Menstrual Cycle

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  • Created by: Becca
  • Created on: 29-12-13 14:16
How are the endometrial & ovarian cycles co-ordinated?
Day 0-7: menstruation, new follicle starts to develop. Day 7-14: proliferation phase, graafian phase. Day 14-21: formation of corpus luteum, ovulation (oocyte release from graafian follicle). Day 21-28: secretory phase
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What hormones are involved in the menstrual cycle? Where are they released from?
Gonadotropin releasing hormone (GnRH, hypothalamus), follicle stimulating hormone (FSH, ant pituitary), luteinizing hormone (LH, ant pituitary) and oestradiol (ovary, oestrogens = oestradiol + oestrone) & progesterone (from ovary)
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What happens in the menstrual cycle day 0-14?
Release of GnRH from hypothalamus -> pituitary stimulated to release FSH -> receptors on ovary, oestradiol produced by granulosa cells in follicle. Negative feedback on anterior pituitary
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What is the effect of FSH & LH in day 0-14 of the menstrual cycle?
FSH act on granulosal cells to increase synthesis of oestradiol. LH act on thecal cells to produce progesterone
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What are the precursor molecules that lead to the production of oestradiol?
Cholesterol -> Pregnenolone -> DHA + Progesterone -> Androstenedione -> Testosterone + Oestrone -> Oestradiol
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Where is oestradiol synthesised? What hormones are involved?
LH in thecal cells is used to convert cholesterol to androstenedione. Androstenedione then moves to granulosal cells & FSH is used to convert it to oestradiol. Oestradiol is then free to move out of the granulosal cells
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What is the effect of oestradiol during day 0-14?
Oestradiol increases proliferation of granulosal cells -> more oestradiol produced
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What happens during ovulation?
High oestradiol levels (late follicular phase) -> pituitary releases more LH (via GnRH). Mid-cycle -ve feedback becomes +ve -> short surge LH released. High oestradiol + FSH changes LH action: cholesterol -> progesterone (rather than androstenedione)
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What happens in ovulation once progesterone leaves the granulosal cells?
Stimulates the appears of LH receptors on granulosal cells. Granulosal cells no long bind oestradiol or FSH but increase progesterone synthesis -> release of oocyte (proteolytic activity to breakdown collagen). Recruitment of 5-9 new follicles
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How does the corpus luteum form? What does it do?
Formed from the collapsed follicle, maintained by LH. It secretes progesterone (maintains endometrium). Oestradiol levels begin to drop (progesterone inhibits oestradiol synthesis)
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What happens during days 14-28 of the menstrual cycle?
Progesterone causes a decrease in gonadotropin secretion (suppresses GnRH secretion). FSH & LH levels are low so no new follicles develop
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What happens during the death of the corpus luteum?
Corpus luteum degenerates -> decrease in progesterone & oestrodiol levels, but increase in FSH & LH levels. Allows new follicles to mature and the onset of menstruation
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Summarise what happens between day 0-14 of the menstrual cycle
Release of recruited follicles, one to develop. Proliferation of granulosal cells, development of Graafian follicle. Proliferation of endometrium and myometrium
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Summarise what happens between day 14-28 of the menstrual cycle
Growth of corpus luteum, endometrium secretory, inhibition of developing follicles, death of corpus luteum and final contraction of spiral arteries in endometrium
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How does hormonal contraception work?
Suppress ovulation by negative feedback of progesterone on the pituitary & hypothalamus. Decrease in GnRH secretion results in low FSH and LH levels -> no new follicles develop
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How do the combined oral contraceptive pill (COC) & progesterone only pill (POP) work?
COC: synthetic oestrogen & progesterone, monocyclie (21 days on - output of GnRH/FSH/LH suppressed. 7 days off - endometrium breaks, menstruation). POP: taken continuously
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What hormonal changes happen during pregnancy?
No menstrual cycle occurs as high levels of progesterone are present. Inhibits secretion of pituitary gonadotrophins
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What hormonal changes happen during the menopause?
50+ years, menstrual cycle becomes less regular. Ovaries lose the ability to respond to FSH & LH. Low oestradiol levels
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What hormonal changes happen at the onset of puberty?
Activation of GnRH pulses to ant pituitary (maturation within CNS), increase in LH & FSH, increase in oestradiol & androgen synthesis
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What hormonal changes happen in the female during puberty?
2-4 years prior to menarche (first menstrual cycle) increase in levels of steroid hormones from ovary & adrenal glands. Ovarian oestrogens regulate growth of breast & female genitalia, androgens control growth of pubic & axillary hair
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What hormonal changes happen in the male during puberty?
Increase in steroid hormones from gonads & adrenal glands. Testicular androgens control development of genitalia & body hair as well of enlargement of larynx and laryngeal muscles
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What is the function of the ovary? What is its attachments?
Function: endocrine, source of haploid ova. Attachments: peritoneum of broad ligament (doesn't cover ovary which has its own coat), ovarian ligament (attaches to body of uterus) & suspensory ligament (connect tissue to the lateral wall of pelvis)
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What is the blood supply to the ovary?
Ovarian artery off the abdominal aorta (at level of renal arteries, passes lat & ant to ureter and inf into pelvis). Right ovarian vein drains into IVC, left vein drains into left renal vein. Anterior branch of internal iliac supplies uterus & ******
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What does the ovarian artery anastomose with? What is the function of these anastomoses?
Gives branches to fallopian tube & anastomoses with uterine artery to supply uterus. Uterine artery also anastomoses with ****** artery, allows rapid transfer of hormones from ovary to uterus+****** & enables co-ordination of menstrual cycle changes
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What is the histology of the ovary surface, cortex & medulla?
Surface epithelium: single layer of cuboidal or low columnar cells. Cortex: stromal cells & gametes (site of gamete formation and follicle maturation). Medulla: stromal cells, very small remnant of embryonic Wolffian duct
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What happens during the embryonic & foetal period of gamete production and follicle development?
Gonadotropic independent. Migration of stromal & primordial germ cells yolk sac->ovary (4/5th wk). Primordial germ cells (PGC) undergo mitotic divisions->oogonia. Stromal cells cluster around oogonia, eventually form thecal layers & secrete steroids
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What happens during the embryonic & foetal period in the 2nd trimester?
Mitotic divisions cease, oogonia increases in size & enters first meitotic division, remains in prophase -> primary oocytes (degenerate birth -> puberty). Surviving primary oocytes acquire single layer of granulosa cells -> primordial follicles
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What happens during the puberty phase of gamete production and follicle development?
Follicular development/maturation, gonadotropic dependent. Primordial follicle -> primary follicle -> secondary -> tertiary/Graafian -> Preovulatory -> Oocyte/corpus luteum. Cyclical secretion of FSH stimulates development of 30-40 follicles
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How do primordial follicles convert to primary follicles? What develops?
By enlargement of oocyte, proliferation and increase granulosa cells. Multilayering of granulosa cells with FSH receptors -> formation of zona pellucida between oocyte & cells
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What is the function of the proteins & gap junctions associated with the zona pellucida?
Protein: 1,2 & 3, protection and avoidance of polyspermy. Gap junctions: between oocyte & granulosa cells, transfer of metabolites & regulatory substances, cAMP from granulosa cells maintains meiotic arrest of oocyte
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What happens during development of the secondary follicle?
Granulosa proliferates, fluid-filled cavities appear, antral cavities rich in hyaluronic acid, stromal cells condense forming theca interna & externa
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What happens during development of the tertiary/Graafian follicle?
Fluid filled spaces form large antrum, oocyte eccentrically located & separated from fluid from coat of granulosa cells -> cumulus oophorus. Increased oestrogen secretion and increased proliferation of granulosa cells, start to express LH receptors
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What happens during development of the pre-ovulatory follicle? How does the corpus luteum form?
Oocyte -> haploid gamete + small polar body. Oocyte breaks free from follicle, still surrounded by some granulosa (corona radiata), expelled into peritoneal cavity. Corpus luteum forms from remaining granulosa cells & cells of theca internus
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What happens if there is no fertilisation?
Corpus luteum becomes the acellular corpus albicans (decreased progesterone and oestrogen)
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What happens if there is fertilisation?
Human chorionic gonadotropin (hCG) from placenta prevents degeneration of corpus luteum & signals to pituitary to secrete LH. Corpus luteum secretes progesterone until end of 4th month, then there is enough placental progesterone to take over
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What does the uterus consist of?
Uterine wall composed of external serosa (covered with pelvic cavity peritoneum), perimetrium, myometrium (middle muscular layer) & endometrium (internal mucosal layer, rich in glands/blood vessels). Uterus has 3 parts: fundus, body & cervix
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What effect does oestrogen have on the endometrium?
Oestrogen stimulates mitotic activity in glands & stroma -> increases endometrial thickness and increases length of endometrial spiral arteries
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What happens to the endometrium during the secretory phase?
Glands become saw-toothed and secretory under progesterone control, spiral arteries enlarge and coil more
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What happens to the endometrium during the receptive phase?
Short microvilli & loss of negative surface charge (allows implantation)
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What happens to the endometrium during the menstrual phase?
Death of corpus luteum -> cessation of progesterone & oestrogen -> involution of functional layer of endometrium, vasoconstriction/rupture of spiral arteries, shedding of blood into uterus (endometrial basal layer remains) & cervical mucus thinning
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Other cards in this set

Card 2

Front

What hormones are involved in the menstrual cycle? Where are they released from?

Back

Gonadotropin releasing hormone (GnRH, hypothalamus), follicle stimulating hormone (FSH, ant pituitary), luteinizing hormone (LH, ant pituitary) and oestradiol (ovary, oestrogens = oestradiol + oestrone) & progesterone (from ovary)

Card 3

Front

What happens in the menstrual cycle day 0-14?

Back

Preview of the front of card 3

Card 4

Front

What is the effect of FSH & LH in day 0-14 of the menstrual cycle?

Back

Preview of the front of card 4

Card 5

Front

What are the precursor molecules that lead to the production of oestradiol?

Back

Preview of the front of card 5
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