Physiology of menstruation


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" Physiology of Menstruation" exclusively for Obstetrics and Gynaecology, Reproductive Endocrinology for postgraduate level and teaching purpose.

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Physiology of menstruation

  1. 1. PHYSIOLOGY OF MENSTRUAL CYCLE Dr (Mrs) Vandana BAGRI BUCKTOWAR Lecturer , Dept. of Obstetrics and Gynaecology Padmashree Dr. D Y Patil Medical College Altima Building, Ebene,Mauritius
  2. 2. Reproductive endocrinology Normal reproductive function requires precise quantitative and temporal regulation of the hypothalamic-pituitary-ovarian axis
  3. 3. Hormone Biosynthesis and Mechanism of Action - Classified as either steroids or peptides PEPTIDE hormones in reproduction: LH,FSH and HCG: glycoproteins, ∞and β Activin, Inhibin and Follistatin –polypeptides Three polypeptide factors—inhibin, activin, and follistatin— initially isolated from follicular fluid Named based on their selective effects on FSH biosynthesis and secretion Inhibin decreases and activin stimulates gonadotrope function.Follistatin supresses FSH gene expression
  4. 4. Inhibin, activin and follistatin Inhibin consists of an ∞-subunit linked to one of two highly homologous β -subunits to form inhibin A (alfa beta A) or inhibin B ( alfa beta B). Activin is composed of homodimers ( A A, B B) or heterodimers ( A B) of the same -subunits as inhibin More recently, a number of additional -subunit isoforms have been identified. In contrast, follistatin is structurally unrelated to either inhibin or activin.
  5. 5. Steroid Hormones in Reproduction Sex steroid hormones are synthesized in the gonads, adrenal gland, and placenta Cholesterol is the primary building block in steroidogenesis Steroid hormone production, which involves at least 17 enzymes, primarily occurs in the abundant smooth endoplasmic reticulum found in steroidogenic cells Steroids are metabolized mainly in the liver and to a lesser extent in the kidney and intestinal mucosa.
  6. 6. Steroid Hormone Classification Sex steroids are divided into three groups based on the number of carbon atoms that they contain. Each carbon in this structure is assigned a number identifier, and each ring is assigned a letter The 21-carbon series includes progestins as well as glucocorticoids and mineralocorticoids. Androgens contain 19 carbons, whereas estrogens have 18.
  7. 7. Derivation of Circulating Estrogens in the Female Circulating estrogens in the reproductive-aged female are a mixture of both estradiol and the less potent estrone. Although a small amount of estriol is produced through peripheral conversion in the nonpregnant female. Estriol production is primarily limited to production by the placenta during pregnancy.
  8. 8. Derivation of Circulating Estrogens in the Female (contd.) Estradiol is the primary estrogen produced by the ovary during reproductive years. Levels are derived from both direct synthesis in developing follicles and through conversion of estrone. Estrone is secreted directly by the ovary and can be converted from androstenedione in the periphery. Androgens are converted to estrogens in many tissues, but mainly result from aromatase activity in skin and adipose tissue
  9. 9. Contribution of the adrenal glands and ovaries to levels of androgens, dehydroepiandrosterone (DHEA), and DHEA-sulfate (DHEAS).
  10. 10. Menstrual Cycle The typical menstrual cycle is defined as 28 ± 7 days, with menstrual flow lasting 4 ± 2 days, and an average blood loss of 20 to 60 mL. To understand the normal menstrual cycle, it is helpful to divide the cycle into three phases: the follicular phase, ovulation, and the luteal phase. The Follicular Phase Ovulation Luteal Phase The Luteal-Follicular Transition The Normal Menstrual Cycle
  11. 11. Menstrual Cycle (contd.) When viewed from a perspective of ovarian and endometrial and E/P functions and characteristics:
  12. 12. The Ovary Size:The adult human ovary is oval with a length of 2 to 5 cm, a width of 1.5 to 3 cm, and a thickness of 0.5 to 1.5 cm. During the reproductive years, ovaries weigh between 5 and 10 g. They are comprised of three parts: an outer cortical region, which contains both the germinal epithelium and the follicles; a medullary region, which consists of connective tissue, myoid-like contractile cells, and interstitial cells; and a hilum, which contains blood vessels, lymphatics and nerves that enter the ovary
  13. 13. Embryology of ovary The ovary develops from three major cellular sources: • (1) Primordial germ cells, which arise from the endoderm of the yolk sac and differentiate into the primary oogonium, • (2) Coelomic epithelial cells, which develop into granulosa cells, and • (3) Mesenchymal cells from the gonadal ridge, which become the ovarian stroma.
  14. 14. Embryology of ovary  Primordial germ cells can be identified in the yolk sac as early as the third week of gestation.  After the primordial cells reach the gonad, they continue to multiply through successive mitotic divisions.  Starting at 12 weeks' gestation, a subset of oogonia will enter meiosis to become primary oocytes.  Primary oocytes are surrounded by a single layer of flattened granulosa cells, creating a primordial follicle.
  15. 15. The Ovary Across the Reproductive Life Span All oogonia either develop into primary oocytes or become atretic. Based on our current understanding of ovarian function, additional oocytes cannot be generated postnatally. The maximal number of oogonia is achieved at the 20th week of gestation, 67 million At Birth:1-2 million oogonia At puberty: 400,000 present at the initiation of puberty, of which less than 500 are destined to ovulate.(most lost through atresia) There is now strong evidence that follicular atresia is not a passive, necrotic process, but rather a precisely controlled active process, namely apoptosis, which is under hormonal control. Apoptosis begins in utero and continues throughout reproductive life.
  16. 16. Drawing illustrates the steps of meiosis and the corresponding stages of oocyte development
  17. 17. Ovarian Steroidogenesis Ovary synthesizes and secretes the sex-steroid hormones— estrogens, androgens, and progesterone, in a precisely controlled pattern determined by FSH and LH. The most important secretory products of ovarian steroid biosynthesis are progesterone and estradiol. The ovary also secretes quantities of estrone, androstenedione, testosterone, and 17-hydroxyprogesterone. Sex-steroid hormones play an important role in the menstrual cycle by preparing the uterus for implantation of a fertilized ovum. If implantation does not occur, ovarian steroidogenesis declines, the endometrium degenerates, and menstruation ensues.
  18. 18. Two-Cell, Two Gonadotropin Theory of Ovarian Steroidogenesis First proposed by Falck in 1959, The two-cell theory of ovarian steroidogenesis explains that estrogen biosynthesis requires the combined action of two gonadotropins (LH and FSH) on two cell types (theca and granulosa cells) Theca cells express all of the genes needed to produce androstenedione This includes high levels of CYP17 gene expression, whose enzyme product catalyzes 17-hydroxylation—the rate-limiting step in the conversion of progesterones to androgens This enzyme is absent in the granulosa cells, so they are incapable of producing the precursor needed to produce estrogens by themselves.
  19. 19. In response to LH stimulation, theca cells synthesize the androgens, androstenedione and testosterone. These androgens are secreted into the extracellular fluid and diffuse across the basement membrane to the granulosa cells to provide precursors for estrogen production. In contrast to theca cells, granulosa cells express high levels of aromatase activity in response to FSH stimulation. Thus, these cells efficiently convert androgens to estrogens, primarily the potent estrogen, estradiol. In sum, ovarian steroidogenesis is dependent on the effects of LH and FSH acting independently on the theca cells and granulosa cells, respectively.
  20. 20. Two-Cell,Two Gonadotropin Theory of Ovarian Steroidogenesis
  21. 21. Steroidogenesis Across the Life Span -Childhood The human ovary has the capacity to produce estrogens by 8 weeks' gestation. Circulating levels of the gonadotropins, LH and FSH, vary markedly at different ages of a woman's life. During the second trimester of fetal development, the plasma levels of gonadotropins rise to levels similar to those observed in menopause The fetal hypothalamic-pituitary axis continues to mature during the second trimester of pregnancy, becoming more sensitive to the high circulating levels of estrogen and progesterone secreted by the placenta . In response to the high levels of these steroids, fetal gonadotropins fall to low levels prior to birth.
  22. 22. Steroidogenesis Across the Life Span -Childhood After delivery, gonadotropin levels rise abruptly in the neonate due to separation from the placenta and subsequent freedom from inhibition by placental steroids. The elevated levels of gonadotropins in the newborn persist for the first few months of life, declining to low levels in early childhood. The hypothalamic-pituitary axis has been found to have increased sensitivity to negative feedback, even by the low circulating levels of gonadal steroids at this stage. There is growing evidence that there is an intrinsic role of the central nervous system in maintaining low gonadotropin levels.
  23. 23. Steroidogenesis Across the Life Span -Puberty One of the first signs of puberty is a sleep-associated increase in LH secretion. Over time, increased gonadotropin secretion is noted throughout the day. An increased FSH:LH ratio is typical in the premenarchal girl and postmenopausal woman. During the reproductive years, LH exceeds FSH levels, reversing this ratio.
  24. 24. Steroidogenesis Across the Life Span –Puberty (Contd.) Increased gonadotropin levels stimulate ovarian estradiol production. The rise in estrogen levels results in the growth spurt, maturation of the female internal and external genitalia, and development of a female habitus including breast enlargement (thelarche). Activation of the pituitary-adrenal axis results in an increase in adrenal androgen production and the associated development of axillary and pubic hair (adrenache or pubarche). Increased gonadotropin levels ultimately lead to ovulation and subsequent menses, with the timing of the first menstrual period defining menarche. This developmental process takes approximately 3 to 4 years.
  25. 25. Diagram illustrates variations in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) during different life stages in the female.
  26. 26. The Follicular phase During the follicular phase an orderly sequence of events takes place that ensures the proper number of follicles is ready for ovulation. In the human ovary the end result of this follicular development is (usually) one surviving mature follicle. This process, which occurs over the space of 10-14 days. It features a series of sequential actions of hormones and autocrineparacrine peptides on the follicle. leading the follicle destined to ovulate through a period of initial growth from a primordial follicle through the stages of the preantral, antral, and preovulatory follicle.
  27. 27. The Primordial Follicle The primordial follicle is nongrowing and consists of an oocyte, arrested in the diplotene stage of meiotic prophase, surrounded by a single layer of spindle-shaped granulosa cells. The mechanism for determining which follicles and how many will start growing on any given day is unknown. The number of follicles in each growing cohort appears to be dependent on the size of the residual pool of inactive primordial follicles. Reducing the size of the pool (e.g., unilateral oophorectomy) causes the remaining follicles to redistribute their availability over time,
  28. 28. The Primordial Follicle (contd.) The follicle that is singled out to play the leading role in a particular cycle is the beneficiary of a timely match of follicle readiness (perhaps prepared by autocrine-paracrine actions in its microenvironment) and appropriate tropic hormone stimulation. The first follicle able to respond to stimulation may achieve an early lead that it never relinquishes. Nevertheless, each cohort of follicles that begins growth is engaged in a serious competition that ends with only one follicle succeeding. The size of this cohort appears to be proportional to the number of inactive primordial follicles within the ovaries and has been estimated at three to eleven follicles per ovary in young women.
  29. 29. Rescue from Atresia -Apoptosis The follicle destined to ovulate is recruited in the first few days of the cycle. The early development of follicles occurs over the time span of several menstrual cycles, but the ovulatory follicle is one of a cohort recruited at the time of the luteal-follicular transition. The total duration of time to achieve preovulatory status is approximately 85 days. The majority of this time (until a late stage) involves responses that are independent of hormonal regulation. Eventually, this cohort of follicles reaches a stage where, unless recruited (rescued) by follicle-stimulating hormone (FSH), the next step is atresia.
  30. 30. Rescue from Atresia –Apoptosis (contd.) Thus, follicles are continuously available (2-5 mm in size) for a response to FSH. An increase in FSH is the critical feature in rescuing a cohort of follicles from atresia, the usual fate of most follicles, eventually allowing a dominant follicle to emerge and pursue a path to ovulation. In addition, maintenance of this increase in FSH for a critical duration of time is essential. Without the appearance and persistence of an increase in the circulating FSH level, the cohort is doomed to the process of apoptosis, programmed physiologic cell death to eliminate superfluous cells. Apoptosis is derived from Greek and means falling off, like leaves from a tree.
  31. 31. Recruitment It has been traditionally used to describe the continuing growth of antral follicles in response to FSH. A more useful concept is that the cohort of follicles responding to FSH at the beginning of a cycle is rescued from apoptosis. Remember that the very early development of follicles begins continuously and independently from gonadotropin influence. The fate of almost all of these follicles is apoptosis; only those exposed to an increase in FSH stimulation because of the juxtaposition of their readiness to respond and the increase in FSH during the luteal-follicular transition have the good fortune to compete for selection as a dominant follicle.
  32. 32. During the luteal-follicular transition, a small increase in FSH levels is responsible for selection of the single dominant follicle that will ultimately ovulate. As previously described, theca cells produce androgens and granulosa cells generate estrogens. • • • Estrogens increase with increased follicular size enhance the effects of FSH on granulosa cells and create a feed-forward action on follicles that produce estrogens.
  33. 33. FOLLICULAR DEVELOPMENTPrimordial follicle The first visible signs of follicular development are an increase in the size of the oocyte, and the granulosa cells becoming cuboidal rather than squamous in shape. These changes may be better viewed as a process of maturation rather than growth. At this same time, small gap junctions develop between the granulosa cells and the oocyte. Gap junctions are channels that when open permit the exchange of nutrients, ions, and regulatory molecules. Thus, the gap junctions serve as the pathway for nutritional, metabolite, and signal interchange between the granulosa cells and the oocyte.
  34. 34. FOLLICULAR DEVELOPMENT(Contd.) With multiplication of the cuboidal granulosa cells (to approximately 15 cells), the primordial follicle becomes a primary follicle. The granulosa layer is separated from the stromal cells by a basement membrane called the basal lamina. The surrounding stromal cells differentiate into concentric layers designated the theca interna (closest to the basal lamina) and the theca externa (the outer portion). The theca layers appear when granulosa proliferation produces 36 layers of granulosa cells.
  35. 35. The Preantral Follicle Once growth is accelerated, the follicle progresses to the preantral stage as the oocyte enlarges and is surrounded by a membrane, the zona pellucida. The granulosa cells undergo a multilayer proliferation as the theca layer continues to organize from the surrounding stroma. This growth is dependent on gonadotropins and is correlated with increasing production of estrogen. The granulosa cells of the preantral follicle have the ability to synthesize all 3 classes of steroids; however, significantly more estrogens than either androgens or progestins are produced.(AROMATISATION)
  36. 36. Contd. Although steroidogenesis in the ovarian follicle is mainly regulated by the gonadotropins, multiple signaling pathways are involved that respond to many factors besides the gonadotropins. Adenylate cyclase enzyme system Ion gate channels Tyrosine kinase receptors, The phospholipase system of second messengers. These pathways are regulated by a multitude of factors, including growth factors, nitric oxide, prostaglandins, and peptides such as gonadotropin-releasing hormone (GnRH), angiotensin II, tissue necrosis factor-α, and vasoactive intestinal peptide.
  37. 37. The fate of the preantral follicle is in delicate balance. At low concentrations, androgens enhance their own aromatization and contribute to estrogen production. At higher levels, the limited capacity of aromatization is overwhelmed, and the follicle becomes androgenic and ultimately atretic. Follicles will progress in development only if emerging when FSH is elevated and LH is low. Those follicles arising at the end of the luteal phase or early in the subsequent cycle would be favored by an environment in which aromatization in the granulosa cell can prevail. The success of a follicle depends on its ability to convert an androgen-dominated microenvironment to an estrogen-dominated microenvironment.
  38. 38. Summary of Key Events in the Preantral Follicle Initial follicular development occurs independently of hormone influence. FSH stimulation rescues a cohort of follicles from apoptosis, propelling them to the preantral stage. FSH-induced aromatization of androgen in the granulosa results in the production of estrogen. Together, FSH and estrogen increase the FSH receptor content of the follicle and stimulate the proliferation of granulosa cells.
  39. 39. The Antral Follicle Under the synergistic influence of estrogen and FSH there is an increase in the production of follicular fluid that accumulates in the intercellular spaces of the granulosa. This eventually coalescing to form a cavity, as the follicle makes its gradual transition to the antral stage. The accumulation of follicular fluid provides a means whereby the oocyte and surrounding granulosa cells can be nurtured in a specific endocrine environment. The granulosa cells surrounding the oocyte are now designated the cumulus oophorus.
  40. 40. Contd. In the presence of FSH, estrogen becomes the dominant substance in the follicular fluid. LH is not normally present in follicular fluid until the midcycle. If LH is prematurely elevated in the circulation and antral fluid, mitotic activity in the granulosa decreases, degenerative changes ensue, and intrafollicular androgen levels rise. Therefore, the dominance of estrogen and FSH is essential for sustained accumulation of granulosa cells and continued follicular growth. Antral follicles with the greatest rates of granulosa proliferation contain the highest estrogen concentrations and the lowest androgen/estrogen ratios, and are the most likely to house a healthy oocyte.and become a PREOVULATORY FOLLICLE. An androgenic milieu antagonizes estrogen-induced granulosa proliferation and, if sustained, promotes degenerative changes in the oocyte.
  41. 41. Summary of Key Events in the Antral Follicle Follicular phase estrogen production is explained by the two-cell, two-gonadotropin mechanism, allowing the critical creation of an estrogen-dominated microenvironment. Selection of the dominant follicle is established during days 5-7, and consequently, peripheral levels of estradiol begin to rise significantly by cycle day 7. Estradiol levels, derived from the dominant follicle, increase steadily and, through negative feedback effects, exert a progressively greater suppressive influence on FSH release. While directing a decline in FSH levels, the midfollicular rise in estradiol exerts a positive feedback influence on LH secretion.
  42. 42. Contd. LH levels rise steadily during the late follicular phase, stimulating androgen production in the theca and optimizing the final maturation and function of the dominant follicle. A unique responsiveness to FSH allows the dominant follicle to utilize the androgen as substrate and further accelerate estrogen production. FSH induces the appearance of LH receptors on granulosa cells by growth factors and autocrine and paracrine peptides Inhibin-B, secreted by the granulosa cells in response to FSH, directly suppresses pituitary FSH secretion. Activin, originating in both pituitary and granulosa, augments FSH secretion and action.IGF enhances all actions of FSH and LH.
  43. 43. Transition from supression to induction of LH release IN midfollicular phase With increasing concentrations of estrogen within the follicle, FSH changes its focus of action, from upregulating its own receptor to generation of the LH receptors. The combination of a capacity for continued response despite declining levels of FSH and a high local estrogen environment in the dominant follicle provides optimal conditions for LH receptor development. LH can induce the formation of its own receptor in FSHprimed granulosa cells, but the primary mechanism utilizes FSH stimulation and estrogen enhancement.
  44. 44. Contd. There are two critical features in this mechanism: The concentration of estradiol, and the length of time during which the estradiol elevation is sustained.  The estradiol concentration necessary to achieve a positive feedback is more than 200 pg/mL, and this concentration must be sustained for approximately 50 hours.  This level of estrogen essentially never occurs until the dominant follicle has reached a diameter of 15 mm.  The estrogen stimulus must be sustained beyond the initiation of the LH surge until after the surge actually begins.  Otherwise, the LH surge is abbreviated or fails to occur at all.
  45. 45. Inside a preovulatory follicle Estrogen production becomes sufficient to achieve and maintain peripheral threshold concentrations of estradiol that are required in order to induce the LH surge. Acting through its receptors, LH initiates luteinization and progesterone production in the granulosa layer. The preovulatory rise in progesterone facilitates the positive feedback action of estrogen and may be required to induce the midcycle FSH peak. A midcycle increase in local and peripheral androgens occurs, derived from the thecal tissue of lesser, unsuccessful follicles.
  46. 46. The preovulatory follicle, through the elaboration of estradiol, provides its own ovulatory stimulus. Ovulation approximately 10-12 hours after the LH peak and 24-36 hours after peak estradiol levels are attained.  The onset of the LH surge is the most reliable indicator of impending ovulation, occurring 34-36 hours prior to follicle rupture. A threshold of LH concentration must be maintained for at least 14-27 hours in order for full maturation of the oocyte to occur.Usually the LH surge lasts 48-50 hours.
  47. 47. OVULATION The gonadotropin surge stimulates a large collection of events that ultimately leads to ovulation, the physical release of the oocyte and its cumulus mass of granulosa cells. A complex series of changes must occur which cause the final maturation of the oocyte and the decomposition of the collagenous layer of the follicular wall. The LH surge initiates the continuation of meiosis in the oocyte (meiosis is not completed until after the sperm has entered and the second polar body is released), luteinization of granulosa cells, expansion of the cumulus, and the synthesis of prostaglandins and other eicosanoids essential for follicle rupture.
  48. 48. Contd. Premature oocyte maturation and luteinization are prevented by local factors. LH-induced cyclic AMP activity overcomes the local inhibitory action of oocyte maturation inhibitor (OMI) and luteinization inhibitor (LI). LI may be endothelin-1, a product of vascular endothelial cells. OMI originates from the granulosa cells, and its activity depends on an intact cumulus oophorous. Activin also suppresses progesterone production by luteal cells, providing yet another means of preventing premature luteinization.
  49. 49. With the LH surge, levels of progesterone in the follicle continue to rise up to the time of ovulation. Progressive rise in progesterone terminate the LH surge as a negative feedback effect. Progesterone increases the distensibility of the follicle wall. A change in the elastic properties of the follicular wall occurs just prior to ovulation, unaccompanied by any significant change in intrafollicular pressure. FSH, LH, and progesterone stimulate the activity of proteolytic enzymes, resulting in digestion of collagen in the follicular wall and increasing its distensibility.
  50. 50. Ovulation (Contd.) The gonadotropin surge also releases histamine. The proteolytic enzymes are activated in an orderly sequence The granulosa and theca cells produce plasminogen activator in response to the gonadotropin surge. Plasminogen activators produced by granulosa cells activate plasminogen in the follicular fluid to produce plasmin. Plasmin, in turn, generates active collagenase to disrupt the follicular wall. The inhibitor system, which is very active in the thecal and interstitial cells, prevents inappropriate activation of plasminogen and disruption of growing follicles.
  51. 51. *Premature luteinisation prevented by OMI and luteinisation inhibitor(left) and events at ovulation(right)
  52. 52. Ovulation (Contd.) A large number of leukocytes enter the follicle prior to ovulation by chemotaxis. Neutrophils are a prominent feature in the theca compartment of both healthy and atretic antral follicles. These immune cells probably contribute to the cellular changes associated with ovulation, corpus luteum function, and apoptosis. Estradiol levels plunge as LH reaches its peak. This may be a consequence of LH down-regulation of its own receptors on the follicle.
  53. 53. Contd. The granulosa cells that are attached to the basement membrane and enclose the follicle become luteal cells. The cumulus granulosa cells attach to the oocyte. The mechanism that shuts off the LH surge is unknown. Within hours after the rise in LH, there is a precipitous drop in the circulating estrogens. The decrease in LH can be due to a loss of the positive stimulating action of estradiol or to an increasing negative feedback of progesterone. The abrupt fall in LH levels may also reflect a depletion in pituitary LH content due to down-regulation of GnRH receptors
  54. 54. Summary of the Key Ovulatory Events The LH surge initiates the continuation of meiosis in the oocyte, luteinization of the granulosa, and synthesis of progesterone and prostaglandins within the follicle. Progesterone enhances the activity of proteolytic enzymes responsible, together with prostaglandins, for digestion and rupture of the follicular wall. The progesterone-influenced midcycle rise in FSH serves to free the oocyte from follicular attachments, to convert plasminogen to the proteolytic enzyme, plasmin, and to ensure that sufficient LH receptors are present to allow an adequate normal luteal phase.
  55. 55. LUTEAL PHASE Before rupture of the follicle and release of the ovum, the granulosa cells begin to increase in size and assume a characteristic vacuolated appearance associated with the accumulation of a yellow pigment, lutein, which lends its name to the process of luteinization and the anatomic subunit, the corpus luteum. During the first 3 days after ovulation, the granulosa cells continue to enlarge. In addition, theca lutein cells may differentiate from the surrounding theca and stroma to become part of the corpus luteum. Dissolution of the basal lamina and rapid vascularization and luteinization make it difficult to distinguish the origin of specific cells.
  56. 56. Contd. Capillaries begin to penetrate into the granulosa layer after the cessation of the LH surge, reach the central cavity, and often fill it with blood. Angiogenesis is an important feature of the luteinization process, By day 8 or 9 after ovulation, a peak of vascularization is reached, associated with peak levels of progesterone and estradiol in the blood. The corpus luteum has one of the highest blood flows per unit mass in the body. On occasion, this ingrowth of vessels and bleeding results in unchecked hemorrhage.and an acute surgical emergency that can present at any time during the luteal phase. Indeed, this is a significant clinical risk in women who are anticoagulated; such women should receive medication to prevent ovulation.
  57. 57. Corpus luteum The lifespan and steroidogenic capacity of the corpus luteum are dependent on continued tonic LH secretion. The corpus luteum is not homogeneous. Contents of Corpus luteum:luteal cells,endothelial cells, leukocytes, and fibroblasts. The nonsteroidogenic cells form the bulk (70-85%) of the total cell population. The leukocyte immune cells produce several cytokines, including interleukin-1 and tumor necrosis factor, cytolytic enzymes, prostaglandins, and growth factors involved in angiogenesis, steroidogenesis, and luteolysis.
  58. 58. Contd. Endothelial cells constitute about 50% of the cells in . a mature corpus luteum The increased perfusion provides these luteal cells with access to circulating low-density lipoprotein (LDL), which is used to provide precursor cholesterol for steroid biosynthesis. These endothelial cells participate in immune reactions and endocrine functions. They produce endothelin-1, a mediator of luteolysis. Luteal cell population are of 2 types:large and small cells. The small cells that contain LH and hCG receptors.and the large luteal cells produce peptides (oxytocin, relaxin, inhibin, and other growth factors).
  59. 59. Large luteal cells produce peptides are more active in steroidogenesis, with greater aromatase activity and more progesterone synthesis than small cells. Human granulosa cells (already luteinizing when recovered from in vitro fertilization patients) contain minimal amounts of P450c17 mRNA. This is consistent with the two-cell explanation, which assigns androgen production (and P450c17) to the cells derived from thecal cells. With luteinization, expression of P450 and 3-hydroxysteroid dehydrogenase markedly increases, to account for the increasing production of progesterone, and the continued expression of mRNAs for these enzymes requires LH. The aromatase system (P450arom) continues to be active in luteinized granulosa cells.
  60. 60. Progesterone levels normally rise sharply after ovulation, reaching a peak approximately 8 days after the LH surge. Initiation of new follicular growth during the luteal phase is inhibited by the low levels of gonadotropins due to the negative feedback actions of estrogen, progesterone, and inhibin-A. With the appearance of LH receptors on the granulosa cells of the dominant follicle and the subsequent development of the follicle into a corpus luteum, inhibin expression comes under the control of LH, and expression changes from inhibin-B to inhibin-A. The circulating levels of inhibin-A rise in the late follicular phase to reach a peak level at the midluteal phase. Inhibin-A, therefore, contributes to the suppression of FSH to nadir levels during the luteal phase, and to the changes at the luteal-follicular transition. The secretion of progesterone and estradiol during the luteal phase is episodic, and the changes correlate closely with LH pulse. Because of this episodic secretion, relatively low midluteal progesterone levels, which some believe are indicative of an inadequate luteal phase, can be found in the course of totally normal luteal phases.
  61. 61. In the normal cycle the time period from the LH midcycle surge to menses is consistently close to 14 days. For practical purposes, luteal phases lasting between 11 and 17 days can be considered normal. The incidence of short luteal phases is about 5-6%. It is well known that significant variability in cycle length among women is due to the varying number of days required for follicular growth and maturation in the follicular phase. The luteal phase cannot be extended indefinitely even with progressively increasing LH exposure, indicating that the demise of the corpus luteum is due to an active luteolytic mechanism. The corpus luteum rapidly declines 9-11 days after ovulation, and the mechanism of the degeneration remains unknown.
  62. 62. Luteolysis The morphologic regression of luteal cells may be induced by the estradiol produced by the corpus luteum. This action of estrogen may be mediated by nitric oxide. Nitric oxide stimulates luteal prostaglandin synthesis and decreases progesterone production. Nitric oxide and hCG have opposing actions in the human corpus luteum; nitric oxide is associated with apoptosis of luteal cells. The final signal for luteolysis, however, is prostaglandin F, produced within the ovary in response to the locally synthesized luteal estrogen. In view of the known estrogen requirement for the synthesis of progesterone receptors in endometrium, luteal phase estrogen may be necessary to allow the progesterone-induced changes in the endometrium after ovulation. Inadequate progesterone receptor content due to inadequate estrogen priming of the endometrium is an additional possible mechanism for infertility or early miscarriage, another form of luteal phase deficiency.
  63. 63. Luteolysis-Factors responsible Experimental evidence indicates that the luteolytic effect of prostaglandin F2 is partially mediated by endothelin-1 Prostaglandin F2α stimulates the synthesis of endothelin; endothelin-1 inhibits luteal steroidogenesis, and in turn, endothelin-1 stimulates prostaglandin production in luteal cells. In addition, endothelin-1 stimulates the release of tumor necrosis factor-α, a growth factor known to induce apoptosis. Gap junctions are a prominent feature of luteal cells, just as they are in the follicle before ovulation. The process of luteolysis involves proteolytic enzymes, especially the matrix metalloproteinases (MMPs). Luteolysis is believed to involve a direct increase in MMP expression. The human ovary contains the complete interleukin-1 system, providing another resource for cytolytic enzymes.
  64. 64. Contd. The survival of the corpus luteum is prolonged by the emergence of a new stimulus of rapidly increasing intensity, hCG. This new stimulus first appears at the peak of corpus luteum development (9-13 days after ovulation), just in time to prevent luteal regression. hCG serves to maintain the vital steroidogenesis of the corpus luteum until approximately the ninth or tenth week of gestation, by which time placental steroidogenesis is well established. In some pregnancies placental steroidogenesis will be sufficiently established by the seventh week of gestation. In addition, the rescue of the corpus luteum by an early pregnancy with hCG is associated with maintenance of the vascular system (not new vessel growth), a process dependent on the angiogenic factors VEGF and angiopoietin-2
  65. 65. Summary of Key Events in the Luteal Phase Normal luteal function requires optimal preovulatory follicular development (especially adequate FSH stimulation) and continued tonic LH support. The early luteal phase is marked by active angiogenesis mediated by VEGF. New vessel growth is held in check by angiopoietin-1 working through its receptor Tie-2 on endothelial cells. Regression of the corpus luteum is associated with a decrease in VEGF and angiopoietin-1 expression and an increase in angiopoietin-2 activity. Progesterone, estradiol, and inhibin-A act centrally to suppress gonadotropins and new follicular growth Regression of the corpus luteum may involve the luteolytic action of its own estrogen production, mediated by an alteration in local prostaglandin concentrations and involving nitric oxide, endothelin, and other factors. In early pregnancy, hCG rescues the corpus luteum, maintaining luteal function until placental steroidogenesis is well established.
  66. 66. The Luteal-Follicular Transition
  67. 67. The interval extending from the late luteal decline of estradiol and progesterone production to the selection of the dominant follicle. It is a critical and decisive time, marked by the appearance of menses, but less apparent and very important are the hormone changes that initiate the next cycle. The critical factors include GnRH, FSH, LH, estradiol, progesterone, and inhibin Through the FSH-mediated actions on the granulosa cells, the recruitment of a new ovulating follicle is directed by a selective increase in FSH that begins approximately 2 days before the onset of menses. There are at least two influential changes that result in this important increase in FSH:  a decrease in luteal steroids and inhibin and  a change in GnRH pulsatile secretion.
  68. 68. ROLE OF INHIBIN , ACTIVIN ,FOLLISTATIN AND OTHER FACTORS AFFECTING FSH Inhibin-B, originating in the granulosa cells of the corpus luteum and now under the regulation of LH, reaches a nadir in the circulation at the midluteal period. Inhibin-A reaches a peak in the luteal phase These may help to suppress FSH secretion by the pituitary to the lowest levels reached during a menstrual cycle. The process of luteolysis, with the resulting demise of the corpus luteum, affects inhibin-A secretion as well as steroidogenesis. Thus, an important suppressing influence on FSH secretion is removed from the anterior pituitary during the last days of the luteal phase. The selective action of inhibin on FSH (and not LH) is partly responsible for the greater rise in FSH seen during the luteal-follicular transition, compared to the change in LH.
  69. 69. Inhibin-B levels begin to rise shortly after the increase in FSH (a consequence of FSH stimulation of granulosa cell secretion of inhibin) and reach peak levels about 4 days after the maximal increase in FSH. Thus, suppression of FSH secretion during the follicular phase is an action exerted by inhibin-B, whereas escape of FSH inhibition during the luteal-follicular transition is partly a response to decreasing inhibin-A secretion by the corpus luteum. Circulating levels of activin increase in the late luteal phase to peak at menses. It contribute to the rise in FSH during the luteal-follicular transition. Activin enhances and follistatin suppresses GnRH activity. Evidence in vivo and in vitro indicates that gonadotropin response to . GnRH requires activin activity
  70. 70. The selective rise in FSH is also significantly influenced by a change in GnRH pulsatile secretion, previously strongly suppressed by the high estradiol and progesterone levels of the luteal phase exerting a negative feedback effect at the hypothalamus. A progressive and rapid increase in GnRH pulses occurs during the luteal-follicular transition. From the midluteal peak to menses, there is a 4.5-fold increase in LH pulse frequency (and presumably GnRH) from approximately 3 pulses per 24 hours to 14 pulses per 24 hours. During this time period, the mean level of LH increases approximately 2-fold, from approximately a mean of 4.8 IU/L to 8 IU/L. The increase in FSH is greater than that of LH. FSH pulse frequency increases 3.5-fold from the midluteal period to the time of menses, and FSH levels increase from a mean of approximately 4 IU/L to 15 IU/L.
  71. 71. An increase in GnRH pulse frequency from a low level of secretion has been associated with an initial selective increase in FSH in several experimental models, including the ovariectomized monkey with destruction of the hypothalamus. Treatment of hypogonadal women with pulsatile GnRH results first in predominance of FSH secretion (over LH). This experimental response and the changes during the lutealfollicular transition are similar to that observed during puberty, a predominance of FSH secretion as GnRH pulsatile secretion begins to increase. The pituitary response to GnRH is also a factor.  Estradiol suppresses FSH secretion by virtue of its classic negative feedback relationship at the pituitary level.  The decrease in estradiol in the late luteal phase restores the capability of the pituitary to respond with an increase in FSH secretion.
  72. 72. Summary of Key Events in the Luteal-Follicular Transition The demise of the corpus luteum results in a nadir in the circulating levels of estradiol, progesterone, and inhibin. The decrease in inhibin-A removes a suppressing influence on FSH secretion in the pituitary. The decrease in estradiol and progesterone allows a progressive and rapid increase in the frequency of GnRH pulsatile secretion and a removal of the pituitary from negative feedback suppression. The removal of inhibin-A and estradiol and increasing GnRH pulses combine to allow greater secretion of FSH compared with LH, with an increase in the frequency of the episodic secretion. The increase in FSH is instrumental in rescuing an approximately 70-dayold group of ready follicles from atresia, allowing a dominant follicle to begin its emergence.
  73. 73. ENDOMETRIUM- Histologic Menstrual Cycle Changes The endometrium consists of two layers: the basalis layer, which lies against the myometrium, and the functionalis layer, which is apposed to the uterine lumen. The basalis layer, which does not change significantly across the menstrual cycle, is critical for regeneration of the endometrium following menstrual sloughing. The functionalis layer of the endometrium can be further divided into the superficial, thin, stratum compactum, which consists of gland necks and dense stroma, and the underlying stratum spongiosum, which contains glands and large amounts of loosely organized stroma and interstitial tissue.
  74. 74. After menstruation, the endometrium is only one to two millimeters thick. Under the influence of estrogen, the glandular and stromal cells of the functionalis layer proliferate rapidly following menses. This period of rapid growth, termed the proliferative phase, corresponds to the ovary's follicular phase. As this phase progresses, glands become more tortuous and cells lining the glandular lumen undergo pseudostratification. The stroma remains compact. Endometrial thickness is about 12 millimeters at the time of the LH surge and does not increase significantly thereafter.
  75. 75. Following ovulation, the endometrium transforms into a secretory tissue. The period defined as the secretory phase of the endometrium and correlates to the ovary's luteal phase. Glycogen-rich subnuclear vacuoles appear in cells lining the glands. Under further stimulation by progesterone, these vacuoles move from the glandular base toward the lumen and expel their contents. This secretory process peaks on approximatelypostovulatory day 6, coinciding with the day of implantation. Glands become increasingly tortuous, and the stroma becomes more edematous. In addition, spiral arteries that feed the endometrium increase their number and coiling.
  76. 76. If a blastocyst does not implant, then the corpus luteum is not maintained by placental hCG, progesterone levels drop, and endometrial glands begin to collapse. Polymorphonuclear leukocytes and monocytes from the nearby vasculature infiltrate the endometrium. The spiral arteries constrict leading to local ischemia, and lysosomes release proteolytic enzymes that accelerate tissue destruction. Prostaglandins (PGs), particularly prostaglandin F2 , are present in the endometrium and likely contribute to arteriolar vasospasm. Prostaglandin F2 also induces myometrial contractions, which may aid in expelling the endometrial tissue. The entire endometrial functionalis layer is thought to exfoliate with menstruation, leaving only the basalis layer to provide cells for endometrial regeneration. Following menstruation, re-epithelialization of the desquamated endometrium is believed to be initiated within 2 to 3 days after the onset of menses and to be completed within 48 hours.
  77. 77. Menstrual phase: fragmented endometrium with condensed stroma and glands with secretory vacuoles are seen in a background of blood.
  78. 78. Implantation Window – In the human, the embryo enters the uterine cavity 2 to 3 days after fertilization with implantation beginning approximately 4 days later
  79. 79. Uterine receptivity It can be defined as the temporal window of endometrial maturation during which trophectoderm attaches to the endometrial epithelial cells with subsequent invasion of the endometrial stroma. Based on a number of studies, the window of implantation in the human is relatively broad, extending from day 20 through day 24 of the menstrual cycle. Several investigators have attempted to correlate biochemical markers and ultrastructural features of the endometrium with the presence of . uterine receptivity
  80. 80. ENDOMETRIAL MATURATION Endometrial maturation is associated with loss of both surface microvilli and ciliated cells, as well as the development of cellular protrusions, called pinopods, on the apical surface of the endometrium The presence of pinopods is considered to be an important morphologic marker of peri-implantation endometrium. Pinopod formation is known to be highly progesterone dependent. Biochemical markers of uterine receptivity have included studies of mucin 1 (MUC1) and keratin sulfate. These transmembrane glycoproteins are significantly increased on the glandular cell surface during the peri-implantation period Integrins are also marker for identification of the implantation window
  81. 81. Placental Steroids-Luteal-Placental Shift The corpus luteum is the major source of steroid production in early pregnancy. By the seventh week of gestation, approximately 50 percent of estrogen in the maternal circulation is produced in the placenta Removal of the corpus luteum will result in miscarriage before the switch to placental steroid production. Using a conservative approach, progesterone supplementation should be considered in any woman who has surgical removal of the corpus luteum before 10 weeks of gestation, with supplementation continued at least to this time.
  82. 82. Progesterone Placental progesterone is synthesized from cholesterol primarily derived from maternal circulation. Progesterone is secreted continuously into the maternal circulation rather than stored, as occurs for peptide products. Maternal progesterone serum levels increase from approximately 25 ng/mL during the midluteal phase to 150 ng/mL at term. Progesterone has been postulated to be the critical mediator of uterine quiescence during pregnancy, possibly via inhibition of prostaglandin synthesis. Progesterone is also a potent immunomodulatory agent that may block immune rejection of the developing fetus
  83. 83. Estriol-The pregnancy estrogen The placenta lacks the steroidogenic enzyme CYP17, which is required for converting C21 steroids, including progesterone, into C19 androgens. Therefore, placental estrogen production is dependent on precursors provided by other systems. While progesterone production is dependent on maternal precursors, estrogen production is dependent on precursors from the fetal adrenal gland. The fetal adrenal gland is nearly as large as the fetal kidney, and therefore is proportionally enlarged relative to the adult adrenal gland. The fetal adrenal cortex produces DHEAS, which is subsequently hydroxylated to form 16 -hydroxy-DHEAS in the fetal liver. The high levels of aromatase activity in the placenta convert 16 -hydroxyDHEAS to estriol, explaining the high circulating levels of this steroid during pregnancy.
  84. 84. Steroid Production Related to Fetal Well Being It has been appreciated for many decades that measurement of urinary estriol can be used as a marker for fetal health. Estrogen levels are markedly blunted in patients making low levels of androgen precursors, such as occurs in anencephaly, adrenal hypoplasia, or fetal demise. Serum estriol is now used in the second trimester as part of the triple screen and quadruple screen to look for Down syndrome and neuraltube defects, among other fetal anomalies.
  85. 85. The Normal Menstrual Cycle Menstrual cycle length is determined by the rate and quality of follicular growth and development, and it is normal for the cycle to vary in individual women. Cycle lengths are the shortest (with the least variability) in the late 30s, a time when subtle but real increases in FSH and decreases in inhibin are occurring. This can be pictured as accelerated follicular growth. At the same time, fewer follicles grow per cycle as a woman ages. Approximately 2-4 years prior to menopause, the cycles lengthen again. In the last 10-15 years before menopause, there is an acceleration of follicular loss. This accelerated loss begins when the total number of follicles reaches approximately 25,000, a number reached in normal women at age 37-38 Eventually menopause occurs because the supply of follicles is depleted.
  86. 86. Variations in menstrual flow and cycle length are common at the extremes of reproductive age, during the early teenage years and the years preceding the menopause. The prevalence of anovulatory cycles is highest in women under age 20 and over age 40. Menarche is typically followed by approximately 5-7 years of relatively long cycles that gradually decrease in length and become more regular. Although menstrual cycle characteristics generally do not change appreciably during the reproductive years, overall cycle length and variability slowly decrease. On average, mean cycle length and variability reach their lows at about age 40-42. Over the subsequent 8-10 years before the menopause, the trend is reversed; both average cycle length and variability steadily increase as ovulations become less regular and frequent. Mean cycle length is greater in women at the extremes of body mass and composition; both high and low body mass index are associated with an increased mean cycle length.
  87. 87. In general, variations in cycle length reflect differences in the length of the follicular phase of the ovarian cycle. Women who have a 25-day cycle ovulate on or about cycle day 1012, and those with a 35-day cycle ovulate approximately 10 days later. Within a few years after menarche, the luteal phase becomes extremely consistent (13-15 days) and remains so until the perimenopause. At age 25, over 40% of cycles are between 25 and 28 days in length; from age 25 to 35, over 60% are. Although it is the most often reported intermenstrual interval, only approximately 15% of cycles in reproductive aged women are actually 28 days in length. Less than 1% of women have a regular cycle lasting less than 21 days or more than 35 days.300 Most women have cycles that last from 24 to 35 days, but at least 20% of women experience irregular cycles.295
  88. 88. Thank you all.