Post on 14-Apr-2018
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Menstrual cycle
Physiology
Dr. Atef Abood
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Ovaries
Primordial follicle one layer of squamouslike follicle
cells surrounds the oocyte
Primary follicle two or more layers of cuboidalgranulosa cells enclose the oocyte
Secondary follicle has a fluid-filled space betweengranulosa cells that coalesces to form a centralantrum
Graafian follicle secondary follicle at its mostmature stage that bulges from the surface of theovary
Ovulation ejection of the oocyte from the ripeningfollicle
Corpus luteum ruptured follicle after ovulation
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Oogenesis
At puberty, one activated primary oocyte producestwo haploid cells
The first polar body
The secondary oocyte
The secondary oocyte arrests in metaphase II and isovulated
If penetrated by sperm the second oocyte completes
meiosis II, yielding: One large ovum (the functional gamete)
A tiny second polar body
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Ovarian Cycle
Monthly series of events associated with the
maturation of an egg
Follicular phase period of follicle growth
(days 114)
Luteal phase period of corpus luteum
activity (days 1428)
Ovulation occurs midcycle
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Follicular Phase
This phase is under the effect of FSH and to a little extent LH.
It starts by activation of several; primordial follicles.
At the 6th day only one follicle starts to grow rapidlybecoming a dominant follicle called the Graffian follicle while
the others regress. The primordial follicle, directed by the oocyte, becomes a
primary follicle
Primary follicle becomes a secondary follicle The theca folliculi and granulosa cells cooperate to produce estrogens
The zona pellucida forms around the oocyte The antrum is formed
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Follicular Phase (Cont.)
The secondary follicle becomes a vesicular
follicle
The antrum expands and isolates the oocyte and
the corona radiata
The full size follicle (vesicular follicle) bulges from
the external surface of the ovary
The primary oocyte completes meiosis I, and thestage is set for ovulation
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Ovulation
Ovulation occurs when the ovary wall ruptures
and expels the secondary oocyte
Mittelschmerz a twinge of pain sometimes
felt at ovulation
1-2% of ovulations release more than one
secondary oocyte, which if fertilized, results in
twins
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Luteal Phase
After ovulation, the ruptured follicle collapses,granulosa cells enlarge, and along with internalthecal cells, form the corpus luteum
The corpus luteum secretes progesterone and
estrogen If pregnancy does not occur, the corpus luteum
degenerates in 10 days, leaving a scar (corpusalbicans)
If pregnancy does occur, the corpus luteum produceshormones until the placenta takes over that role (atabout 3 months)
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Uterine (Menstrual) Cycle
Series of cyclic changes that the uterineendometrium goes through each month in responseto ovarian hormones in the blood
: Menstrual phase Days 1-5
uterus sheds all but the deepest part of the endometrium
Days 6-14: Proliferative (preovulatory) phaseendometrium rebuilds itself
Days 15-28: Secretory (postovulatory) phase
endometrium prepares for implantation of theembryo
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Endometrium
Has numerous uterine glands that change in length
as the endometrial thickness changes
Stratum functionalis:
Undergoes cyclic changes in response to ovarian hormones
Is shed during menstruation
Stratum basalis:
Forms a new functionalis after menstruation ends
Does not respond to ovarian hormones
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Proliferative phase
Duration: 2 weeks
Thickness: 0.5mm 5mm
Under the influence of estrogens from the developing
follicle, the endometrium increases rapidly in thickness
from the fifth to the fourteenth days of the menstrual
cycle.
As the thickness increases, the uterine glands are
drawn out so that they lengthen, but they do notbecome convoluted or secrete to any degree. These
endometrial changes are also called the preovulatory or
follicular phase of the cycle.
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Secretory phase
Duration: 2 weeks
Thickness: 5-6mm After ovulation, the endometrium becomes more
highly vascularized and slightly edematous underthe influence of estrogen and progesterone from
the corpus luteum. The glands become coiled and tortuous, and they
begin to secrete a clear fluid. Consequently, thisphase of the cycle is called the secretory or luteal
phase. Late in the luteal phase, the endometrium, like the
anterior pituitary, produces prolactin, but thefunction of this endometrial prolactin is unknown.
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Menses
If fertilization does not occur, progesterone levels fall,depriving the endometrium of hormonal support
Spiral arteries kink and go into spasms and endometrialcells begin to die
The functional layer begins to digest itself
Spiral arteries constrict one final time then suddenlyrelax and open wide The rush of blood fragments weakened capillary beds
and the functional layer sloughs Nonclotting menstrual blood mainly comes from artery
(75%) Interval: 24-35 days (28 days). duration: 2-6 days. the
first day of menstrual bleeding is consideredy by day 1 Shedding: 30-50 ml
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Menstruation
Menstrual blood composition
is predominantly arterial, with only 25% of theblood being of venous origin. It contains tissuedebris, prostaglandins, and relatively large amountsof fibrinolysin from endometrial tissue. Thefibrinolysin lyses clot, so that menstrual blood doesnot normally contain clots unless the flow isexcessive.
The usual duration: 3-5 days, but flows as short as 1day and as long as 8 days can occur in normal women.
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Menstruation
The amount of blood lost may range normally
slight spotting to 80 mL; the average amount lost
is 30 mL.
Loss of more than 80 mL is abnormal. Obviously,
The amount of flow can be affected by various
factors, including the thickness of the
endometrium, medication, and diseases that
affect the clotting mechanism. After
menstruation, a new endometfrom rium
regenerates from the stratum basale.
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Menses (Cont.) When the corpus luteum regresses, hormonal
support for the endometrium is withdrawn.
The endometrium becomes thinner, which adds tothe coiling of the spiral arteries. Foci of necrosis
appear in the endometrium, and these coalesce. There is in addition spasm and then necrosis of the
walls of the spiral arteries, leading to spottyhemorrhages that become confluent and produce
the menstrual flow.
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Menses (Cont.)
The vasospasm is probably produced by locally
released prostaglandins. There are large
quantities of prostaglandins in the secretory
endometrium and in menstrual blood, and
infusions of PGF2 produce endometrial necrosisand bleeding.
One theory of the onset of menstruation holds
that in necrotic endometrial cells, lysosomalmembranes break down, with the release of
enzymes that foster the formation of
prostaglandins from cellular phospholipids.
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Changes of other genital organs
Cervix
During follicular phase estrogen causes mucus to be
thin,clear, watery and the the midcycle a drop can be
stretched into a long, thin thread that may be 8-12cm or more in length. In addition, it dries in an
arborizing, fern-like pattern
During luteal phase progesterone causes mucus to
be thick, opaque, tenacious and cellular and loss of
ability to form fern like appearance.
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Changes of other genital organs
Cyclic changes in the vagina
Under the influence of estrogens, the vaginal
epithelium becomes cornified,
Under the influence of progesterone, a thick
mucus is secreted, and the epithelium proliferates
and becomes infiltrated with leukocytes.
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Changes of other genital organs
Cyclic changes in the breast Estrogens cause proliferation of mammary ducts.
progesterone causes growth of lobules and alveoli.
The breast swelling, tenderness, and painexperienced by many women during the 10 days
preceding menstruation are probably due to
distention of the ducts, hyperemia, and edema of
the interstitial tissue of the breast. All these changesregress, along with the symptoms, during
menstruation.
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Establishing the Ovarian Cycle
During childhood, ovaries grow and secrete
small amounts of estrogens that inhibit the
hypothalamic release of GnRH
As puberty nears, GnRH is released; FSH and
LH are released by the pituitary, which act on
the ovaries
These events continue until an adult cyclic
pattern is achieved and menarche occurs
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Hormonal Interactions During the Ovarian
Cycle
Day 1 GnRH stimulates the release of FSH and LH
FSH and LH stimulate follicle growth and maturation, and low-level estrogen release
Rising estrogen levels: Inhibit the release of FSH and LH
Estrogen levels increase and high estrogen levels have apositive feedback effect on the pituitary, causing a suddensurge of LH
The LH spike stimulates the primary oocyte to completemeiosis I, and the secondary oocyte continues on tometaphase II
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Hormonal Interactions During the Ovarian
Cycle
Day 14 LH triggers ovulation
LH transforms the ruptured follicle into a corpus
luteum, which produces inhibin, progesterone, and
estrogen These hormones shut off FSH and LH release and
declining LH ends luteal activity
Days 26-28 decline of the ovarian hormones
Ends the blockade of FSH and LH
The cycle starts anew
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Summary of hormonal control of the cycle
In an important sense, regression of the corpus luteum
(luteolysis) starting 3-4 days before menses is the key to themenstrual cycle. PGF2 appears to be a physiologic luteolysin,
but this prostaglandin is only active when endothelial cells
producing ET-1 are present. Therefore it appears that at least in
some species luteolysis is produced by the combined action ofPGF2
and ET-1. In some domestic animals, oxytocin secreted by
the corpus luteum appears to exert a local luteolytic effect,
possibly by causing the release of prostaglandins. Once
luteolysis begins, the estrogen and progesterone levels fall andthe secretion of FSH and LH increases. A new crop of follicles
develops to start a new cycle
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Menstrual Abnormalities
Anovulatory cycle
Amenorrhea
Primary amenorrhea: period never occurs
Secondary amenorrhea stop of the cycle after normal
periods have occurred. Menorrahgia: excessive bleeding during
menstruation
Hypomenorrhea: scanty or little bleeding
Metrorrahgia: bleeding between cycles.
Oligomenorrhea: reduced frequency of the periods.