Why do girls have periods? What causes periods?

Physiological changes during periods.

Periods are female structure and physiological function of the reproductive organs.

Why do girls have periods, menstrual period?

Hypothalamus, pituitary and ovarian interact with reproductive hormones to regulate the menstrual cycle, during period of menstrual period and proliferating, blood levels of estradiol and progesterone are low, negative feedback towards pituitary and thalamus weakened or eliminated, resulting in hypothalamus secretion of gonadotropin releasing hormone increased. Thils will lead to pituitary secretion of follicle-stimulating hormone and luteal LH increase, making follicular development, estrogen secretion gradually increased.

At this time, estrogen stimulates endometrial proliferation into the proliferative stage. Luteinizing hormone progestin secretion increased, leading to ovulation. This period of estrogen and progesterone levels were elevated.

This results in the hypothalamus and pituitary strengthen the negative feedback of inhibition, thus the ovulation-stimulating hormone and luteinizing hormone levels decline, resulting in luteal degradation, lead to estrogen and progesterone levels decrease. Endometrial lose the support of these two hormones, peeling, bleeding, occurs menstruation.

At this time, estrogen and progesterone decrease, the next menstrual cycle start.

Ovulation Period.

Ovulation refers to the egg and surrounding cumulus granulose cells in the process of being discharged together. Women's ovulation date is 14 - 16 days before the next menstruation.

Male sperm fertilizing capacity can be maintained for 2-3 days in a woman's reproductive tract. Therefore, sexual intercourse before and after the ovulation period will be easy to conceive.

An egg from the ovary after it has discharged in the fallopian tubes can survive 1-2 days, to wait for fertilization; man's sperm fertilizing capacity can be maintained for 2-3 days in a woman's reproductive tract. Again, this means it will be a lot easier to conceive before and after the ovulation period.

Period Change process.

Menstrual cycle is interact to regulate by three reproductive hormones produced by the hypothalamus, pituitary, and ovary, the following changes occur in the course of the menstrual cycle:

After women reach puberty, control by the hypothalamus of gonadotropin-releasing hormone, the anterior pituitary secretion of follicle-stimulating hormone (FSH) and a small amount of luteinizing hormone (LH) induce ovarian follicles mature and begin to secrete estrogen. Under the action of estrogen, endometrium makes proliferative change;

Follicle matures, estrogen secretion gradually increased, when reach to certain concentration, by a positive feedback effect on the pituitary, promote anterior pituitary gonadotropin secretion increases, LH secretion increase more obvious, the formation of luteinizing hormone-releasing reach its peak, it causes the mature follicle ovulation;

By the function of luteinizing hormone, after follicle ovulation, corpus luteum produce, estrogen and progesterone secret. This phase, progesterone work on endometrium, accelerate endometrium growth and differentiation, change into secretory endometrium;

Since the corpus luteum secrete large amounts of estrogen and progestin, two hormones blood concentration increased, give negative feedback inhibition of the hypothalamus and pituitary gland, the pituitary secretion of follicle stimulating and luteinizing hormone decrease, corpus luteum shrink and thus progesterone and Estrogen also rapidly reduced, endometrial suddenly lost the support of both sex hormones, collapse, bleeding, lead to endometrial shedding and menstrual cramps.