Fertilisation And Luteal Phase Flashcards
Capacitation
molecular changes in sperm to enable the acrosome reaction
Acrosome reaction
Reaction in sperm as approaching the egg releasing enzymes
Luteal phase
latter phase of the menstrual cycle after ovulation
Corpus luteum
a hormone-secreting structure that develops from a follicle after ovulation
Cortical reaction
release of cortical granules from the egg at fertilisation, preventing polyspermy
Syngamy
the fusion of two cells, or of their nuclei, in reproduction
Pronuclei
gametic nucleus after meiosis but before fusion that forms of the nucleus of the zygote
Blastocyst
5 day old embryo with fluid filled cavity
Ejaculated Sperm
Ejaculated semen is coagulated
Prostatic and seminal vesicle secretions comprise seminal fluid which coagulates - prevents loss, later liquefies.
Movement through cervical mucus removes seminal fluid, abnormally morphological sperm and cellular debris.
Sperm passes into cervix
Cervical mucus is less viscous in the absence of progesterone allowing sperm to pass.
Sperm can inhabit cervical crypts which may form a reservoir.
Some evidence of thermotaxis, but mechanism not yet elucidated.
Fertilisation typically within 24-48 hours but sperm have been recovered alive after 5 days.
Journey to the Egg
Passage through uterus not well understood, currents set up by uterine or tubal cilia may have a role.
Chemo-attractants released from the oocyte cumulus complex may attract the sperm.
Sperm become hyperactivactivated.
Forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via CatSper channels.
Sperm capacitation & acrosome reaction
Capacitation is partly achieved by removing the sperm from the seminal fluid, also uterine or tubal fluid may contain factors which promote capacitation.
Biochemical rearrangement of the surface glycoprotein and changes in membrane composition must occur before the acrosome reaction can occur.
Acrosome reaction occurs in contact with the zona –cumulus complex; 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.
Ovulation
LH spike causes resumption of meiosis and ovulation. Converts the primary oocyte to secondary oocyte plus 1st polar body.
Basement membrane breaks so blood pours into the middle.
Oocyte cumulus complex extruded out and caught by fimbrae of uterine tube.
Theca and granulosa become mixed and the empty follicle is known as the
corpus luteum. It produces progesterone in the luteal phase.
Luteal/Secretory Phase
Progesterone
Makes the endometrium secretory and receptive to implantation.
Supresses cilia in uterine tubes once oocyte has already passed.Makes cervical mucus viscous again to prevent further sperm penetration.
Estrogen
Helps to maintain endometrium in luteal phase (causes proliferation in follicular phase).
Demise of the Corpus Luteum
If fertilisation does not occur, CL has an inbuilt finite lifespan of 14 days.
Regression of CL essential to initiate new cycle.
Fall in CL-derived steroids causes inter-cycle rise in FSH.
Cell death occurs, vasculature breakdown, CL shrinks. Over time it becomes a corpus albicans.
CL rescued in pregnancy by hCG from embryo binding to its LH receptors. CL continues to produce progesterone and maintain endometrium.
Menstrual cycle achieves…
Selection of a single follicle and oocyte.
Regular spontaneous ovulation.
Correct haploid number of chromosomes in the oocyte by completing meiosis I and beginning meiosis II.
Cyclical changes in the cervix and uterine tubes, to enable egg transport and sperm access.
Preparation of the endometrium of the uterus to receive the fertilised egg.
Support of the implanting embryo and endometrium by corpus luteum progesterone.
Initiating a new cycle if fertilisation does not occur.
