Menstrual Cycle

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  • Created by: Saoirse
  • Created on: 23-12-14 02:31

Menstrual Cycle

  • Regulated by gonadotrophins released by the anterior pituitary gland
  • Aims to release one follicle (ovulate) and prepare the uterus for implantation after fertilisation
  • 3 phases

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Menstrual phase (menses): Day 1

  • Functional zone (stratum functionalis) of endometrium degenerates and is shed
  • Spiral arteries are constricted = ischaemia (inadequate blood supply)
  • o2 and nutrient deprived so degenerates

(http://o.quizlet.com/H4Cq9X5ezXo-.8mUxu15ow_m.jpg)

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Follicular/proliferative phase: Day 8

  • Ovarian follicles rapidly grow
  • Epithelial multiplication in basilar zone = restoation of uterine lining
  • Uterine glands enlarge and blood vessels develop

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Luteal (Secretory) phase

  • Endometrium thickens and becomes spongy
  • uterine glands enlarge
  • arteries enlongate into functional zone
  • begins after ovulation and peaks approx 12 days later
  • uterine cycle ends approx 14 days after ovulation (corpus luteum stops producing stimulatory hormones)
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Hormonal regulation

  • Requires coordination of ovarian and uterine cycles
  • Regulated by hypothalamus secreting GnRH
  • Pulse frequency of GnRH varies throughout cycle but is constant in males

Follicular phase

  • All 4 hormones relativelt low but FSH is dominant.
  • Enlarging follicles secrete oestrogen which initiates repair of endometrium
  • Secondary follicle releases inhibin = negative feedback on FSH
  • Surge in oestrogen at end of follicular phase = inc in GnRH pulse frequency
  • High oestrogen stimulates surge in LH which stimulates completion of meiosis 1, rupture of follicular wall and ovulation
  • High levels of oestrogen make cervical mucus thinner and easily penetrable

Luteal phase

  • Progesterone is dominant hormone, triggered by ovulation
  • Oestrogen continues to develop uterus for implantation - inc blood supply and glandular secretions
  • GnRH pulses = 1-4 per day (LH dominant hormone at this frequency)
  • 12 days after ovulation oestrogen and progesterone drop due to degeneration of corpus luteum
  • Drop in O and P = restricted blood supply to functional zone (degenerates), GnRH pulses inc, stimulating FSH which starts the cycle again
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Hormone chart

(http://media.tumblr.com/296aaa60470259adff32415524e0b3e2/tumblr_inline_mlrmjxW57b1qz4rgp.gif)

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