The Reproductive System

1. The Reproductive System

2. Animal Reproductive Strategies • Sexual Reproduction • Asexual Reproduction • Fission • Budding

3. Different Reproductive Strategies • Parthenogenesis • Common in many species of arthropods • Females produce offspring from unfertilized eggs • Honeybees • Hermaphroditism • Individual has both ovaries and testes • Tapeworms and earthworms • Fish • Protogyny • Protandry

4. Sex Determination • SRY gene is important • If no functional SRY gene is present, the organism will be a female

5. Vertebrate Fertilization and Development • External fertilization • Female fish release their eggs and males release their sperm into the water, where they meet • Internal fertilization • Introduction of male gametes directly into the female reproductive tract

6. Development Strategies • 3 strategies • Oviparity – laying eggs • Ovoviviparity – development of eggs inside the mother and the organisms are fully developed when hatched and born • Viviparity – organism develops inside the mother

7. Fertilization • Most fishes and amphibians have external fertilization • Reptiles and birds have internal fertilization and lay eggs • Shelled eggs of reptiles and birds are an important adaptation of vertebrates to life on land

8. Ovulation • Periodic release of mature ovum from the ovary • Estrous cycle • Period of sexual receptivity • Menstrual cycle • Human and ape females shed the inner lining of their uterus during menstruation

9. Monotremes, Marsupials, and Placental Mammals • Monotremes- incubate eggs in nest or specialized pouch. Young obtain milk from mother’s mammary glands by licking skin • Ex. Duck-billed platypus, Echidna • Marsupials- fetuses are incompletely developed at birth and finish development in a pouch in the mother’s skin • Ex. Kangaroo, Opossum • Placental- fetuses nourished by placenta and remain in the mother for a longer period of time • Ex. Humans

10. Male Reproductive System • Seminiferous tubules- sites of sperm production, developed in a male fetus about 43-50 days after its conception • Leydig Cells- begin to secrete testosterone at about 9-10 weeks • Testosterone secretion during embryonic development converts different structures into male external genitalia • In the absence of testosterone, structures develop female external genitalia

11. Cell divisions leading to sperm • Spermatogonium cell divides by mitosis to produce two diploid cells • One of the two cells undergoes meiotic division to produce four haploid cells that will become sperm • The other cell remains as spermatogonium • Primary spermatocyte- Diploid daughter cell that begins meiosis • Secondary spermotocyte- Two haploid cells that are produced after the first meiotic division • Spermatids- Two haploid cells produced after spermotyocytes second meiotic division

12. Seminiferous tubules consist of spermatogonia, and supporting sertoli cells

13. Sperm Structure • Consists of head, body, and flagellum, or tail • Head encloses a compact nucleus capped by an acrosome • Body and flagellum help with the sperm’s movement

14. Accessory Organs • Epididymis- long coiled tube where sperm are delivered after production. Sperm must remain here for at least 18 hours • Vas deferens- Long tube where sperm enter

15. Semen • Complex mixture of fluids and sperm • Prostate gland- helps to make up about 30% of semen. In the gland, the ejaculatory duct merges with the urethra from the bladder • Urethra carries the semen out of the body

16. Two Columns of Erectile Tissue • Corpora Cavernosa- along the dorsal side • Corpus Spongiosum- along ventral side • In an erection, the erectile tissue becomes hard as it fills with blood

17. Hormones regulate male reproductive function • The production of sperm and the secretion of testosterone are controlled by a follicle stimulating hormone (FSH) and a leutinizing hormone (LH) from the anterior pituitary

18. Female Reproductive System • Ovaries develop much slower than testes • Ovaries contain microscopic structures called ovarian follicles • Each follicle contains a potential egg cell called a primary oocyte and smaller granulosa cells • Granulosa cells begin to secrete estrogen at puberty and stimulate menstrual cycling

19. Oocytes and Granulosa Cells

20. Ovarian Cycles has 3 Phases • Follicular phase- the primary oocyte completes the first meiotic division and produces one large daughter cell, the secondary oocyte, and one tiny daughter cell, a polar body • Ovulation- a released oocyte is propelled through the Fallopian tube toward the uterus. If not fertilized, the oocyte disintegrates within a day. If fertilized, the zygote takes about 3 days to reach the uterus and another 2-3 days to implant in the endometrium. • Luteal Phase- the corpus luteum is formed and secretes estrogen and progesterone, another steroid hormone. The two hormones exert negative feedback inhibition of FSH and LH. This acts as a natural contraceptive mechanism and prevents both the development of additional follicles and continued ovulation.

21. Secretory Phase and Menstrual Phase • During luteal phase, estrogen and progesterone cause the endometrium to become enriched with glycogen deposits, which is called the Secretory Phase. These changes prepare the uterine lining for embryo implantation. • Menstrual Phase- the corpus luteum degenerates which declines the blood concentration of estrogen and progesterone and onsets menstruation • If implantation occurs the embryo produces human chorionic gonadotropin (hCG), and it maintains the corpus luteum and prevents menstruation until the placenta takes over.

22. Contraception and Infertility Treatments • Methods of birth control are termed contraception • Abstinence • Condom • Diaphragm • Infertility- pregnancy is unable to occur due to a variety of reasons

23. Prevention of Ovulation • Birth control pills block ovulation and no ovum is available to be fertilized • Intrauterine device- is inserted and prevents implantation of an embryo because of the irritation it produces

24. Sterilization and Infertility • Sterilization is accomplished by the surgical removal of portions of the tubes that transport the gametes from the gonads. It can be performed for males and females. • Infertility in females can be caused from hormonal imbalance, lack of ovulation, blockage of Fallopian tubes, and age. • - Male infertility is usually due to a reduction in sperm number, viability, motility, hormonal imbalance, or damage to the vas deferens. • Hormone Treatment can induce ovulation or by the use of assisted reproductive technologies, such as in vitro fertilization and intracytoplasmic sperm injection.