The Reproductive System Chapter 17

1. The Reproductive SystemChapter 17

2. Introduction The Reproductive System seeks to ensure the survival of the species. Is not essential to life of the animal but for perpetuation of the species. Generally requires a second animal of the opposite sex in order to carry out its functions. Complete reproductive system is all the structures both male and femal required for reproduction.

3. Fertilization • Fertilization occurs when the spermatazoon penetrates the cytoplasm of the ovum • Once egg is fertlized, must be provided with hospitable environment in order to develop. • In order for this to occur both male and female systems must be in sync.

4. Meiosis • Unique process of cell division • Is a reduction division of reproductive cells so that a chromosome number goes from a diploid number to a haploid number. • It ensures that each animal’s genetic make up is unique.

5. Chromosomes • Coiled masses of DNA are chromosomes and is the genetic “blueprint” for all structures and functions of the body. • All cells with exception of reproductive cells contain identical chromosomes. • Diploid Chromosomes • The total number of chromosomes in the nucleus of each cell. • Always an even number. • Is expressed as a 2n number with n being number of chromosomes and 2 indicating the number is doubled.

7. Chromosomes Continued • Sex Chromosomes • Determine the gender of the animal. • Designated as X or Y. • XX=Female • XY= Male • YY combination is not possible since all males produce an XY and females only produce XX. • Full diploid number may be expressed as 2n, XX or 2n, XY.

9. Chromosomes Continued • Haploid Chromosome Number • Haploid is half of the diploid number. • Why are reproductive cells haploid in nature? • Is abbreviated as n, X or n, Y depending on sex of the chromosome present. • Haploid number is a result of meiosis. • Reduction Division

11. Meiosis vs. Mitosis • Mitosis • Chromosomes duplicate themselves and then pull apart into two daughter cells. Preserves diploid number. • Ensures that genetic information stays the same throughout all of the body’s cells.

13. Meiosis vs. Mitosis • Meiosis • Do not produce copy before daughter cells are pulled apart. • Therefore half of total chromosomes go to each daughter cell. • This makes process entirely random, resulting in unique offspring.

15. Spermatogenesis • Process of producing spermatozoa- the male sex cells. • Spermatozoa are produced continuously. • Designed to produce large numbers of spermatozoa. • Occurs in seminiferous tubules of the testes.

16. Spermatogenesis • Begin with cell called primary spermatocyte. • Primary spermatocyte has normal diploid number. • Divides by meiosis into two secondary spermatocytes. • Now are haploid in number and are pushed to tubule lumen. • Secondary spermatocytes divide by mitosis into four spermatids. • Why mitosis at this point? • 2 will have X markers and two will have Y markers • So it is the sperm that dictate gender of offspring. • Why are there more females than males produced? • In center of tubular lumen at this point. • Do not undergo any more cell divisions, but will grow tails and be converted to spermatozoa • Once mature, will be transported to epididymis for storage before ejaculation.

18. Oogenesis • Ova- female sex cells, are produced in the follicles of the ovaries through process known as oogenesis. • Have fixed number of oocytes-precursor cells to ova, soon after birth. • Oocyte has diploid number. • Do not become active until start ovarian cycle. • Once activated will divide by meiosis. • Division produces a secondary oocyte and a polar body. • Then another mitotic division takes place to become ovum and 3 polar bodies. • Polar bodies never mature into ovum. Just are where excess chromosomes are stored. • Each cycle produces one or more mature ova. • Why just one or few ova are produced?

19. Oogenesis Continued • Takes place in developing ovarian follicle.

20. Male Reproductive System • Functions are: • 1. Produce male sex hormones • 2. Develop male reproductive cells • What are these cells called? • 3. Deliver reproductive cells to female

21. Male Reproductive Organs • Many and complex, but include: • Testes • Scrotum • Spermatic Cord • Seminiferous Tubules • Ducts • Epididymis • Vas Deferens • Urethra • Penis • Prostate gland • Bulbourethral glands • Seminal vesicles

24. Testes • Are male gonads- organs where male reproductive cells are formed. • Usually housed in scrotum. • Size and exact location may vary by animal • Outside abdomen • Why? • Have two main functions: • Spermatogenesis • Previously discussed. • Where does this take place? • Hormone production • Takes place in interstitial cells between the seminiferous tubules. • Also may be called androgens. • What is main hormone/androgen that is produced?

27. Testes Development and Location • Located in abdominal cavity before birth near kidneys. • Attached to scrotal area by gubernaculum- connective band of tissue. • As embryo grows, gubernaculum does not so in a way, testes are “pulled” toward scrotum. • Eventually are pulled through inguinal rings into scrotum. • What we call testicles “descending”.

28. 1. gubernaculum 4. testes 2. Penis 5. abd cavity 3. inguinal ring 6. vas deferens

29. Undescended Testicles • Generally all testicles should have descended to scrotum by 16 weeks of age. • If testicles do not descend, then these male dogs are termed cryptorchid or have a retained testicle in the abdomen or inguinal area. • May be able to still breed, but should be surgically removed as may cause testicular cancer. • Is a genetic trait that may be passed down to future generations.

31. Testosterone • Main male androgen that is produced in testes. • Responsible for: • Development of secondary sex characteristics • Which are? • Male libido • Which is? • Anabolic effect on body • Which does what?

32. Spermatozoa • Long thin cells composed of: • Head • Contains nucleus • Covered by acrosome- caplike structure • Acrosome has digestive enzymes that helps spermatozoa penetrate ovum • Midpiece • Has large amount of mitochondria arranged in spiral pattern. • Tail • Muscle-like fibers that help with propulsion once activated.

34. Scrotum • The sac of skin that houses the testes • Helps to regulate temperature in order for production of spermatozoa to take place. • Cremaster muscle is what can adjust position of testicles in relation to body.

35. Spermatic Cord • Link the testes with the rest of the body. • Contain blood vessels, nerves, lymphatic vessels, and vas deferens. • Only one artery (testicular artery) carries blood down to the testis. • Artery is surrounded by pampiniform plexus-network of veins. • This network helps keep temperature lower than rest of body. • As blood passes down from body, it is cooled by blood returning from the testis in the pampiniform plexus. • Also blood in pampiniform plexus is warmed by the blood in the testicular artery as it goes back to body.

37. Structure of the Testes • Composed of two layers of vaginal tunics • Surround testes in scrotum and spermatic cord. • Inner layer is visceral vaginal tunic or proper vaginal tunic. • Derived from visceral layer of peritoneum that coat the testes as they develop in the abdomen. • Thin and transparent to the naked eye. • Outer parietal vaginal tunic or common vaginal tunic. • Derived from the parietal layer of peritoneum that lines abdominal cavity. • Forms fibrous sac around each testis and spermatic cord.

39. Tunics importance • Important during an orchiectomy- a castration. • Incision is made through outer parietal tunic and testis is everted through tunic to expose blood vessels and spermatic cord. • Blood vessels are ligated-tied off and testis is removed.

40. Capsule of Testes • Each testis is enclosed in a capsule beneath the tunics. • Heavy fibrous connective tissue capsule is called tunica albuginea. • Supports and protects contents of the testis • Many small partitions extend into the testis from the capsule. Called septa. • Septa divide each testis into tiny lobules that contain seminiferous tubules, other cells and structures.

41. Seminiferous Tubules • Where spermatogenesis takes place. • Produce spermatozoa through meiosis. • Long tubules that are U-shaped and attached at both ends to rete testis- a complex system of ducts. • Intersitial cells are located between seminiferous tubules. • Interstitial cells are what produce androgens under influence of Luteinizing Hormone (LH) from the anterior pituitary gland. • In male LH may also be referred to as Interstitial cell-stimulating hormone (ICSH).

43. Seminiferous Tubules Continued • Once spermatids are undergoing changes, they are attached to Sertoli cells- large “nurse” cells. • Sertoli cells help to shield spermatozoa from body’s immune system. • If not shielded, proteins on surface of spermatozoa would stimulate immune system to produce antibodies.

45. Sertoli Cell Tumors • If Sertoli cells multiply out of control. • Produce small amount of estrogen so can result in some feminization characteristics. • Castration usually resolves issues.

46. Duct System • Once spermatozoa have completed development, they are trasnported via rete testis to the efferent ducts of the testes to epididymis.

47. Epididymis • Flat, ribbon-like structure that lies along surface of testis. • If stretched out would be 20 feet long • Connects efferent ducts of testis with the vas deferens. • Made up of 3 regions: • Head • Where spermatozoa enter from efferent ducts • Body • Main portion that lies next to testis • Tail • Continues on to become vas deferens

48. Epididymis continued • Functions as storage for spermatozoa. • Spermatozoa must mature in epididymis for a week or more before they can be ejaculated. • In vasectomies- spermatozoa never leave this site.

49. Vas Deferens • When ejaculation occurs, this muscular tube connects the epididymis with the urethra. • Must propel spermatozoa quickly at time of ejaculation. • Also may be referred to as the ductus deferens. • In abdomen, separates from spermatic cord and loops back to connect with urethra. • At this point, may enlarge and contain glands to contribute to semen. This enlargement is called the ampulla.