The regularly recurring cycle of physiological events, including ovulation and menstruation.
A period, usually of 28 days, during which a woman ovulates, the walls of the uterus swell and bleeding takes place if the ovum has not been fertilised.
The regular growth of the endometrium (lining of the uterus) to prepare for a possible fertilized egg and, if no pregnancy occurs, the expulsion of the unused lining in a bloody fluid at the end of the cycle, in the process called menstruation.
Recurring cycle, beginning at menarche and ending at menopause, in which the endometrial lining of the uterus proliferates in preparation for pregnancy and, if pregnancy does not occur, is shed at menstruation. The menstrual cycle is under the control of female reproductive hormones and is necessary for reproduction to occur. In the average woman, about 30 milliliters of blood is lost during menstruation. Because of this blood loss, women have higher dietary requirements for iron than do males to prevent iron deficiency. The menstrual cycle is divided into three phases— the menstrual phase, the proliferative phase, and the secretory phase. During each, the hormonal milieu differs, as do anatomic changes within both the uterus and in the ovaries. The average menstrual cycle is 28 days—the first day of menstrual flow is considered day one of the cycle. The length of the cycle varies greatly among women. The proliferative phase (sometimes called the follicular phase) follows menstruation. During this time (average 8 days), the pituitary gland produces follicle-stimulating hormone (FSH) that promotes the growth of a graafian follicle (egg sac; also called a follicle) within the ovary. The ovum (egg) matures in the follicle during the proliferative phase. FSH also stimulates the ovary to produce estrogen (predominantly in the form of estradiol), causing endometrial tissue to build up and line the inside of the uterus. The mature ovum bursts from the follicle (ovulation or the ovulatory phase) about 2 weeks prior to the next menstrual cycle. The sexually mature female releases one egg (or occasionally two) at the time of ovulation. The ovum then travels from the ovary down the fallopian tube, and into the uterus. The follicle then becomes known as the corpus luteum. The secretory phase (sometimes called the luteal phase) follows—after ovulation and formation of the corpus luteum, luteinizing hormone (LH) released by the pituitary gland causes the corpus luteum to grow and to secrete progesterone. Progesterone makes the endometrial lining stronger and spongy in texture. It also stimulates glands in the endometrium that produce uterine fluid to support embryonic development if fertilization occurs. If pregnancy does not occur, the levels of progesterone and estrogen peak about a week after ovulation and then begin to drop. The flow of blood to the endometrium decreases, and its upper portion is broken down and shed during menstruation. At the same time, the corpus luteum withers. Once menstruation occurs, the cycle begins anew.
The periodic sequence of events in sexually mature nonpregnant women by which an egg cell (ovum) is released from the ovary at “monthly” intervals until the change of life. The stages of the menstrual cycle are shown in the diagram. An ovum develops within a ‘Graafian follicle in the ovary. When mature, it bursts from the follicle and travels along the fallopian tube to the womb. A temporary gland (the corpus luteum) develops in the ruptured follicle and secretes the hormone ‘progesterone, which causes the lining of the womb to become thicker and richly supplied with blood in preparation for pregnancy. If the ovum is not fertilized the cycle continues: the corpus luteum shrinks and the womb lining is shed at ‘menstruation. If fertilization does take place the fertilized ovum becomes attached to the womb lining and the corpus luteum continues to secrete progesterone, i.e. pregnancy begins.
The periodically recurrent series of changes occurring in the uterus and associated sex organs (ovaries, cervix, and vagina) associated with menstruation and the intermenstrual period. The human cycle averages 28 days in length, measured from the beginning of menstruation. The menstrual cycle is, however, quite variable in length, even in the same person from month to month. Variations in the length of the cycle are due principally to variation in the length of the proliferative phase.
A monthly series of hormone controlled changes that prepare the uterine lining for a pregnancy.
The process during which an egg matures and is released, and the uterus prepares to receive it; on average, the menstrual cycle lasts 28 days.
The regular, roughly monthly process of preparing the lining of the uterus for the implantation and support of a fertilized egg; if no egg is fertilized, it ends in the shedding of the lining (menstruation). This cycle is regulated by the fluctuations and interactions of various hormones.