PHYSIOLOGY OF MENSTRUAL CYCLE

FOLLICULOGENESIS

SELECTION

•10-15 primordial follicles start maturing but only one  matures fully dominant  ( Graffian )  follicle  &  rest undergo atrophy

 

• Selection occurs at day 5-7

• It depends on  

       -  intrinsic capacity of follicle to  synthesize estrogen.

        - no. of FSH receptors.

       

• Follicle with  highest no. of FSH receptors will continue  to thrive.

 

• These changes are under influence of  (mainly) FSH and LH  from anterior pituitary.  

 

•FSH ACTIONS

   

   -Recruitement

   -Mitogenic effect which leads to 

       Increase in  No.of granulosa cells

OVULATION

• Release of secondary oocyte from  ovary (following  rupture  of Graffian  follicle)  into  peritoneal cavity is called ovulation 

 

• Occurs at 14th  day   ( 28-day cycle )

 

• 36 hrs after mid-cycle LH surge.

 

PREOVULATORY PERIOD

• NEGATIVE FEEDBACK  ON  PIUITARY

 

-Estradiol and inhibin have negative feed back on pituitary secretion of FSH

 

 • POSITIVE FEEDBACK ON PITUITARY

•Estradiol (reaching a threshold concentration) have +ve feed back on pituitary (facilitated by low levels of progestrone) which leads to LH surge and  secretion of progestrone.

•Operates after puberty.

•+ve feed back on pituitary secretion of FSH.

 

OVULATION

• During follicular phase, low level of estrogen suppresses production of LH. (Negative feedback )

 

• When ovum is almost matured, estrogen levels reaches threshold above which they stimulate production of LH , LH SURGE (Positive feedback )

 

• FSH surge occurs .

 

• Gonadotropin surge causes ovulation after 36 hrs.

 

POSTOVULA TORY  PHASE

 

•Remarkably  constant  period  - 14 days.

 

 •Development of Corpus  luteum - luteal  phase.

 

 

          Ovulation

                ↓

Corpus  haemorrhagicum

                ↓

      Corpus luteum

                ↓

          1. Corpus albicans

     2. Corpus  luteum of pregnancy.

 

•FORMATION OF CORPUS HEMORRHAGICUM

•It is  Graafian  follicle  is  filled with blood . Minor  bleeding  from  follicle  into  abdominal  cavity  may  cause  peritoneal  irritation  and  lower  abdominal   pain (mittelschmerz).

 

•FORMATION OF CORPUS LUTEUM

•Ruptured follicle heals &  forms corpus luteum (Yellow body)  .

• LH is responsible  for  this.

•They  secrete progesterone and to a lesser  extent estrogen . Progesterone has negative  feedback effect on anterior pituitary and  decreases secretion of both LH & FSH.

     The fate of corpus  luteum  depends  on conception.

 

•FORMATION OF CORPUS ALBICANS

•If  no fertilization  ,it involute after 24th  day  and is replaced  by a whitish  scar tissue,  called  corpus  albicans.  

      

      This is  due to falling levels  of  FSH  and  LH  and inhibin secreted  by lutein cells.  With   involution  of corpus luteum, on 26th  day , levels of oestrogen,  progesterone and  inhibin fall.   

     

      This removes feedback inhibition of   anterior pituitary consequently FSH and in a few days LH secretion begins  and next cycle  is initiated.

 

•CORPUS LUTEUM OF PREGNANCY 

  •If  ovum  is  fertilized ,corpus luteum  persists and secretes  oestrogen  and  progesterone  till 3rd month of pregnancy   when placenta takes over its endocrine   function.

 

  •An embryo in the uterus will secrete a HCG . 

  •It prevents  corpus luteum from decomposing which maintains progesterone levels so that endometrium is not shed.

 

LUTEAL PHASE

    •Corpus luteum  produces significant amounts of  progesterone, which  makes  endometrium receptive to implantation of  blastocyst.

    •High levels of estrogen and progesterone suppress production of FSH and LH that  corpus luteum needs to maintain itself.

 

UTERINE  CHANGES   

ENDOMETRIAL CYCLE

 

•Cyclic  changes  occurring in  endometrium   during  reproductive period  in females.

 

PHASES  OF ENDOMETRIAL  CYCLE

•1st day  of bleeding - first  day of cycle

 

•Three  phases

    1)Menstrual  phase      :    1st - 5th day

    2)Proliferative  phase  :    6th - 14th day

    3)Secretory   phase      :   15th - 28th day

 

FOLLICULAR OR PROLIFERATIVE PHASE 

    Estrogen leads to increase in mitotic activity in the glands and in stroma.

    Endometrial thickness increases from 2 to 8 mm. (from basalis to opposed basalis layer)

LUTEAL OR SECRETORY PHASE

    Progestrone increases which leads to restriction of  Mitotic activity.

    Endometrial glands secrete glycogen rich vacoules and the following changes are seen

              -Stromal edema

              -Stromal cells enlargement

              -Spiral arterioles develop, lengthen and coil

                                     

MENSTRUATION

•Periodic desquamation of the endometrium.

•The external hallmark of the menstrual cycle

     •Just before menses the endometrium is infiltrated with leucocytes

    •Prostaglandins are maximal in  the endometrium just before menses.

    •Prostaglandins increases which leads to constriction of the spiral arterioles leading to ischemia and desquamation.

   Followed by arteriolar relaxation, bleeding and tissue breakdown.

 

SECRETORY PHASE 

• 15th to 28th day.

 

•Changes - due to both estrogen and progesterone secreted by corpus luteum .

 

• It coincides with luteal phase of ovarian cycle.

 

CHATRESTERIC CHANGES IN SECRETORY PHASE 

   

   1. Prominent corkscrew-shaped glands  

   

    2. Increased vascularity

    3. Endometrial glands –

    Increases in size and thickness of endometrium and become tortuous.

    They secrete thick viscous fluid containing glycogen.

    4. Blood supply of endometrium further  increases. 

    5. Thickness of endometrium increases to 5-6 mm.

   6. These changes provide appropriate conditions for implantation.

   7. If their is no fertilization then corpus luteum involutes and oestrogen and progesterone level falls.

 

MENSTRUAL PHASE 

 

26th or 27th day of  previous cycle

               ↓

reduction in  estrogen  & progesterone  from ovary

              ↓

    menstruation

 

Average duration -  3-5 days .

 

CHANGES IN CERVIX

•PROLIFERATIVE PHASE 

  Cervical secretions become thin.  

  •At ovulation , it is thinnest and its elasticity  is maximum.It can be stretched like elastic thread  (spinnbarkeit  effect) which favours    transport of sperms.

  •When Mucus is spread on slide it shows fern-like pattern.

SECRETORY PHASE

  

  Cervical secretions decrease in quantity and  becomes thick.

  It make a plug and prevent entry of sperm  through cervix.

CYCLIC CHANGES IN VAGINA

PROLIFERATIVE PHASE 

  

Epithelium becomes thickened and cornified.

and contain glycogen granules.

 

SECRETORY PHASE 

  

Epithelium proliferates and infiltrated with leucocytes.  

Secretions become thick and viscid which   increases resistance to infection.

 

HORMONAL CONTROL OF MENSTRUAL  CYCLE

•Hormones involved are:

1.Hypothalamic hormone - GnRH

2.Anterior pituitary hormones – FSH and LH

3.Ovarian hormones – Estrogen and progesterone.