1. End Show Slide 1 of 47 Biology Mr. Karns Development Fertilization

2. End Show Slide 2 of 47 39–4 Fertilization and Development

3. End Show 39–4 Fertilization and Development Slide 3 of 47 When an egg is fertilized, human development begins. In this process, a single cell undergoes a series of cell divisions that results in the formation of a new human being. Development

4. End Show 39–4 Fertilization and Development Slide 4 of 47 Fertilization During sexual intercourse, sperm are released when semen is ejaculated through the penis into the vagina. Sperm swim through the uterus into the Fallopian tubes. if an egg is present in one of the Fallopian tubes, its chances of being fertilized are good.

5. End Show 39–4 Fertilization and Development Slide 5 of 47 Fertilization The egg is surrounded by a protective layer that contains binding sites to which sperm can attach. When a sperm attaches to a binding site, its head releases enzymes that break down the protective layer of the egg. The sperm nucleus enters the egg, and chromosomes from the sperm and egg are brought together.

6. End Show 39–4 Fertilization and Development Slide 6 of 47 What is fertilization? Fertilization

7. End Show 39–4 Fertilization and Development Slide 7 of 47 Fertilization The process of a sperm joining an egg is called fertilization.

8. End Show 39–4 Fertilization and Development Slide 8 of 47 Fertilization After the two haploid (N) nuclei fuse, a single diploid (2N) nucleus is formed. A diploid cell has a set of chromosomes from each parent cell. The fertilized egg is called a zygote.

9. End Show 39–4 Fertilization and Development Slide 9 of 47 Early Development While still in the Fallopian tube, the zygote begins to undergo mitosis. Four days after fertilization, the embryo is a solid ball of about 64 cells called a morula.

10. End Show 39–4 Fertilization and Development Slide 10 of 47 Early Development What are the stages of early development?

11. End Show 39–4 Fertilization and Development Slide 11 of 47 Early Development The stages of early development include implantation, gastrulation, and neurulation.

12. End Show 39–4 Fertilization and Development Slide 12 of 47 Early Development Implantation As the morula grows, it becomes a hollow structure with an inner cavity called a blastocyst. 6–7 days after fertilization, the blastocyst attaches to the uterine wall. The embryo secretes enzymes that digest a path into it. This process is known as implantation.

13. End Show Slide 13 of 47 39–4 Fertilization and Development Fertilization Fertilization and Implantation

14. End Show 39–4 Fertilization and Development Slide 14 of 47 Early Development Blastocyst cells specialize due to the activation of genes. This process, called differentiation, is responsible for the development of the various types of tissue in the body.

15. End Show 39–4 Fertilization and Development Slide 15 of 47 Early Development A cluster of cells, known as the inner cell mass, develops within the inner cavity of the blastocyst. The embryo will develop from these cells, while the other cells will differentiate into tissues that surround the embryo.

16. End Show 39–4 Fertilization and Development Slide 16 of 47 Early Development Gastrulation The inner cell mass of the blastocyst gradually sorts itself into two layers, which then give rise to a third layer.

17. End Show Slide 17 of 47 39–4 Fertilization and Development Mesoderm Amniotic cavity Primitive streak Ectoderm Endoderm Early Development The third layer is produced by a process of cell migration known as gastrulation.

18. End Show 39–4 Fertilization and Development Slide 18 of 47 Early Development The result of gastrulation is the formation of three cell layers—the ectoderm, the mesoderm, and the endoderm. Amniotic cavity Primitive streak Ectoderm Endoderm Mesoderm

19. End Show 39–4 Fertilization and Development Slide 19 of 47 Early Development The ectoderm develops into the skin and nervous system. The endoderm forms the digestive lining and organs. Mesoderm cells differentiate into internal tissues and organs.

20. End Show 39–4 Fertilization and Development Slide 20 of 47 Early Development Neurulation Gastrulation is followed by neurulation. Neurulation is the development of the nervous system.

21. End Show 39–4 Fertilization and Development Slide 21 of 47 Early Development Shortly after gastrulation is complete, a block of mesodermal tissue begins to differentiate into the notochord.

22. End Show Slide 22 of 47 39–4 Fertilization and Development Neural crest Neural fold Notochord Early Development As the notochord develops, the neural groove changes shape, producing neural folds.

23. End Show Slide 23 of 47 39–4 Fertilization and Development Neural crest Neural tube Ectoderm Notochord Early Development Gradually, these folds move together to create a neural tube from which the spinal cord and the nervous system develop.

24. End Show 39–4 Fertilization and Development Slide 24 of 47 Early Development Extraembryonic Membranes As the embryo develops, membranes form to protect and nourish the embryo. Two of these membranes are the amnion and the chorion.

25. End Show 39–4 Fertilization and Development Slide 25 of 47 Early Development The amnion develops into a fluid-filled amniotic sac, which cushions and protects the developing embryo. Uterus Amnion Fetus Amniotic sac Placenta Umbilical cord

26. End Show 39–4 Fertilization and Development Slide 26 of 47 Fingerlike projections called chorionic villi form on the outer surface of the chorion and extend into the uterine lining. Early Development Fetal portion of placenta Maternal portion of placenta Maternal artery Maternal vein Umbilical vein Umbilical arteries Umbilical cord Amnion Chorionic villus

27. End Show 39–4 Fertilization and Development Slide 27 of 47 The chorionic villi and uterine lining form the placenta. The placenta connects the mother and developing embryo. Early Development

28. End Show 39–4 Fertilization and Development Slide 28 of 47 Early Development What is the function of the placenta?

29. End Show 39–4 Fertilization and Development Slide 29 of 47 Early Development The placenta is the embryo's organ of respiration, nourishment, and excretion.

30. End Show 39–4 Fertilization and Development Slide 30 of 47 Early Development The placenta acts as a barrier to some harmful or disease-causing agents. Some disease causing agents, such as German measles and HIV can cross the placenta. Some drugs, including alcohol and medications also can penetrate the placenta and affect development.

31. End Show 39–4 Fertilization and Development Slide 31 of 47 Early Development After eight weeks, the embryo is called a fetus. After three months, most major organs and tissues are formed. During this time, the umbilical cord also forms. The umbilical cord connects the fetus to the placenta.

32. End Show 39–4 Fertilization and Development Slide 32 of 47 Control of Development The fates of many cells in the early embryo are not fixed. The inner cell mass contains embryonic stem cells, unspecialized cells that can differentiate into nearly any specialized cell type. Researchers are still learning the mechanisms that control stem cell differentiation.

33. End Show 39–4 Fertilization and Development Slide 33 of 47 Later Development 4–6 months after fertilization: The heart can be heard with a stethoscope. Bone replaces cartilage that forms the early skeleton. A layer of soft hair grows over the fetus’s skin. The fetus grows and the mother can feel it moving.

34. End Show 39–4 Fertilization and Development Slide 34 of 47 Later Development During the last three months, the organ systems mature. The fetus doubles in mass. It can now regulate its body temperature. The central nervous system and lungs completely develop.

35. End Show 39–4 Fertilization and Development Slide 35 of 47 Childbirth About nine months after fertilization, the fetus is ready for birth. A complex set of factors affects the onset of childbirth.

36. End Show 39–4 Fertilization and Development Slide 36 of 47 Childbirth The mother’s posterior pituitary gland releases the hormone oxytocin, which affects involuntary muscles in the uterine wall. These muscles begin rhythmic contractions known as labor. The contractions become more frequent and more powerful.

37. End Show 39–4 Fertilization and Development Slide 37 of 47 Childbirth The opening of the cervix expands until it is large enough for the head of the baby to pass through it. At some point, the amniotic sac breaks, and the fluid it contains rushes out of the vagina. Contractions force the baby out through the vagina.

38. End Show 39–4 Fertilization and Development Slide 38 of 47 Childbirth The baby now begins an independent existence. Its systems quickly adapt to life outside the uterus, supplying its own oxygen, excreting waste on its own, and maintaining its own body temperature.

39. End Show 39–4 Fertilization and Development Slide 39 of 47 Multiple Births If two eggs are released during the same cycle and fertilized by two different sperm, fraternal twins result. A single zygote may split apart to produce two embryos, which are called identical twins.

40. End Show 39–4 Fertilization and Development Slide 40 of 47 Early Years The first two years of life are called infancy. It is a period of rapid growth and development. Childhood lasts from infancy until puberty. Adolescence begins with puberty and ends with adulthood. Puberty produces a growth spurt that will conclude in mid-adolescence.

41. End Show 39–4 Fertilization and Development Slide 41 of 47 Adulthood Development continues during adulthood. Adults reach their highest levels of physical strength and development between the ages of 25 and 35. Most people begin to show signs of aging in their 30s. Around age 65, most body systems become less efficient, making homeostasis more difficult to maintain.

42. End Show - or - Continue to: Click to Launch: Slide 42 of 47 39–4

43. End Show Slide 43 of 47 39–4 Fertilization takes place in the a.ovary. b.Fallopian tube. c.cavity of the uterus. d.cervix.

44. End Show Slide 44 of 47 39–4 The process in which a blastocyst attaches to the wall of the uterus is called a.fertilization. b.implantation. c.gastrulation. d.neurulation.

45. End Show Slide 45 of 47 39–4 The central nervous system develops during which phase of early development? a.gastrulation b.neurulation c.implantation d.fertilization

46. End Show Slide 46 of 47 39–4 The placenta is a structure that a.belongs entirely to the mother. b.belongs entirely to the fetus. c.brings blood from the mother and fetus close together. d.provides an impermeable barrier between the mother and the fetus.

47. End Show Slide 47 of 47 39–4 Which of the following is not a primary germ layer? a.neural tube b.endoderm c.ectoderm d.mesoderm

48. END OF SECTION