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Chapter 16

Chapter 16. The Reproductive System. Outline. Functions of the Reproductive Systems Male Reproductive System Penis Anatomy; Testes and Sperm; Hormonal Regulation Female Reproductive System Genital Tract Hormonal Levels and Ovulation Ovarian Cycle Uterine Cycle

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Chapter 16

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  1. Chapter 16 The Reproductive System

  2. Outline • Functions of the Reproductive Systems • Male Reproductive System • Penis Anatomy; Testes and Sperm; Hormonal Regulation • Female Reproductive System • Genital Tract • Hormonal Levels and Ovulation • Ovarian Cycle • Uterine Cycle • Fertilization and Pregnancy • Steps of Fertilization • Cleavage of Cells • Implantation • Development before Birth • Extra-embryonic Membranes • Fetal Circulation • Birth • Female Breast and Lactation

  3. Functions of the Reproductive System • To produce offspring; maintain the species. • Estrogen stimulates fat deposition. • Estrogen stimulates liver to produce important transport proteins. • Estrogen stimulates synthesis of bone matrix proteins, prevents bone loss. • Testosterone stimulates synthesis of proteins for skeletal muscle and bone growth. • Testosterone influences liver and kidney enzymes and stimulates release of erythropoietin. • Both hormones influence cardiovascular health.

  4. Male Reproductive System • Male gonads, testes, are paired organs suspended in scrotum • Sperm, the male reproductive cells, are produced in testes and mature in epididymis (some storage in epididymis) • Travel to vas deferens for storage • Each vas deferens empties into a ejaculatory duct • Sperm are ejaculated from urethra • Ejaculate consists of a fluid called semen composed of sperm and secretions from the seminal vesicles, prostate gland, and bulbourethral glands • Seminal vesicles- 60% of total volume; alkaline, viscous, clotting proteins, fructose • Prostate gland- 25% of total volume; slightly acidic, milky, citric acid, proteolytic enzymes-breakdown clot caused by seminal vesicle secretions, lysozyme & seminalplasmin- both antibiotic • Bulbourethral gland- alkaline, mucus

  5. Male Reproductive System

  6. Figure 16.2a Male reproductive organs. Ureter Urinary bladder Seminal vesicle Prostatic urethra Ampulla ofductus deferens Pubis Membranous urethra Ejaculatory duct Urogenital diaphragm Rectum Erectile tissueof the penis Prostate Bulbo-urethral gland Spongy urethra Shaft of the penis Ductus (vas) deferens Glans penis Epididymis Testis Prepuce Scrotum External urethralorifice

  7. Male Reproductive System (Cont.) • Penis has a long shaft and an enlarged tip, glans penis • During sexual arousal, autonomic nerve impulses cause erectile tissue to fill with blood; outflow veinsbecome compressed keeping penis erect • Parasympathetic neurons release nitric oxide (NO); causes arterioles to dilate, filling erectile tissue • Compression of outflow veins-sustains erection • Ejaculation • Urethral contractions(sympathetic neurons) expel semen from the penis during male orgasm. • Urinary bladder sphincter closes • Around 400 million sperm contained in 3.5 ml of semen.

  8. Penis Anatomy Skin Deep dorsal vein Superficial (subcutaneous) dorsal vein Subcutaneous layer Dorsal artery Fascia Transverse plane Dorsal Corpora cavernosa penis Tunica albuginea of corpora cavernosa Deep artery of penis Corpus spongiosum penis Spongy (penile) urethra Ventral Tunica albuginea of corpus spongiosum penis (b) Transverse section

  9. The Testes and Sperm • Testes develop inside abdominal cavity and descend into the scrotum during last two months of fetal development • Scrotum helps regulate temperature of testes for proper sperm production • Testes packed with seminiferous tubules with cells undergoing spermatogenesis, the process of becoming a sperm • Sertoli cells- critical for proper spermatogenesis; create blood-testis barrier (prevents immune system entry); nurture spermatocytes; produce fluid for sperm transport; control release of sperm into lumen of tubules • Testosterone secreted by Leydig cells (interstitial cells) in between seminiferous tubules

  10. One Testis and Sperm

  11. Leydig cell Blood capillary SPERMATOGENIC CELLS: Basement membrane Spermatogonium (2n) (stem cell) Sertoli cell nucleus Primary spermatocyte (2n) Blood–testis barrier (tight junction) Secondary spermatocyte (n) Spermatid (n) Sperm cell or spermatozoon (n) Lumen of seminiferous tubule (b) Transverse section of part of seminiferous tubule

  12. Seminiferoustubule Basementmembrane Daughter cell type A(remains at basementmembrane as a stem cell) Spermatogonium(stem cell) 2n 2n Mitosis Figure 16.3 Spermatogenesis. 2n Growth Daughter cell type B(moves toward tubulelumen) Entersprophase ofmeiosis I 2n Primaryspermatocyte Meiosis Icompleted Meiosis Secondaryspermatocytes • n n Meiosis II Early spermatids • n n n n Spermatogenesis Late spermatids • n n n n Spermiogenesis Sperm • n n n n Lumen ofseminiferoustubule

  13. The Testes and Sperm (Cont.) • Mature sperm have three distinct parts. • Head. • Nucleus covered by acrosome • Contains proteolytic enzymes to help sperm penetrate the corona radiata and zona pellucida of the oocyte during fertilization • Middle Piece. • Filled with mitochondria; provide energy for movement; use fructose & citric acid in semen as fuel sources • Tail. • Flagellum for movement.

  14. Provides geneticinstructions and ameans of penetratingthe follicle cellcapsule andoocyte membrane Providesenergy formobility Plasma membrane Figure 16.5 Structure of sperm. Neck Providesfor mobility Tail Head Midpiece Axial filament of tail Acrosome Nucleus (a) Mitochondria Proximal centriole (b)

  15. Hormonal Regulation in Males • Hypothalamus secretes gonadotropin-releasing hormone (GnRH). • Stimulates anterior pituitary to secrete: • Follicle-stimulating hormone (FSH) • Promotes sperm production • Testosterone also needed for proper sperm production- synergism between the two hormones • Luteinizing hormone (LH) • Controls testosterone production from Leydig cells • Testosterone is essential for reproductive organs and male secondary sex characteristics

  16. Hypothalamus • The hypothalamus releasesgonadotropin-releasing hormone(GnRH). 1 1 GnRH GnRH stimulates the anteriorpituitary to release gonadotropins—FSH and LH. Anteriorpituitary 2 FSH stimulates spermatogeniccells to produce sperm. 3 5 2 LH stimulates the interstitialcells to release testosterone,which serves as the final triggerfor spermatogenesis.Testosterone then enhancesspermatogenesis. 4 LH FSH Figure 16.6 Hormonal control of the testis. Testosterone 4 3 5 Leydig Cells (interstitial cells) Rising level of testosteroneexerts feedback inhibition on thehypothalamus and pituitary. 5 Primary and secondarysex characteristics Testosterone Seminiferoustubule in testis Supporting cell FSH andtestosteronestimulatespermproduction Spermatogeniccells Spermatogenesis KEY: Stimulates Inhibits

  17. Female Reproductive System

  18. Female Reproductive System: The Genital Tract • Female gonads are pairedovaries. • Oviducts extend from uterus to ovaries • Have ciliatedsimple columnar cells- help move oocyte/zygote down tube • Have peg cells- provide fluid to nourish the oocyte • Oviducts join the uterus at its upper end, and at the lower end the cervix enters the vagina. • Vagina receives penis during intercourse; serves as birth canal and exit for menstrual flow. • Fimbriaesweep egg, the female reproductive cell, into the oviduct.

  19. Female Reproductive System Suspensory ligament of ovary(part of broad ligament) Infundibulum Uterine tube Ovary Figure 16.8a The human female reproductive organs. Fimbriae Uterus (fundus) Uterosacralligament Round ligament Urinary bladder Pubic symphysis Rectum Mons pubis Cervix Urethra Vagina Clitoris Anus Hymen Labium minus Greater vestibular gland Labium majus (a)

  20. Suspensoryligament of ovary Uterine (fallopian) tube Lumen (cavity)of uterus Fundusof uterus Ovarianblood vessels Figure 16.8b The human female reproductive organs. Ovary Infundibulum Broadligament Uterinetube Fimbriae Ovarian ligament Round ligament of uterus Body of uterus Endometrium Wall of uterus Myometrium Perimetrium Ureter Uterine bloodvessels Cervical canal Uterosacral ligament Vagina Cervix (b)

  21. Female Reproductive System: External Genitals • External female genital organs collectively called vulva. • Labia majora - Large skin folds. • Labia minora - Small skin folds. • Mons pubis - Prominence under pubic hair. • Glans clitoris - Contains erectile tissue.

  22. External Female Genitalia Mons pubis Labia majora Prepuce ofclitoris Figure 16.9 External genitalia of the human female. Clitoris Vestibule Urethral orifice Vaginal orifice Opening of ductof greatervestibular gland Labia minora Perineum Anus

  23. Female Reproductive System (Con’t) • Upon sexual stimulation, labia minora, vaginal wall, and clitoris become engorged with blood. • Labia majora enlarge, redden, and spread away from the vaginal opening. • Clitoris plays a significant role in female orgasm. • During orgasm walls of uterus and oviducts rhythmically contract.

  24. Hormone Levels and Ovulation • Oogenesis is the production of an egg. • Ovulation is the process of an egg bursting from an ovary and entering an oviduct. • The Ovarian Cycle. • Development of a vesicular follicle, ovulation, and development of corpus luteum. • Under control of FSH and LH. • Follicular Phase - FSH promotes development of an ovarian follicle; estrogen and small amount of progesterone produced by follicle. • Luteal Phase - LH promotes development of corpus luteum; progesterone and small amount of estrogen produced by corpus luteum.

  25. Growing follicles Primary follicle Degeneratingcorpus luteum Figure 16.7 Sagittal view of a human ovary showing the developmental stages of an ovarian follicle. Bloodvessels Antrum Coronaradiata Mature vesicular(Graafian) follicle Germinalepithelium Corpus luteum Developingcorpus luteum Secondary oocyte Rupturedfollicle Ovulation

  26. Follicle Developmentin Ovary Meiotic Events Before birth Oogonium (stem cell) 2n Follicle cells Mitosis Oocyte Primaryfollicle Primary oocyte 2n Growth Primary oocyte(arrested in prophase I;present at birth) Primaryfollicle 2n Figure 16.10 Events of oogenesis. (ovary inactive) Childhood Monthly frompuberty to menopause Primaryfollicle Primary oocyte(still arrested in prophase I) 2n Growingfollicle Maturevesicular(Graafian)follicle Meiosis I (completed by oneprimary oocyte each month) Secondary oocyte(arrested in metaphase II) n First polar body Ovulation Sperm Ovulatedsecondaryoocyte Meiosis II of polar body(may or may not occur) Meiosis II completed(only if spermpenetration occurs) n n n n Polar bodies(all polar bodiesdegenerate) Ovum Secondpolar body

  27. Hormone Levels and Ovulation (Cont.)

  28. Hypothalamus GnRH High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH 1 GnRH promotes release of FSH and more LH 2 Anterior pituitary LH 3 LH surge brings about ovulation Ovulated secondary oocyte Ovary Almost mature (graafian) follicle Corpus hemorrhagicum (ruptured follicle)

  29. Hormone Levels and Ovulation (Con’t) • The Uterine Cycle • Development and preparation of the uterus wall (endometrium) for implantation of an embryo. • Under control of estrogen and progesterone • Proliferative Phase- Estrogen from follicle promotes endometrium to thicken, vascularize and become glandular. • Secretory Phase- Progesterone from corpus luteum causes endometrium to triple in thickness and glands to mature with thick mucoid secretions. Endometrium now ready to receive the developing embryo.

  30. Hormone Levels and Ovulation (Con’t)

  31. Hormone Levels and Ovulation (Con’t) • Estrogen and progesterone: • Foster development of reproductive organs. • Maintain uterine cycle. • Bring about female secondary sex characteristics. • During menopause, usually between age 45 and 55, the uterine cycle ceases, and the ovaries no longer produce estrogen and progesterone.

  32. Fertilization and Pregnancy • Fertilization, the joining of a sperm and an egg, usually occurs in oviducts. • Developing embryo arrives in the uterus after several days and implants in the lining of the uterine wall (endometrium). • Outer membrane of implanted embryo produces human chorionic gonadotropin (HCG) which maintains the corpus luteum in ovary so progesterone is still around; keeps endometrium from sloughing off. • Following implantation, the placenta forms from maternal and fetal tissues. • Placenta begins its own production of progesterone and estrogen.

  33. Fertilization and Pregnancy • Steps of fertilization. • Several sperm penetrate corona radiata of egg as it travels down oviduct. • Several sperm attempt to penetrate zona pellucida. • Only one sperm is successful and enters egg. • Egg’s plasma membrane depolarizes and zona pellucida moves away from surface; no more sperm can bind to the plasma membrane; prevents polyspermy. • Nuclei fuse, producing a zygote.

  34. Steps of Fertilization Optimal site of fertilization Oviduct Uterus Secondary oocyte Acrosome Head Corona radiata Sperm Ovary Midpiece Cytoplasm Tail Nucleus Plasma membrane Cervix First polar body Vagina Zona pellucida • The male gamete, or sperm. The size of a sperm relative to the secondary oocyte has been greatly exaggerated. b) Fertilization. Fertilization generally takes place in the upper third of the oviduct. c) The female gamete. The female gamete is a secondary oocyte that is in an arrested state of stage II of meiosis. Figure 21.1

  35. Steps of Fertilization

  36. Fertilization and Pregnancy (Con’t) • Cleavage of zygote cells. • When a zygote begins dividing, it is termed an embryo. • Traveling down oviduct, many cell cleavages occur. • Morula - Solid mass of cells resulting from cleavage. • Blastocyst – Hollow ball of cells with inner cell mass. • Inner cell mass are embryonic stem cells.

  37. Fertilization and Pregnancy (Con’t)

  38. Fertilization and Pregnancy (Con’t) • Implantation • Embryo eventually implants in endometrium. • After implantation trophoblastcells begin to produce human chorionic gonadotropin (HCG); maintains corpus luteum and progesterone levels. • If implantation does not occur, a woman never knows fertilization took place. • Home pregnancy tests measure HCG breakdown products in the urine.

  39. Implantation Amniotic cavity Ectoderm Cells derived from trophoblast Endometrium Endoderm Inner cell mass Yolk sac Amniotic cavity Embryonic disk Trophoblast Blastocyst Figure 21.6

  40. Extraembryonic Membranes • Membranes that extend out beyond the embryo. • Amnion - Provides fluid environment for developing embryo and fetus. • Chorion- Becomes part of the placenta.

  41. Extraembryonic Membranes

  42. Decidua basalis of uterus (maternal portion of placenta) Chorionic villi of chorion (fetal portion of placenta) Chorionic villi Maternal endometrial venule Umbilical cord: Intervillous space containing maternal blood Umbilical arteries Umbilical vein Maternal endometrial arteriole Mucous connective tissue Amnion Fetal blood vessels (a) Details of placenta and umbilical cord

  43. Fetal Circulation and the Placenta

  44. Fetal Circulation • The umbilical cord stretches between the placenta and the fetus and contains the umbilical arteries and veins. • Exchange of gases and nutrients between maternal and fetal blood takes place in the umbilical arteries. • Umbilical veincarries blood and oxygen away from the placenta to the fetus. • Lungs are not functional in fetus; most right heart blood goes directly into the left atrium via the oval opening (foramen ovale) and the aorta via the arterial duct (ductus arteriosus).

  45. Arch of aorta Superior vena cava Left atrium DUCTUS ARTERIOSUS becomes Ligamentum arteriosum Right atrium Lung Pulmonary artery Pulmonary veins Heart Left ventricle Right ventricle FORAMEN OVALE becomes Fossa ovalis Inferior vena cava Liver DUCTUS VENOSUS becomes Ligamentum venosum Hepatic portal vein UMBILICAL VEIN becomes Ligamentum teres Umbilicus Inferior vena cava Abdominal aorta Common iliac artery UMBILICAL ARTERIES become Medial umbilical ligaments Urinary bladder (b) Circulation at birth Urethra UMBILICAL CORD Oxygenated blood Mixed oxygenated and deoxygenated blood Deoxygenated blood Placenta (a) Fetal circulation

  46. Birth • True labor is marked by uterine contractions that occur regularly every 15-20 minutes and last for 40 seconds or more. • Positive feedback control. • Parturition. • Stage 1. • Mucous plug may be expelled from cervical canal. • Cervix dilates completely.

  47. Birth • Stage 2. • Baby’s head descends into the vagina. • Baby is delivered. • Stage 3. • Placenta delivered.

  48. Stages of Parturition Factors in Parturition

  49. Female Breast and Lactation • Female breast contains 15-20 lobules, each with a milk duct beginning at the nipple and ending in alveoli. • In pregnancy, breasts enlarge as ducts and alveoli increase in number and size due to estrogen and progesterone. • Milk usually not produced during pregnancy. • Prolactin suppressed due to increase in estrogen and progesterone; but then released after birth; prolactin causes milk production • Then suckling maintains prolactin secretion; stimulates release of prolactin-releasing hormone (PRH) • Suckling stimulates release of oxytocin- causes milk let-down

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