Premenstrual phase definition

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NCBI Bookshelf. Dhanalakshmi K. Thiyagarajan ; Hajira Basit ; Rebecca Jeanmonod. Authors Dhanalakshmi Premenstrual phase definition. Thiyagarajan ; Hajira Basit 1 ; Rebecca Jeanmonod 2. The reproductive system of a female, unlike men, shows regular cyclic changes that teleologically may be regarded as periodic preparation for pregnancy and fertilization.

In primates and humans, the cycle is a menstrual cycle, and its most conspicuous feature is the periodic vaginal bleeding that occurs with the shedding of uterine mucose menstruation. The length of the cycle is notoriously variable, but an average figure is 28 days from the start of one menstrual period to the start of next.

By common usage, the days of the cycle are identified by starting with the first days of menstruation. It begins at puberty, ranging from the ages of 10 to 16, and ends at menopause at an average age of Hormones are secreted in a negative and positive feedback manner to control the menstrual cycle. Hormone secretion begins in the hypothalamus where gonadotropin-releasing hormone GnRH is secreted in an increased, pulsatile fashion once puberty starts.

GnRH is then transported to the anterior pituitary, where it activates its 7-transmembrane G-protein receptor. This provides a al to the anterior pituitary to secrete stimulating follicle hormone FSH and luteinizing hormone LH. FSH and LH provide input to the ovaries. Within the ovarian follicle, there are 2 cell types responsible for hormone production, theca cells and granulosa cells. LH stimulates theca cells to produce progesterone and androstenedione by activating the enzyme, cholesterol desmolase. Once androstenedione is secreted, the hormone diffuses to Premenstrual phase definition nearby granulosa cells.

Here, FSH stimulates the granulosa cells to convert androstenedione to testosterone then beta-estradiol by activating the enzyme, aromatase. As levels of beta-estradiol or progesterone increase based on the phases of the menstrual cycle, there is negative feedback back to the anterior pituitary to lower the levels of FSH and LH being produced and subsequently, the levels of beta-estradiol and progesterone produced. An exception to this is during ovulation.

In this case, once a critical amount of beta-estradiol is produced, it provides positive feedback to the anterior pituitary Premenstrual phase definition produce increased amounts of FSH and LH. This feedback system is represented in figure 1.

Additionally, within the feedback system, the granulosa cells produce inhibin and activin, which inhibit and stimulate FSH release from the anterior pituitary, respectively. This feedback mechanism is controlled by upregulating, to increase hormone Premenstrual phase definition, or downregulating to decrease hormone production, the GnRH receptors on the anterior pituitary.

The first phase of the menstrual cycle is the follicular or proliferative phase. It occurs from day zero to day 14 of the menstrual cycle, based on the average duration of 28 days. The variability in length of the menstrual cycle occurs due to variations in the length of the follicular phase. The main hormone during this phase is estrogen, specifically beta-estradiol.

The increase in this hormone occurs by the upregulation of the FSH receptors within the follicle at the beginning of the cycle. However, as the follicular phase progresses to the end, the increased amounts of beta-estradiol will provide negative feedback to the anterior pituitary. The purpose of this phase is to grow the endometrial layer of the uterus. Additionally, this phase is also essential to create Premenstrual phase definition environment that is friendly and helpful to possible incoming sperm.

During this phase, a primordial follicle begins to mature into a Graafian follicle. The surrounding follicles begin to degenerate, which is when the Graafian follicle becomes the mature follicle. This sets up the follicle for ovulation, the next step. Ovulation always occurs 14 days before menses; therefore, with an average day cycle, ovulation occurs on day At the end of the proliferative phase, beta-estradiol levels are at a high due to the follicle maturation and increased production of the hormone.

This occurs when a critical level of beta-estradiol is reached, at least picograms per milliliter of plasma. As a result, the mature follicle breaks, and an oocyte is released. The changes to the cervix as initiated during the follicular phase further increase, allowing for increased, waterier cervical mucous to better accommodate the possible sperm—the levels of beta-estradiol fall at the end of ovulation. The next phase of the menstrual cycle is the luteal or secretory phase. This phase always occurs from day 14 to day 28 of the cycle.

Progesterone stimulated by LH is the dominant hormone during this phase to prepare the corpus luteum and the endometrium for possible fertilized ovum implantation. As the luteal phase ends, progesterone will provide negative feedback to the anterior pituitary to decrease FSH and LH levels and, subsequently, the beta-estradiol and progesterone levels. The corpus luteum is a structure formed in the ovary at the site of the mature follicle rupture to produce beta-estradiol and progesterone, which is predominant at the end of the phase due to the negative feedback system.

The endometrium prepares by increasing its vascular supply and stimulating more mucous secretions. This is achieved by the progesterone stimulating the endometrium to slow down endometrial proliferation, decrease lining thickness, develop more complex glands, accumulate energy sources in the form of glycogen, and provide more surface area within the spiral arteries. Contrary to the cervical mucous changes seen during the proliferative phase and ovulation, progesterone decreases and thickens the cervical mucous making it non-elastic since the fertilization period passed, and sperm entry is no longer a priority.

Additionally, progesterone increases the hypothalamic temperature, so body temperature increases during the luteal phase. Near the end of the secretory phase, plasma levels of beta-estradiol and progesterone are produced by the corpus luteum. If pregnancy occurs, a fertilized ovum is implanted within the endometrium, and the corpus luteum will persist and maintain the hormone levels. However, if no fertilized ovum is implanted, then the corpus luteum regresses, and the serum levels of beta-estradiol and progesterone decrease rapidly.

When the hormone levels decrease, the endometrium layer, as it has been changed throughout the menstrual cycle, is not able to be maintained. This is called menses, considered day 0 to day 5 of the next menstrual cycle.

The duration of menses is variable. It contains prostaglandins, tissue debris, and relatively large amounts of fibrinolysis from endometrial tissue. The fibrinolysis lyses clot so that menstrual blood does not contain clots typically unless the flow is heavy. The usual duration of the menstrual flow is days, but flows as shorts as 1 day and as long as 8 days can occur in a normal female. The amount of blood loss can range from slight spotting to 80 mL and the average being 30 mL.

Loss of more than 80 mL of the blood is considered abnormal. Various factors can affect the amount of blood flow, including medications, the thickness of the endometrium, blood disorders, and disorders of blood clotting, etc.

In some cases, ovulation fails to occur during the menstrual cycle. Such cycles are called anovulatory cycles, and they are common Premenstrual phase definition the first months after menarche The occurrence of the first menstrual period and again before the onset of the menopause. When ovulation does not occur, usually no corpus luteum is found, and the effect of progesterone on the endometrium is absent.

The time it takes for the bleeding to occur is fluctuating, but it generally occurs in less than 28 days from the menstrual period. The flow is also inconsistent and ranges from scanty to relatively profuse. A female has an average of menses throughout her lifetime; therefore, it is important to understand the menstrual cycle and its physiology because of the various complications, consequences, and distress that it may have for a female patient. A female presenting with primary or secondary amenorrhea will need to undergo clinical testing to diagnose the reason.

Still, reasonable testing from the level of the ovaries to the hypothalamus cannot be performed unless a clinician thoroughly understands the hormone feedback system. Additionally, there may be problems with her menses itself, such as premenstrual syndrome, dysmenorrhea, or menorrhagia. Without an understanding of the female anatomy and menstrual cycle physiology, a clinician would be unable to obtain a complete history and physical to allow understanding of the underlying cause.

As clinicians, we must understand the menstrual cycle in its entirety to provide relevant clinical care to our female patients. Hormone secretion feedback system; Hormone variation throughout the menstrual cycle. Contributed by Dhanalakshmi Thiyagarajan.

This book is distributed under the terms of the Creative Commons Attribution 4. Turn recording back on. National Center for Biotechnology InformationU. StatPearls [Internet]. Search term. Physiology, Menstrual Cycle Dhanalakshmi K. Author Information Authors Dhanalakshmi K. Affiliations 1 Brookdale University. Introduction The reproductive system of a female, unlike men, shows regular cyclic changes that teleologically may be regarded as periodic preparation for pregnancy and fertilization.

Function Hormones are secreted in a negative and positive feedback manner to control the menstrual cycle. Mechanism Phase 1: Premenstrual phase definition Follicular, or Proliferative Phase The first phase of the menstrual cycle is the follicular or proliferative phase. Ovulation Ovulation always occurs 14 days before menses; therefore, with an average day cycle, ovulation occurs on day Phase 2: The Luteal or Secretory Phase The next phase of the menstrual cycle is the luteal or secretory phase.

Normal Menstruation When the hormone levels decrease, the endometrium layer, as it has been changed throughout the menstrual cycle, is not able to be maintained. Pathophysiology Anovulatory Cycles In some cases, ovulation fails to occur during the menstrual cycle. Clinical ificance A female has an average of menses throughout her lifetime; therefore, it is important to understand the menstrual cycle and its physiology because of the various complications, consequences, and distress that it may have for a female patient.

Review Questions Access free multiple choice questions on this topic. Comment on this article. Figure Hormone secretion feedback system; Hormone variation throughout the menstrual cycle. References 1. Physiology, Female Reproduction. Puberty and menstruation knowledge among young adolescents in low- and middle-income countries: a scoping review. Int J Public Health. Pan B, Li J. The art of oocyte meiotic arrest regulation. Reprod Biol Endocrinol. Harlow SD.

Premenstrual phase definition

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