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

2. Other sets of multiple births soon followed
What accounted for the sudden rash of multiple births?
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 In asexual reproduction Binary fission
One parent produces genetically identical offspring
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. Fragmentation is the breaking of a parent body into several pieces
Regeneration, which follows fragmentation, is the regrowth of a whole animal from the pieces
Budding
Is the splitting off of new individuals from existing ones

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

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

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

10. Some animals can reproduce both sexually and asexually

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

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

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

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

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

16. The ovaries contain follicles
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
Oviducts
Convey eggs to the uterus

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

18. Ovulation
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

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

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

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

22. Second stage of ejaculation (expulsion stage)

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

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

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

26. Oogenesis 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

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 female reproductive cycle involves two sets of changes
The ovarian cycle controls the growth and release of an ovum
The menstrual cycle prepares the uterus for possible implantation of an embryo
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. Plateau Orgasm Resolution Continuation of excitement responses
Increase in breathing and heart rates
Orgasm
Rhythmic contraction of the reproductive structures
Extreme pleasure
Ejaculation by the male
Resolution
Reverse previous phase responses
Structures return to normal size
Muscles relax
Passion subsides

31. REPRODUCTIVE HEALTH Contraception
Two issues of human reproductive health
Contraception
Transmission of disease
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
Sexually transmitted diseases (STDs)
Are contagious diseases spread by sexual contact
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
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
Female infertility can result from a lack of eggs or a failure to ovulate
There are technologies available to help treat the many forms of infertility
In Vitro Fertilization
In vitro fertilization (IVF)
Happens under artificial, laboratory conditions

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

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

40. Fertilization results in a zygote and triggers embryonic development
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. Embryonic development
Begins with fertilization, the union of sperm and egg to form a zygote

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. Development begins with cleavage, a series of rapid cell divisions that results in a multicellular ball
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
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. The three layers produced in gastrulation
Ectoderm, the outer layer
Endoderm, an embryonic digestive tract
Mesoderm, which partly fills the space between the ectoderm and endoderm

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

51. Embryonic induction initiates organ formation
Induction is the mechanism by which one group of cells influences the development of tissues and organs from ectoderm, endoderm, and mesoderm
Adjacent cells and cell layers use chemical signals to influence differentiation
Chemical signals turn on a set of genes whose expression makes the receiving cells differentiate into a specific tissue

52. Pattern formation organizes the animal body
Pattern formation is the emergence of a body form with structures in their correct relative positions
It involves the response of genes to spatial variations of chemicals in the embryo

53. Pregnancy and Early Development
Pregnancy, or gestation
Is the carrying of developing young within the female reproductive tract
Is measured as 40 weeks from the start of the last menstrual cycle in humans

54. Gestation is pregnancy
It begins at conception and continues until birth
Human gestation is 266 days (38 weeks or 9 months)
Mouse gestation is 1 month
Elephant gestation is 22 months

55. About one week after conception
The embryo, which has become a blastocyst, implants itself in the uterine wall
The outer cell layer, the trophoblast, becomes part of the placenta

56. Four structures develop that assist the developing embryo
The amnion, a fluid filled sac that encloses and protects the embryo
The yolk sac, which produces the embryo’s first blood and germ cells
The allantois, which forms part of the umbilical cord
The chorion, which becomes part of the placenta

57. The placenta allows for a variety of substances to pass from mother to fetus
Protective antibodies
German measles virus
HIV
Drugs (prescription and nonprescription)
Alcohol
Chemicals in tobacco smoke

58. The Stages of Pregnancy
Pregnancy is divided into three trimesters

59. The First Trimester
A human embryo about 5 weeks after fertilization

60. A human embryo, now called a fetus, about 9 weeks after fertilization

61. By the end of the first trimester
The fetus looks like a miniature human being
The sex of the fetus can be determined by ultrasound

62. The Second Trimester
The main developmental changes during the second and third trimesters involve an increase in size and general refinement of the human features
A fetus at 14 weeks, 2 weeks into the second trimester

63. At 20 weeks, the fetus
Is about 19 cm (7.6 in.) long and weighs about half a kilogram (1 lb)
Has the face of an infant

64. The Third Trimester The third trimester At birth
Is a time of rapid growth
Includes many important physical changes
At birth
A typical baby is about 50 cm (20 in.) long and weighs 2.7–4.5 kg (6–10 lb)

65. Childbirth
The birth of a child is brought about by a series of strong, rhythmic contractions of the uterus called labor

66. Hormones play a key role in inducing labor
Estrogen, oxytocin, and prostaglandins are all involved

67. There are three stages of labor
Dilation of the cervix is the first stage
Cervix reaches full dilation at 10cm
Longest stage of labor (6-12 hours or longer)

68. Expulsion is the second stage
Period from full dilation of the cervix to delivery of the infant
Uterine contractions occur every 2-3 minutes
Mother feels urge to push down with her abdominal muscles
Infant is forced down and out of uterus and vagina within a period of 20 minutes

69. The delivery of the placenta is the final stage of labor
Usually occurs within 15 minutes after the birth of the baby

70. Hormones continue to be important after the baby and placenta are delivered
Decreasing progesterone and estrogen levels allow the uterus to return to its pre-pregnancy state
Oxytocin and prolactin stimulate milk secretion