FROM GAMETE TO EMBRYO Flashcards
Follicular phase
regression of corpus luteum to ovulation
Follicles are present
Dominated by oestrogen
Luteal phase
Ovulation to regression of corpus luteum
Corpus lutea are present
Involves preparation for pregnancy
Dominated by progesterone
Is the oocyte attached to the follicular wall in tertiary follicle?
Yes, it detaches during the antral stage of maturation
LH causes
Causes the follicular cells to become compromised and start to be transformed into luteal cells
Hence inducing ovulation
How does ovulation occur?
Oestrogen levels are high
Triggers surge release of GnRH
Releases lots of LH
LH causes the follicular cells to become compromised and start to transform into luteal cells
At the same time as the presence of LH, oestrogen causes muscle constriction which combined with the high presence of follicular fluid causes the follicle to burst and release its egg
Egg will hopefully be picked up by oviduct
Corpus haemorrhagicum
A red spot on the ovary where an ovulation has occurred because the follicle has burst and capillaries have been broken and there is blood remaining on the ovary - rare to see
Regulation of follicular growth
Recruitment phase:
Small follicle being recruited into pool of follicles where they can start to become receptive to FSH
Release of GnRH causes preferential release of FSH - Follicles continue to grow despite negative feedback loop as they are exposed to FSH and other local factors that promote growth
Selection phase:
Follicles are now producing a lot of oestrogen - at the same time they start to produce another hormone inhibin which switches the preferential release of gonadotropins from FSH to LH as it inhibits release of FSH
Dominance phase:
Follicles are now very big - oestrogen reaches threshold level - targets surge centre of hypothalamus - huge release of gonadotropins, preferentially LH because inhibin is blocking LH - LH then triggers ovulation
When does the oocyte exude its first polar body?
At the time of ovulation
2n chromosomes inside polar body & 2n inside oocyte
When does the oocyte exude its second polar body?
Introduction of sperm causes the release of a second polar body
( 1n inside polar body & 1n remains in oocyte)
In microscopy if you see an oocyte with 2 polar bodies what does this tell you?
That the egg has been fertilised
Granulosa and theca cells release local hormones that help the fertilised egg to
mature
follicles continue to grow after ovulation - become corpus lutea
Formation of the corpus luteum
Antral follicle full of follicular fluid
Basement membrane starts to breakdown due to exposure to LH surge which signals for the breakdown of the walls of the follicle
Eventually due to muscle contractions (oestrogen), pressure of follicular fluid and compromised follicular walls from LH surge - it breaks down altogether
Theca and granulosa cells go form being nicely differentiated to being all mushed up together
Follicle cells convert to corpus lutea cells
Goes from predominantly oestrogen production to progesterone production
Luteolysis
Break down of the corpus luteum:
Progesterone feeds into the uterus which causes the uterus to start producing PGF2alpha (prostaglandin F2 alpha)
Series of things in positive feedback loop cause more and more PGF2alpha to be released which then feeds back to ovary and causes the breakdown of corpus luteum
If there is an embryo in the uterus blocks this pathway - PGF2alpha is not produced and corpus luteum remains
Acrosomal cap (sperm head)
Contains lots of enzymes which means that the sperm can break into the egg
Why do sperm have flagella?
Flagella movement keeps them suspended in media so that the contractions of the female reproductive tract can move them up to where the egg is
Once they reach the egg the flagella start to move in a different way - they start to thrash which is thought to help keep the acrosomal cap pressed against the egg so it can break its way in
Where does sperm mature (motile)?
Towards the end of the epididymis
Sperm journey (male system only)
Sertoli cells
Seminiferous tubules
Rete tubules
Efferent ducts
Epididymis
Ductus deferens
Pelvic urethra
Penile urethra
Sperm journey (female system only)
Sperm is usually deposited in the vagina or cervix
Lots of sperm is lost due to retrograde loss (falls out of female) and phagocytosis
Cervix blocks abnormal sperm from getting through - “Privileged pathways”
Finally sperm make it to the uterus - More maturation occurs called capacitation and more phagocytosis (this is why we need so much sperm to be deposited)
Eventually, due to contractions of the female repro tract the sperm arrive at the oviduct - meet the oocyte and hopefully fertilisation will occur
Zona pellucida
Shell of the egg that sperm has to break through
Perivitelline space
Contains enzymes that help to stop more than one sperm from entering the egg
What causes the zygote to move down the oviduct and start dividing?
Progesterone produced by corpus luteum
Why is it important that corpus luetum is being formed whilst fertilisation is occurring?
Progesterone causes zygote to start moving down oviduct and start dividing
Progesterone also gets the uterus ready for implantation before the zygote arrives
If embryo doesn’t reach uterus in time - female will go into next cycle and embryo would be lost
Blastocyst stage of embryo development
Cavity starts to form
Start to see cell differentiation
Inner mass (will become foetus)
All other cells will become support tissues (i.e. placenta & amnion)
Attachment to the uterus will occur in some species at this stage 5-8
The stages of embryo development, in order, are:
Zygote, 2 cell, 32-64 cell, Morulae, Blastocyst
True or false:
Prior to luteolysis, PGF2α and oxytocin receptor formation work in a positive feedback loop
True
Describe the key differences in the gross anatomical structure of the uterus and
cervix of the bitch (female dog) and sow (female pig).
Uterine horns: Pig - Long, curl over, with “wavy” arrangement to accommodate large litter size
Dog- Relatively long, extend up
in “Y” shape towards
kidneys
Cervix:
Pig - Corkscrew arrangement
Dog - normal arrangement
Placentation:
Pig - diffuse
Dog - Zonary
