Hormonal Regulation of Menstrual Cycle Flashcards
Menstrual Cycle:
: Recurring cycle of events in uterus and ovaries under the influence of hormones in females (Menstruus means “monthly”)
Anatomy of Ovaries
Ovarian Follicles
Ovaries are made of many sac like structures called ovarian follicles
Ovarian follicles contain oocyte and cells that produce oestrogen and progesterone
Thecal cells and granulosa cells produce oestrogen and progesterone when stimulated with FSH and LH
Development of Ovarian Follicles
Stages of Oogenesis
Overview of Menstrual Cycle
Early Follicular Phase (pre-ovulation)
Negative Feedback
Late Follicular Phase (just before ovulation)
Late Follicular Phase (just before ovulation)
LH Surge
Re-starts meiosis in the oocyte…which becomes haploid
Activates enzymes - dissolve follicle wall and promote vascular leakage so that antrum swells and bulges
Follicle ruptures
OVULATION
Oestrogen production dives
Ovarian Cycle and Corpus Luteum
Luteal Phase (after ovulation)
The Corpus Luteum (CL)
If fertilization does NOT occur:
CL degenerates spontaneously
Progesterone falls
Uterus loses its endocrine support
Menstruation
FSH & LH get to work again on the follicles
If fertilization DOES occur:
CL maintained by hCG from the chorion
Becomes the Corpus Luteum of Pregnancy
Maintains uterine lining until placenta takes over as main producer of progesterone at 3 months
Mechanism of action of the combined contraceptive pill
Low dose of oestrogen
↓ FSH from Anterior Pituitary
↓ development of follicle
No ovulation
Progestogens:
Makes cervical mucus sperm-unfriendly
↓ LH from Anterior Pituitary
↓ GnRH from hypothalamus
↓ motility of fallopian tube
Progestogen-only pill
Low dose progestogen taken continuously (e.g. either norethisterone or levonorgestrel);
Makes cervical mucus inhospitable to sperm;
Hinders implantation; through its effect on the endometrium and on the motility and secretions of the fallopian tubes;
Menstruation often ceases initially but usually returns with prolonged use;
Main adverse effects: Breakthrough bleeding and irregular menses.
Oestrogen prepares the way:
promotes growth of endometrium & myometrium
promotes formation of progesterone receptors
Progesterone acts on the oestrogen-primed endometrium..
Loosens and softens connective tissue - makes implantation easier
Promotes secretion of nutrients (glycogen)
Quietens uterine activity
No occupants..(no embryo) no hCG so Corpus Luteum degenerates
Progesterone (and oestrogen) support lost
Uterine prostaglandins → vasoconstriction → tissue death
Blood and endometrial debris (menses) lost through vagina
Menstrual Disorders
Dysmenorrhea – painful periods
Menorrhagia – heavy or prolonged periods
Amenorrhea – Absence of periods (primary or secondary)
Oligomenorrhea – light periods
