1 Guangxi medical university

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3 一、 GENERAL EMBRYOLOGY 1. Embryology A science that studies the normal development as well as the congenital malformation of a human being before the parturition. It takes 38 weeks from fertilization to parturition of a mature fetus. Fertilization Parturition

4 It is divided three periods: 1.PREEMBRYONIC PERIOD (First 2 weeks) 2.EMBRONIC PERIOD (Weeks 3 - 8) 3.FETAL PERIOD (Week 9 - Birth) 2.The stage of the normal development of embryo

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6 Preembryonic period: The first week: Fertilization to formation of the Blastocyst.

7 The second week: Implantation and the formation of the Bilaminar germ disc The 3 – 8 weeks The formation of the 3 germ layers. Primordia of all major organs develop from the 3 germ layers.

8 FETAL PERIOD (Week 9 - Birth) Growth of the organ systems

9 8 weeks

10 12 weeks

11 16 weeks

12 20 weeks

13 24 weeks

14 32 weeks

15 CHAPTER 2 BEGINNING OF HUMAN DEVELOPMENT THE FIRST WEEK FERTILIZATION The process of union of a sperm and oocyte to form a zygote 1.Time:12—24 hours after ovulation. 2.Site: The ampulla of the uterine tube. 3. Process: a. Acrosome reaction b. Penetration the corona radiata and zona pellucida c. Fusion of the membranes zona reaction d. Formation of two pronuclei e. Meeting of two pronuclei

16 ovulation

17 FERTILIZATION The process of union of a sperm and oocyte to form a zygote

18 Meeting of two pronucleus

19 4. Significance of the fertilization a.Restoration of the diploid number of chromosomes b. Determination of the sex (DNA) c. Activation of zygote and initiation of the cleavage

20 CLEAVAGE AND BLASTOCYST FORMATION CLEAVAGE A series of mitotic divisions of the zygote, produces a number of smaller cells called blastomeres The morula, a solid ball of 12 to 16 blastomeres, forms about three days after fertilization. This process occurs at the movement from the ampulla of the uterine tube to the cavity of the uterus.

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25 morula

26 About the time the morula enters the uterine cavity,the zona pelluzida has disappeared,the fluid begins to penetrate through the zona pellucida into the intercellular spaces of the Blastomeres. the spaces becomes confluent gradually, and forms a single cavity that is named the blastocele. Blastocyst Formation

27 Morula

28 Trophoblast Inner cell mass ( embryoblast ) Blastocele

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30 A blastocyst come into the uterine cavity

31 Inner cell mass ( embryoblast ) Blastocele Trophoblast

32 The first week

33 A process of the blastocyst embedding into the endometrium 1.Time: Starting at about the 5-6 th day Finishing at the th day 2.Site: Along the posterior or anterior wall of the body of the uterus 3.Requirements: a.Zona pellucida disappears in time b.Normal development and transport of the young embryo c.Endometrium in the secretory phase d.Normal endocrine reguration of estrogen and progesterone A. Implantation CHAPTER 3 Formation of the embryo the 2ed week

34 A process of the blastocyst embedding into the endometrium A. Implantation

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36 ectopic pregnancy extrauterine pregnancy

37 placenta previa

38 B. Formation of the bilaminar germ disc Cells of the inner cell mass differentiate into two layers Hypoblast layer: a layer of small cuboidal cells adjacent to the blastocyst cavity. Epiblast layer: a layer of high columnar cells adjacent to the amniotic cavity The cell of each of germ layers form a flat disc and together they are know as bilaminar germ disc At the same time of the implantation

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40 Epiblast layer Hypoblast layer

41 C.The trophoblast has differentiated into two layers: Cytotrophoblast: an inner layer of the mononucleated cells Syncytiotrophoblast: an outer multinucleated zona without distinct cell boundaries A small space appears between the epiblast and the trophoblast, and enlarges to become a cavity Amniotic cavity. The epiblast cells adjacent to the cytotrophoblast forms a membrane Amnioblast

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43 syncytiotrophoblast cytotrophoblast Epiblast layer Hypoblast layer

44 A small space appears between the epiblast and the trophoblast, and enlarges to become a cavity Amniotic cavity. The epiblast cells adjacent to the cytotrophoblast forms a membrane Amnioblast An layer flattened cells originating from the hypoblast lines the inner surface of the cytotrophoblast, and forms the primitive yolk sac. D. Formation of the Amniotic cavity and the yolk sac

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46 syncytiotrophoblast cytotrophoblast Epiblast layer Hypoblast layer Amniotic cavity Amnioblast

47 Extraembryonic mesoblast : A new population of cells that derived from the yolk sac, forms a loose tisse. They appears between the inner surface of the cytotrophoblast and the outer surface of the yolk sac. Extraembryonic coelom : A large cavity develops in the extraembryonic mesoderm Extraembryonic somatopleuric mesoblast: that lining the cytotrophoblast and amnion Extraembryonic splanchnopleuric mesoblast: that covering the yolk sac E. Formation of the Extraembryonic mesoblast

48 Extraembryonic coelom Extraembryonic somatopleuric mesoblast Extraembryonic splanchnopleuric mesoblast

49 CHAPTER 4 Formation of the trilaminar germ disc the third week 1.Formation of the primitive streak Proliferation of the epiblast cells in the midline of the caudal part of disc to form a cell cord. Primitive node is the swelling cephalic end of the primitive streak 2.Formation of the mesoderm Cells of the epiblast proliferate and migrate in between the Epiblast and the hypoblast to form a new germ layer--- intraembryonic mesoderm, the short name mesoderm. Buccopharyngeal menbrane: Cloacal menbrane: Two regions have no mesoderm:

50 4. Formation of the Notochord The epiblast cells invaginating in the primitive pit move straight cephalically to form a tube-like process, which later forms a solid cord. 3. Formation of the trilaminar germ disc With the mesoderm formation, the epiblast cells move in the hypoblast and take place of it forming the endoderm. Cells remaining in the epiblast comprise the ectoderm. Trilaminar germ disc ectoderm mesoderm endoderm

51 Primitive node Primitive streak Ectoderm Notochord

52 Ectoderm Mesoderm Endoblast Primitive streak Formation of the mesoderm

53 Primitive streak Formation of the mesoderm mesoderm

54 ectoderm Oropharyngeal membrane notochord mesoderm primitive node primitive streak cloacal membrane

55 Buccopharyngeal menbrane: Cloacal menbrane: Mesoderm

56 Differentiation of Germ Layers 1. Differentiation of the ectoderm a.Neural plate are formed by the thicking ectoderm over the notochord. b. The central axis of the neural plate invaginates forming Neural groove. The lateral edges forms the neural folds. c. The neural folds move closer and fuse to form the neural tube d. Neural crests : some cells of the neural fold are not incorporated into the tube A. Neural ectoderm

57 Neural groove Neural fold Neural crest

58 Surface ectoderm Neural crest Neural tube

59 B. Surface ectoderm The rest of the ectoderm will differentiate into the epidermis The remainder of the surface ectoderm develops into the epidermal layer of the skin with its derivatives (appendages). These appendages include the following : hair (12th week) sebaceous glands (16th week) sweat glands (10th week) mammary glands (6th week) nails (10th week).

60 neural tube Surface ectoderm

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62 2. Differentiation of the mesoderm a.Paraxial mesoderm: immediately adjacent to the notochord, has segmented (starting at about 20 days) to form somites. b.Intermediate mesoderm: The intermediate mesoderm lies lateral to each paraxial column of mesoderm c. Lateral mesoderm: The lateral plate mesoderm has split into somatopleure mesoderm adjacent to ectoderm and splanchnopleure mesoderm adjacent to endoderm. d. The rest is named mesenchyme The somites give rise to most of the skeleton and related musculature, dermis, and most subcutaneous structures. Intermediate mesoderm is the primordium of the urogenital system

63 Somite Intermediate mesoderm Somite Intermediate mesoderm

64 Intermediate mesoderm Somatic mesoderm Primitive body cavity Splanchnic mesoderm

65 somite notochord somatic esoderm splanchnic mesoderm neural tube ectoderm endoderm

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67 amniotic cavity neural tube ectoderm primitive gut yolk sac

68 yolk sac hindgut neural tube midgut cardiogenic area foregut Allantoic cyst

69 yolk sac hindgut midgut notochord foregut neural tube ectoderm body stalk Allantoic cyst

70 chapeter 5 Formation of basic organs and systems the fourth to eighth weeks A. Folding of the embryonic disc 1.Head and Tail folds 、 Lateral fold: As a result of the rapid growth of the central nervous systerm and the amniotic cavity. 2.Formation of the umbilical cord: As the result of the embryo bulges into the enlarged amniotic cavity, the body stalk is reduced to form the umbilical cord. A significant event in the establishment of body form is folding of the flat trilaminar embryonic disc into a cylindrical embryo

71 tail fold head fold yolk sac

72 Head and Tail folds: As a result of the rapid growth of the central nervous systerm and the amniotic cavity.

73 tail fold head fold yolk sac

74 yolk sac Lateral fold

75 Lateral fold: As a result of the rapid growth of the central nervous systerm and the amniotic cavity.

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80 Thank you very much ! Chen,weiping Thursday, May 26, 2016