Menstrual Cycle Lect 2013

7/30/2019 Menstrual Cycle Lect 2013

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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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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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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.

Documents

Menstrual Cycle Lect 2013