Menstrual Cycle

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MENSTRUAL CYCLE
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The Menstrual Cycle

• Rhythmical series of physiological changes that
  occur in fertile women
• Includes a series events which occur about every
  28 days throughout child bearing age of 35 years
• Under the control of the endocrine system
• Necessary for reproduction
• The cycle consists of changes taking concurrently
  in the ovaries, uterus
• cervix

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Phases of the Menstrual Cycle

• Menstrual cycle can be divided into 3 phases
• Menstrual Phase
• Proliferative / Follicular (Estrogen) Phase
• Secretory / Luteal Phase (Progesterone) Phase

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Phase Average start and end day(assuming a 28-day cycle)
Menstrual phase 1-4
Proliferative phase 5-13
Ovulation 13-16
Secretory phase 16-28
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Menstrual CycleDiagrammatic Representation
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The Menstrual Cycle

• Anterior lobe of the pituitary -- secretes FSH
  -initiates growth of the follicle in the ovary.
• As the ovum matures the follicle secretes
  estrogen which is necessary for the growth of the
  Endometrium to receive the fertilized ovum
• At peak levels of estrogen --FSH secretion is
  prevented LH is secreted by the anterior
  pituitary
• Midcycle LH surge is responsible for ovulation
• Following ovulation LH converts the ruptured
  follicle into corpus luteum which secretes
  progesterone

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Changes in Pituitary Hormones Days 1-14

• During the first half of the cycle (Days 1-14)
  the pituitary produces FSH, which stimulates
  egg production.
• This hormone also triggers the release of
  estrogen from the ovaries.

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Changes in Pituitary Hormones Days 14-28

• On the 14th day the pituitary begins releasing LH
  causing ovulation
• LH also directs the production of progesterone
  which maintains the growth of the endometrium.
• If the egg is not fertilized upon arrival in the
  uterus progesterone levels drop causing estrogen
  levels to drop leading to menstruation.

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Pituitary Hormones
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Changes in the Ovaries
Stage 2 - Egg Continues To Ripen Follicle Growth.
Stage 3 - Ovulation Fully Mature Egg Bursts Out
Of Follicle.
Stage 1 Ovum Begins To Develop.
Stage 4 - Egg Enters Fallopian Tube Follicle
Remains And Forms The Corpus Luteum.
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Changes in the Ovaries

• Stage 1 - An egg is beginning to mature within a
  cluster of cells called a follicle
• Stage 2 - Rapid follicle and egg growth
• Stage 3 - Ovulation occurs fully mature egg
  bursts out of the follicle (fertile) empty
  follicle transforms into the corpus luteum
• Stage 4 - Egg travels through fallopian tube (7
  days) if not fertilized upon arrival in uterus
  the corpus luteum shrinks triggering menstruation
  and ripening of new egg.

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Changes in Ovarian Hormones

• Estrogen -gradually increases during days 1-14
  signals body to thicken the lining of the uterus.
  Levels drop sharply after ovulation.
• Progesterone -Levels remain low during the first
  half of the cycle and then increase sharply
  during the second half of the cycle. Maintaining
  the growth of the endometrium lining.

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Changes in the Uterus
Stage 2 Day 5- 13 pre-ovulatory stage
Stage 1- Day 1-5 menstruation
Stage 3 Day 14 Ovulation
Stage 4 Day 15-28 post-ovulatory stage
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The uterine lining slowly thickens from day 5
through day 28
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Changes in the Uterus

• Stage 1- Menstruation- Endometrium breaks down
  and blood, mucus, tissue, and the egg are shed
  through the vagina.
• Stage 2- Menstrual flow stops endometrium
  begins to thicken.
• Stage 3- Endometrium continues to thicken.
• Stage 4- The endometrium is at its thickest
  point.

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Menstruation RUAL PHASE

• Menstrual bleeding, menses, period
• Discharge of Endometrium breaks down and blood,
  mucus, tissue, and the egg are shed through the
  vagina
• Result of the previous menstrual cycle

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FOLLICULAR PHASE

• Due to the rise of follicle stimulating hormone
  (FSH) during the first days of the cycle, several
  ovarian follicles are stimulated
• Follicles compete with each other for dominance
• The follicle that reaches maturity is called a
  Graafian follicle
• As they mature, the follicles secrete increasing
  amounts of estrogen, which thickens the new
  functional layer of endometrium in the uterus
• Estrogen also stimulates the cervix to produce
  fertile cervical mucus
• At the end of this phase ovulation occurs

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OVULATION

• During the follicular phase, estrogen suppresses
  production of luteinizing hormone (LH) from the
  pituitary gland
• When the ovum has nearly matured, levels of
  estrogen reach a threshold above which they
  stimulate production of LH (positive feedback
  loop)
• The release of LH matures the ovum and weakens
  the wall of the follicle in the ovary, causing
  the fully developed follicle to release its
  secondary oocyte
• After being released from the ovary, the ovum is
  swept into the fallopian tube

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POST OVULATION

• Progesterone completes development of the
  Endometrium
• Ovum not fertilized -
• CL degenerates-- progesterone level falls--
  Endometrium shed out I .E. Menstruation
• Low P levels --feedback to ant. Pit.--More FSH is
  secreted --cycle begins
• Ovum fertilized -
• Secretes HCG.-- CL maintained -- secretes P -
  maintains pregnancy

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LUTEAL PHASE

• Corpus luteum solid body formed in an ovary
  after the ovum has been released into the
  fallopian tube
• Produces significant amounts of progesterone,
  which plays a vital role in making the
  endometrium receptive to implantation of the
  blastocyst
• Falling levels of progesterone trigger
  menstruation and the beginning of the next cycle

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No Of Ovarian Follicles

• 20 weeks gestation 7,000,000
• At birth 1,000,000
• At puberty 400,000
• Fertile age approx...
  475 will ovulate

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Menopause

• The time when processes, which occur at puberty,
  are reversed.
• The ovaries gradually becomes less responsive to
  the FSH and LH.
• Ovulation and menstrual cycle become irregular
  and eventually ceases.
• Female secondary sex characters begin to regress.

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