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Reproductive System

Reproductive System. Chapter 27. Male Reproductive System. Anatomy Scrotum Testes Penis Duct system Accessory glands & semen . Scrotum. Maintains testicular temperature at ~ 3 o C lower than core temperature Surface area varies in response to external temperature. Figure 27.2.

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Reproductive System

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  1. Reproductive System Chapter 27

  2. Male Reproductive System • Anatomy • Scrotum • Testes • Penis • Duct system • Accessory glands & semen

  3. Scrotum • Maintains testicular temperature at ~ 3oC lower than core temperature • Surface area varies in response to external temperature Figure 27.2

  4. Testes • Primary reproductive organ of the male: • Produces sperm & testosterone • Testicular lobules contain coiled seminiferous tubules. • Seminiferous tubules: the location of sperm production • Interstitial cells in the connective tissue around the seminiferous tubules produce testosterone Figure 27.3a

  5. Penis • Designed to deliver sperm into the female reproductive tract • Penile root • Penile shaft • Glans penis Figure 27.4

  6. Penis • Corpus spongiosum • midline & ventral surrounds urethra; proximally forms the bulb of the penis; distally forms glans penis • Corpora cavernosa • paired dorsal erectile bodies that terminate proximally in the crura (crus) of the penis that are anchored to the pubic arch

  7. Duct system: male • Epididymus • Vas deferens • Urethra; (three regions) • Prostatic urethra • Membranous urethra • Penile urethra

  8. Duct system: male • Epididymus: receives immature sperm from the rete testis; as the sperm move through the epididymus (~20 days) they become fully motile Figure 27.3a

  9. Duct system: Male • Ductus (vas) deferens: from the epididymus merges with the • Seminal vesicle duct to form the • Ejaculatory duct which enters the • Prostate & empties into the urethra Figure 27.3a

  10. Duct system: male • Urethra: serves both urinary & reproductive systems • Three regions • Prostatic urethra • Membranous urethra • Penile urethra Figure 27.1

  11. Accessory glands – Seminal Vesicles • on posterior bladder wall: • make alkaline, seminal fluid containing: fructose, ascorbic acid, vesiculase (coagulating enzyme) & prostaglandins: • Seminal fluid: 2/3 of volume of semen Figure 27.1

  12. Accessory glands - Prostate gland • Surrounds urethra • Produces a milky, slightly acidic fluid • citrate, multiple enzymes & PSA (prostate specific antigen): • Prostatic fluid: ~1/3 of semen volume Figure 27.1

  13. Accessory glands • Bulbourethral glands: • Produce a thick clear mucous that neutralizes acidic urine Figure 27.1

  14. Semen • Semen: • Milky white mixture of sperm & accessory gland secretions • Provides: • Nutrients for sperm • Chemical protection / activation • Acts as a transport medium for sperm

  15. Male Sexual Response • Erection: enlargement & stiffening of the penis • Parasympathetic reflex • Triggers local release of Nitric Oxide causing • Arteriolar dilation & increased blood flow to erectile tissues • Expansion of erectile tissues interferes with veins that drain the system & maintains erection

  16. Male Sexual Response • Ejaculation: propulsion of semen through the duct system • SNS discharge causes • Contraction throughout the ductal system • Contraction of bladder sphincter & • Contraction of the bulbospongiosus muscles of the penis

  17. Male Sexual Response • Refractory period: After ejaculation there is a refractory period during which a male is unable to have another ejaculation (minutes  hours)

  18. Spermatogenesis • Cell differentiation events that produces male gametes (spermatozoa)

  19. Spermatogenesis • Diploid (2n): • having 2 of each chromosome type (n) human 2n=46 • Haploid: • having 1 of each chromosome type human n = 23 • body cells are diploid (2n) • Gametes are haploid (n) • When 2 gametes fuse at fertilzation, n + n = 2n • diploidy restored

  20. Comparison of Mitosis & Meiosis • Meiosis: • Two consecutive nuclear divisions producing • Four haploid daughter cells Figure 27.6

  21. Meiotic Cell Division: Meiosis I • Meiosis: • Meiosis I: separates homologous chromosomes into different cells (i.e. diploid  haploid) • cells still retain 2 copies of each gene Figure 27.7

  22. Meiotic Cell Division: Meiosis II • Meiosis: • Meiosis II: separates chromatids into separate cells • generates cells with only 1 copy of each gene Figure 27.7

  23. Spermatogenesis • Occurs in the seminiferous tubules; • Spermatogonia form epithelial basal layer of cells • Spermatogonia (sperm stem cell) • Divide by mitosis until puberty forming a large population

  24. Spermatogenesis • At puberty mitotic divisions of spermatogonia form • Two daughter cells with different functions • Type A cells • Type B cells

  25. Spermatocytes to Spermatids • Type A: remains to maintain the spermatogonia stem cell • Type B: primary spermatocyte (2n): • Pushed toward lumen • Meiosis I forming secondary spermatocytes (n) which undergo • Meiosis II forming 4 spermatids (immature sperm)

  26. Spermatogenesis: Spermatids to Sperm • Spermatogenesis: (spermatids  sperm) a streamlining process • Sperm head (filled with DNA) • Acrosome (filled with lysosomal enzymes) • Midpiece (mitochondrial wrapped contractile filaments) • Tail (flagellum) Figure 27.9a

  27. Spermatogenesis • Sertoli (Sustentacular) cells: • Divide seminiferous tubule into 2 compartments; • Isolate newly formed sperm from blood: • blood-testis barrier prevents formation of antibodies against sperm

  28. Hormonal Regulation: Male • Brain-testicular axis: • Interactions between: • Hypothalamus • Anterior pituitary • Testes

  29. Brain-testicular axis • Hypothalamus  Gonadotropin-Releasing Hormone (GnRH) • GnRHAnterior pituitary secretion of • Leutinizing Hormone (LH a.k.a. Interstitial Cell Stimulating Hormone: ICSH) • Stimulates interstitial cells to produce testosterone • Follicle Stimulating Hormone (FSH) • allows spermatogenesis by making cells receptive to testosterone

  30. Brain-testicular axis • Testosterone acts locally as the trigger for spermatogenesis • Testosterone inhibits: • Release of GnRH (hypothalamus) • Release of gonadotropins (anterior pituitary) • Inhibin is produced by Sertoli cells when sperm counts are high; inhibits GnRH & FSH release

  31. Hormonal Regulation of Testicular Function • Feedback inhibition on hypothalamus & pituitary from: • Rising levels of testosterone • Increased inhibin Figure 27.10

  32. Brain-testicular axis • Perinatal FSH, LH & testosterone levels: • Near pubertal levels to allow development of the male reproductive system; • After a few months of age the levels drop to low levels until onset of puberty

  33. Testosterone mechanism & effects: • Testosterone is synthesized from cholesterol & exerts effects by activating specific genes • Testosterone targets accessory organs (ducts, glands & penis) causing them to grow to adult proportions

  34. Testosterone mechanism & effects: • Testosterone induces: • Secondary sex characteristics: • pubic & axillary hair • voice change • facial hair • thickening of the skin • increased sebum production • increase in bone & muscle mass

  35. Female Reproductive System Figure 27.11 • Anatomy • Ovaries • Duct System: • Fallopian Tubes • Uterus • Vagina & external genitalia

  36. Ovaries • Ovaries: primary female reproductive organ • Ovaries produce the female • Gamete (ova/egg) • Sex hormones (estrogens & progesterone) Figure 27.14a

  37. Ovaries • Ovaries: paired organ • Found on either side of the uterus • Held in place by ligaments Figure 27.14a

  38. Ovaries Figure 27.12 • Ovarian follicles within the ovary consist of an: • Oocyte (immature ovum) encased in one or more layers of cells • Single layer: follicle cells; • Multiple layers: granulosa cells • Follicles at different stages have different structures

  39. Ovaries Figure 27.12 • Follicle stages & structures: • Primordial follicle: single layer of follicle cells surrounding oocyte • Primary follicle: two or more layers of granulosa cells • Secondary follicle: fluid filled spaces appear within granulosa & merge to form the vesicular follicle.

  40. Ovaries Figure 27.12 • Follicle stages (cont): • Vesicular (Graafian) follicle: bulges from the ovary surface & will rupture at ovulation releasing the oocyte • Corpus luteum: follicle remnant after rupture that forms the glandular corpus luteum

  41. Female Duct System Figure 27.14a • Fallopian tubes: uterine tubes, oviducts • Infundibulum: open funnel shaped structure with finger-like projections (fimbriae) that drape over ovary • Ampulla: widened region arching over ovary (the usual site of fertilization) • Isthmus: narrowed region where tube enters upper region of uterus

  42. Female Duct System - Uterus • hollow, thick walled, pear shaped, muscular organ that receives, retains & nourishes a fertilized ovum • Uterine support comes from the mesometrium, the lateral cervical ligaments, the uterosacral ligaments & the round ligaments

  43. Female Duct System: Uterine Wall • Endometrium: mucosal lining of columnar epithelium • Myometrium: muscular middle layer: interlaced bundles of smooth muscle • Perimetrium: outer covering of visceral peritoneum

  44. Female Duct System: Uterine Wall • endometrium is a dynamic layer of epithelium with two layers • Stratum functionalis: undergoes cyclic changes in response to ovarian hormones & is shed during menstruation • Stratum basalis: deeper layer that forms a new stratum functionalis after menstruation Figure 27.15

  45. Vagina Figure 27.14a • female organ of copulation & birth canal

  46. Vagina Figure 27.14a • 3 layers • Mucosa: stratified squamous epithelium with rugae (ridges) • Muscularis: smooth muscle • Adventitia: fibroelastic connective tissue

  47. Vagina Figure 27.14a • Environment: • In adults, vaginal pH is decreased • Helps to prevent infection • Also hostile to sperm • In adolescents, vaginal pH is increased • More alkaline environment presents an increased risk for Sexually Transmitted Disease

  48. Vagina • Proximal end of the vagina: • Surrounds the cervix of the uterus • Forming a recess (fornix) around the cervix; • Distal end forms the vaginal orifice with mucosal hymen (in virginal females)

  49. External Genitalia • Mons pubis: rounded fat pad overlying the pubic symphysis • Labia • Labia majora: two fatty skin folds with hair (homologous to scrotum) • Labia minora: two smaller, hairless skin folds (homologous to the male ventral penis) Figure 27.16

  50. External Genitalia • Vestibule = the recess surrounded by the labia minora includes: • Urethral opening • Vaginal orifice • Vestibular gland orifices Figure 27.16

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