BY
MUNEEB HASAN KHAN
FEMALE REPRODUCTIVE CYCLES
OVARIAN
CYCLE
“Monthly
changes resulting in maturation and release of an oocyte and its supporting
structures in ovary that cease at menopause
during the climacteric.”
1.
Follicular phase:(pre-ovulatory
development of follicles that prepares an oocyte for release).
·
Requires FSH throughout and LH in final stages.
·
Involves growth and differentiation of primary
oocyte e.g. formation of microvilli in oolemma and cortical
granules in cytoplasm.
·
Zona
pellucida is secreted into perivitelline space by follicle &oocyte. Consists of a meshwork of filaments with
pores. Made of 3 glycoproteins i.e. ZPA, ZPB, ZPC.
·
Connective tissue around growing follicle differentiates into theca folliculi, consisting of 2 layers:
o Theca
externa – capsule-like
fibrous outer layer.
o Theca
interna – inner vasculoglandular layer that
produces:
Ø
Angiogenesis
factor that promotes growth of blood
vessels to provide nutrition Follicular fluid
Ø
Estrogen + androgens that are converted to estrogen by interstitial glands of ovary
•
By action of FSH, a pool of 15-20 primordial follicles is recruited
to become growing
follicles, which increase in size and develop
as follows:
a)
Primary
Follicle: Follicular cells change from flat to
cuboidal/columnar, and divide to form a stratified layer of cells i.e granulosa around oocyte, that rest on a basement membrane and produce estrogen.
b) Secondary
Follicle:
Ø Formation of crescent-shaped space antrum by accumulation of follicular
fluid (from ovary interstitium and theca
interna) between granulosa cells.
Ø Eccentric primary oocyte buried in a
mound of granulosa i.e. cumulus
oophorous.
Ø Interdigitations
between cellular processes of
granulosa and microvilli on oolemma, forming a
transfer
channel for nutrients across zona pellucida.
c)
Tertiary
(Graafian) Follicle: Large, fully
mature, end-stage follicle with enlarged antrum & secondary oocyte ready
for ovulation.
2. Ovulatory phase: (concerns
ovulation and the changes that occur in ovary after it).
•
LH + FSH cause Graafian follicle to undergo a growth spurt, producing a cystic bulge on ovary surface, which develops an
avascular spot i.e. stigma
•
In mid-cycle, a high estrogen level in blood causes a surge in LH
production that causes:
a)
Resumption of 1st meiotic division resulting in
formation of secondary
oocyte, which detaches from interior of
follicle with zona pellucida and a portion of cumulus oophorous i.e. corona radiata.
b)
Ovulation
- contraction of smooth muscle in
theca externa by prostaglandins, leads to increased intrafollicular
pressure that causes the stigma to swell and
burst – expelling secondary oocyte (with its ZP and CR) as well as follicular
fluid.
o LH influence
causes collapsed walls of follicle & theca to develop into corpus luteum, a gland that secrets progesterone (and some estrogen) to prepare endometrium for implantation. It
has 2 fates:
a)
Corpus
luteum graviditis – when oocyte is
fertilized and pregnancy occurs; maintained by human
chorionic gonadotrophin from
blastocyst. Functionally active for 1st 20 weeks, after which role
of progesterone production is assumed by placenta.
b) Corpus luteum
of menstruation– when oocyte
remains unfertilized. Cells degenerate by luteolysis in 10-12 days, forming
scar tissue i.e. corpus albicans.
UTERINE CYCLE (MENSTRUAL CYCLE)
“Monthly
changes occurring in uterus in correspondence with events of ovarian cycle,
that prepare the endometrium for implantation of a blastocyst.”
|
Phase |
Trigger |
Duration (days) |
Features |
|
Menstrual |
End result of
ischemic phase |
4-5 |
·
Menses is discharged from vagina, containing: a.
20-80ml of blood that bleeds from torn spiral arteries & pools
under endometrium then breaks out through surface epithelium b.
Sloughed –off cellular debris of entire functional layer (all of
compact + most of spongy layer) of endometrium, resulting in its thinning. |
|
Proliferative/
Follicular |
Growth of ovarian follicles and estrogen secreted by them |
|
·
Regeneration of endometrium from the remnants of its spongy &
basal layers, restoring its thickness, water content, vascularity and
surface epithelium. ·
Spiral arteries elongate. ·
No. of uterine glands increases. |
|
Progestational/ Luteal/ Secretory |
Formation and growth of corpus Luteum & progesterone secreted by it |
13 |
·
Further thickening of endometrium under hormonal influence and
increased fluid in C.T. ·
Glands become wide, tortuous and saccular and produce
glycogen-rich secretions. o Spiral arteries grow into superficial compact
layer and become increasingly coiled. ·
Large venous spaces (lacunae) develop and from direct Av anastomoses. |
|
Ischemic |
Non-fertilization of oocyte - causing degeneration
of corpus luteum and decrease in levels of estrogen &
progesterone |
1 |
·
Shrinkage of endometrium due to loss of interstitial fluid. ·
Stoppage of glandular secretions. o Constriction of spiral
arteries, leading to pale appearance. ·
Eventually leads to venous stasis in lacunae & patchy ischemic
necrosis in superficial tissues. |
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