Menstruation

Question 1

what is menstruation?

Answer 1

Periodic /cyclic discharge of blood & tissue debris (fragments of endometrial tissue, desquamated vaginal epithelium, mucus) monthly. Combination of ovarian and uterine cycles.  Period extending from beginning of a period (menses) to beginning of next one is called menstrual cycle.
 First menstruation (menarche) occurs between 11–15 years with a mean age of 13 yrs. Once menstruation starts, it continues cyclically at intervals of 21–35 days with a mean of 28 days. Ultimately, it ceases between ages 45–50 when menopause sets in. Duration of menses is about 4-5 days & amount of bld loss is estimated to be 20 to 80 mL with an average of 35mL.
 Menstruation occurs when an egg released by the ovary remains unfertilized.

Question 2

factors involved in onset and continuation of normal menstruation.

Answer 2

These are:
a) Normal female chromosomal pattern (46XX).
b) Coordinated hypothalamopituitary ovarian axis.
c) Anatomical presence and patency of the outflow tract.
d) Responsive endometrium.
e) Active support of thyroid and adrenal glands.

Question 2

what cyclic Events leading to menstruation

Answer 2

1) Endocrine cycle: secretion of HPO hormones, GnRH, FSH/LH, E₂ & P₄
2) Uterine cycle: a) menstruation, b) proliferative phase, c) secretory phase
3) Ovarian cycle: a) follicular Phase, b) ovulation, c) Luteal phase

Question 2

outline the menstrual phase of the uterine cycle

Answer 2

1. Menstruation phase (7 days). Regression of corpus luteum with fall in the level of estrogen and progesterone is an invariable preceding feature leading to menses
    When fertilization of the oocyte and embryonic implantation do not occur, the corpus luteum regresses and circulating levels of progesterone and estrogens begin to decrease 8 to 10 days after ovulation, causing the onset of menstruation
    Following demise of CL, progesterone levels plummet, leads to spiral artery spasm & endometrial ischemia. The resulting anoxia causes infarction and shedding of the superficial endometrium leading to menstruation.
    Endometrial Basal layer, not dependent on progesterone-sensitive spiral arteries, remains intact & is never shed but major portions of functional layer; surface epithelium, most of each glands, stroma and blood-filled lacunae, detach from endometrium & slough away as menstrual flow or menses
    A fall in circulating levels of oestrogen & progesterone approx 14 days after ovulation leads to loss of tissue fluid, vasoconstriction of spiral arterioles and distal ischaemia. Enhanced fibrinolysis reduces clotting.
    PGF2a, endothelin-1 and platelet activating factor (PAF) are vasoconstrictors produced within endometrium & are vessel constrictors, both initiating and controlling menstruation
    Cells undergoing hypoxic injury release cytokines that increase vascular permeability and immigration of leukocytes. Leukocytes release collagenase & several other matrix metalloproteinases (MMPs) that degrade basement membranes & other ECM components
    Duration of the menstrual cycle may be variable but averages 28 days and last for 3-7days with blood loss of 20-80mls
    Day 1 of menstrual cycle is taken as day when menstrual bleeding appears, with myometrial contraction, which can be painful
    Menstrual flow consists of: Bld, tissue debris (fragments of endometrial tissue, desquamated vaginal epith, mucus) transudate of vaginal fliud, bacteria, enzymes & PG.
    At the end of the menstrual phase, the endometrium is usually reduced to a thin layer and is ready to begin a new cycle as its cells begin dividing to reconstitute the mucosa

Question 3

outline the feedback mechanism in menstruation

Answer 3

Negative and Positive Feedback
 Pattern of gonadotropin secretion is critically regulated by both negative and positive feedback from estrogen/ progesterone and inhibin/ activin.
 At the beginning of menstrual cycle, in response to low estrogen levels, the pituitary secretes FSH which in turn stimulates ovaries to secrete estrogen. Rising levels of estrogen in turn suppresses pituitary FSH
Positive feedback
 Just before ovulation, if the pituitary detects a high enough level of estrogen (> 200 pg/ ml), it responds with gonadotrophin (LH) surge.
 The LH surge triggers ovulation.
 Ovulation normally occurs about 9 hrs after the peak of the “LH surge” at mid cycle.

Question 4

outline the proliferative phase of the uterine cycle

Answer 4

2. Proliferative phase (7 days) -
    From 7th to 14th day there is estrogen induced endometrial growth (priming) i.e. estrogen produced by granulosa cells.
    Estrogens act on the endometrium, inducing regeneration of the functional layer lost during menstruation.
    Cells in the basal ends of glands proliferate, migrate, and form the new epithelial covering over the surface exposed during menstruation.
    Endometrial lining is a simple columnar surface epithelium
    Uterine glands become tubular, with narrow, nearly empty lumens & lie perpendicular to surface.
    Epith becomes columnar with nuclei placed at the base.
    Stromal cells become spindle shaped, increase in number & size and show numerous mitosis & are compact.
    Short glands elongate until they become tortuous and cells show prolific mitotic activity.
    Spiral arterioles lengthen, become more spiral and convoluted as functional layer is reestablished and grows
    Endometrium becomes thicker (max 3-5 mm) and more vascular.
    Also called the follicular or estrogenic phase, coincides with the rapid growth of a small group of ovarian follicles growing as vesicular follicles.
    With development of their thecae interna, the follicles actively secrete estrogen & increase its plasma conc

Question 5

outline the secretory phase of the uterine cycle

Answer 5

3. Secretory phase (14 days) - begins on day 15 and ceases 5–6 days prior to menstruation and are due to combined effects of estrogen and progesterone liberated from the corpus luteum after ovulation.
    Endometrium contains progesterone receptors induced by estrogen. Thus, progesterone only act on endometrium previously primed by estrogen.
    The endometrial changes include the following
    Surface epithelium becomes more columnar and ciliated at places
    Glands increase in size, become mature, tortuous with “corkscrew” appearance.
    Endometrium thickens (thickness 6–8 mm) and endometrial surface is thrown into folds. Growth ceases 5–6 days prior to menses (22nd or 23rd day of cycle) in an infertile cycle
    Vacuoles appearance between nuclei & basement membrane (subnuclear vacuolation) due to secretion of glycogen
    Blood vessels undergo marked spiraling
    Stromal cells become swollen, large and polyhedral decidual cells
    Superficial compact and deep spongy layers are formed
    Endometrial regressive changes are pronounced 24–48 hours prior to menstruation