Menstrual cycle Flashcards
What is the purpose of the menstrual cycle?
- Generate oocyte
- facilitate fertilisation
- optimise endometrium for implantation
- protect developing embryo
When does it begin?
Menarche
When does it end?
menopause
What does the hypothalamus secrete?
GnRH (Gonadotropin releasing hormone)
What does anterior pituitary secrete?
FSH and LH
What does ovary secrete?
Oesttrogen
what kind of peptide is GnRH
Decapeptide
What is the GNRH secreted by?
Mid basal hypothalamic neurons
How is GnRH transported to pituitary?
Via hypophyseal portal blood system
What cells in the anterior pituitary secrete FSH and LH
Basophils
What does FSH do?
Stimulates follicular activity Promotes estradiol (form of oestrogen) production from granulosa cells
What does LH do?
Triggers release of egg from dominant follicle.
Promotes development of the corpus luteum (a hormone-secreting structure that develops in an ovary after an ovum has been discharged).
Production of progesterone
What is GnRH, LH and FSH production inhibited by?
Rising estradiol (E2) levels
What is the exception? When does high levels of estradiol lead to a surge in LH release?
Midcycle to trigger ovulation
Describe the stages of the follicles?
Primordial follicle –> Primary/preantral follicle –>secondary/antral follicle –> preovulatory follicle –> ovulation
How do follicles develop?
- proliferation of granulosa cells: antrum develops
- Gap junctions and cytoplasmic processes allows communication and passage of low molecular weight materials. - nutrients
- Proliferation of thecal cells
How is estradiol 17-B produced?
Androgens secreted by theca interna cells, this is then converted to estradiol 17-B in granulosa cells.
How does ovulation occur?
1) High levels of oestrogens from mature follicle stimulate release of more GnRH and LH.
2) GnRH promotes release of FSH and more LH
2) LH surge brings about ovulation
What happens after ovulation?
Graafian follicle becomes empty.
Granulosa cells undergo luteinisation (LH) and become corpus luteum (12d)
What happens if no fertilisation?
Corpus luteum degenrates to become corpus albicans
What is the endometrium?
Lining of the uterus
What is the proliferative phase?
The proliferative phase is the stage of the menstrual cycle in which ovarian follicles, structures in the ovary that each contain a single egg, mature and prime themselves for ovulation.
What happens in the proliferative phase?
Endometrium thickens (action of E2) Increased stromal cells increased glands (blood vessels)
What is the secretory phase?
Following ovulation, the follicle that released the egg is transformed into a corpus luteum, a structure that produces the pregnancy hormone progesterone, which thickens the lining of the uterus in preparation for a fertilized egg to make its home there for the next nine months
What is the main hormone of the secretory phase?
Progesterone
What happens in the secretory phase?
Increased secretion, increased lipids and glycogen, increased blood supply, THICK endometrium
What are the optimal conditions for implantation of fertilised egg?
Stable, vascular and nutrient rich
What happens during menstruation?
Vasodilation
Necrotic outer layers of endometrium separate from uterus
Uterine contraction - expel contents
What does cervix do?
Mucous production from columnar glands
Stringy and runny during midcycle (easier access of sperm at ovulation)
Tenacious and inelastic in luteal phase (prevents microbes)
What does combined oral contraceptive do?
- contains estradiol and progestagen
- Inhibits GnRH/FSH/LH
- prevents ovulation
- thin endometrium
