The Menstrual Cycle and its Hormonal Control Flashcards
3 physiological systems that regulate the female reproductive (menstrual) cycle
– Hypothalamic-pituitary-ovarian axis – Ovarian cycle (events in ovary) • Follicular, Ovulation, Luteal – Endometrial cycle (events in endometrium) • Menstrual, Proliferative, Secretory
Length of menstrual cycle
mean 28 days (+/- 3.95) for about 40 years
MENARCHE
end of puberty and marks beginning of potential fertility
– maturation of GnRH pulsatility so primarily hypothalamic
MENOPAUSE
- occurs around 45 - 55 yrs (average 51 yrs ) and marks end of
natural fertility
– “Exhaustion” of primordial follicles so primarily ovarian
– Premature Ovarian Failure (POF)
early menopause
- Menopause can occur in women under the age of 40 (idiopathic, autoimmune disorders, genetic disorders such as Fragile X, chemotherapy, radiation)
- Symptoms can be treated with oestrogen replacement (hormone replacement therapy – HRT)
Gonadotrophin releasing hormone
secreted by small body neurons in arcuate nucleus & preoptic area of hypothalamus
where is GnRH secreted into
Secreted into median eminence and hypophyseal portal system
what is the function of GnRH
- GnRH binds to receptors on gonadotophic cells of the anterior pituitary
- Leads to release of follicule-stimulating hormone (FSH) and luteinising hormone (L
Hypothalamic-pituitary- ovarian axis
- GnRH neurons release GnRH in rhythmic pulses (about 1/hr)
* GnRH half-life in blood 2-4mins
What cells do LH act on
theca cells which produce androgens and progestins
What cells do FSH act on
Granuloma cells (these also have LH receptors) which produce inhibins activins and oestrogen’s
Theca cells
Superficial layer of follicle
• Have LH receptors
• Convert cholesterol into pregnenolone
• Then produce androstenedione and testosterone
Granulosa cells
• Deep compared to theca
• Layer increases in size markedly during 1°
to 2° follicle development
• Have LH and FSH receptors
• Also convert cholesterol into pregnenolone + activate aromatase
• Oestrogens & • Positive feedback occurs near ovulation (end of follicular phase)
– Most of cycle have negative feedback on pituitary and hypothalamus
– Reduce LH and FSH production
• Positive feedback occurs near ovulation (end of follicular phase)
– Oestradiol levels gradually increase after reached a certain threshold for a min of 2 days,
HP axis reverses its sensitivity to oestrogens
– Leads to oestrogen positive feedback
– Increased sensitivity of anterior pituitary to GnRH leads to LH surge
Roles of Oestradiol in tubal epithelium
– Stimulates proliferation of epithelial lining
– Secretes sugar-rich fluid
Roles of Oestradiol in endometrium
– Stimulates hyperplasia and hypertrophy of epithelial lining
– Glands elongate and spiral arteries grow
Roles of Oestradiol in smooth muscle
– Up regulates receptors for prostaglandins and oxytocin
– Spontaneous activity increased
Roles of Oestradiol in cervix
– Increases mucous volume
– Decreases mucous viscosity
Roles of Oestradiol - Induces expression of progesterone receptors in target tissues
required for corpus luteum to work
Roles of Oestradiol
• Prepare female reproductive tract for fertilisation and implantation
Roles of Progesterone in tubual epithelium
– Reduced proliferation of epithelial lining
– Reduces secretion of sugar-rich fluid
Roles of Progesterone in endometrium
– Stimulates secretory phase menstrual cycle
– Stimulates further growth and secretion from glands
Roles of Progesterone in esmooth muscle
– Reduces sensitivity to oxytocin by down regulating receptors
– Brings about relaxation of smooth muscle in reproductive tract and elsewhere
Roles of Progesterone in cervix
– Reduces mucous volume and increases its viscosity
Dysmenorrhoea - Painful Periods
- Menstrual cramps
- Main cause is overproduction of prostaglandins by endometrium in response to decreased plasma oestrogen and progesterone
- Leads to excessive uterine contractions
systemic symptoms
• Prostaglandins can affect smooth muscle elsewhere and may account form some of the systemic symptoms that sometimes accompany cramps e.g. nausea, vomiting, headache
Premenstrual Syndrome (PMS)
Progesterone has anxiolytic (anti-anxiety) effect. Therefore may be due to falling progesterone levels at the end of the cycle
Amenorrhoea - No Periods
• Primary – Anatomical/ congenital abnormality (underdevelopment or absence of uterus/vagina) – Genetic (Turner’s syndrome) • Secondary – Pregnancy – Lactation – Exercise/Nutrition – Menopause – Polycystic Ovarian Syndrome – Iatrogenic (surgery, medication)
• Symptoms of PMS
– Oestrogen deficiency (Hot flushes (flashes), Vaginal dryness)
– Loss of bone mineralisation (Reduction in peak bone mass attained, Osteopenia/ osteoporosis)
Therapeutic uses of GnRH
• Pulsatile release of GnRH stimulates FSH and LH secretion
• Continuous administration of GnRH causes suppression of gonadotropin
secretion
• Endometriosis
– Common condition with growth of endometrial tissue outside the uterine cavity
– Tissue responds to oestrogens of menstrual cycle
• results in pain and infertility
– Treatment?
– Continuous administration of GnRH analogue inhibits gonadotropin secretion and
reducing oestrogen levels, leading to reduced endometriotic tissue
• IVF
– GnRH analogues used before controlled IVF cycle commences
Birth Control Pill
• Fixed combination OCP
– Dosage of oestrogen and progestin is the same
• Varying-dose OCP
– 2 or 3 different dosages of oestrogen and progestin
• Progestin-only (“minipill”) OCP
how does brith control pill work
• Contraceptive steroids feedback on hypothalamic neurons and gonadotropin cells and suppress LH and FSH secretion
– So no follicular development or LH surge (ovulation)
• Progestin effect causes cervical mucous thickening and increase viscosity,
reduces uterus and oviduct motility, endometrial changes
– Inhibits sperm penetration
– Reduces chances of implantation
