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Copyright 2009, John Wiley & Sons, Inc. Chapter 28: The Reproductive Systems
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Copyright 2009, John Wiley & Sons, Inc. Male reproductive system Gonads – testes Produces sperm and secretes hormones System of ducts – transport and stores sperm, assists in their maturation, and conveys them to the exterior Epididymis, ductus deferens, ejaculatory ducts, and urethra Accessory sex glands – adds secretions to semen Seminal vesicles, prostate, and bulbourethral glands Supporting structures Scrotum supports testes and penis delivers sperm into female reproductive tract
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Copyright 2009, John Wiley & Sons, Inc. Male reproductive organs
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Copyright 2009, John Wiley & Sons, Inc. Scrotum Supporting structure for testes Raphe – external median ridge Scrotal septum – internally divides scrotum into two sacs, each with a single testis Made up of subcutaneous layer and dartos muscle Associated with each testis is the cremaster muscle Normal sperm production requires a temperature 2-3°C below core body temperature Cremaster and dartos muscle contracts or relaxes
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Copyright 2009, John Wiley & Sons, Inc. The Scrotum
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Copyright 2009, John Wiley & Sons, Inc. Testes or testicles Paired oval glands in the scrotum Develops near kidney and descends through inguinal canals near 7th month of fetal development Tunica vaginalis partially covers testes Tunica albuginea – internal to tunica vaginalis Extends inward forming septa that divide testis into lobules Each of 200-300 lobules contains 1-3 seminiferous tubules Sperm produced here through spermatogenesis
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Copyright 2009, John Wiley & Sons, Inc. Internal and external anatomy of a testis
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Copyright 2009, John Wiley & Sons, Inc. Seminferous tubule cells Spermatogenic cells – sperm-forming cells Spermatagonia (stem cell) develop from primordial germ cells that arise in yolk sac and enter testes in 5th week of development Primary spermatocytes → secondary spermatocytes → spermatids → sperm cells → lumen Sertoli cells or sustenacular cells– support cells Tight junction form blood-testis barrier – prevents immune response against sperm cell surface antigens Nourish spermatocytes, spermatids and sperm, phagocytize excess spermatid cytoplasm, control movements of spermatogenic cells, release sperm into lumen, produce fluid for sperm transport, secrete inhibin, regulate effects of testosterone and follicle-stimulating hormone (FSH) Leydig (interstitial) cells found in spaces between seminiferous tubules Secrete testosterone
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Copyright 2009, John Wiley & Sons, Inc. Seminiferous tubules and stages of sperm production
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Copyright 2009, John Wiley & Sons, Inc. Spermatogenesis Takes 65-75 days Begins with spermatogonia – diploid (2n) Stem cells undergo mitosis to replace themselves and some continue development Primary spermatocytes – diploid (2n) Each duplicates its DNA and meiosis begins Meiosis I – homologous pairs line up, crossing over occurs Secondary spermatocytes (haploid or n) 2 cells at end of Meiosis I Each chromosome made up of 2 chromatids attached at centromere Meiosis II – 2 chromatids separate Spermatids – 4 haploid cells at end of meiosis II Cells remain attached to each other by cytoplasmic bridges Spermiogenesis – development of spermatids into sperm Spherical spermatids transform into elongated sperm Acrosome and flagella form, mitochondria multiply Sertoli cells dispose of excess cytoplasm Spermiation – release from connections to Sertoli cells Not yet able to swim
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Copyright 2009, John Wiley & Sons, Inc. Events in spermatogenesis
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Copyright 2009, John Wiley & Sons, Inc. Sperm Each day about 300 million sperm complete spermatogenesis Head Nucleus with 23 chromosomes (haploid or n) Acrosome – vesicle filled with oocyte penetrating enzymes Tail Neck – contains centrioles forming microtubules that comprise remainder of tail Middle piece – contains mitochondria Principal piece – longest portion of tail End piece – terminal, tapering portion of tail Once ejaculated, sperm do not survive more than 48 hours in female reproductive tract
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Copyright 2009, John Wiley & Sons, Inc. Parts of a sperm cell
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Copyright 2009, John Wiley & Sons, Inc. Hormonal control of testes At puberty, secretion of gonadotropin-releasing hormone (GnRH) increases Stimulates anterior pituitary to increase secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) LH stimulates Leydig cells to secrete testosterone Synthesized from cholesterol mainly in testes Suppresses secretion of LH and GnRH via negative feedback Enzyme 5 alpha-reductase converts testosterone into dihydrotestosterone (DHT) in external genitals and prostate FSH acts indirectly on spermatogenesis FSH and testosterone act on Sertoli cells to stimulate secretion of androgen-binding protein (ABP) ABP binds testosterone keeping concentration high Testosterone stimulates spermatogenesis Sertoli cells release inhibin which inhibits FSH
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Copyright 2009, John Wiley & Sons, Inc. Hormonal control of spermatogenesis
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Copyright 2009, John Wiley & Sons, Inc. Androgens (testosterone and DHT) Prenatal development Testosterone stimulates male pattern of development or reproductive system ducts and descent of testes DHT stimulates development of external genitalia Development of male sexual characteristics At puberty, they bring about development of male sex organs and development of male secondary sexual characteristics Development of sexual function Androgens contribute to male sexual behavior, spermatogenesis and sex drive (libido) Stimulation of anabolism Stimulate protein synthesis – heavier muscle and bone mass in men
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Copyright 2009, John Wiley & Sons, Inc. Negative feedback regulates testosterone production
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Copyright 2009, John Wiley & Sons, Inc. Reproductive system ducts in males Ducts of testis Pressure generated by fluid produced by Sertoli cells push sperm along seminiferous tubules into straight tubules, rete testis, efferent ducts in epididymis and then ductus epididymis Epididymis Consists of tightly coiled ductus epididymis Stereocilia are microvilli that reabsorb degenerated sperm Site of sperm maturation – acquire motility and ability to fertilize Can store sperm for several months Continues as ductus (vas) deferens Ductus (vas) deferens Conveys sperm during sexual arousal through peristaltic contractions Can also store sperm several months
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Copyright 2009, John Wiley & Sons, Inc. Male reproductive system ducts Spermatic cord Ascends out of scrotum Consists of ductus deferens as it ascends through scrotum, testicular artery, veins that drain testes and carry testosterone, autonomic nerves, lymphatic vessels, and cremaster muscle Spermatic cord and ilioinguinal nerve pass through inguinal canal Ejaculatory ducts Formed by union of duct from seminal vesicle and ampulla of ductus deferens Terminate in prostatic urethra Eject sperm and seminal vesicle secretions just before release of semen into urethra Urethra Shared terminal duct of reproductive and urinary systems Subdivided into prostatic urethra, membranous urethra, and spongy (penile) urethra Ends at external urethral orifice
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Copyright 2009, John Wiley & Sons, Inc. Accessory reproductive organs in males
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Copyright 2009, John Wiley & Sons, Inc. Accessory sex glands – secrete most of liquid portion of semen Seminal vesicles - About 60% of semen volume Secrete alkaline, viscous fluid containing fructose, prostaglandins, and clotting proteins (different from blood) Prostate - About 25% of semen volume Secretes milky, slightly acidic fluid containing citric acid, several proteolytic enzymes, acid phosphatase, seminalplasmin (antibiotic) Bulbourethral glands Secrete alkaline fluid that protects passing sperm by neutralizing acids from urine in urethra Mucus lubricates end of penis and lining of urethra
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Copyright 2009, John Wiley & Sons, Inc. Semen and Penis Semen Mixture of sperm and seminal fluid Typical volume 2.5-5 mL with 50-150 million sperm/mL Slightly alkaline pH of 7.2-7.7 due to seminal vesicle secretions Provides transport medium, nutrients, and protection Coagulates after ejaculation due to clotting proteins Penis Contains urethra Passageway for ejaculation of semen and excretion of urine Body of penis – 3 cylindrical masses of tissue with erectile tissue Glans penis – terminal opening is external urethral orifice Prepuce or foreskin covers glans in uncircumcised men Root of penis is attached portion Erection – parasympathetic fibers release and cause local production of nitric oxide (NO) causing smooth muscle in arterioles to relax and dilate allowing large amounts of blood to enter penis
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Copyright 2009, John Wiley & Sons, Inc. Internal structure of the penis
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Copyright 2009, John Wiley & Sons, Inc. Female reproductive system Gonads – ovaries Uterine (fallopian) tubes or oviducts Uterus Vagina External organs – vulva or pudendum Mammary glands
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Copyright 2009, John Wiley & Sons, Inc. Female organs of reproduction and surrounding structures
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Copyright 2009, John Wiley & Sons, Inc. Ovaries Paired glands homologous to the testes Produce Gametes – secondary oocytes that develop into mature ova (eggs) after fertilization Hormones including progesterone, estrogens, inhibin and relaxin Series of ligaments hold ovaries in place Broad ligament – part of parietal peritoneum Ovarian ligament – anchors ovaries to uterus Suspensory ligament – attaches ovaries to pelvic wall
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Copyright 2009, John Wiley & Sons, Inc. Relative positions of the ovaries, the uterus, and supporting ligaments
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Copyright 2009, John Wiley & Sons, Inc. Histology of ovary Germinal epithelium – covers surface of ovary Does not give rise to ova – cells that arise form yolk sac and migrate to ovaries do Tunica albuginea Ovarian cortex Ovarian follicles and stromal cells Ovarian medulla Contains blood vessels, lymphatic vessels, and nerves Ovarian follicles – in cortex and consist of oocytes in various stages of development Surrounding cells nourish developing oocyte and secrete estrogens as follicle grows Mature (graafian) follicle – large, fluid-filled follicle ready to expel secondary oocyte during ovulation Corpus luteum – remnants of mature follicle after ovulation Produces progesterone, estrogens, relaxin and inhibin until it degenerates into corpus albicans
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Copyright 2009, John Wiley & Sons, Inc. Histology of the ovary
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Copyright 2009, John Wiley & Sons, Inc. Oogenesis and follicular development Formation of gametes in ovary Oogenesis begins before females are born Essentially same steps of meiosis as spermatogenesis During early fetal development, primordial (primitive) germ cells migrate from yolk sac to ovaries Germ cells then differentiate into oogonia – diploid (2n) stem cells Before birth, most germ cells degenerate – atresia A few develop into primary oocytes that enter meiosis I during fetal development Each covered by single layer of flat follicular cells – primordial follicle About 200,000 to 2,000,000 at birth, 40,00 remain at puberty, and around 400 will mature during a lifetime
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Copyright 2009, John Wiley & Sons, Inc. Follicular development Each month from puberty to menopause, FSH and LH stimulate the development of several primordial follicles Usually, only one reaches ovulation Primordial follicles develop into primary follicles Primary oocyte surrounded by granulosa cells Forms zona pellucida between granulosa cells and primary oocyte Stromal cells begin to form theca folliculi Primary follicles develop into secondary follicles Theca differentiates into theca interna secreting estrogens and theca externa Granulosa cells secrete follicular fluid in antrum Innermost layer of granulosa cells attaches to zona pellucida forming corona radiata
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Copyright 2009, John Wiley & Sons, Inc. Ovarian follicles
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Copyright 2009, John Wiley & Sons, Inc. Follicular development Secondary follicle becomes mature (graffian) follicle Just before ovulation, diploid primary oocyte completes meiosis I Produces 2 unequal sized haploid (n) cells – first polar body is discarded and secondary oocyte At ovulation, secondary oocyte expelled with first polar body and corona radiata If fertilization does not occur, cells degenerate If a sperm penetrates secondary oocyte, meiosis II resumes Secondary oocyte splits into 2 cells of unequal size – second polar body (also discarded) and ovum or mature egg Nuclei of sperm cell and ovum unite to form diploid zygote
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Copyright 2009, John Wiley & Sons, Inc. Oogenesis
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Copyright 2009, John Wiley & Sons, Inc. Summary of oogenesis and follicular development
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Copyright 2009, John Wiley & Sons, Inc. Uterine (fallopian) tubes or oviducts Provide a route for sperm to reach an ovum Transport secondary oocytes and fertilized ova from ovaries to uterus Infundibulum ends in finger-like fimbriae Produce currents to sweep secondary oocyte in Ampulla – widest longest portion Isthmus – joins uterus 3 layers Mucosa – ciliary conveyor belt, peg cells provide nutrition to ovum Muscularis – peristaltic contractions Serosa – outer layer
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Copyright 2009, John Wiley & Sons, Inc. Relationship of the uterine tubes to the ovaries, uterus, and associated structures
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Copyright 2009, John Wiley & Sons, Inc. Histology of the uterine (fallopian) tube
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Copyright 2009, John Wiley & Sons, Inc. Uterus Anatomy Fundus, body, isthmus, and cervix (opens into vagina) Normal position is anteflexion – anterior and superior over bladder Ligaments maintain position – broad, uterosacral, cardinal and round Histology – 3 layers Perimetrium – outer layer Part of visceral peritoneum Myometrium 3 layers of smooth muscle Contractions in response to oxytocin from posterior pituitary
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Copyright 2009, John Wiley & Sons, Inc. Uterus Endometrium – inner layer Highly vascularized Stratum functionalis –lines cavity, sloughs off during menstruation Stratum basalis – permanent, gives rise to new stratum functionalis after each menstruation Blood supply Uterine arteries, arcuate arteries, radial arteries Just before branches enter endometrium divide into Straight arterioles supplying stratum basilis Spiral arteries supplying stratum functionalis change markedly during menstrual cycle Cervical mucus - produced by secretory cells of cervix mucosa Water, glycoproteins, lipids, enzymes, and inorganic salts More hospitable to sperm near ovulation – thinner, more alkaline Supplements energy needs of sperm, protect sperm from phagocytes and hostile environment of tract
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Copyright 2009, John Wiley & Sons, Inc. Histology of the uterus
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Copyright 2009, John Wiley & Sons, Inc. Blood supply of the uterus
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Copyright 2009, John Wiley & Sons, Inc. Vagina Fibromuscular canal extending from exterior of body to uterine cervix Mucosa continuous with uterine mucosa Decomposition of glycogen makes acidic environment hostile to microbes and sperm Alkaline components of semen raise pH Muscularis – 2 layers of smooth muscle Adventitia – anchors vagina to adjacent organs Hymen – forms border around and partially closes vaginal orifice
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Copyright 2009, John Wiley & Sons, Inc. Vulva or pudendum – external female genitalia Mons pubis – cushions pubic symphisis Labia majora – homologous to scrotum Labia minora – homologous to spongy (penile) urethra Clitoris – 2 small erectile bones and numerous nerves and blood vessels Homologous to glans penis Vestibule – region between labia minora External urethral orifice, openings of several ducted glands, and vaginal orifice Bulb of the vestibule – 2 elongates masses of erectile tissue on either side of vaginal orifice
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Copyright 2009, John Wiley & Sons, Inc. Components of the vulva (pudendum)
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Copyright 2009, John Wiley & Sons, Inc. Perineum Diamond-shaped area medial to thighs and buttocks of males and females Contains external genitalia and anus
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Copyright 2009, John Wiley & Sons, Inc. Breast / Mammary glands Nipple has openings of lactiferous ducts Areola – pigmented area Mammary gland – modified sudoriferous gland that produces milk 15-20 lobes divided into lobules composed of alveoli (milk-secreting glands)
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Copyright 2009, John Wiley & Sons, Inc. The Female Reproductive Cycle Encompasses ovarian and uterine cycle, hormonal changes that regulate them, and related changes in breast and cervix Ovarian cycle – series of events in ovaries that occur during and after maturation of oocyte Uterine (menstrual) cycle – concurrent series of changes in uterine endometrium preparing it for arrival of fertilized ovum
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Copyright 2009, John Wiley & Sons, Inc. Hormonal regulation Gonadotropin-releasing hormone (GnRH) Secreted by hypothalamus controls ovarian and uterine cycle Stimulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from anterior pituitary FSH Initiate follicular growth Stimulate ovarian follicles to secrete estrogens LH Stimulates further development of ovarian follicles Stimulate ovarian follicles to secrete estrogens Stimulates thecal cells of developing follicle to produce androgens to be converted into estrogens Triggers ovulation Promotes formation of corpus luteum – produces estrogens, progesterone, relaxin and inhibin
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Copyright 2009, John Wiley & Sons, Inc. Hormonal regulation Estrogens secreted by ovarian follicles Promote development and maintenance of female reproductive structures and secondary sex characteristics Increases protein anabolism including building strong bones Lowers blood cholesterol Inhibit release of GnRH, LH and FSH Progesterone Secreted mainly by corpus luteum Works with estrogens to prepare and maintin endometrium for implantation and mammary glands for milk production Inhibits secretion of GnRH and LH
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Copyright 2009, John Wiley & Sons, Inc. Hormonal regulation Relaxin Produced by corpus luteum Relaxes uterus by inhibiting contraction of myometrium At end of pregnancy, increases flexibility of pubic symphysis and dilates uterine cervix Inhibin Secreted by granulosa cells of growing follicles and by corpus luteum Inhibits secretion of FSH and LH
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Copyright 2009, John Wiley & Sons, Inc. Secretion and physiological effects of hormones in the female reproductive cycle
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Copyright 2009, John Wiley & Sons, Inc. 4 Phases Typical duration 24-35 days Assume a duration of 28 days Menstrual phase Preovulatory phase Ovulation Postovulatory phase
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Copyright 2009, John Wiley & Sons, Inc. The female reproductive cycle
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Copyright 2009, John Wiley & Sons, Inc. Menstrual phase or menstruation Roughly first 5 days of cycle First day of menstruation is day 1 of new cycle Events in ovaries Under FSH influence, several primordial follicles develop into primary follicles ad then into secondary follicles Takes several months Follicle that begins to develop in one cycle may not mature for several cycles later Events in uterus Menstrual discharge occurs because declining levels of estrogens and progesterone stimulate release of prostaglandins causing uterine spiral arterioles to constrict Cells deprived of oxygen begin to die Only stratum basilis remains
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Copyright 2009, John Wiley & Sons, Inc. Preovulatory phase More variable in length Lasts from days 6-13 in a 28 day cycle Events in ovaries Some of secondary follicles begin to secrete estrogens and inhibin Dominant follicle – one follicle outgrown all others Estrogens and inhibin of dominant follicle decrease FSH causing other follicles to stop growing Fraternal (nonidentical) twins result when 2 or 3 secondary follicles become codominant and are ovulated and fertilized at the same time
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Copyright 2009, John Wiley & Sons, Inc. Preovulatory phase Normally, one dominant follicle becomes the mature (graffian) follicle In ovarian cycle, menstrual and preovulatory phases are termed follicular phase because follicles are growing Events in uterus Estrogens stimulate repair of endometrium Cells of stratum basalis undergo mitosis to form new stratum functionalis Thickness of endometrium doubles In uterine cycle, preovulatory phase is the proliferative phase because endometrium is proliferating
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Copyright 2009, John Wiley & Sons, Inc. Ovulation Rupture of mature (graffian) follicle and release of secondary oocyte Day 14 of 28 day cycle High levels of estrogens exert a positive feedback effect on cells secreting LH and GnRH
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High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH Hypothalamus Anterior pituitary Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH Hypothalamus Anterior pituitary GnRH promotes release of FSH and more LH Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 2 High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH LH surge brings about ovulation Ovulated secondary oocyte Hypothalamus Anterior pituitary GnRH promotes release of FSH and more LH Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 2 3
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Copyright 2009, John Wiley & Sons, Inc. Postovulatory phase Duration most constant of phases Lasts for 14 days in 28 day cycle (day 15-28) Events in one ovary After ovulation, mature follicle collapses to form corpus luteum under the influence of LH Secretes progesterone, estrogen, relaxin and inhibin In the ovarian cycle, this is the luteal phase
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Copyright 2009, John Wiley & Sons, Inc. Corpus luteum If oocyte not fertilized, corpus luteum lasts 2 weeks Degenerates in corpus albicans As levels of progesterone, estrogens and inhibin decrease, release of GnRH, FSH, and LH rise sue to loss of negative feedback Follicular growth resume as new ovarian cycle begins If oocyte is fertilized, corpus luteum lasts more than 2 weeks Human chorionic gonadotropin (hCG) produced by chorion of embryo about 8 days after fertilization stimulates corpus luteum
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Copyright 2009, John Wiley & Sons, Inc. Events in uterus Progesterone and estrogens produced by corpus luteum promote growth of endometrium Because of secretory activity of endometrial glands, this is the secretory phase of uterine cycle Changes peak about 1 week after ovulation when a fertilized ovum might arrive in uterus If fertilization does not occur, levels of progesterone and estrogens decline due to degeneration of corpus luteum Withdrawal of estrogens and progesterone causes menstruation
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Copyright 2009, John Wiley & Sons, Inc. Hormonal interactions in the ovarian and uterine cycles
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Copyright 2009, John Wiley & Sons, Inc. End of Chapter 28 Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.