Reproductive Physiology PDF

Reproductive Physiology Puberty – onset of sexual maturation Girls – begins at approximately ages 8 to 9 years of age with the larche (breast development). ○ Obese girls mature earlier, perhaps because of higher estrogen levels related to leptin and gonadotropin secretion. Boys – begins at approxima...

Reproductive Physiology Puberty – onset of sexual maturation Girls – begins at approximately ages 8 to 9 years of age with the larche (breast development). ○ Obese girls mature earlier, perhaps because of higher estrogen levels related to leptin and gonadotropin secretion. Boys – begins at approximately 11 years of age. Estradiol – breast development; maturation of the vagina, uterus, and ovaries; fat deposit in the hips in girls Estrogen – increased production of growth factors: Rapid skeletal growth in both boys and girls Testosterone – growth of testes, scrotum, and penis Positive feedback loop – created to produce more sex hormone Extrahypothalamic factors – cause the hypothalamus to secrete gonadotropin-releasing hormone (GnRH). GnRH – stimulates the anterior pituitary gland to secrete gonadotropins: FSH and LH. FSH and LH – stimulate the gonads (ovaries or testes) to secrete female or male sex hormones. Paracrine hormones (inhibin, activin, follistatin) – influence positive and negative feedback loops for the HPG axis. Adrenarche – the increased production of adrenal androgens prior to puberty which occurs in both sexes, and exhibited by axillary and pubic hair growth; separate from gonadarche Gonadarche – gonadal maturation In females: ○ Ovaries begin to release mature ova. ○ FSH stimulates growth of ovarian follicles and with LH there is stimulation of production of estradiol by ovaries ○ Early estradiol stimulates breast development and growth of skeleton pubertal growth spurt ○ Later there is interaction b/t pituitary secretion of FSH and LH and secretion of estradiol by ovarian follicles which leads to ovulation and menstrual cycles. ○ Estradiol also induces maturation of skeleton, and eventually fusion of growth plates and cessation of linear growth ○ Female puberty is complete at the first ovulatory menstrual period. In males: ○ Testes begin to produce mature sperm. ○ LH stimulates the Leydig cells of testes to produce testosterone, with high local concentration stimulates the growth of seminiferous tubules, leading to increase in testicular volume ○ FSH stimulates further growth of seminiferous tubules and increases in testicular volume ○ Testosterone induces growth of penis, deepening of voice, growth of hair, and increases in muscularity ○ Some testosterone one is converted to estradiol, which has same effects on skeletal maturation as in girls, and can lead to some breast development in males ○ Male puberty is complete with the first ejaculation that contains mature sperm. Ovary Components Medulla – inside Cortex – outside; contains ovarian follicles, theca cells, and granulosa cells Ovulation – release of an ovum; once every menstrual cycle usually only one of the follicles reaches maturation and discharges its ovum through the ovary’s outer covering Ovulation and Ovarian Cycle After ejecting the mature ovum, the follicle develops into the corpus luteum If ovum is fertilized then the corpus luteum enlarges and secretes hormones to support pregnancy If ovum is not fertilized the corpus luteum secretes hormones for 14 days then degenerates which triggers the maturation of another follicle – primarily progesterone This process is generally referred to as the ovarian cycle Gonadotropins and hormones regulate the ovarian function so that any disorder that disrupts this process can cause ovarian dysfunction and infertility ○ Such as abnormal pituitary or thyroid function, benign or malignant growths, cysts, infection or inflammation Female Sex Hormones Estrogens ○ Estradiol – most potent and plentiful. ○ Estrone – converted from androgens in the ovaries. ○ Estriol – peripheral metabolite of estradiol and estrone. Progesterone – needs LH and is the hormone of pregnancy. Androgens – mainly male sex hormones; produced in small amounts in women. Menstrual Cycle Menarche – first menstruation Menopause – cessation of flow Normal cycle – 28 days Phases of menstruation (menses) ○ Follicular/proliferative phase are the first days of the cycle. ○ Ovulation is the beginning of the luteal or secretory phase. ○ If no implantation occurs, then menses begins. Regulated by gonadotropins High FSH levels stimulate follicle and ovum maturation (follicular phase) ○ During the follicular phase of the ovarian cycle, estrogen produced by the follicle causes the endometrium to proliferate (proliferative phase) ○ This induces the LH surge and progesterone production in the granulosa layer – surge of LH causes ovulation Followed by development of the corpus luteum (luteal phase) Ovarian hormones control the uterine (endometrial) events of the menstrual cycle During the luteal phase, estrogen maintains the thickened endometrium and progesterone cause it to develop blood vessels and secretory glands (secretory phase) As the corpus luteum degenerates, production of both hormones drops sharply and the “starved” endometrium degenerates and sloughs off, causing menstruation Body temperature changes ○ Progesterone – increases body temperature. ○ Follicular phase – body temperature is 98° F. ○ After the LH surge – average temperature increases. ○ At the end of the luteal phase, 1 to 3 days before menstruation – temperature declines Aging and the Female Reproductive System Perimenopause – ovaries produce erratic and high levels of estrogen ○ Contributing to hot flashes, breast tenderness and nodularity, and migraine h/a’s ○ Menstrual cycles shorten and then become irregular as anovulation occurs Menopause – cessation of menstruation ○ Defined as 1 yr after the cessation of menstruation and occurs at the average age of 51.4 years ○ Levels of sex hormones decrease with the last menstrual cycle ○ Reduced female sex hormones result in reproductive organ atrophy, thinning of vaginal epithelium, decreased glandular secretions that are more alkaline, and continued sexual activity and orgasm reduce vaginal changes Ovarian Changes – ovaries begin to decrease in size around the age of 30 years; decrease accelerates after the age of 60 years; 500,000 follicles are present at the onset of puberty; the number dwindles to approximately 1000 with menopause. Uterine Changes – thickness of the endometrium is greater; periods are heavier; menorrhagia (heavy bleeding) or metrorrhagia (mid cycle bleeding) occur. Breast tissue changes – size and firmness reduces. Urogenital tract changes – ovaries shrink; uterus atrophies; vagina shortens, narrows, and loses some elasticity; lubrication of vagina diminishes and vaginal pH increases, creating higher incidence of vaginitis. Skeletal changes – brittleness and porosity increases; risk for osteoporosis and fracture increases. Cardiac changes – coronary heart disease significantly increases after menopause. Other changes – skin dryness and wrinkling increases. Structure and Function of the Breast Breast tissue can extend into the axilla known as the tail of Spence Glands of Montgomery – sebaceous glands located in the areola and aid in lubrication of the nipple during lactation Gynecomastia is a condition in men in which the breasts enlarge temporarily as a result of hormonal fluctuations Testes Are essential organs of reproduction. Produce gametes (sperm) and sex hormones (androgens, testosterone). Structure ○ Tunica vaginalis: Outer covering ○ Tunica albuginea: Inner covering ○ Seminiferous tubules: Bulk of testes; site of sperm production (spermatogenesis) Leydig cells – produce androgens, chiefly testosterone Epididymis Sperm matures here. Is a comma-shaped structure that curves over the posterior portion of each testis. Vas Deferens Is a duct with muscular layers capable of powerful peristalsis that transports sperm toward the urethra. Sperm is stored here. Enters the pelvic cavity through the spermatic cord. Penis Penis components ○ Glans – contains the opening of the urethra ○ Prepuce – foreskin ○ Two corpora cavernosa ○ Corpus spongiosum ○ Urethra Penis erectile reflex ○ Corpora cavernosa and corpus spongiosum becoming engorged with blood ○ Parasympathetic nerves causing the arterioles to dilate through the release of nitric oxide ○ Emission versus ejaculation Male Internal Gentialia Seminal vesicles ○ Are a pair of glands that lie behind the urinary bladder. ○ Provide fructose as a source of energy for ejaculated sperm. ○ Secrete prostaglandins that promote smooth muscle contraction, assisting with sperm transport. ○ Join the ampulla of vas deferens through ducts – ejaculatory duct, which contracts rhythmically during emission and ejaculation. Prostate gland ○ Size of a walnut ○ Has three zones ○ Surrounds the urethra Prostatic fluid ○ Is a thin, milky substance with an alkaline pH helps sperm survive in acid environment of female reproductive tract ○ Contains clotting enzymes and fibrinolysin – helps mobilize sperm after ejaculation Bulbourethral glands ○ Are also called Cowper glands. ○ Secrete mucus into the ejaculate. Vasectomy – vasa deferentia are severed and then tied to prevent sperm from entering the ejaculate; permanent male birth control Spermatogenesis – continuous process Spermatogonia – primitive male gametes These undergo continuous mitosis within the seminiferous tubules of the testes Spermatogonia develop into primary spermatocytes which divide mechanically into secondary spermatocytes, and then into spermatids. Spermatids develop into sperm with the help of nutrients and hormonal signals from the Sertoli cells Process takes about 70-80 days Mature sperm migrate from the seminiferous tubules to the epididymis, where their capacity for fertilization continues to develop Completely mature on ejaculation Ability to be motile happens because of activation by biochemicals in semen and in the female reproductive tract Male Sex Hormones Androgens ○ Primary androgen—testosterone Produced mainly in the Leydig cells of the testes Sexual differentiation Urogenital system development Nervous and skeletal tissue development Libido ○ Dihydrotestosterone – necessary for external virilization Prolactin – maintains biosynthesis of testosterone. LH – acts on Leydig cells to regulate testosterone secretion. FSH – acts on Sertoli cells to promote spermatogenesis Inhibin – secreted by the Sertoli cells. ○ Inhibits FSH secretion. ○ Functions as an autocrine/paracrine regulator in the male gonad. ○ Inhibits the proliferation of spermatogonia. ○ Facilitates LH stimulation of androgen biosynthesis in the Leydig cells.