Histology of the Menstrual Cycle
Describe the changes that occur to the endometrium during menses.
Corpus luteum degnerates - PG and OE drops. This causes vasospasm of vessels and loss of blood supply to the endometrium. As a result, the endometrium undergoes necrosis and is sloughed off.
What hormone stimulates the growth of primary follicles? What is the consequence of this?
FSH - growing follicles increase production of oestrogen, which consequently increases the follicle's sensitivity to FSH and LH by increasing receptors.
Describe what happens to progesterone levels in the situation of fertilization and no fertilization.
Fertilization; the blastocyst takes over and produces hCG to continue PG synthesis No fertilization; the corpus luteum degenerates, PG falls, and the negative feedback is lost
What are the two phases of the ovarian cycle?
Follicular phase (before ovulation) Luteal phase (After ovulation)
Describe the histological changes to the endometrium during the secretory phase.
Increased vascularity - spiral arterioles Increased number of glands and secretions - glands are tortuous and show secretions Increased cytoplasm of stoma
What triggers ovulation in the maturing follicle?
Increasing oestrogen above threshold (due to growing follicle) has a postive feedback on LH, causing an LH surge. LH surge triggers ovulation
Describe what happens to the endometrium during the proliferative phase.
Increasing oestrogen results in stromal and epithelial proliferation, with gland and blood vessel formation. Glands produce mucus, which lines cervical canal.
What are the 3 phases of the endometrial cycle?
Menses and proliferative phase (before ovulation) Secretory phase (after ovulation)
Describe the hormonal MOA of the combined contraceptive pill.
Prevent ovulation through synergistic suppression of LH surge/ovulation and FSH-mediated follicle development
Describe the Hypothalamic-Pituitary-Ovarian axis in relation to the menstrual cycle.
Pulsatile release of GnRH with corresponding release of LH and FSH LH and FSH stimulate follicular development, and release of ovarian hormones oestrogen and progesterone, which provide negative feedback on GnRH, FSH and LH
What is the major histological sign that can be seen in the endometrium during ovulation?
Sub-nuclear vacuolisation
Describe the hormonal MOA of the progesterone only contraceptive pill.
Suppression of the LH surge and ovulation with variable efficacy, viscous mucus to deter sperm penetration, prevention of endometrial growth and development, reduction in cilia motility Used in those with contraindications to OE pill.
Describe the rationale behind hormonal contraception.
Sustained blood levels cause negative feedback and suppression of GnRH, FSH and LH The reduced FSH prevents follicular development, and release of oestrogen Lack of oestrogen peak inhibits mid-cycle LH surge, preventing ovulation NB: progesterone also causes thickening of cervical mucus, reducing sperm penetration
Following ovulation, what do the follicular cells become? What is their function?
The remaining cells become the corpus luetum, which secretes progesterone to prepare the endometrium for implantation, and further inhibits FSH production
Describe the histological changes in the endometrium during the proliferative phase.
Tubular, non-secretory glands Cellular endometrial stroma, progressively oedematous Mitotic activity in gland and stroma
