Fertilisation and the Luteal Phase Flashcards
What happens to ejaculated sperm?
how does cervical mucus let sperm pass? + also what can the sperm do inside the cervix?
when does fertilisation occur VS how long can sperm stay alive for ?
When a male ejaculates, seminal fluid coagulates to prevent sperm loss, but later liquefies to allow sperm to swim to cervix.
Sperm swims up runny cervical mucus. Sperm can also inhabit cervical crypts, which may form a reservoir
Some evidence of thermotaxis= sperm moves towards warmer temps.
Fertilization occurs within 24-48 hrs after ejaculation, but sperm can live for up to 5 days.
How is the sperm attracted to the oocyte? + what happens to the sperm en route to oocyte & cause of this?
Cumulus oocyte complex releases chemoattractants, which attract the sperm towards the egg.
En route, sperm undergoes hyperactivation, = flagellum beat with increased frequency & amplitude
This is due to Ca influx thru CatSper channels in flagellum
2 ways sperm capacitation can occur?
When does the acrosome reaction occur and what happens?
Biochem rearrangement of surface glycoprotein & membrane composition must occur before acrosome reaction!
This capacitation is achieved by removing sperm from seminal fluid. Uterine/ tubal fluid may also have capacitation factors!
Acrosome reaction occurs when acrosomal sperm head fuses w zona–cumulus complex, releasing hyaluronidases that cut through the complex
Acrosin bound to the inner acrosomal membrane digests ZP so sperm can enter
What happens to primary oocyte, follicle & COC in ovulation? + what causes this
what happens to theca & granulosa cells after ovulation?
LH spike causes resumption of meiosis & ovulation.
This converts primary oocyte to the secondary oocyte + 1st polar body.
Follicle basement membrane breaks, so blood pours into the middle
Cumulus oocyte complex is extruded out & picked up by the fimbriae of the uterine tube(fallopian tube)
Theca & granulosa cells become mixed after ovulation & the empty follicle= CL + releases Pg!
What is the effect of oestrogen vs Pg on endometrium?
what does Pg do to cilia in uterine tubes?
What happens if there is no pregnancy?
Estrogen: maintains endometrium in luteal phase (causes proliferation in follicular phase).
Pg: makes endometrium secretory & receptive to implantation. Suppresses cilia in uterine tubes once oocyte has passed
No🤰: CL lives for 14 days + the fall in CL-derived steroids causes inter-cycle rise in FSH.
Cell death occurs, vasculature breakdown, CL shrinks -> corpus albicans
During ovulation, a cumulus-oocyte complex (COC) is released by the dominant follicle in the ovary
5 things the COC contains?
Cumulus oophorus: protective layer derived from GCs
Corona radiata: innermost cumulus cell layer, is in contact w ZP - Formed from GCs adhering to oocyte before it leaves the follicle
ZP: glycoprotein layer secreted by oocyte. Becomes impenetrable after cortical reaction (stops polyspermy).
Cortical granules: contain enzymes, found below the ZP. When sperm enters, they burst and release peroxidases, hardening ZP (cortical reaction)
1st polar body: half of the chroms. from the uneven division that occurs in meiosis I -eventually expelled from Oocyte
When sperm comes into contact with the zona-cumulus complex –> acrosome reaction occurs.
6 steps of this reaction?
Acrosome releases hyaluronidase, breaking down cumulus
Sperm now bind to ZP via ZPr (adhesion molecules)
Sperm + oocyte membranes fuse, sperm tail breaks down.
Sperm head taken into oocyte by phagocytosis
Phospholipase zeta (PLZ) is activated by basal Ca2+ inside oocyte & converts PIP2–> IP3 + DAG. IP3 -> intracellular Ca2+ release
Ca2+ wave sweeps around egg; release of proteases, peroxides & hyaline prevents polyspermy= cortical reaction
how many chromosomes does oocyte have after meiosis 1? + how are they arranged
2 steps of first part of syngamy?
After meiosis I, the oocyte has 23Chr, but 2 copies of each arranged as sister chromatids
PLZ activation increases Ca–> causes cortical reaction and meiosis II, separating the sister chromatids
1 copy of chromosome ends up in oocyte, the other copy is expelled in the 2nd polar body
Sperm nuclear membrane breaks down, chromatin decondenses & chromosomes separate
What happens in the 2nd part of syngamy, 4-7hrs after sperm penetration?
Pronuclei fuse (true fertilisation)
Mitosis is completed, zygote becomes a 2 cell embryo Then divides by cleavage (rapid division w/o getting bigger) until compaction occurs, forming a blastocyst
Blastocyst -> ICM, blastocoel & trophoblast
Give a timeline of Oocyte to Embryo Progression
day: 0, 2, 4, 5, 7
