St A - The Menstrual Cycle Flashcards
What are the 3 physiological systems that regulate the menstrual cycle?
- Hypothalamic-pituitary-oviarian axis.
- Ovarian cycle (Follicular, ovulation and luteal),
- Endometrial cycle (Menstrual, proliferative and secretory)
Define menarche
Endo of puberty which marks the beginning of potential fertility.
Define menopause
Marks the end of natural fertility and occurs at around 45-55 years old. Mostly occurs due to exhaustion of primordial follicle but can occur as premature ovarian failure (menopause below 40 years), symptoms can be treated with oestrogen replacement therapy.
Describe the hypothalamic-pituitary axis
- Gonadotrophin releasing hormone also known as luteinising hormone releasing hormone is secreted in the arcuate nucleus and preoptic area of hypothalamus. It is secreted into the median eminence of the hypophyseal portal system
- GnRH binds to receptors on gonadotrophic cells of anterior pituitary.
Binding of GnRH to receptors causes what?
Release of follicule-stimulating hormone (FSH) and Lutenising hormone (LH)
Describe the different hormones and their levels throughout the menstrual cycle
FSH - Increases in end of luteal phase and beginning of follicular phase, spikes just before ovulation.
LH - Surges 18 hours before ovulation which stimulates progesterone production.
Oestrodiol - As follicle develops it rapidly increases, stimulates LH surge.
Progesterone - Large increase in luteal phase due to corpus luteum.
Inhibin - Released by ovaries and follicular cells.
Describe the changes that occur to the endometrium throughout the cycle?
In the menstrual phase the endometrial layer decreases in size. It beings to thicken from the proliferative to the secretory phase. If no fertilisation occurs then the endometrial lining sheds.
Describe features of hypothalamic-pituitary-ovarian axis
- GnRH neurons release GnRH in rhythmic pulses which causes the release of LH and FDH. Theca cells have LH receptors, granulosa cells have LH and FSH receptors
Describe features of theca cells
They are the superficial layers of the follicle which have LH receptors. They convert cholesterol into pregnenolone and then produce androstenedione and testosterone.
Describe features of granulosa cells
Deep to theca. Converts androstenedione (which is takes up from theca cells) into testosterone and estrone, both of which convert to oestradiol. Activates aromatase.
Describe the feedback of ovarian steroids
Oestrogens and progestins have negative feedback on the pituitary and hypothalamus for most of the cycle. However near ovulation the oestradiol levels increase and the HP axis reverses its sensitivity to oestrogens (pos feedback). Increased sensitivity of anterior pituitary to GnRH leads to LH surge.
What are the roles of oestradiol?
- Induces expression of progesterone receptors in target tissue,
- Tubal Epithelium (stimulates proliferation of epithelial lining and secretes sugar-rich fluid),
- Endometrium (stimulates hyperplasia and hypertrophy of epithelial lining),
- Smooth muscle (upregulates receptors for prostaglandins and oxytocin)
- Cervix (increased mucous volume, decreases mucous viscosity)
What is the role of progesterone?
- Tubule epithelium (reduced proliferation and reduces secretion of sugar-rich fluid),
- Endometrium (Stimulates secretory phase, stimulates growth and secretions from glands),
- Smooth Muscle (reduces sensitivity to oxytocin, relaxation of smooth muscle),
- Cervix (reduces mucous volume and increases viscosity)
Explain dysmenorrhoea
Menstrual cramps due to overproduction of prostaglandins by endometrium due to decreased plasma oestrogen and progesterone. Leads to excessive uterine contractions. Prostaglandins can cause systemic symptoms too.
Describe features of premenstrual dysphoric disorder (PMDD)
Thought to be due to fall in progesterone. It can cause;
Anxiety, mood swings, tiredness, irritability, depression, headaches, feeling bloated, a change in appetite, joint pain, enlarged tender breasts, abdominal pain.
