CHAPTER 27 Reproduction and Embryonic Development

1. CHAPTER 27Reproduction and Embryonic Development Overview: Animal Reproduction Asexual & Sexual Human Reproductive System Female Male Female Reproductive Cycle Fertilization Pregnancy

2. What accounted for the sudden rash of multiple births? • Other sets of multiple births soon followed • All of these multiple births were by women who had taken fertility drugs because they couldn’t become pregnant naturally • Couples turn to fertility drugs to overcome their natural reproductive limitations

3. UNIFYING CONCEPTS OF ANIMAL REPRODUCTION • Reproduction is the creation of new individuals from existing ones • ASEXUAL AND SEXUAL REPRODUCTION Sexual and asexual reproduction are both common among animals

4. Asexual Reproduction • One parent produces genetically identical offspring • In asexual reproduction • Binary fission • Is the simplest type of asexual reproduction • Involves a single parent cell splitting through mitosis into two genetically identical offspring cells

5. Some multicellular organisms reproduce by a similar means called fission, in which one organism splits into two or more individuals

6. Regeneration, which follows fragmentation, is the regrowth of a whole animal from the pieces • Fragmentation is the breaking of a parent body into several pieces • Budding • Is the splitting off of new individuals from existing ones

7. It allows a species to perpetuate itself if its individual members are sessile or isolated from one another • It allows organisms to multiply quickly • Asexual reproduction has a number of advantages • One potential disadvantage of asexual reproduction is that it produces genetically uniform populations

8. Sexual Reproduction • Involves the fusion of gametes (sperm and egg) from two parents • Increases the genetic variability among offspring • Sexual reproduction

9. Increases genetic variation • Enhances reproductive success in changing environments • Disadvantage of sexual reproduction • Locating a mate • Advantages of sexual reproduction

10. Some animals can reproduce both sexually and asexually

11. Some species are hermaphrodites with both male and female reproductive systems

12. Many organisms use external fertilization, in which parents discharge their gametes into the water, where fertilization occurs • The mechanics of fertilization play an important part in sexual reproduction

13. Internal fertilization requires copulation, or sexual intercourse • Other organisms use internal fertilization, which occurs within the female’s body

14. HUMAN REPRODUCTION • A pair of gonads, the organs that produce gametes • Ducts to store and deliver the gametes • Structures to facilitate copulation • Both sexes of humans have

15. Female Reproductive Anatomy • Are the site of gamete production in human females • The ovaries

16. Each follicle consists of a single developing egg cell surrounded by layers of cells that nourish and protect it • The follicles also produce estrogen, the female sex hormone • The ovaries contain follicles • Oviducts • Convey eggs to the uterus

17. - Actual site of pregnancy • Development of fertilized egg • Opens into the vagina • Vagina • Receives penis during intercourse • Forms the birth canal • Uterus

18. Is the process by which an egg cell is ejected from the follicle • An egg cell is released from a follicle at the surface of an ovary • The orange mass below the ejected oocyte is part of the ovary • Ovulation

19. Male Reproductive Anatomy • Contains erectile tissue • The penis • The testes • Are the male gonads, enclosed in a sac called the scrotum • Produce sperm

20. Contribute to the formation of the fluid that carries, nourishes, and protects sperm • Semen • Consists of this fluid and sperm • Several glands

21. First stage of ejaculation • There are two stages of ejaculation

22. Second stage of ejaculation (expulsion stage)

23. They also maintain homeostasis by a negative feedback mechanism that inhibits the secretion of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) • Androgens stimulate sperm production

24. The formation of sperm and ova requires meiosis • Gametogenesis • Spermatogenesis • Produces sperm in the male • Oogenesis • Produces ova in the female • Is the production of gametes • Human gametes • Are haploid cells that develop by meiosis

25. Increases genetic variation • Primary spermatocytes are produced throughout a male’s reproductive years • Diploid cells undergo meiosis to form four haploid sperm • Spermatogenesis

26. Most of the process occurs within the ovaries • Lifetime supply of primary oocytes is present at birth • One primary oocyte matures each month to form a secondary oocyte • If the secondary oocyte is fertilized, it completes meiosis and becomes a haploid ovum • Oogenesis

27. The Female Reproductive Cycle • Human females have a reproductive cycle, a recurring series of events that produces gametes, makes them available for fertilization, and prepares the body for pregnancy

28. The ovarian cycle controls the growth and release of an ovum • The menstrual cycle prepares the uterus for possible implantation of an embryo • The female reproductive cycle involves two sets of changes • Hormones • Synchronize cyclical changes in the ovaries and uterus

29. The human sexual response occurs in four phases • Excitement • Sexual passion builds • Penis and clitoris become erect • Testes, labia, nipples swell • Vagina secretes lubricating fluid • Muscles of arms and legs tighten

30. Continuation of excitement responses • Increase in breathing and heart rates • Orgasm • Rhythmic contraction of the reproductive structures • Extreme pleasure • Ejaculation by the male • Plateau • Resolution • Reverse previous phase responses • Structures return to normal size • Muscles relax • Passion subsides

31. REPRODUCTIVE HEALTH • Contraception • Transmission of disease • Two issues of human reproductive health Contraception • Contraception • Is the deliberate prevention of pregnancy

32. Contraception prevents pregnancy in one of three ways • Blocking the release of gametes • Preventing fertilization • Preventing implantation

33. There are many forms of contraception, each with varying degrees of reliability

34. Contraceptive methods and their effectiveness

35. Sexually Transmitted Diseases • Are contagious diseases spread by sexual contact • Sexually transmitted diseases (STDs) • Viral STDs, such as AIDS, genital herpes, and genital warts, cannot be cured but can be controlled by medications

36. REPRODUCTIVE TECHNOLOGIES • Can help solve problems related to the inability to conceive a child • Reproductive technologies Infertility • Infertility • Is the inability to have children after one year of trying • Is most often due to problems in the man, such as underproduction of sperm or impotence

37. In Vitro Fertilization • There are technologies available to help treat the many forms of infertility • Female infertility can result from a lack of eggs or a failure to ovulate • In vitro fertilization (IVF) • Happens under artificial, laboratory conditions

38. Begins with the surgical removal of eggs and the collection of sperm • Involves fertilization of eggs in a petri dish • IVF

39. Offers choices that nature does not • Raises many moral and legal issues • IVF

40. PRINCIPLES OF EMBRYONIC DEVELOPMENT Fertilization results in a zygote and triggers embryonic development • The shape of a human sperm cell is adapted to its function

41. Begins with fertilization, the union of sperm and egg to form a zygote • Embryonic development

42. Fertilization • Copulation releases hundreds of millions of sperm into the vagina, but only a few hundred survive the trip to the egg, and only one will fertilize it

43. Basic Concepts of Embryonic Development • The key to development in all organisms is that each stage of development takes place in a highly organized fashion

44. Cleavage continues as the embryo moves down the oviduct toward the uterus • About 6–7 days after fertilization, the embryo has reached the uterus as a fluid-filled hollow ball of about 100 cells called a blastocyst • Development begins with cleavage, a series of rapid cell divisions that results in a multicellular ball • The next stage of development is gastrulation, a process that produces the three embryonic tissue layers

45. Gastrulation produces a three-layered embryo • Gastrulation is the second major phase of embryonic development • It adds more cells to the embryo • It sorts all cells into three distinct cell layers • The embryo is transformed from the blastula into the gastrula

46. Ectoderm, the outer layer • Endoderm, an embryonic digestive tract • Mesoderm, which partly fills the space between the ectoderm and endoderm • The three layers produced in gastrulation

47. Development of frog gastrula

48. Organs start to form after gastrulation • Embryonic tissue layers begin to differentiate into specific tissues and organ systems • In chordates • the notochord develops from the mesoderm • the neural tube develops from the ectoderm • The neural tube becomes the brain and spinal cord

49. Somites are blocks of mesoderm that will give rise to segmental structures • The body cavity, or coelom, also develops from the mesoderm

50. Changes in cell shape, cell migration, and programmed cell death give form to the developing animal • Tissues and organs take shape in a developing embryo as a result of • cell shape changes • cell migration