyte is penetrated by more than 1 sperm)
- Depolarisation of oocyte membrane
- Cortical reaction (zona pellucida hardening)
Cortical granules are released to harden the zona pellucida (goes green)
