ENDOMETRIAL CYCLE, Schemes and Mind Maps of Human Biology

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ENDOMETRIAL CYCLE

Dr. Sagarika Sarkar

• Also known as MENSTRUAL CYCLE or UTERINE CYCLE
• It refers to the cyclic changes occurring in the endometrium during active reproductive period (menarche to menopause) in females leading to recurrent monthly bleeding per vaginum (menstruation).
• These cyclic changes are under control of the endocrine system.
• It is necessary for reproduction
• Average length: 28 days (21 to 35 days)

PHASES OF ENDOMETRIAL CYCLE

• Menstrual phase: 1st^ – 6 th^ day
• Proliferative phase: 7th^ – 14 th^ day
• Secretory phase: 15th^ – 28 th^ day

• DAYS

PROLIFERATIVE PHASE

• After menstruation only a thin layer of endometrial stroma remains, and the epithelial cells left are those located in the deeper portions of the glands and crypts of endometrium.
• In the first part of the monthly ovarian cycle, ie. Follicular phase, estrogens (secreted by the granulosa cells and theca interna) causes increased mitotic activity in the glands and stroma.
• The endometrial surface is reepithelialized within 4 to 7 days after the beginning of menstruation.

Changes in endometrium during proliferative phase:

Hormone responsible: estrogens

Thickness of endometrium, which is less than 1 mm at the end of menstrual phase, increases to 3 – 4 mm at the end of proliferative phase

Angiogenesis in the stratum functionale leads to proliferation of blood vessels, which become spiral arterioles

Endometrial glands are stimulated to grow. They contain glycogen but they are non-secretory

Changes in endometrium during secretory phase:

Hormone responsible: estrogen and progesterone

There is elongation and coiling of the endometrial mucous glands (corkscrew-shaped glands). These glands secrete thick viscous fluid containing glycogen

Blood supply of endometrium further increases as progesterone promotes spiraling of blood vessels

Thickness of endometrium increases to 5-6 mm at the end of this phase Thus the thickened endometrium with large amounts of nutrients is ready to provide appropriate conditions for implantation of a fertilized ovum

MENSTRUAL PHASE

• If fertilization does not , the corpus luteum in the ovary involutes to form corpus albicans and on Day 26th^ of the endometrial cycle the levels of estrogens and progesterone fall suddenly, marking the end of secretory phase. Menstruation follows.

Endometrial debris contains sloughed off necrosed tissue, blood, serous fluid and a large amount of prostaglandins and fibrolysins

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

The menstrual fluid is normally nonclotting because of presence of fibrolysins along with the debris

If excessive bleeding occurs, the quantity of fibrolysins may not be sufficient to prevent clotting

Within 4 – 7 days after menstruation starts, the loos of blood ceases due to reepithelialization of the endometrium

During menstrual phase, about two-thirds of the superficial endometrium is sloughed off and only a thin basal layer (1mm thick) is left behind

CYCLIC CHANGES IN CERVIX

• During menstrual phase, the mucosa of cervix is not shedded off
• During proliferative phase, the secretions of mucosal cells of the endocervix become thin watery and alkaline. At the time of ovulation, the cervical mucus is thinnest and its elasticity is maximum. It can be stretched like a long, thin elastic thread up to 8 – 12 cm (spinbarkeit effect). The mucous also produces a fern-like pattern when spread on glass slide and allowed to dry (fern test).
• Fern test: presence of fern pattern of cervical mucus in the proliferative phase and its disappearance in the secretory phase is indicative of ovulatory cycle, whereas persistence of fern pattern throughout the cycle indicates anovulatory cycle
• The mucus strings actually align themselves along the length of the cervical canal, forming channels that help guide sperm in the proper directionfrom the vagina into the uterus

ABNORMALITIES OF MENSTRUATION

• Anovulatory cycles: menstrual cycles occur at normal intervals, but ovulation does not occur
• Amenorrhoea: absence of menstrual bleeding. It is of two types:
• Primary amenorrhoea: menstrual bleeding has never occurred.it occurs due to failure of sexual maturation
• Secondary amenorrhoea: cessation of menstrual cycles in a woman who previously had normal and regular cycles. Pregnancy is the most common cause.
• Hypomenorrhoea: scanty menstrual bleeding
• Oligomenorrhoea: infrequent and reduced frequency of menstruation

• Menorrhagia: abnormally profuse bleeding during normal regular cycles
• Metrorrhagia: occurrence of uterine bleeding in between the periods
• Dysmenorrhoea: painful menstruation
• Pre-menstrual syndrome: about 7 – 10 days before menstruation some women experience symptoms like irritability, lack of concentration, depression, heaviness, headache and constipation which is called pre-menstrual syndrome

Assignment

Name:

Roll No.:

Attempt all questions

1. At which stage in the endometrial cycle does the secretory phase occur?

a) days 1 – 5 b) days 5 – 14 c) days 14 – 28 d) days 4 – 10

2. At which point in the menstrual cycle is a woman most fertile?

a) days 1 – 5 b) days 9 – 14 c) days 17 – 21 d) days 22 -

3. Which of the following statement is true about menstruation?

a) in a normal 28 day menstrual cycle you would expect menstruation to last approximately 6 – 8 days b) during menstruation the entire endometrium is shed c) only stratum functionale is shed d) absence of menstruation also indicates an active pregnancy