The Reproductive System

1. The Reproductive System

2. Reproductive System • Primary sex organs (gonads) – testes in males, ovaries in females • Gonads produce sex cells called gametes and secrete sex hormones • Secondary sex organs • Accessory reproductive organs – ducts, glands, and external genitalia • Sex hormones – androgens (males), and estrogens and progesterone (females)

3. Male Reproductive System • The male gonads (testes) produce sperm and lie within the scrotum • Sperm are delivered to the exterior through a system of ducts: epididymis, ductus deferens, ejaculatory duct, and the urethra • Accessory sex glands: • Empty their secretions into the ducts during ejaculation • Include the seminal vesicles, prostate gland, and bulbourethral glands

4. The Testes • Seminiferous tubules produce the sperm • Surrounding the seminiferous tubules are interstitial (Leydig) cells that produce androgens and sustentacular (Sertoli) cells that release androgen-binding proteins (ABP) • Epididymis functions to mature and store sperm cells (at least 20 days) • Spermatic cord – encloses PNS and SNS nerve fibers, blood vessels, and lymphatics that supply the testes

5. The Scrotum • Contains paired testicles that hangs outside the abdominopelvic cavity • Its external positioning keeps the testes 3C lower than core body temperature (needed for sperm production) Intrascrotal temperature is kept constant by two sets of muscles: • Dartos – smooth muscle that wrinkles scrotal skin • Cremaster – bands of skeletal muscle that elevate the testes

6. The Penis • Urethra Conveys both urine and semen (at different times!) • Three cylindrical bodies of erectile tissue • Corpus spongiosum and corpora cavernosa • Columns of spongy connective tissue and smooth muscle riddled with vascular spaces • Glans penis: This is the expanded tip of the penis that surrounds the urethral opening. It is continuous with the corpus spongiosum • Prepuce (Foreskin): This is a lose fold of skin that surrounds the glans penis (expanded tip of the penis). It secretes a waxy material called smegma.

7. Thoughts of Sex!! KEY Stimulus Receptor Afferent pathway Higher brain centers Erotic stimuli Integrating center Efferent pathway Effector Tissue response Descending autonomic pathways Ascending sensory pathway Parasympathetic stimulated Sympathetic inhibited Penile arterioles vasodilate. Spinal cord Penis Erection Tactile stimuli Sensory neuron Mechanoreceptor Male Sexual Response • During sexual arousal, erection of the penis is due to a parasympathetic reflex that promotes the release of nitric oxide • Nitric oxide causes erectile tissue to fill with blood causing the penis to enlarge and become rigid • Expansion of the corpora cavernosa: • Compresses their drainage veins • Retards blood outflow and maintains engorgement • The corpus spongiosum functions in keeping the urethra open during ejaculation

8. Accessory Glands: Seminal Vesicles • Secretes a viscous alkaline fluid that accounts for 60% of the volume of semen • Fructose nutrient for sperm • Coagulating enzyme similar to fibrinogen • Prostaglandins – facilitates the conveyance of sperm • Join the ductus deferens to form the ejaculatory duct where sperm and seminal fluid mix

9. Accessory Glands: Prostate Gland • Gland that encircles part of the urethra inferior to the bladder • Produces a milky, slightly acid fluid that accounts for one-third of the semen volume • Citrate - nutrient for sperm • Enzymes involved in the activation of sperm • Seminalplasmin – antibiotic

10. Accessory Glands: Bulbourethral Glands (Cowper’s Glands) • Pea-sized glands inferior to the prostate • Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

11. Sperm Conveyance • From seminiferous tubules, the sperm enter the epididymis • Upon ejaculation the epididymis contracts, expelling sperm into the ductus deferens • Ductus deferens merges with the duct of the seminal vesicle form the ejaculatory duct • From ejaculatory duct, sperm enter urethra • Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

12. Spermatogenesis: Sperm Production in the Testis

13. KEY GnRH Hypothalamus Integrating center Efferent pathway Effector Tissue response Anterior pituitary FSH LH Leydig cells Spermatogonium Inhibin Spermatocyte Testosterone (T) Testes Sertoli cell Second messenger To body for secondary effects Cell products Sertoli cell Androgen-binding protein (ABP) ABP T Regulation of Spermatogenesis • Spermatogenesis and testicular androgen production involve the hypothalamus, anterior pituitary gland, and the testes • Testicular regulation involves 3 sets of hormones: • GnRH, which indirectly stimulates the testes via the gonadotropins: • Follicle stimulating hormone (FSH) • Luteinizing hormone (LH) • Gonadotropins directly stimulate the cells of the testes • Testicular hormones, which exert negative feedback controls • Testosterone • Inhibin

14. Hormonal Regulation of Testes • The hypothalamus releases gonadotropin-releasing hormone (GnRH) • GnRH stimulates the anterior pituitary to secrete FSH and LH • FSH causes sustentacular (Sertoli) cells to release androgen-binding protein (ABP) • LH stimulates interstitial (Leydig) cells to release testosterone • ABP binding of testosterone enhances spermatogenesis • Feedback inhibition on the hypothalamus and pituitary results from rising levels of testosterone and increased production of inhibin

15. Effects of Testosterone Activity • Testosterone is synthesized from cholesterol • Testosterone is necessary for fetal development of male external genitalia • Increased levels of testosterone at puberty are responsible for further growth of male genitalia and for the development and maintenance of male secondary sex characteristics • Testosterone also stimulates protein synthesis and accounts for the greater muscular development of the male

16. Male Secondary Sex Characteristics • Male hormones make their appearance at puberty and induce changes in nonreproductive organs, including • Appearance of pubic, axillary, and facial hair • Enhanced growth of the chest and deepening of the voice • Skin thickens and becomes oily • Bones grow and increase in density • Skeletal muscles increase in size and mass • Testosterone is the basis of libido in both males and females

17. Female Reproductive System • Ovaries are the primary female reproductive organs • Make female gametes (ova) • Secrete female sex hormones (estrogen and progesterone) • Internal genitalia – ovaries, uterine tubes, uterus, vagina • External genitalia – vulva,clitoris, labia, and hymen

18. Ovaries • Embedded in the ovary cortex are ovarian follicles • Each follicle consists of an immature egg called an oocyte

19. Ovaries • Primordial follicle – one layer of squamous-like follicle cells surrounds the oocyte • Primary follicle – two or more layers of cuboidal granulosa cells enclose the oocyte • Secondary follicle > tertiary follicle – at its most mature stage bulges from the surface of the ovary (AKA vesicular or Graafian follicle) • Ovulation – ejection of the oocyte from the ripening follicle • Corpus luteum – ruptured follicle after ovulation

20. Primordial follicles before puberty Primordial follicles Secondary follicle Tertiary follicle Antrum containing follicular fluid Follicle cells Primary oocyte Zona pellucida Primordial follicles Nucleus of primary oocyte Primary oocytes Zona pellucida Follicle cells Zona pellucida Primordial follicles Primary follicle Secondary follicle Tertiary follicle OVULATION Outer surface of ovary Released secondary oocyte Degenerating corpus luteum Corpus luteum Corona radiata Corpus luteum

21. Uterine Tubes (Fallopian Tubes) • Receive the ovulated oocyte and provide a site for fertilization • The uterine tubes have no contact with the ovaries and the ovulated oocyte is cast into the peritoneal cavity • Beating cilia on the fimbriae create currents to carry the oocyte into the uterine tube • The oocyte is carried toward the uterus by peristalsis and ciliary action

22. Uterus • Hollow, thick-walled organ • Body – major portion of the uterus • Fundus – rounded region superior to the entrance of the uterine tubes • Cervix – narrow outlet that protrudes into the vagina • Functions of the uterus: receives, retains and nourishes the fertilized egg

23. Uterine Wall • Composed of three layers • Perimetrium – outermost serous layer; the visceral peritoneum • Myometrium – middle layer; interlacing layers of smooth muscle, during labor this layer contracts to expel fetus • Endometrium – mucosal lining of the uterine cavity

24. Endometrium • Inner layer • Allows for implantation of a fertilized egg • Sloughs off if no pregnancy occurs (menses) • Has numerous uterine glands that change in length as the endometrial thickness changes

25. Vagina • Thin-walled tube lying between the bladder and the rectum, extending from the cervix to the exterior of the body • Organ of copulation - receives the penis during sexual intercourse • Provides a passageway for birth, menstrual flow • Vaginal mucosa does not have glands, lubrication is provided by cervical mucus glands / vestibular glands lubricate the vestibule and facilitates entry of the penis • pH of vagina in women is acidic • Maintained by glycogen stores that are used by resident normal flora • Keeps vagina healthy • Low pH is hostile to sperm

26. Vulva • Mons pubis - mound of fatty tissue overlying the pubic symphysis (pubic bone) • Labia majora - outer folds of skin contains fat, sudoriferous and sebaceous glands, covered with pubic hair (homologous to scrotum) • Labia minora - inner folds of skin containing sebaceous glands and nerve endings that provide stimulation • Clitoris - cylindrical mass of erectile tissue covered by a layer of skin called the prepuce (homologous to penis) • Vestibule - cleft between the labia minora includes the urethral orifice, vaginal orifice and vestibular glands that produce lubricants during sexual intercourse • Urethra – muscular tube, opening is anterior to opening of vagina, carries urine from bladder to exterior

27. Mammary Glands • Modified sweat glands consisting of 15-25 lobes that radiate around and open at the nipple • Lobes contain glandular alveoli that produce milk in lactating women

28. Overview

29. Ovarian Cycle • Monthly series of events associated with the maturation of an egg • Follicular phase – period of follicle growth (days 1–14) • Luteal phase – period of corpus luteum activity (days 14–28) • Ovulation occurs midcycle

30. Establishing the Ovarian Cycle • During childhood, ovaries grow and secrete small amounts of estrogen that inhibit the hypothalamic release of GnRH • As puberty nears, GnRH is released; FSH and LH are released by the pituitary, which act on the ovaries • These events continue until an adult cyclic pattern is achieved and menarche occurs

31. (a) Early to mid-follicular phase GnRH Hypothalamus Pituitary LH FSH Follicle Granulosa cells Thecal cells Androgens Estrogens LH FSH KEY Ovum Stimulus Integrating center Follicle Corpus luteum Efferent pathway Inhibin Progesterone Estrogen Tissue response Hormonal Interactions of Ovarian Cycle • Day 1 – GnRH stimulates the release of FSH and LH • FSH and LH stimulate follicle growth and maturation, and low-level estrogen release • Rising estrogen levels initially: • Inhibit the release of FSH, LH, GnRH • Gonadotropins accumulate in pituitary • Positive feedback on granulosa cells produce more estrogen

32. (a) Early to mid-follicular phase (b) Late follicular phase and ovulation GnRH GnRH Hypothalamus Pituitary FSH LH LH FSH Follicle Follicle Thecal cells Granulosa cells Granulosa cells Thecal cells Androgens Inhibin Androgens High estrogen output Small amount of progesterone Estrogens LH FSH Ovum Follicle Corpus luteum Inhibin Progesterone Estrogen Hormonal Interactions of Ovarian Cycle • Further increase in estrogen levels have a positive feedback effect on the pituitary, causing a sudden surge of LH • The LH spike stimulates the primary oocyte to complete meiosis and transforming into a secondary oocyte, then induces ovulation

33. (b) Late follicular phase and ovulation (c) Early to mid-luteal phase (d) Late luteal phase GnRH GnRH GnRH Tonic secretion resumes FSH LH FSH LH FSH LH Corpus luteum dies Follicle New follicles begin to develop Corpus luteum (from ovulated follicle) Thecal cells Granulosa cells secretes Androgens Inhibin Estrogen and progesterone Estrogen Progesterone High estrogen output Small amount of progesterone Inhibin LH FSH KEY Ovum Stimulus Integrating center Follicle Corpus luteum Efferent pathway Inhibin Progesterone Estrogen Tissue response Hormonal Interactions of Ovarian Cycle • Day 14 – LH triggers ovulation • LH transforms the ruptured follicle into a corpus luteum, which produces inhibin, progesterone, and estrogen - shuts off FSH and LH release and declining LH ends luteal activity • Days 26-28 – decline of the ovarian hormones, ends the blockade of FSH and LH, cycle starts anew

34. Feedback Mechanisms in Ovarian Function

35. Uterine (Menstrual) Cycle • Series of cyclic changes that the uterine endometrium goes through each month in response to ovarian hormones in the blood • Days 1-5: Menstrual phase (menses) • Degeneration of the endometrium • Uterus sheds all but the deepest part of the endometrium • Days 6-14: Proliferative (preovulatory) phase – Restoration of the endometrium • Days 15-28: Secretory (postovulatory) phase • Endometrial glands enlarge and accelerate their rates of secretion • Endometrium prepares for implantation of the embryo

36. Phases of the Ovarian Cycle Follicular Phase Luteal Phase Gonadotrophic hormone levels FSH LH Ovarian cycle Primary follicle Corpus luteum formation Mature corpus luteum Corpus albicans Theca Ovulation Antrum Ovarian hormone levels Estrogen Inhibin Progesterone Uterine cycle Phases of the Uterine Cycle PROLIFERATIVE PHASE MENSES SECRETORY PHASE 36.7 Basal body temperature (˚C) 36.4 DAYS 28/0 7 14 21 28/0 The Menstrual and Uterine Cycles

37. Extrauterine Effects of Estrogens and Progesterone • Estrogen levels rise during puberty • Promote oogenesis and follicle growth in the ovary • Stimulate bone and muscle growth • Exert anabolic effects on the female reproductive tract • Uterine tubes, uterus, and vagina grow larger and become functional • Uterine tubes and uterus exhibit enhanced motility • Vaginal mucosa thickens and external genitalia mature

38. Estrogen • Establishes and maintains female secondary sex characteristics • Growth of the breasts • Increased deposition of subcutaneous fat, especially in the hips and breasts • Widening and lightening of the pelvis • Growth of axillary and pubic hair • Increase sex drive