The Human Menstrual Cycle!  Consists of 3 distinct phases  The cycle is typically 28 days  It is not always 28 days for all women all the time  For example Athletics/stress/malnutrition may cause a cycle to STOP  Or some women may based on stress/age/ health have longer or shorter cycles

I – Menstrual Phase :  Occurs between Day 28/1 to Day 3-4  Most hormones are low (FSH, LH, Progesterone & Estrogen), but Oxytocin is HIGH.  The endometrium lining breaks down to be SHED  1 st day of bleeding is the 1 st day of the NEW CYCLE  2-8 day loss period, where 20-80ml of blood is SHED

II – Follicular Phase :  Named for the developing FOLLICLE (Day 4-14)  Release of FSH & LH increases  The ovary is stimulated to release ESTROGEN  ENDOMETRIUM thickens to support the IMPLANTATION of the ZYGOTE!  Ovulation occurs at the peak of FSH & LH release (Day 14)  Body temperature increases at the time of ovulation  Fertility remains high for 3-5 days!

III – Luteal Phase :  Named for the CORPUS LUTEUM (forms after Ovulation) (Day 14-25)  The envelop of the Follicle becomes the CORPUS LUTEUM  Corpus Luteum produces PROGESTERONE a) maintains the endometrium b) –ve feedback to APG to stop FSH release  Why is this important?

III – Luteal Phase …  Corpus Luteum maintains progesterone throughout pregnancy or until Day 25 if no fertilization has occurred!  PLACENTA eventually takes over PROGESTERONE production to maintain the PREGNANCY!  see green line above, it may continue for 9 months!

A simple view of Pro & Estro & Endometrium

See your handout & write Note the peaks of each hormone & when they occur!

How Menstrual Feedback works! *** write on your handout***  Hypothalamus contains the chemoreceptors that respond to increasing Progesterone & Estrogen levels (Pro & Estro)  As Pro & Estro increase the hypothalamus stops release of GnRH (Gonadotropin Releasing Hormone  Puberty initiator)  As GnRH decreases the APG ceases FSH & LH release RU Ready!

How Menstrual Feedback works…  After Day 14 no more eggs will be stimulated to grow! WHY?  This is the basis of the PILL  mimic an existing –ve feedback system by introducing Pro & Estro during the Follicular Phase!  Pill is also medicinal  regulate cycles, treats menstrual disorders (like endometriosis) etc  Our Catholic Faith calls for us to examine our reasons for this artificial treatment to the body & the decisions we make!  It is not meant to cheat our biological nature & abdicate our responsibilities for the creation of life!

See your handout & write  Note the targets of estrogen & progesterone!  Also note the event before & after ovulation!

What Now!  Menstrual Cycle Review Worksheet 1, 4, & 5  STS assignments on CLONING Dolly the 1 st mammal clone  A sheep Now Pigs for various reasons What next  Humans for various reasons!