Reproduction 14 Flashcards
Describe ejaculation
Semen= Sperm (5%) + seminal plasma 1-6ml in humans
seminal plasma secreted by accessory sex glands- seminal vesicles (provides ejaculate volume, rich in fructose) , prostate (alkaline secretions, high in zinc, enzymes for ejaculate clotting and liquefaction), bulbourethral gland (pre-ejucaculate, lubriation, neurlisation) - for transport, nutrition, buffering, antioxidants
Coagulates to form a gel/plug and then is liquefied by enzymes from the prostate so it can flow out of the vagina
Spermatozoa leave the testes immotile and unable to recognise or bind to the egg. Need to undergo maturation in the male tract and capacitation in the female tract.
Describe sperm capacitance
Happens in the female reproductive tract
Hyperactivation- not well understood - changes the way in which sperm swims to get to the egg. THen the acrosome reaction occurs after capacitation
Now can penetrate the egg
Describe sperm transport through the female reproductive tract
100 million deposited in the upper vagina
Seminal plasma- short term buffering against the acidic pH in the vagina
Cervical mucous least viscous (more permissable to sperm) during days 9-16 of the menstrual cycle
100,000 sperm enter the uterus
1000 sperm enter each uterine tube (possible chemotaxis in humans from cumulus? Progesterone?)
Muscular actions of the female tract and sperm motility
Cilia line the uterine tubes that move the fluid surrounding them to assist sperm movement
Describe egg penetration
Egg is ovulated as the cumulus-oocyte complex and is picked up by the ciliated fimbrae on the end of the uterine tubes
Fertiliastion happens in the ampulla region
Sperm remain capable for about 5 days, egg remains viable for about 24 hours Sperm must disperse the cumulus (hyaluronidase enzyme for the gelatinous matrix), bind to the zona pellucida (extracellular protein matix- 4 glycoproteins ZP1-4- persists after fertliation), acrosome reaction, pentrate the zona-exposes the oocyte membrane for fusion
Describe Sperm and Egg Fusion
Sperm pentrates the ZP and ocupies the pereviteline space
Oocyte engulfs the front of the sperm head, sperm nucleus is encased in a vesicle of internalised oocyte membrane
Izumo- sperm membrane receptor for fusion, detectable on sperm surface only after acrosome reaction
Juno- Izumo receptor on oocyte plasma membrane
Describe oocyte activation
within 1-3mins of fusion a large rise in [Ca] sweeps across the egg from the point of sperm fusion, lasts 2-3 mins
Followed by Ca oscillations every 15mins that last several hours- triggered by PLC zeta (sperm specific phospholipase C)
Release from meiotic block-
Maturation promoting factoe (MPF)= cdk1+cylcin B- blocks metaphase to anaphase transition
Stabilised by cytostatic factor (CSF)- suppressed by calcium levels and destroy cyclin B
Acting via the anaphase-promoting complex/cyclosome (APC/C) a ubiquitin (E3) ligase- degraded securin so seperase can cleave the scc1 subunit of the cohesin protein complex that hold the sister chromatids together so they can be pulled apart by the microtubules Completion of meiosis 2
Block to polyspermy-
fast block- electrical- membrane depolarisation
Slow block- the cortical reaction, triggered by increase in Ca (granules release enzymes that induce the zona reaction (cleavage of ZP2 by ovastacin protease) so sperm can no longer pentrate
Loss of Juno- shed from the membrane with the cortical granules, undetectable within 40mins of fusion
What are the sperm and egg contributions to the resulting blastocyst?
Sperm- haploid male genome (sex of baby) and centriole- forms the spindle for the first cell division
Oocyte- Haploid female genome, cytoplasm, all organelles, mitochondria (maternally inherited)
What is the Zygotic/Pronucleate stage?
Decondensation of sperm DNA- protamine/histone exchange
Male and female pronuclei replicate their DNA, migrate towards each other-guided by sperm aster (microtubles radiating from the centrosome)
Describe syngamy
After 18-24 hours, pronuclear membranes breakdown and the chromatin intermixes
Nuclear envelope reforms around zygote nucleus
End of fertilisation and start of embryogenesis
Describe transport of the embryo to the uterus
Increased progesterone:oestrogen ratio relaxes musculature in the female reproductive tract- isthmic sphincter
Mostly transported via cillia
Describe the zygote development to implantation
Zygote cleaves to form two blastomeres- 8 cell stage- totipotent, pre-implantation genetic diagnosis.
Compaction- inside-outsidepolarity satrts to develop with fluid absorption- formation of intracellular junctions between the outer trophoblast cells via Na/K ATPases Morula- 16-32 cells- near end of the uterine tube
Each cell division yields smaller cells as there is not cytoplasm synthesis and the ZP is still in place
Blastocoel- late day 4/5, distinct inner cell mass (embryonic pole) a single cell trophoblast layer
Hatching- Late day 6, blastocyst expands out of hole in ZP at the abembryonic pole –>Implantation
Describe the endometrium
Uterus lining has 2 layers:
basal layer- attached to the myometrium (the muscular layer)- remains intact during menstruation
Functional layer- undergoes proliferation and shedding- reconstituted out of the underlying basal layer
Glandular epithelial extensions penetrate into the basal layer (stroma) is rich in blood vessels- the spiral arteries and a venous outflow system
Briefly describe menstruation
Follicular phase- proliferation in first 14 days after menstruation
Luteal phase- after ovulation, the ovaries produce progesterone which synthesis of secretory material by the glands for the blastocyst
Receptive endometrium- stromal thickening, fully developed spiral arteries, cellular secretions by the glands, oestrogen primed
Describe ectopic pregnancy
1/100 pregnancies implantation not in uterus
Epithelium provides enough vasculature to support early development by results in rupture of the vessels- life threatening to mother risk factors- pelvic inflammatory disease, tubal surgery, failed steralisation, IUD in place
Describe twins
Monozygotic vs dizygotic twins
increased risk of dizygotic twins with maternal age and fertility treatments
increase risk of monozygotic twins with longer embryo in vitro culture
Monochorionic- risk of twin-twin transfusion syndrome- blood inbalance
Monoamniotic- umbilical cord
Risks: baby- premature birth, low birth weight, cerebral palsy Mother- pre-eclampsia, hyertension, gestational diabetes, mortality
