Fertilisation and the Luteal Phase Flashcards
how do the sperm reach the uterus? how is slow release controlled?
deposited in coagulated sperm at the base of the cervix
heat of the vagina causes activation of the sperm - increased frequency and amplitude to the tails thrashing
swim through the cervical mucous - removes the amorphic and dead sperm on the way - removes the seminal fluid
they are then deposited in cervical crypts which allow the slow release into the uterus (acts as a resivour)
what happens to the sperm when it reaches the uterus?
it is guided towards the egg via chemotaxisis and thermotaxisis – also by currents set up by the uterine and tubular cilia
biochemical rearrangement of glycoproteins - makes the membrane more fluid - takes 6 hrs
what changes occur as the sperm become close to the egg?
CatSperm channels open - causing hyperactivity of the sperm - swims towards the sperm
Sperm fuses to the ZP3 receptors n the zona pellucida - triggering completion of Meiosis II and production of the second polar body
what is the acrosome reaction?
once the sperm has bound to the ZP3 receptors - acromsomal enzymes are released - digest through the cumulus oophorus and bona pelucida - allowing the sperm to bind to the plasma membrane of the oocyte
what happens once the sperm and egg have fused their membranes?
there is a phospholipase C messenger system in the sperm - causes activation of intracellular calcium channels in the oocyte - there is a Ca2+ spike which spreads through out the cell – leads to the CORTICAL REACTION
what is the cortical reaction?
Cortical granules release proteases- which cut the matrix ties between the ZP and oocyte
Peroxide release causes the ZP to harden
hyaluronin causes the swelling of the ZP - so that it moves away from the zygote
4-7 hours after the meeting of the sperm and egg - what happens?
Syngamy
haploid nuclei become surrounded by nuclear membrane - forming pronuclei
prepare for mitosis to become the embryo
what are the time scales for development of the zygote? when does it implant into the uterus?
4-8 cell morula by day 4
100+ blastocyst by day 5
implants by day 7 becoming the embryo
how is the corpus luteum formed?
the LH spike causes the completion of meiosis I and extrusion of the secondary oocyte from the ovary
Theca and granulose cells become mixed and form the corpus luteum - this produces progesterone for 14 days
there is also cytokine release meaning the follicular fluid is extrude
how is the corpus luteum lost or retained?
it has a life span of 14 days
if fertilised - the endometrium releases hCG - binds tot eh LH receptors in the corpus luteum - causing it to remain in situ and continue producing progesterone
if there is no hCG - the the corpus luteum regresses after 14 days
how is IVF carried out?
capacitated sperm are mixed with the egg - left over night
able to tell if the egg has been fertilised as it will be two pronuclei and two polar bodies
culture the zygote in the lab for 5 days – 100 cell blastocyst - then implanted in the endometrium
what is capacitation?
removal of cellular debris, seminal fluid and amorphic sperm via the cervix
movement of the sperm towards the oocyte - CatSperm channel activation - causing hyperactivity
biochemical rearrangement of the surface proteins allowing the membrane to become more fluid
how long does capacitation take?
6 hours
what is the role of the progesterone produced by the corpus luteum?
makes the endometrium secretory and ready for implantation
dediffernetaion of the cillia once the egg has past - stop beating
cervical mucous becomes more viscous
endothelium becomes more vascularised - easier to implant
what occurs when the corpus luteum regresses?
fall in progesterone causes a rise in FSH and LH
cell death occurs - vasculature breasks down - prostaglandin release means arteriole constriction - necrosis of tissue
sudden vasodilation classes shedding of the endometrium via mensturation
