Physiology of menstruation

Physiology of menstruation: 

Normal menstrual blood continues for 2-7 days, with a cycle length range 21-35 days with average 28 days. The amount of menstrual blood about 30- 50 cc, if exceeds 80 cc its considered as menorrhagia. Menorrhagia also considered if the duration of bleeding exceeds 7 days. Cycle length greater than 35 days is considered as oligomenorrhae while cycle length shorter than 21 days is considered as poly- menorhhaea. Duration of periods less than 2 days is considered as hypomenorrhae. 

Menstruation occurs as a consequence of hormonal interaction between hypothalamus and the pituitary (Hypothalamo-pituitary axis), pituitary and ovarian axis, lastly the effect of these axis on the uterus. 

Hypothalamo-pituitary Ovarian axis: 

First hypthalamos which secretes a polypeptide called gonadotrophic relasing hormone(Gn RH) in a pulsatile manner all through the day (day and night). GnRH reach the pituitary gland stimulate the gonadotrophin to secrete a polypeptide hormone called FSH (follicular stimulating hormone). 

Second FSH which secreted from anterior lobe of the pituitary gland travel through blood to the ovary stimulating the germ cells to develop. The germ cells contains more receptors to FSH will be the primary oocyte. This primary oocyte is arrested in the prophase of the first meiotic division. 

Other cells with less receptors will be the granulosa cells. 

In the ovary these cells will arrange themselves around the primary oocyte. In the beginning day the primary oocyte is surrounded by a single flattened granulosa cells forming the primordial follicle. 

Granulosa cells produce estradiol hormone and inhibin hormone. Not only that but granulosa cells produces anti Mullerian hormone (AMH) as well. AMH first made in the primary follicles that advance from the primordial follicle stage. AMH can be measured at any time during the cycle. It is a marker for ovarian reserve. 

Third both estradiol and inhibin travel through the blood back to pituitary gland to decrease the production of FSH (negative feed back). Although the decreasing amount of the FSH, E2 (estradiol) increase as number of granulosa increase and receptors of FSH increases on the surfaces of the granulosa cells. 

Fourth when E2 reaching to 200 pg/ml and should be maintained for 24-48 hours a positive feed back to pituitary occurs leading to secretion of a hormone called LH (Luteinizing hormone). The release of the LH is in excess so called LH surge.

Fifth, LH surge function as

• completion of the first meiotic division
• Release of the ovum
• Luteinization of the granulosa cell
• Formation and maintenance of corpus lutetium 

Ovulation (release of the ovum )occurs after 34-36 hours after LH surge. Life span of the released ovum (secondary oocyte) is 24 hours. Time since ovulation till the next cycle is a constant 14 days.

So the ovary during the ovulation cycle may be classified into a follicular phase where the primordial follicle under the effect of FSH and the granulose secrete increasing amount of E2 and inhibin hormone. Stage of ovulation during which E2 reach up to 200 pg/ml for 24-48 hours followed by LH Surge and peak and 36 hours after the surge to release the ovum.

After ovulation is the lutinizing phase during which the corpus lutetium formation proliferation, vascularization , maturation, and finally regression take place. The life span of the corpus lutium in non pregnant woman is 12-14 days

Progesterone hormone reach a peak 8 days post LH surge.

Fi 6 the ovary shows growth of follicles ovulation and formation of corpus luteum

 The endometrium cycle 

1. Proliferative phase: Under the effect of increasing E2 secreted from granulosa cells, the endometrial glands becomes tubular with glandular cells proliferate and stroma cells proliferate with evidences of mitosis. Blood vessels continues to grow unbranched. The endometrium thickness is 3-4 mm 
2. Secretory phase; under effect of progesterone the glands branches , blood vessels branches and stroma becomes edematous. The endometrium thickness is 6-8 mm 
3. Menstrual phase during which menstruation occurs 

Why menstruation happened? 

Regression of the corpus lutium leads to fall in the level of E2 and progesterone. The fall level of these hormone will lead to vasospasm of the endometrial vessels with release of endothelin and prostaglandin, these ischemia will lead to sloughing of the endometrium except the basal layer with shedding of all of the endometrim leaving the basal layer for later regeneration with the next cycle. This phase lasts 2- 7 days.