Menstrual Cycle

menstrual cycle

[′men·strə·wəl ′sī·kəl] (physiology) The periodic series of changes associated with menstruation and the intermenstrual cycle; menstrual bleeding indicates onset of the cycle.

Menstrual Cycle

a complex physiological process characterized by changes throughout the female body that recur every 21-30, but in most cases, every 28 days. The principal external manifestation of the menstrual cycle is bleeding from the genitalia (specifically, from the uterus), or menstruation. Menstruation begins during puberty, at age 11-15, and continues until the menopause at age 45-55. The onset of menstruation (menarche) varies with climate, living conditions, nutrition, and social and hygienic conditions. The cycle is not always established immediately. At first there may be delays, but after six to 12 months the cycle acquires a rhythm that recurs at regular intervals in each girl (woman). Menstruation does not occur before puberty, during pregnancy and breast feeding, and after the onset of the climacteric. Only human beings and anthropoid apes have menstrual cycles.

The menstrual cycle is regulated by highly differentiated nerve nuclei, the sex centers, which are located in the middle of the diencephalon in the hypothalamus. Complex substances called releasing hormones, or releasing factors, originate and accumulate in these centers. The hormones travel through the neural and vascular pathways to the hypophysis (pituitary), where they influence the secretion of gonadotropins, or gonadotropic hormones. The synthesis and secretion of each of the gonadotropic hormones by the hypophysis are controlled by a specific releasing factor. The gonadotropic hormones are carried in the bloodstream to every organ.

The most pronounced changes caused by the menstrual cycle occur in the uterus and ovaries. In the ovaries hormones affect the growth and maturation of the follicle containing the ovum. The mature follicle ruptures, and the ovum and the follicular fluid enter the abdominal cavity and, subsequently, the uterine tube. The process by which the follicle ruptures and the mature ovum emerges, ready for fertilization, is called ovulation, which in a 28-day cycle generally occurs between the 13th and 15th day, counting from the first day of menstruation. The corpus luteum is formed from the ruptured follicle. These morphological changes in the ovary are accompanied by the secretion of the steroid sex hormones—estrogens, which are secreted by the maturing follicle, and progesterone, which is released by the corpus luteum.

In the first phase of the menstrual cycle, the estrogens stimulate the regeneration and proliferation of the mucous membrane of the uterus (the endometrium) and the growth of the glands, which lengthen and become convoluted. The endometrium becomes four to five times thicker. The cervical glands secrete more mucus, and the cervical canal dilates, making it easier for spermatozoa to pass into the uterus. Epithelium is proliferated in the lactiferous ducts of the mammary glands.

In the second phase of the menstrual cycle, progesterone slows the metabolic rate. The proliferation of the endometrium in the body of the uterus ceases. The endometrium becomes looser and hydrated. The endometrial glands begin to secrete, creating favorable conditions for the fertilized ovum to attach itself to the endometrium and for the embryo to develop. The glands stop secreting mucus, and the cervical canal closes. In the mammary glands alveoli capable of producing and secreting milk develop from the epithelium that was proliferated in the terminal portions of the lactiferous ducts.

If pregnancy does not occur, the corpus luteum degenerates, the functional layer of the endometrium is sloughed off, and menstruation begins. The first day of menstruation is considered the first day of the new menstrual cycle. Menstrual bleeding lasts from three to six or seven days, depending on a woman’s physiological and physical characteristics. The blood loss varies from 40 to 150 g. Prior to menstruation some women have a somewhat rapid pulse and high arterial blood pressure. Some are irritable, tire easily, or feel sleepy. Owing to physiological changes in the functioning of the nervous system, wavelike changes occur in the circulation, thermoregulation, and metabolism. If the menstrual cycle is normal, these changes are within the limits of normal physiological vacillations and do not lower the woman’s capacity for work.

The main hygienic requirements during menstruation are cleanliness and sufficient physical and mental rest. Swimming in a river or ocean is not recommended, and showers are preferable to baths. Spicy food and alcohol should not be consumed because they cause blood to rush to the abdominal organs, thus increasing uterine bleeding. Sexual relations during menstruation are out of the question.

The menstrual cycle may be disrupted by certain diseases, by inadequate nutrition, or by psychological stress. Disturbances of the cycle are manifested by the absence of menstruation (amenorrhea), decreased menstrual flow (hypomenorrhea), extremely profuse flow (menorrhagia), brief or infrequent menstruation (oligomenorrhea), and painful menstruation (dysmenorrhea). Treatment aims at eliminating the main causes of the disruption of the cycle.

REFERENCES

Osnovy endokrinologicheskoi ginekologii. Moscow, 1966.
Kvater, E. I. GormonaVnaia diagnostika i terapiia v akusherstve i ginekologii, 3rd ed. Moscow, 1967.

L. S. PERSIANINOV

menstrual cycle

cycle

[si´k'l] a succession or recurring series of events.cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.

Cardiac cycle. From Applegate, 2000.cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G₂ phase, a relatively quiescent period; the M phase, consisting of the four phases of mitosis; and the G₁ phase of interphase, which lasts until the S phase of the next cycle.citric acid cycle tricarboxylic acid cycle.estrous cycle the recurring periods of estrus in adult females of most mammalian species and the correlated changes in the reproductive tract from one period to another.hair cycle the successive phases of the production and then loss of hair, consisting of anagen, catagen, and telogen.Krebs cycle tricarboxylic acid cycle.menstrual cycle see menstrual cycle.ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation; see also ovulation and reproduction.reproductive cycle the cycle of physiologic changes in the reproductive organs, from the time of fertilization of the ovum through gestation and childbirth; see also reproduction.sex cycle (sexual cycle) 1. the physiologic changes that recur regularly in the reproductive organs of nonpregnant female mammals.2. the period of sexual reproduction in an organism that also reproduces asexually.TCA cycle tricarboxylic acid cycle.tricarboxylic acid cycle the cyclic metabolic mechanism by which the complete oxidation of the acetyl portion of acetyl-coenzyme A is effected; the process is the chief source of mammalian energy, during which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide, water, and high-energy phosphate bonds. Called also citric acid cycle, Krebs cycle, and TCA cycle.

Central pathways of metabolism: How the body produces energy from the energy-containing nutrients using the tricarboxylic acid cycle. From Davis and Sherer, 1994.urea cycle a cyclic series of reactions that produce urea" >urea; it is a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney.

menstrual

[men´stroo-al] pertaining to menstruation.menstrual cycle the regularly recurring physiologic changes in the endometrium that culminate in its shedding (menstruation). Menstrual cycles vary in length, with the average being about 28 days. The length of time of menstrual flow is also variable, with an average of about 5 days. Women menstruate from puberty to menopause, except during pregnancy. The first 14 days of the cycle are called the follicular phase; a follicle containing an ovum is developing in one of the ovaries. It begins as the menstrual flow ceases; the lining of the uterus is stimulated by estrogen and begins to increase in thickness to prepare for the possibility of reproduction. On the twelfth or thirteenth day of the cycle, the ovulatory phase begins with a surge in levels of hormone" >luteinizing hormone and hormone" >follicle-stimulating hormone; ovulation then takes place and the ovary discharges the ovum. The ruptured follicle is transformed into a yellowish material called the corpus luteum; the luteal phase begins as the corpus luteum secretes progesterone. Progesterone acts on the endometrium, building up tissues with an enriched supply of blood to nourish the future embryo. If fertilization and conception do not take place, the estrogen level in the blood falls, the endometrium is no longer stimulated, and the uterus again becomes thinner. Blood circulation slows, blood vessels contract, and the menstrual phase begins; unused tissue breaks down into the bloody discharge known as menstruation. The cycle then starts again.

Average 28-day menstrual cycle. The cycle begins when hormones from the pituitary gland stimulate the development of an egg in a follicle inside one of the ovaries. About the fourteenth day, ovulation occurs: The follicle bursts, and the egg is discharged from the ovary. If the egg is not fertilized, the cycle ends in menstruation on the twenty-eighth day. If the egg is fertilized, pregnancy begins.

men·stru·al cy·cle

the period in which an ovum matures, is ovulated, and enters the uterine lumen through the fallopian tubes; ovarian hormonal secretions effect endometrial changes such that, if fertilization occurs, nidation will be possible; in the absence of fertilization, ovarian secretions wane, the endometrium sloughs, and menstruation begins; this cycle lasts an average of 28 days, with day 1 of the cycle designated as that day on which menstrual flow begins. Compare: endometrial menstrual cycle.

menstrual cycle

A monthly cycle that occurs in women from menarche (the first onset of menstruation) to menopause (the cessation of thereof), which is measured from the beginning of one menstrual period to the beginning of the next, ±28 days. The menstrual cycle is characterised by changes in hormone levels and physical changes in the endometrium, and prepares the latter for implantation of an embryo.

men·stru·al cy·cle

(men'strū-ăl sī'kĕl) The period in which an oocyte or ovum matures, is ovulated, and enters the uterine lumen through the uterine tube; ovarian hormonal secretions effect endometrial changes such that, if fertilization occurs, nidation will be possible; in the absence of fertilization, ovarian secretions wane, the endometrium sloughs, and menstruation begins; this cycle lasts an average of 28 days, with day 1 of the cycle designated as that day on which menstrual flow begins.

PHASES OF THE MENSTRUAL CYCLE

menstrual cycle

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. See: illustration

The menstrual cycle is divided into four phases characterized by histological changes that take place in the uterine endometrium. They are:

Proliferative Phase: Following blood loss from the endometrium, the uterine epithelium is restored to normal; the endometrium becomes thicker and more vascular; the glands elongate. During this period, the ovarian follicle is maturing and secreting estrogens; with the estrogen stimulation, the endometrium hypertrophies, thickening and becoming more vascular, and the glands elongate. The phase is terminated by the rupture of the follicle and the liberation of the ovum at about 14 days before the next menstrual period begins. Fertilization of the ovum is most likely to occur in the days immediately following ovulation.

Luteal or Secretory Phase: After releasing the ovum, the corpus luteum secretes progesterone. With the progesterone stimulation, the endometrium becomes even thicker; the glands become more tortuous and produce an abundant secretion containing glycogen. The coiled arteries make their appearance; the endometrium becomes edematous; the stroma becomes compact. During this period, the corpus luteum in an ovary is developing and secreting progesterone. This phase lasts 10 to 14 days.

Premenstrual or Ischemic Phase: If pregnancy has not occurred, the coiled arteries constrict and the endometrium becomes anemic and shrinks a day or two before menstruation. The corpus luteum of the ovary begins involution. This phase lasts about 2 days and is terminated by the opening up of constricted arteries, the breaking off of small patches of endometrium, and the beginning of menstruation with the flow of menstrual fluid.

Menstruation: The functional layer of the endometrium is shed.

The menstrual cycle is altered by pregnancy, the use of contraception, intercurrent illnesses, diet, and exercise.

menstrual cycle

the modified OESTROUS CYCLE of most primates, which results in the periodic destruction of the mucosa of the uterine wall at the end of the LUTEAL PHASE.

This results in a discharge of blood known as menstruation, the shedding of the ENDOMETRIUM, every 28 days in women.

Menstrual cycle

A hormonally regulated series of monthly events that occur during the reproductive years of the human female to ensure that the proper internal environment exists for fertilization, implantation, and development of a baby. Each month, a mature egg is released from the follicle of an ovary. If an egg is released, fertilized, and implanted, the lining of the uterus continues to build. If fertilization and/or implantation does not occur, the egg and all of the excess uterine lining are shed from the body during menstruation.Mentioned in: Human Chorionic Gonadotropin Pregnancy Test

men·stru·al cy·cle

(men'strū-ăl sī'kĕl) The period in which an oocyte matures, is ovulated, and enters the uterine lumen through the uterine tube; ovarian hormonal secretions effect endometrial changes such that, if fertilization occurs, nidation will be possible; in the absence of fertilization, ovarian secretions wane, the endometrium sloughs, and menstruation begins; this cycle lasts an average of 28 days, with day 1 of the cycle designated as that day on which menstrual flow begins.

Patient discussion about menstrual cycle

Q. is it normal to get a nausous feeling around the time i would start my menstrual cycle? A. Yes, it is absolutely normal to feel nausea before and during menstrual cycle. The shift in hormonal levels can cause also headaches, mood changes, feeling of bloating and other common symptoms.

Q. can you get poly-cystic ovarian syndrome when you still have your menstrual cycle? A. polycystic ovarian syndrome is when the egg does not come out- so i guess there is no menstrual that month. but as far as i know it's not every month that an egg decides to stay at home after 18... i guess you can check up more exact at this site:
http://www.pcosupport.org/

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Menstrual Cycle

REFERENCES

menstrual cycle

cycle

menstrual

men·stru·al cy·cle

menstrual cycle

men·stru·al cy·cle

menstrual cycle

menstrual cycle

Menstrual cycle

men·stru·al cy·cle

Patient discussion about menstrual cycle

menstrual cycle

Words related to menstrual cycle

noun a recurring cycle (beginning at menarche and ending at menopause) in which the endometrial lining of the uterus prepares for pregnancy

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