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17. The Reproductive System


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17. The Reproductive System

  1. 1. The Reproductive System
  2. 2. Learning Objectives <ul><li>Differentiate between meiosis and mitosis </li></ul><ul><li>Describe the processes of spermatogenesis and oogenesis </li></ul><ul><li>Describe the structure of spermatozoa </li></ul><ul><li>List the components of the male reproductive system and describe the functions of each </li></ul><ul><li>List the characteristics and functions of the accessory structures of the male reproductive system </li></ul><ul><li>List the components of the female reproductive system and describe the functions of each </li></ul><ul><li>Describe the events that occur during the ovarian cycle </li></ul><ul><li>List the stages of the estrous cycle and describe the events that occur during each stage </li></ul><ul><li>Differentiate between monoestrous, diestrous, polyestrous, and seasonally polyestrous estrous cycle intervals </li></ul>
  3. 3. Chromosomes <ul><li>Coiled masses of DNA in the nuclei of cells </li></ul><ul><li>Each cell in an animal's body (except spermatozoa or ova) contains identical chromosomes </li></ul><ul><li>Diploid chromosome number </li></ul><ul><ul><li>Total number of chromosomes in the nucleus of each body cell is the same (except for reproductive cells) </li></ul></ul><ul><ul><li>Always an even number - chromosomes occur in pairs. </li></ul></ul>
  4. 4. Sex Chromosomes <ul><li>Designated as either &quot;X&quot; chromosomes or &quot;Y&quot; chromosomes </li></ul><ul><li>If both of the sex chromosomes are X chromosomes (XX), the individual is genetically female. </li></ul><ul><li>If one is an X and the other is a Y (XY), the individual is genetically male </li></ul>
  5. 5. Haploid Chromosome Number <ul><li>Reduction division - total number of chromosomes in each of the daughter cells is reduced to half the number of the parent cell </li></ul><ul><li>Ensures that the fertilized ovum from the union of spermatozoa and the ova has diploid number. </li></ul><ul><li>Haploid chromosome number in the reproductive cells results from meiosis </li></ul>
  6. 6. Mitosis <ul><li>Most body cells divide after the cell first makes a duplicate copy of its chromosomes </li></ul><ul><li>Half the chromosomes go to one daughter cell and half go to the other </li></ul><ul><li>Genetic makeup of the two daughter cells is exactly the same as each other and as the parent cell. </li></ul>
  7. 7. Meiosis <ul><li>Chromosomes do not produce duplicate copies of themselves before daughter cells divide </li></ul><ul><li>Half of the total chromosomes (one from each diploid chromosome pair and one sex chromosome) go to each daughter cell. </li></ul><ul><li>Which chromosomes go to which daughter cell is entirely random </li></ul>
  8. 8. Spermatogenesis <ul><li>Production of male sex cells </li></ul><ul><li>Occurs in seminiferous tubules of the testes </li></ul><ul><li>Produced continuously and in very large numbers </li></ul>
  9. 9. Spermatogenesis <ul><li>Primary spermatocyte divides by meiosis into secondary spermatocytes – haploid number </li></ul><ul><li>The secondary spermatocytes divide by mitosis into four spermatids </li></ul><ul><li>Spermatids grow tails and undergo other physical changes that convert them to spermatozoa . </li></ul>
  10. 10. Spermatogenesis <ul><li>When the spermatozoa are fully developed, they detach and are carried to the epididymis for storage before ejaculation </li></ul><ul><li>Half of the spermatozoa produced have an X sex chromosome, and half have a Y sex chromosome. </li></ul>
  11. 11. Oogenesis <ul><li>Production of female sex cells </li></ul><ul><li>Occurs in ovarian follicles </li></ul><ul><li>Female has fixed number of primary </li></ul><ul><li>oocytes at or soon after birth </li></ul><ul><li>Oogenesis produces small numbers of </li></ul><ul><li>ova at a time </li></ul>
  12. 12. Oogenesis <ul><li>Primary oocyte divides by meiosis into a large secondary oocyte and a small &quot;polar body.&quot; </li></ul><ul><li>Each has the haploid chromosome number </li></ul>
  13. 13. Oogenesis <ul><li>Secondary oocyte and the first polar body divide by mitosis into an ovum and three polar bodies </li></ul>
  14. 14. Male Reproductive System <ul><li>Produces male sex hormones </li></ul><ul><li>Develops spermatozoa </li></ul><ul><li>Deliver the spermatozoa to the female system at the appropriate time </li></ul>
  15. 15. Testes <ul><li>Produce sperm and hormones </li></ul><ul><li>Located outside the abdomen in the inguinal region </li></ul><ul><li>Housed in a sac of skin - the scrotum. </li></ul>
  16. 16. Spermatozoa Structure <ul><li>Head - contains nucleus of the cell </li></ul><ul><li>Covered by the acrosome ; contains digestive enzymes that help the spermatozoon reach and penetrate the ovum </li></ul><ul><li>Midpiece - large concentration of mitochondria arranged in a spiral pattern </li></ul>
  17. 17. Spermatozoa Structure <ul><li>Tail - contains musclelike contractile fibrils </li></ul><ul><li>Produces a whiplike movement of the tail and propel the cell forward </li></ul>
  18. 18. Development of Testes <ul><li>Gubernaculum – band of connective tissue that attaches testes to scrotum </li></ul><ul><li>Testes gradually pulled caudally and ventrally </li></ul><ul><li>Inguinal rings - openings in abdominal muscles through which testes descend </li></ul>
  19. 19. Scrotum <ul><li>Sac of skin that houses the testes </li></ul><ul><li>Helps regulate temperature of testes </li></ul><ul><ul><li>Testes must be kept slightly cooler than body temperature </li></ul></ul><ul><li>Cremaster muscle passes down through the inguinal ring and attaches to the scrotum. </li></ul><ul><li>Adjusts the position of the testes relative to the body depending on temperature </li></ul>
  20. 20. Spermatic Cords <ul><li>Blood and lymphatic vessels, nerves, and the vas deferens. </li></ul><ul><li>Pampiniform plexus - meshwork of veins that surrounds testicular artery </li></ul><ul><ul><li>Maintains testes at a temperature slightly lower than body temperature </li></ul></ul><ul><ul><li>Warms blood back to body temperature before it returns to the abdomen. </li></ul></ul>
  21. 21. Tunics <ul><li>Connective tissue that forms sheath-like layers around the testes and the spermatic cord. </li></ul><ul><li>Visceral vaginal tunic - very thin inner layer </li></ul><ul><li>Parietal vaginal tunic - thick outer layer </li></ul><ul><ul><li>forms a fibrous sac around each testis and spermatic cord </li></ul></ul><ul><li>Tunica albuginea - fibrous connective tissue capsule surrounding each testis beneath tunics </li></ul>
  22. 22. Seminiferous Tubules <ul><li>Site of spermatogenesis </li></ul><ul><li>Long, convoluted U-shaped tube attached at both ends to system of ducts (rete testis) </li></ul><ul><li>Interstitial cells – endocrine cells between the seminiferous tubules -produce androgens </li></ul><ul><li>Sertoli cells - Support developing spermatids </li></ul>
  23. 23. Duct System <ul><li>After detaching from Sertoli cells, spermatozoa enter the rete testis </li></ul><ul><li>Then flow through the efferent ducts to the epididymis. </li></ul><ul><ul><li>Single, long, convoluted tube that connects the efferent ducts of the testis with the vas deferens </li></ul></ul><ul><ul><li>Storage and maturation of spermatozoa </li></ul></ul>
  24. 24. Epididymis <ul><li>“ Head&quot; region - site where spermatozoa enter from efferent ducts </li></ul><ul><li>“ Body&quot; region - lies </li></ul><ul><li>along surface of testis </li></ul><ul><li>“ Tail&quot; region – continues </li></ul><ul><li>on as the vas deferens. </li></ul>
  25. 25. Vas deferens <ul><li>Ductus deferens ; part of the spermatic cord </li></ul><ul><li>Passes through inguinal ring then separates from spermatic cord and connects with urethra </li></ul><ul><li>Ampulla – enlargement of the vas deferens just before it joins the urethra found in some species </li></ul><ul><ul><li>contain glands that contribute material to semen. </li></ul></ul>
  26. 26. Vas deferens <ul><li>Thick smooth muscle </li></ul><ul><li>walls </li></ul><ul><li>Functions to propel </li></ul><ul><li>sperm quickly from </li></ul><ul><li>epididymis to urethra </li></ul><ul><li>at time of ejaculation </li></ul>
  27. 27. Urethra <ul><li>Pelvic portion - entry point of vas deferens and accessory reproductive glands </li></ul><ul><li>Penile portion - runs down the length of the penis </li></ul><ul><li>Spermatozoa from vas deferens and secretions from accessory reproductive glands enter urethra and are pumped out as semen </li></ul><ul><li>Carries urine from the urinary bladder outside the body. </li></ul><ul><ul><li>Urine flow temporarily blocked when ejaculation occurs </li></ul></ul>
  28. 28. Accessory Reproductive Glands <ul><li>Ducts of all accessory reproductive glands enter pelvic portion of the urethra </li></ul><ul><li>Different species have different combinations of accessory reproductive glands </li></ul><ul><li>Produce alkaline fluid that helps counteract the acidity of the female reproductive tract </li></ul>
  29. 29. Accessory Reproductive Glands <ul><li>Prostate gland </li></ul><ul><li>Surrounds the urethra </li></ul><ul><li>Multiple ducts carry </li></ul><ul><li>secretions into urethra </li></ul>
  30. 30. Accessory Reproductive Glands <ul><li>Bulbourethral glands </li></ul><ul><li>Cowper's glands </li></ul><ul><li>Ducts enter urethra near </li></ul><ul><li>caudal border of pelvis </li></ul><ul><li>Secrete mucinous fluid </li></ul><ul><li>just before ejaculation </li></ul><ul><li>that clears and lubricates </li></ul><ul><li>the urethra </li></ul>
  31. 31. Penis <ul><li>Composed of muscle, erectile tissue, and connective tissue </li></ul><ul><li>Large blood supply and many sensory nerve endings </li></ul><ul><li>Three main parts of the penis - the roots, the body, and the glans. </li></ul>
  32. 32. Penis <ul><li>Roots of the penis - bands of connective tissue (crura) that attach penis to the brim of the pelvis </li></ul><ul><li>Body of the penis - Two bundles of erectile tissue (corpus cavernosum urethrae and corpus cavernosum penis) </li></ul><ul><ul><li>Fibrous connective tissue and blood-filled sinuses </li></ul></ul><ul><ul><li>When sinuses engorge with blood, inelastic connective tissue around the sinuses generates hydraulic </li></ul></ul>
  33. 33. Penis <ul><li>Glans of the penis – distal end; numerous sensory nerve </li></ul><ul><li>Prepuce - sheath of skin that encloses the penis when it is not erect </li></ul><ul><ul><li>Inner portion is smooth, moist mucous membrane </li></ul></ul>
  34. 34. Canine Penis <ul><li>Os penis - bone in the penis; urethra runs through groove on ventral surface </li></ul><ul><li>Bulb of the glans - enlargement toward rear of the glans </li></ul><ul><ul><li>Engorges with blood; reaches full size after ejaculation </li></ul></ul><ul><ul><li>Remains clamped in place by contractions of muscles surrounding vagina and vulva </li></ul></ul><ul><ul><li>Erection of the bulb subsides in 15 – 20 minutes </li></ul></ul>
  35. 35. Sigmoid Flexure <ul><li>S shape of nonerect penis of the bull, ram, and boar </li></ul><ul><li>Higher proportion of connective tissue to erectile tissue than other species </li></ul><ul><li>Erection results from straightening of the sigmoid flexure from internal hydraulic pressure </li></ul><ul><li>Causes the penis to protrude from the prepuce for breeding </li></ul>
  36. 36. Reproductive Functions <ul><li>Erection: results from a parasympathetic reflex triggered by sexual stimuli </li></ul><ul><ul><li>Often involves olfactory cues and behavioral changes </li></ul></ul><ul><ul><li>Arteries dilate and increase blood flow into penis </li></ul></ul><ul><ul><li>Veins are compressed against brim of the pelvis by contractions of muscles in roots of the penis </li></ul></ul>
  37. 37. Reproductive Functions <ul><li>Ejaculation: reflex expulsion of semen </li></ul><ul><ul><li>Semen moves from accessory reproductive glands into pelvic portion of the urethra </li></ul></ul><ul><ul><li>Rhythmic contractions of the urethra pump the semen out into the female reproductive tract </li></ul></ul>
  38. 38. Female Reproductive System <ul><li>Ligaments </li></ul><ul><li>Ovaries </li></ul><ul><li>Oviducts </li></ul><ul><li>Uterus </li></ul><ul><li>Cervix </li></ul><ul><li>Vagina </li></ul><ul><li>Vulva </li></ul>
  39. 39. Ligaments <ul><li>Broad ligaments: sheets of peritoneum </li></ul><ul><li>Suspend ovaries, oviducts, and uterus </li></ul><ul><ul><li>Mesovarium </li></ul></ul><ul><ul><li>Mesosalpinx </li></ul></ul><ul><ul><li>Mesometrium </li></ul></ul><ul><li>Contain blood vessels and nerves </li></ul>
  40. 40. Ligaments <ul><li>Suspensory ligament of the ovary </li></ul><ul><ul><li>Ovarian end of broad ligament attached to body wall in area of last rib </li></ul></ul><ul><li>Round ligament of the uterus </li></ul><ul><ul><li>Fibrous tissue and smooth muscle in lateral fold of the broad ligament on each side </li></ul></ul>
  41. 41. Ovaries <ul><li>In dorsal abdomen near kidneys </li></ul><ul><li>Species variation in appearance </li></ul><ul><li>Site of oogenesis </li></ul><ul><li>Production of estrogens and progestins </li></ul>
  42. 42. Ovarian Cycle <ul><li>Development of ovum, ovulation, formation of corpus luteum, and degeneration of unripened follicles and corpus luteum </li></ul><ul><li>Influenced by follicle stimulating hormone (FSH) and luteinizing hormone (LH) </li></ul>
  43. 43. Ovarian Cycle <ul><li>Uniparous species </li></ul><ul><ul><li>One mature ovum produced per cycle </li></ul></ul><ul><ul><li>Horse, cow, and human </li></ul></ul><ul><li>Multiparous species </li></ul><ul><ul><li>Multiple ova produced per cycle </li></ul></ul><ul><ul><li>Cat, dog, and sow </li></ul></ul>
  44. 44. Ovarian Cycle <ul><li>Primordial (primary) follicle: immature oocyte surrounded by a single layer of follicular cells </li></ul><ul><li>Follicular recruitment or follicular activation: follicle growth is triggered </li></ul><ul><li>Follicular cells thicken and multiply into multiple layers: granulosa cells </li></ul><ul><li>Follicle grows rapidly as granulosa cells multiply </li></ul>
  45. 45. Ovarian Cycle <ul><li>Granulosa cells produce increasing amounts of estrogens as follicle becomes larger </li></ul><ul><li>Fluid-filled spaces form between granulosa cells </li></ul><ul><ul><li>Spaces gradually merge into one large fluid-filled space: the antrum </li></ul></ul><ul><li>Mature follicle (graafian follicle, vesicular ovarian follicle) - production of estrogens peaks </li></ul><ul><ul><li>Oocyte on top of granulosa cell mound (cumulus oophorus) surrounded by thin layer of granulosa cells (corona radiata) </li></ul></ul>
  46. 46. Ovulation <ul><li>Rupture of mature follicle and release of reproductive cell into oviduct </li></ul><ul><li>Surface of mature follicle weakens, ruptures </li></ul><ul><li>Fluid released from antrum along with ovum (still surrounded by corona radiata) </li></ul><ul><li>Empty follicle fills with blood (corpus hemorrhagicum) </li></ul>
  47. 47. Ovulation <ul><li>Occurs spontaneously in most species </li></ul><ul><li>as a result of rising levels of LH </li></ul><ul><li>Induced ovulators: ovulation occurs after breeding </li></ul><ul><ul><li>Cat, rabbit, and ferret </li></ul></ul>
  48. 48. Corpus Luteum <ul><li>Formed by divisions of granulosa cells that line the blood-filled follicle </li></ul><ul><li>Influenced by continued stimulation of LH </li></ul><ul><li>Produces progestins (primarily progesterone) </li></ul><ul><ul><li>Necessary for maintenance of pregnancy </li></ul></ul><ul><li>Endocrine signal to ovary causes corpus luteum to be maintained if ovum implants in uterus </li></ul>
  49. 49. Oviducts <ul><li>Also known as fallopian tubes and uterine tubes </li></ul><ul><li>Extend from the tips of the uterine horns </li></ul><ul><li>Infundibulum: enlarged opening at the ovarian end of each oviduct </li></ul><ul><li>Fimbriae: muscular projections form margin of infundibulum; help properly position infundibulum </li></ul>
  50. 50. Oviducts <ul><li>Smooth muscle fibers in walls </li></ul><ul><li>Ciliated cells in lining </li></ul><ul><li>Muscle contractions and cilia movements guide ovum toward the uterus </li></ul><ul><li>Usual site of fertilization </li></ul>
  51. 51. Uterus <ul><li>Hollow muscular organ </li></ul><ul><li>Usually Y shaped </li></ul><ul><ul><li>Uterine body forms the base of the Y </li></ul></ul><ul><ul><li>Uterine horns form the arms </li></ul></ul>
  52. 52. Uterus <ul><li>Uterine wall layers: </li></ul><ul><li>Endometrium: lining composed of simple columnar epithelium and simple tubular glands </li></ul><ul><ul><li>Secrete mucus and other substances </li></ul></ul><ul><li>Myometrium: thick layers of smooth muscle </li></ul><ul><li>Perimetrium: outermost layer covered by the visceral layer of peritoneum </li></ul>
  53. 53. Cervix <ul><li>Smooth muscle sphincter between the body of the uterus and the vagina </li></ul><ul><ul><li>Controls access to the lumen of the uterus from the vagina </li></ul></ul><ul><li>Normally tightly closed, except during estrus and parturition </li></ul>
  54. 54. Vagina and Vulva <ul><li>Vagina: </li></ul><ul><li>Muscular tube extends caudally from the cervix and connects it with the vulva </li></ul><ul><li>Vulva: </li></ul><ul><li>Composed of the vestibule, clitoris, and labia </li></ul><ul><ul><li>Urethra opens on the floor of the vestibule </li></ul></ul>
  55. 55. Estrous Cycle Intervals <ul><li>Polyestrous: animals that cycle continuously throughout the year if they are not pregnant (cattle and swine) </li></ul><ul><li>Seasonally polyestrous: animals with seasonal variations in estrous cycles (horse, sheep, cat ) </li></ul><ul><li>Diestrous: animals with two cycles per year, usually spring and fall (dog) </li></ul><ul><li>Monoestrous: animals with one cycle per year (fox and mink) </li></ul>
  56. 56. Estrous Cycle <ul><li>Time from the beginning of one heat period (estrus) to the next </li></ul><ul><li>Estrous cycle stages: </li></ul><ul><ul><li>Proestrus </li></ul></ul><ul><ul><li>Estrus </li></ul></ul><ul><ul><li>Metestrus </li></ul></ul><ul><ul><li>Diestrus </li></ul></ul><ul><ul><li>Anestrus (in some species) </li></ul></ul>
  57. 57. Proestrus <ul><li>Follicles begin developing and growing </li></ul><ul><li>Output of estrogen increases accordingly </li></ul><ul><li>Linings of the oviduct, uterus, and vagina thicken </li></ul><ul><li>Vaginal epithelium begins to cornify; forms layer of keratin on its surface </li></ul>
  58. 58. Estrus <ul><li>Period of sexual receptivity in the female </li></ul><ul><li>Estrogen level production peaks </li></ul><ul><li>Ovulation occurs near end of estrus in some species </li></ul><ul><li>Induced ovulator species (e.g., cat, rabbit) remain in a prolonged state of estrus if not bred </li></ul>
  59. 59. Metestrus <ul><li>Period during which corpus luteum develops </li></ul><ul><li>Progesterone produced by corpus luteum temporarily inhibits follicular development in the ovary </li></ul><ul><li>Lining of the uterus prepared for implantation of a fertilized ovum </li></ul><ul><li>Cornified epithelial lining that developed in the vagina during proestrus and estrus is lost </li></ul>
  60. 60. Diestrus <ul><li>Corpus luteum at maximum size and exerting maximum effect </li></ul><ul><li>If fertilized ovum implants, corpus luteum is retained well into the pregnancy </li></ul><ul><li>If no pregnancy occurs, corpus luteum degenerates at the end of diestrus </li></ul><ul><ul><li>Animal then either goes back into proestrus or ovary shuts down and animal goes into anestrus </li></ul></ul>
  61. 61. Anestrus <ul><li>Period of temporary ovarian inactivity </li></ul><ul><li>Seen in seasonally polyestrus, diestrous, and monoestrous animals </li></ul><ul><li>Ovary temporarily shuts down </li></ul>