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MENSTRUAL CYCLE (DOC)

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					                MENSTRUAL CYCLE.
                            Learning Objectives
At the end of the tutorial, the student should be able to :

   •   Define menstrual cycle.

   •   Tell us the duration of menstrual cycle.

   •   Describe the physiologic changes that occur in the female reproductive organs during the
       menstrual cycle.

   •   Explain the regulation of menstrual cycle.

   •   Express the applied physiology.


                              Menstrual Cycle
Definition:
 Periodic vaginal bleeding that occurs with the shedding of the uterine mucosa (menstruation).
                               Menstruation
•   Indicate periodic shedding of the stratum functionale of the endometrium, which becomes
    thickened prior to menstruation under the stimulation of ovarian steroid hormones.
               A : Functional Layer.
               B: Basal layer.




                       Duration of the cycle
•   Variable,
•   an average figure is 28 days from the start of one menstrual period to the start of the next.
•   First day of menstruation “day one “ of the cycle.
       Timing events in the menstrual cycle.
                      1. Onset of menstruation




       Day 1                                                         Day 1




   0         4        8        12        16        20       24         28

       Menstruation




                  Phases of the menstrual Cycle
Changes in ovary :

          – THE FOLLICULAR PHASE:
     From first day of menstruation until day of ovulation.
          – LUTEAL PHASE:
   After ovulation is luteal phase until first day of menstruation
              Phases of the menstrual Cycle
•   Changes in the endometrium:
      – Menstrual ,
      – Proliferative and
      – Secretory Phase.




                             Ovarian Cycle
•   Follicular Phase ( Day 1 to Day 13 ):

       –   Menstruation lasts from 1 to day 4 or 5 of the average cycle.
       –   Secretion of Ovarian steroid hormones are at their lowest.
       –   Ovaries contain only primary follicles.
                               Ovarian Cycle
 •   Follicular Phase ( Day 1 to Day 13 ):
        – Some primary follicles grow, and become secondary follicles.
        – Towards the end , one follicle in one ovary reaches maturity and reaches graffian
            follicle.
        – As follicles grow, the granulosa cells secrete estradiol ( the principal estrogen),
            which reaches its highest concentration in the blood at about day 12 of the cycle,
            2 days before ovulation.




                                     Growth of follicles:

                            Antral follicle           Graafian
                                                       follicle




Primordial
  follicle




Oocyte                                                            Ovulation
                                                Antrum
                                              (fluid filled
       Granulos                                  space)
        a cells         Thecal
                         cells
                               Ovarian Cycle
 •   Follicular Phase ( Day 1 to Day 13 ):
        – Growth of follicles and secretion of estradiol are stimulated by FSH.
        – FSH in early follicular phase is slightly greater then in late follicular phase.
        – Towards the end , FSH and estradiol also stimulate the production of LH
            receptors in the graffian follicle.
        – Graafian follicle is prepared for the next major event.


                                    LH Surge
 •   Begins about 24 hours before ovulation.
 •   Reaches its peak 16 hours before ovulation.
 •   LH surge acts to trigger ovulation.
         Positive feedback effect of estradiol on the pituitary , an increase in LH secretion
            in late follicular phase culminates in an LH s.




                Timing events in the menstrual cycle.
                                       2. LH surge
                                    Ovulation
 • LH Surge causes graafian follicle to rupture at about
day 14.
 • Secondary oocyte arrested at metaphase II of meiosis , is released from ovary into the
     uterine tube.
 • Ovulation occurs.
                                Luteal phase
•   After Ovulation, the empty follicle is stimulated by LH to become corpus luteum.
•   Corpus luteum secretes both estradiol an progesterone.
•   Progesterone levels in the blood are negligible before ovulation but rise rapidly to a peak
    level during the luteal phase, approximately one week after ovulation.




                               Luteal phase
•   Progesterone with estradiol during the luteal phase exert an inhibitory, or negative
    feedback effect on FSH n LH secretion.
•   Corpus luteum produces inhibin which may help to suppress FSH secretion.
•   This retards the development of new follicles.
•   Further ovulation does not occur.
•   Multiple ovulations and possible pregnancies on succeeding days of cycle are prevented.
                                Luteal phase
•   New follicles develop towards the end of one cycle in preparation for the next.

•   Inhibin production is decreased at the end of luteal phase.

•   Estrogen and progesterone levels also fall during the late luteal phase ( starting about day
    22) because corpus luteum regresses and stops functioning.

•   With the declining function of corpus luteum, esterogen and progesterone fall to very low
    levels by day 28 of the cycle.
                              Luteal phase
•   WITHDRAWL OF OVARIAN STEROIDS CAUSES MENSTRUATION AND
    PERMETS A NEW CYCLE OF FOLLICLE DEVELOPMENT TO PROGRESS.

         Cyclic changes in the Endometrium
•   Development of the endometrium is timed by the cyclic changes in the secretion of
    estradiol and progesterone from the ovarian follicles.
•   Three phases can be identified:
        – The proliferative phase.
        – The secretory phase.
        – The menstrual phase.
                    The proliferative Phase
•   occurs while the ovary is in follicular phase.
•   Increasing amounts of estradiol stimulate proliferation of stratum functionale of the
    endometrium.
•   Spiral arteries develop in the endometrium.
•   Estradiol stimulates the production of receptor proteins for progesterone at this time, in
    preparation for the next phase of the cycle.


                       The secretory phase
•   Occurs when ovary is in its luteal phase.
•   Increased progesterone secretion stimulates the development of uterine glands.
•   Endometrium becomes thick, vascular and ‘ spongy’ in appearance.
•   Uterine glands becomes engorged with glycogen during the phase following ovulation.
•   Endometrium is well prepared to accept and nourish an embryo

              Uterine changes in the menstrual cycle.
                      The menstrual Phase
•   Occurs as a result of fall in ovarian hormone secretion during the late luteal phase .
•   Necrosis and sloughing of the stratum functionale may be produced by constriction of
    spiral arteries.
•   It seems spiral arteries are responsible for menstrual bleeding.




Cyclic changes in the female reproductive tract
   •   High levels of estradiol secretion cause cornification of vaginal epithelium. ( the upper
       cells die and become filled with keratin.
   •   During luteal phase, high levels of progesterone cause the cervical mucus to thicken and
       become sticky after ovulation has occured.


                                     CLINICAL
ABNORMAL MENSTRUATION :
Most common disorders of female reproductive tract.

   •   Amenorrhea: Absence of Menstruation.
   •   Dysmenorrhea : Painful menstruation which may be marked by severe cramping.
   •   Menorhagia: Excessively profuse or prolonged bleeding.


                                    References
Human Physiology.
 Stuart Ira Fox. Seventh Edition.

Human Phsiology.
Lauralee Sherwood. From Cells to Systems.
 Fifth Edition.

				
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