Menstrual Cycle

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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

References in periodicals archive ?
Why not see your doctor, who will check for breast and pubic hair development, which might suggest Aunt Flo could be coming Soon.
Aunt Flo had no trouble, in taking the four-runner two-year-old maiden, as her starting price of 1-6 might have indicated, though the Michael Bell-trained daughter of Royal Academy did tend to hang away from the rail, suggesting the ground was plenty firm enough for her.
NOTTINGHAM: 6.30 Xylem, 7.00 Aunt Flo, 7.30 Break For Peace, 8.00 Prospector's Cove, 8.30 Hebony, 9.00 Pressurise.
Kieren wasn't the only man under threat at Newbury - newcomer Aunt Flo twice threw off Frankie Dettori.
NEGATIVES: Wannabe Grand, unlucky over course last month against Rose Of Mooncoin, returned to win a Listed event from Aunt Flo. Not that impressive, and may have problems confirming earlier form with Spirit Willing.
A well-backed 7-4 favourite, the Danehill filly got first run on her rivals and held the strong finish of Michael Bell's Aunt Flo by three- quarters of a length.
"GO with the Flo!" is the message emanating from Michael Bell's Newmarket yard, with the trainer confident that Aunt Flo can win today's feature two-year-old race -the British Horse Racing Directory Empress Stakes at Newmarket.
The Manila colt's winning debut came only last week, when he beat Aunt Flo on soft ground, and Meehan said yesterday: "I want to give myself more time before making my mind up about the Chesham.
The Italian escaped without injury after the Michael Bell-trained newcomer Aunt Flo became unruly as he tried to mount her before the Kingsclere Conditions Stakes.
Similar, but not identical, comments apply to Aunt Flo, who was runner- up to Tumbleweed Quartet, though in this instance her trainer Michael Bell was not at the course to speak to the stewards.
NEWBURY: 2.00 Poliziano (nap), 2.30 Aunt Flo, 3.00 Kpolo, 3.30 Zante, 4.00 Adeste Fideles, 4.30 Craigievar, 5.00 Xylem.
KEMPTON: 6.30 Aunt Flo, 7.00 Catchascatchcan (nap), 7.30 Deep Space, 8.30 Tarashaan, 9.00 Star Invader.