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Ovarian Hormones and the Menstrual Cycle

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					Ovarian Hormones and
the Menstrual Cycle

   Dr. Eeman At-Taras
       Oct. 5, 2010
Objectives
 Describe the regulation of the menstrual cycle by the
  hypothalamic-pituitary axis.

 Discuss the phases of the menstrual cycle.

 Discuss the interrelationship of the ovarian and
  uterine cycles.

 Describe the process of ovulation and its regulation.
The Menstrual Cycle
 Menstrual comes from the
  Latin mensis, i.e. month

 Average length of the
  menstrual cycle is that of a
  lunar month (29.5 days)

 Most cycles are 21-35 days
  in length
   Variation in the Follicular Phase
― Both menstrual and follicular phase are variable
Folliculogenesis
Phases of the Menstrual Cycle
 Menstrual Phase (Menses)
 Follicular Phase (Proliferative, estrogenic)
 Luteal (secretory, progestational)
Ovarian and Uterine Cycles
The Menstrual Phase
The Menstrual Phase
 Shedding of the stratum functionalis due to
  ischemia (blood vessels constrict and dilate
  sporadically)

 An average of 33 to 83 ml of blood lost during
  menstruation

 Discharge contains uterine fluids and debris
  of endometrium along with blood
The Uterus
The Ovarian Cycle




Early         Late




 Follicular Phase    Luteal Phase
The Follicular Phase
 Characterized by rapid growth of ovarian
  follicles
 Only one follicle usually dominates and
  ovulates
 The remaining follicles undergo atresia
 FSH is the major driving gonadotropin during
  this phase
 Major circulating ovarian steroid is estrogen
     Targets the uterine endometrium – proliferation
     Feedback effect on hypothalamus and pituitary
Early to
Mid-
Follicular
Phase:
Negative
Feedback
of Estrogen
The Two-Cell Theory
Late
Follicular
Phase:
Positive
Feedback
Effects of
Estrogen
       Estrogen Feedback on the Pituitary
                                      Positive feedback causes a 10 fold increase
                                      in GnRH and LH pulse amplitude and an
                                      increase in pulse frequency from hourly to
                                      every half hour




EFP = early follicular phase, MFP = mid-follicular phase, LFP = later follicular phase
The LH Surge
            Fig. 28.27

Ovulation
Process of Ovulation

                    Luteinization
                       Granulosa cells of the
                        dominant follicle
                        acquire LH receptors
                        and begin to secrete
                        progesterone

                    Proteolytic enzyme
                       production

                    Increased
                       vascularization and
                       prostaglandin
                       production
The Luteal Phase
 Lasts from ovulation to the beginning of menstruation


 High progesterone


 Negative feedback on LH and FSH


 Corpus luteum (CL) secretes estradiol and progesterone
  which prepare uterus for implantation

 CL also secretes relaxin which inhibits uterine muscle
  contractions

 End of luteal phase – luteolysis – regression of the CL
Fig. 28.25
The Luteal Phase: Progesterone
References
 Essential Reproduction. Johnson & Everitt,
  2000

 Human Reproductive Biology. Jones and
  Lopez, 2006

 Textbook of Medical Physiology. Guyton and
  Hall, 11th edition.