folliculogenesis Flashcards
what are the 2 parts of the ovary?
cortex and medulla
what are the functions of the 2 sections of the ovaries?
cortex = gametogenic
medulla = supportive
what differences are there between species and the arrangement of the 2 regions of the ovaries
bovine, ovine and porcine have the medulla on the inside.
equines have the cortex on the inside.
what is folliculogenesis?
the development of ovarian follicles eligible for ovulation.
what is oogenesis?
development of primary egg cells into a mature ovum which Is competent for fertilisation.
what are the 2 stages of oogenesis?
prenatal.
after puberty ( during each cycle)
oogenesis occurs simultaneously with folliculogenesis.
what is the aim of prenatal oogenesis?
to maximise the gametes, meaning to get a large pool of primary oocytes when born
what are the stages of prenatal oogenesis?
Primordial germ cells (2N) (2N = diploid)
undergo mitosis
Oogonia (2N)
undergo mitosis again
Primary oocyte (2N)
undergo meiosis, prophase 1 begins
Primary oocyte (2N)
nothing more can happen until puberty
meiotic inhibitors cause nuclear arrest, prevent any more meiosis
what occurs during post-puberty oogenesis ( each cycle)
cytoplasmic growth from the oocyte formation of Zona pellucida removes the meiosis inhibitors so meiosis can occur again
causing a secondary oocyte (1N) = Haploid.
what occurs during post-puberty oogenesis ( each cycle)
cytoplasmic growth from the oocyte formation of Zona pellucida removes the meiosis inhibitors so meiosis can occur again ( LH surges)
causing a secondary oocyte (1N) = Haploid.
what are the processes in the post-puberty oogenesis cycle?
a primary oocyte (2N) turns into a secondary oocyte (1N) via meiosis.
a polar body is added
the secondary oocyte ( after fertilisation) becomes a mature ovum via meiosis 2
second polar body is added
what are the 4 stages of oocyte maturation
prenatal mitotic divisions
nuclear arrest
cytoplasmic growth
resumption of meiosis
folliculogenesis is essential to support these processes
what are the first stages of folliculogenesis?
An oogonia has no follicle.
The primary oocyte will have granulosa cells around it and a primordial follicle
A primordial follicle is immature and flattened granulosa cells
what happens next in folliculogenesis, after the primordial follicle?
Still on the primary oocyte, a primary follicle develps
the primary follicle consists of cuboidal granulosa cells
what occurs after the primary follicle is formed?
Still on the primary oocyte, the number of granulosa cells increases
theca cells develop
and a secondary follicle is developed.
The secondary follicle:
2 or more layers of granulosa cells
a small number of theca cells
Zona pellucida has an initial formation
what occurs after a secondary follicle has developed?
on the primary oocyte, theca interna and theca externa have developed
there are lots of granulosa cells
there is now an antrum
this is what the tertiary follicle
what occurs after the tertiary follicle is produced?
the oocyte has developed into a secondary oocyte.
the antrum is a lot bigger
developing into a preovulatory follicle
Graafian follicle
Mature
when does each process take place?
prenatal pool
oogonia
primordial follicle
pre and post-puberty: not gonadotropic hormone dependent:
primary follicle
secondary follicle
post-puberty: gonadotropic hormone-dependent, throughout the oestrous cycle:
tertiary follicle
preovulatory follicle
what are the antral follicle dynamics?
recruitement
selection
dominance
atresia (over 90% of follicles)
what does growing follicles secrete?
secrete oestradiol
which increases as the follicle grows
what are the 3 hormones responsible for folliculogenesis?
follicle-stimulating hormone (FSH)
luteinising hormone (LH)
oestradiol from follicle helps to control
hormone levels during folliculogenesis?
recruitment = ++ FSH and +LH
selection = ++ LH and + FSH
dominance = +++LH and + FSH
what is the role of granulosa cells?
FSH receptors
use androstenedione to produce oestradiol
(oestrogen)
what is the role of theca cells?
LH receptors
Use cholesterol to produce androstenedione
where does ovulation occur in the mare?
in the ovulation fossa
where does ovulation occur in other animals?
in the ovarian surface
how does ovulation occur?
triggered by the preovulatory surge of LH
LH causes:
increase bloodflow
ovarian contractions
connective tissue destruction
this increases follicular pressure and weakened and thinned follicle walls
leading to ovulaiton
what is ovulation?
ovulation is the release of the ovum
for the ovum to undergo fertilisation and meiosis 2
and follicular fluid
what occurs after ovulation?
corpus luteum forms post ovulaiton
first, corpus Haemorrhagicum forms
follicle walls collapse
theca, granulosa and connective tissue cells mix
blood vessels rupture
small blood clot in the cavity
what happens next after the initial Corpus Haemorrhagicum forms?
corpus luteum will increase in size
Luteinisation of theca interna and granulosa cells
More structure to the luteal tissue than in early Corpus Haemorrhagicum
Active corpus luteum = red/ orange / yellow
produces progesterone
cholesterol = precursor
what happens next after the initial Corpus Haemorrhagicum forms?
corpus luteum will increase in size
Luteinisation of theca interna and granulosa cells
More structure to the luteal tissue than in early Corpus Haemorrhagicum
Active corpus luteum = red/orange/yellow
produces progesterone
cholesterol = precursor
what is the final stage of corpus luteum formation?
luteolysis breaks down the corpus luteum
corpus albicans are formed
no glandular tissue
scar tissue
light yellow / white
