Ovarian Cycle PDF

CYCLES AND SEASONS DR. B.E ARAYOMBO  Estrous Cycle Estrous is a Greek word meaning sexual desire. Estrous cycle- a succession of observable sexual phenomenon in adult female mammals reccuring at regular interval and similar sequence accompanying changes in the reproductiv...

CYCLES AND SEASONS DR. B.E ARAYOMBO  Estrous Cycle Estrous is a Greek word meaning sexual desire. Estrous cycle- a succession of observable sexual phenomenon in adult female mammals reccuring at regular interval and similar sequence accompanying changes in the reproductive tract from one period to the next. This excludes human being. The Estrous Cycle starts after puberty in female, and are interrupted by anestrous phases of pregnancies. Estrous cycle , is the ovarian cycle in most non- pregnant adult mammals ,it involves periodic regression of follicles &activity associated with instinct of sexual receptivity known as estrus.  Menstrual cycle Menstrual cycle is the succession of endometrial changes observable in female humans and some primates,that recur regularly during the reproductive years. Menstruation is the physiologic shedding of the uterine endometrium accompanied by uterine bleeding that occurs at approximately monthly intervals from menarche to menopause. It begins at the end of luteal phase and prior to the follicular phase. Menstruation removes the stratum- functionale;i.e the stratum compactum and part of stratum spongiosum, which build up during proliferative Phase , so that there can be a new sloughable layer in the next cycle.  Ovarian cycle Ovarian cycle is the sequence of physiologic changes in the ovary, including development and rupture of the follicle,discharge of the ovum as well as corpus luteum formation and regression. Ovarian cycle also called oogenic cycle is regulated by the hypothalamus, which responds to external & physiological cues. Ovarian cycle is divided into; 1.Follicullar or proliferative phase(overlapped by desquamative phase) 2.Ovulatory phase 3.Luteal phase or progestational phase  Ovarian cycle in non-pregnant females is accompanied by periodic sloughing of uterine lining and consequent bleeding called menstrual cycle. Corpus luteum of pregnancy ( high progesterone condition )inhibits the progression of any cycle. These cycles exists in only non pregnant females.  Categories Of Estrous Cycle Polyestrous (most animals) more than one estrous cycle per year. Can either be ; non seasonal [cycles all year round ] e.g cattle & pigs. seasonal [cycles at only certain time of the season.] Monoestrous –one estrous cycle per year (whales , bears , foxes ,roe ,deer, )  Stages of estrous cycle Estrous (ovulation)- period of ovulation. Metestrous (luteal phase) immediately after estrous when females are no longer receptive to male. Early diesterus (luteal phase)- corpus luteum is formed ,and progesterone secretion increases. Late diestrus (luteal phase)-Corpus luteum is being destroyed , progestrone secretion drops. Pro esterus (follicullar phase )- Estrogen level is high,stimulates high LH. If pregnancy ensues, estrous cycle ceases and a period of anestrous follows until parturition or termination of the pregnancy.  Proestrous phase Proestrous -One or several follicles start to grow. This phase can last as little as 1 day and as long as 3 weeks depending on species. With estrogen influence, lining of the endometrium starts to develop. Some animals may have bloody vaginal discharge [not menses]. Females are not sexually receptive in this phase.  Estrus phase Estrus- The phase when female is sexually receptive with GnRH ,ovarian follicles develops &are maturing and estrogen secretions exert their biggest influence she then exhibits sexually receptive behaviour one of the observable features of estrus is the lordoisis reflex and reddened labia.  Categories of ovulation spontaneous ovulators (human being) ovulates at a regular period in non-pregnant state. induced ovulators [felines , camels]- ovulation is induced by act of copulation ,or other cues.  Variation in menstrual cycle. Human are one of very few species with menstrual cycle without the display of estrous behaviour. Why the absence of estrous in human. For monogamy - loss of estrous serves to promote sexual receptivity over the cycle and helps to maintain monogamous pair bonds by encouraging repeated sexual contact.  Estrous vs Menstrual Cycle
Differences In Estrous Cycle the endometrium is resorbed if conception does not occur during the cycle, while endometrial shedding occur in menstrual cycle. Moreover,females are generally only sexually active during the heat period in Estrous cycle. In contrast to menstrual cycle, females can be sexually active at anytime in their cycle. Though human has concealed ovulation (no obvious external sign to receptivity at ovulation.) Puberty: Body changes & differences
 What is puberty? Puberty is the stage of physical maturation in which an individual becomes physiologically capable of sexual reproduction. Puberty is the stage in life when an individual begins to be physiologically competent to proliferate (i.e begin to become an adult). This means a lot of changing and growing – both inside and out. Some of the changes that happen in puberty are also known as adolescence. Which is the transition period between childhood and adulthood. Puberty starts because of sex hormones.  More Definitions on Puberty Period when the gonads grow rapidly, output of sex hormones leads to the development of secondary sexual characters and mature gamates are released for the first time. SIGNS OF PUBERTY In girls the first signs of puberty tend to occur about 1.5 -2years before the signs in boys. About 5% of boys show some signs of puberty at the age of 10 years. 5% of normal boys show no signs until they are 15 years old. In girls the first signs are pubic hair growth and breast development. These precede menarche by about two years  Timing of Puberty Partially genetically determined Mean difference of menarchal age in identical twins is only 3 months while in non-identical twins it is up to 12 months. Nutrition is very important in modifying pubertal timing. Well-nourished children reach puberty earlier than poorly nourished ones. In most industrial nations, the timing of menarche has been advancing by about 4-6 months per decade since the mid 19th century. Influence of nervous stimuli such as light and temperature is well known in the regulation of sexual activity in birds and mammals. Artificially long days have been known to advance puberty in animals. In blind girls menarche is significantly earlier than normal ones. Continual bombardment of the nervous system with erotica can also advance puberty.  Mechanism of Puberty Both Adrenals and gonads are concerned with puberty. In childhood the output of gonadal steroids and adrenal androgens is low. Before puberty, tiny amounts of steroids produced by the prepubertal gonad is enough to inhibit gonadotrophin output. At puberty the sensitivity of the hypothalamus to the steroids diminishes. Amount of steroids are no longer enough to inhibit gonadotrophin output and so this (FSH,LH,and Prolactin) rises. This begins in about the 8 year of life; and usually th culminating in the onset of puberty and menstruation between the ages of 11 and 16 years in girls (Average 13 years).  Growth Spurt in Puberty Before puberty there is relatively little difference between the average heights and weights of girls and boys. Between the ages of 8 and 13, girls tend to be heavier than boys of similar age because of the earlier pubertal growth spurt before menarche. Little growth occurs afterwards. Boys are finally taller than girls Appearance of pubic hair and growth spurt are associated with adrenal androgens. In female they depend almost entirely on the adrenals. In the male, testicular androgens modify the distribution of pubic hair and forehead hair line and increase the intensity of the spurt.  HORMONAL CHANGES
OF PUBERTY Gonadotropic-Releasing Hormone Gonadotropins Adrenal steroids Ovarian development Testis development Role of GH, IGF-I and insulin Leptin  PHYSIOLOGY OF PUBERTY The biological changes include: neurosecretory factors and/or hormones modulation of somatic growth initiation of the development of the sex glands  PHYSIOLOGY OF PUBERTY Activation of the hypothalamic-pituitary gonadal axis: induces and enhances the progressive ovarian and testicular sex hormone secretion responsible for the profound biological, morphological, and psychological changes to which the adolescent is subjected sex steroid production: appearance and maintenance of sexual characteristics capacity for reproduction  PHYSICAL CHANGES OF
PUBERTY
Puberty proceeds through five stages from childhood to full maturity (P1 to P5) as described by Marshall and Tanner. In both sexes, these stages reflect the progressive modifications of the external genitalia and of sexual hair. Secondary sex characteristics appear at a mean age of 10.5 years in girls and 11.5 to 12 years in boys.  PUBERTAL STAGES (TANNER)
FEMALE
P1 Prepubertal P2 Early development of subareolar breast bud +/-small amounts of pubic hair and axillairy hair P3 Increase in size of palpable breast tissue and areolae, increased amount of dark pubic hair and of axillary hair P4 Further increase in breast size and areola that protrude above breast level adult pubic hair P5 Adult stage, pubic hair with extension to upper thigh PUBERTAL STAGES (TANNER)
FEMALE
 UTERINE DEVELOPMENT
The prepubertal uterus is tear-drop shaped, with the neck and isthmus accounting for up to two-thirds of the uterine volume; then, with the production of estrogens, it becomes pear shaped, with the uterine body increasing in length and thickness proportionately more than the cervix.  MENARCHE
During puberty, plasma estradiol levels fluctuate widely, probably reflecting successive waves of follicular development that fail to reach the ovulatory stage. The uterine endometrium is affected by these changes and undergoes cycles of proliferation and regression, until a point is reached when substantial growth occurs so that withdrawal of estrogen results in the first menstruation (menarche).  OVULATION Under the influence of FSH and LH, the secondary follicle develops rapidly to a diameter of 25 mm. with sudden increase in LH that causes the primary oocyte to complete meiosis I and the follicle to enter the pre- ovulatory stage. Meiosis II then commences, but the oocyte is halted in metaphase about 3 hours before ovulation. Meanwhile, the surface of the ovary begins to bulge locally, and at the apex, an avascular spot, the stigma, appears. The high concentration of LH increases collagenase activity,resulting in digestion of collagen fibers surrounding the follicle.  OVULATION
Prostaglandin levels also increase in response to the LH surge and cause local muscular contractions in the ovarian wall. Those contractions extrude the oocyte, which together with its surrounding granulosa cells from the region of the cumulus oophorus, breaks free and floats out of the ovary this process is referred to as ovulation Some of the cumulus oophorus cells then rearrange themselves around the zona pellucida to form the corona radiata  OVULATION
Plasma testosterone levels also increase at puberty although not as markedly as in males. Plasma progesterone remains at low levels even if secondary sexual characteristics have appeared. A rise in progesterone after menarche is, in general, indicative that ovulation has occured. The first ovulation does not take place until 6-9 months after menarche because the positive feedback mechanism of estrogen is not developed.  FEMALE SECONDARY
SEXUAL CHARACTERISTICS
If breast development, pubic and/or axillary hair, and menses occur earlier than normal variations from the mean, the terms premature thelarche, pubarche and/or adrenarche, and menarche are used.  PUBERTAL STAGES (TANNER)
MALE
P1 Prepubertal, testicular length less than 2.5cm P2 Early increase in testicular size, scrotum slightly pigmented, few long and dark pubic hair P3 Testicular length 3.3-4 cm, lenghtening of the penis, increase in pubic hair P4 Testicular length 4.1-4.5cm, increase in length and thickening of the penis, adult amount of pubic hair P5 Testicular length greater than 4.5cm, full spermatogenesis PUBERTY: MALE
 PUBERTY: MALE
Secondary sexual development in boys: Growth kinetics are enhanced from early puberty on. Maximal velocity is attained only around 14 to 15 years of age Testis increases in size, mainly at the expense of the seminiferous tubules The interstitial (Leydig) cells develop and ensure synthesis and secretion of testosterone  PUBERTY: MALE
Secondary sexual development in boys: a testicular volume of 4 ml or a longitudinal diameter greater than or equal to 2.5 cm and a slight progressive increase in scrotal folds, and pigmentation as well as growth of pubic hair and penis constitute the first signs of puberty.  TESTES DEVELOPMENT:1
The increase in testicular size observed during prepuberty and puberty results essentially from the development of the seminiferous tubules under the stimulating effect of FSH. The testicular volume increases throughout puberty up to Tanner stage P4 when a longitudinal diameter of 5.0 + 0.5 cm or a volume of 17.6 + 4.0 ml is reached.  TESTES DEVELOPMENT:2
Long-standing pulsatile LH secretion induces the differentiation of interstitial cells into testosterone-secreting Leydig cells, which, in turn, exert a negative feedback control on LH secretion. As puberty progresses, spermatogenesis is initiated and then sustained by FSH and by testosterone produced by the Leydig cells under LH control.  TESTES DEVELOPMENT:3
A significant increase of plasma testosterone is found only between Tanner pubertal stages P3 and P4. Dihydrotestosterone shows a pattern similar to that of testosterone, and the proportion of dihydrotestosterone to testosterone decreases gradually until adulthood, when dihydrotestosterone levels are approximately 10% of those of testosterone.  BONE AGE
Puberty is completed usually within 3 to 4 years of its onset, and the final height resulting from complete fusion of the epiphyses occurs within approximately 2 years after menarche.  CHRONOLOGICAL ASPECT
GIRLS – acceleration of growth rate – development of breasts and pubic hair – axillary hair – menarche BOYS – increase of penile length pubic hair – increased growth rate – axillary hair – deepening of the voice --increase of testicular volume  HORMONAL CHANGES:
In prepubertal children, no significant luteinizing hormone (LH) or follicle-stimulating hormone (FSH) response to intravenous or subcutaneous administration of GnRH is observed. During adolescence, the LH response to GnRH increases progressively in both sexes. The increase of FSH is much less marked than that of LH.  HORMONAL CHANGES:
Gonadotropin-Releasing Hormone 3 1. One of the factors involved in « triggering » GnRH secretion is the GPR54 gene, encoding a G protein-coupled receptor. 2. Human mutations found in hypogonadotropic hypogonadism. 3. Defect in migration and/or final differentiation o the neurons in the hypothalamus. 4. Modulate the activity of GnRH. 5. GPR54 regulates the release of GnRH at hypothalamic level.  HORMONAL CHANGES:
Gonadotropins The first demonstrable biological change of puberty is the appearance of pulsatile LH release during sleep. As puberty progresses, the frequency and amplitude of LH secretory peaks increase, although peaks are also found during the wake period. At the end of puberty, the difference between sleep and wake LH secretory patterns disappears.  HORMONAL CHANGES:
Gonadotropins In girls, circulating FSH levels increase progressively from 10 to 11 years of age (stage P2), approximately 1 year prior to those of LH. Thereafter, gonadotropins continue to increase throughout puberty, but important fluctuations are observed in relation to the menstrual cycle.  HORMONAL CHANGES:
Gonadotropins 3 In boys, a significant increase in both plasma FSH and LH is also found from the onset of puberty (stage P2), closely linked to the rapid increase in testicular size characteristic of this pubertal stage. A further significant increase in circulating gonadotropins is also observed at late puberty (stages P4 and P5). HYPOTHALAMO-PITUITARYGONADAL
AXIS
 HORMONAL CHANGES:
Adrenal Steroids 1 Adrenal androgens vary from infancy through adolescence. This phenomenon is called adrenarche. In girls, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) increase as early as 6 to 7 years of age, followed within 1 to 2 years by a concomitant increase in androstenedione.  HORMONAL CHANGES:
Adrenal Steroids 2 In boys, DHEA and DHEAS increase as early as 8 to 9 years of age, followed by androstenedione 1 to 2 years later. Adrenarche begins before the rise in gonadotropin secretion. The adrenal androgens are responsible for the appearance of axillary hair and, in part, for the appearance of pubic hair in the adolescent; however they do not appear to play a decisive role in determining the initiation of puberty.  GH, IGF-I and INSULIN in
PUBERTY
Growth hormone-releasing factor (GRF) levels and GH secretion increase considerably during puberty, mainly at night. The amplitude of GH peaks increases early in puberty. IGF-I is an important modulator of growth during childhood and adolescence.  LEPTIN in PUBERTY
Peptide hormone Regulates food intake and energy expenditure at the hypothalamic level (satiety factor) Expressed predominantly in adipocytes Regulated by body weight and nutrition Involved in the regulation of GnRH secretion Permissive factor for puberty (48kg) Interacts with insulin, IGF1, GH and glucocorticoids