Menstrual cycle + hormones Flashcards
What are the 4 main purposes of the menstrual cycle?
- Generate an oocyte
- Facilitate fertilisation
- Optimise endometrium for implantation
- Protect developing embryo
When does the follicular phase occur?
-Day 1-14 (if 28 day cycle)
-Aligns with menstrual phase + proliferative phase
-Oocyte released at day 14 (if 28 day cycle)
What controls the menstrual cycle?
-Hypothalamo-pituitary ovarian axis
-Hypothalamus –> hourly pulsatile GnRH release
-GnRH –> anterior pituitary stimulation
-Anterior pituitary –> FSH and LH release from basophils
-FSH –> stimulates follicular activity, promoting estradiol production from granulosa cells
-LH –> triggers ovulation, promotes corpus luteum development and progesterone production
Do oestrogens stimulate a positive or negative feedback loop on the hypothalamus?
-Rising oestrogen levels INHIBIT GnRH, LH and SH levels (ie NEGATIVE feedback loop)
EXCEPTION = near midcycle
-High oestrogen levels STIMULATE LH release, triggering ovulation (ie POSITIVE feedback loop)
What is the role of GnRH and where is it secreted?
-A decapeptide
-Secreted by mid basal hypothalamic neurons in hourly pulses
-Stimulates release of LH and FSH from anterior pituitary
-Secretion affected by life stresses eg bereavement, anxiety, time zone, exercise, weight loss
What is the role of FSH and where is it secreted?
-Stimulates follicular activity (generation of oocyte)
-Therefore promoting oestradiol production from granulose cells surrounding oocyte
-Secreted from basophils in anterior pituitary
What is the role of LH and where is it secreted?
-Triggers release of oocyte from dominant follicle
-Promotes development of the corpus luteum and production of progesterone in the luteal phase
-Secreted from basophils in anterior pituitary
What are the layers of the pre-antral follicle and what are its roles?
-Oocyte –> zona pellucida –> granulosa cells –> theca
-Granulosa cells forms corona radiata (protective layer) in later antral follicle
-Granulosa and theca cells produce progesterone and oestrogen
How many primordial follicles are present at birth and how many develop to produce an egg?
-In foetus at 6 months = 2,000,000
-At birth = 750,000
-At puberty = 400,000
-450 develop to produce an egg, remainder degenerate
What is the development of the follicles to ovulation?
- Primordial follicle
- Primary / pre-antral follicle
- Secondary / antral follicle
- Pre-ovulatory follicle
- Ovulation
- Corpus luteum left in ovary once egg is expelled
What are the roles of the different follicular cell types?
-Theca interna cells = secrete androgens
-Granulose cells = convert androgens to estradiol 17-beta
How is the corpus luteum formed?
-Once follicle is empty post-ovulation, granulosa cells undergo luteinisation by LH
-Forms the corpus luteum (lifespan = 14 days)
-If no fertilisation occurs, it degenerates to become the corpus albicans
What changes happen to the endometrium during the proliferative phase?
-Estradiol the dominant hormone
-Promotes endometrium thickening
-Proliferation of stromal cells, glands and blood vessels
-By ovulation, the endometrium is 2-3mm thick
What happens to the endometrium during the secretory phase?
-Progesterone the dominant hormone
-Promotion of secretion, increase in lipid and glycogen production, increased blood supply
-Endometrium becomes 4-6mm thick
-Optimal conditions for implantation of fertilised egg
–Stable, vascular, nutrient-rich
What occurs to the endometrium during the menstrual phase?
- Failed implantation
- Progesterone levels fall –> destabilisation
- Vasodilation - necrotic outer layers of endometrium separate from the uterus
- Separated tissue and blood initiate uterine contractions –> expel contents
Where is mucus produced and how does it change throughout the cycle?
-From the columnar glands in the cervix
-Mid-cycle = stringy and runny to facilitate sperm access at ovulation
-Luteal phase = tenacious and inelastic to prevents embryo from microbial infection / maintains integrity of the cervix during pregnancy
What is mittelschmerz?
-Lower abdo pain associated with ovulation
Where and when does implantation occur?
-Day 23
-Blastocyst implants into decide of uterus
-hCG produced instantly, detectable from day 9-10, falls off around 20 weeks
-Progesterone received from corpus luteum, until 10-12 weeks from which placenta takes over
What is the main hormone in pregnancy?
-Progesterone
How is the cardiovascular system affected by pregnancy?
-Increased circulating volume (5-7L)
-Increased HR
-Increased SVR
-Increased CO
-BP decreases unless there is pathology
–Drops to allow more blood to reach peripheral organs ie placenta
How is the respiratory system affected by pregnancy?
-Increased RR
-Increased respiratory effort due to lung compression from uterus
-NB difficult to investigate for PEs
How is the GI system affected by pregnancy?
-Gastric / intestinal motility reduced
–More likely to get heartburn and constipation
How is the immune system affected by pregnancy?
-Down-regulation to prevent rejection of foetus
-Neutropenia
–Increased risk of infection eg UTIs v common
How is the renal system affected by pregnancy?
-Poor ureteric drainage
