Menstrual CycleMenstrual Cycle

Menstruation is also called Menstrual bleeding, Menses, a period.

The flow of menses normally serves as a sign that a woman has not become pregnant.

Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).

The menstrual fluid is largely a mixture of blood and tissue from the uterine lining (Endometrium).

The average blood loss during menstruation is 35 milliliters with 10–80 ml considered normal.

Gonads. Male gonad and Female gonad.Gametes. Spermatozoa (Spermatozoon). Ova (Ovum).Gametogenesis:

spermatogenesis Oogenesis

During the reproductive years, failure to menstruate may provide the first indication to a woman that she may have become pregnant.

Gametogenesis in females (Oogenesis) is initiated in the fetus but is immediately arrested and does not commence until puberty when a single oocyte (usually) in alternating ovaries responds to a surge of gonadotropins once a month until menopause at about the age of 45 to 50.

Human Menstrual cycleHuman Menstrual cycle

~28 days in lengthIncludes menses for 3 to 5 days.Ovulation occurs spontaneouslyCycles occur throughout the yearOne egg produced / monthThree phases:

◦Follicular phase (proliferative, estrogenic)

◦Luteal phase (secretory, progestational)◦Menstrual phase (destructive)

To understand the menstrual cycle, it is necessary to know the structure of the uterus. The wall of the uterus is made up of three layers.

1. The outermost layer or perimetrium is made up of peritoneum.

2. The main thickness of the wall is made up of smooth muscle. This is the myometrium.

3. The innermost layer (corresponding to mucous membrane) is called the endometrium. It is this layer which undergoes changes during the menstrual cycle.

The constituents of the endometrium are as follows:

The surface of the endometrium is covered by a lining of epithelium.

The stroma fills the interval between surface epithelium and myometrium. It contains numerous simple tubular glands (uterine glands).

The arteries that supply the endometrium tend to run vertically towards the surface. Some of these run spirally and supply the whole thickness of the endometrium, while others that remain straight are confined to the basal part.

Stages of the menstrual Stages of the menstrual cyclecycle

The menstrual cycle has three stages. Viz:

Follicular/ estrogenic/ proliferative stage

Luteal/ secretory stageMenstrual / ischemic stage

Note: The stages of the menstrual cycle run parallel to the ovarian cycle

Follicular phaseFollicular phase It constitutes the 1st half of the menstrual cycle.Begins on last day of mensesPhase lasts until ovulation (~day 14)

In the ovaries follicles grow, secrete increasing amounts of estrogen.

During most of this phase, estrogen exerts “negative feedback”.

By days 10-12, a few ripe tertiary follicles existBy day 13, 1 Graffian follicle is present

In the uterus, the endometrium thickens; uterine glands enlarge, uterine blood supply increases

OvulationOvulationShedding of the ovum from the ovary is

called ovulation.occurs at end of follicular phase (day 14)Triggered by peak in estrogen (days 12-

13; “positive feedback”)Estrogen causes GnRH surge, LH surgeestrogen also “primes” (sensitizes)

pituitary gland to GnRHFSH surge also occursLH surge initiates meiosis in oocyte of

Graafian follicle (now a preovulatory follicle)

LH also triggers ovulation (9-12 hrs after LH surge peaks)

other antral follicles doomed to atresia

Luteal phaseLuteal phaseLast half of menstrual cycle (~14 days)Follicle is transformed to corpus luteum

(CL) by LH surgeCL secretes progesterone, oestrogen(very

little amounts)High progesterone, estrogen exert

negative feedback on hypothalamusUterine lining becomes thick, spongyLH, FSH levels are negligible > atresiaIf fertilization takes place and conceptus

implants, placental hCG rescues corpus luteum

No hCG(human chorionic gonadotrophin) > menstrual phase

Menstrual phaseMenstrual phase4-5 days in lengthuterine lining degeneratesfollicle development continues

◦several antral follicles exist◦follicles stimulated by LH, FSH pulses◦estrogen levels in blood begin to rise

Post menstrual

Proliferative

Menstrual

Secretory

LUTEAL LUTEAL PHASEPHASE

FOLLIC-ULAR PHASE

1 TO 4 DAYS– MENSTRUAL PHASE,5 TO 8 DAYS- POST MENSTRUAL PHASE,9 TO 17 DAYS- PROLIFERATIVE PHASE,20 TO 28 DAYS- SECRETORY PHASE.

OVULATION BEGINS BETWEEN 14 AND 15TH DAYCORPUS LUTEUM BEGINS TO DEGENERATE BETWEEN 24 TO 25TH

DAY

Name of phaseAverage start dayassuming a 28-day cycle

Average end day

menstrual phase 1 4

follicular phase (also known as proliferative phase)

5 13

ovulation (not a phase, but an event dividing phases)

14 14

luteal phase (also known as secretory phase)

15 26

ischemic phase (some sources group this with secretory phase)

27 28

Few Terms Few Terms Infrequent or irregular ovulation is called Oligoovulation.

The absence of ovulation is called Anovulation.

Normal menstrual flow can occur without ovulation preceding it: an anovulatory cycle. Anovulatory cycles commonly occur prior to menopause (perimenopause) and in women with polycystic ovary syndrome.

Very little flow (less than 10ml) is called Hypomenorrhea.

Regular cycles with intervals of 21 days or fewer are Polymenorrhea.

Frequent but irregular menstruation is known as Metrorrhagia.

Sudden heavy flows or amounts in excess of 80 ml are termed Menorrhagia.

Heavy menstruation that occurs frequently and irregularly is Menometrorrhagia.

The term for cycles with intervals exceeding 35 days is Oligomenorrhea.

Amenorrhea refers to more than three to six months without menses (in the absence of pregnancy) during a woman's reproductive years.