DH 356 - Chapter 3 Overview of Prenatal Development.ppt

Chapter 3: Overview of Prenatal Development DH 356 1  Periods of Development Prenatal development  Preimplantation period  Embryonic period  3rd – 8th week  Fetal period  9th week until birth Overvie...

Chapter 3: Overview of Prenatal Development DH 356 1  Periods of Development Prenatal development  Preimplantation period  Embryonic period  3rd – 8th week  Fetal period  9th week until birth Overview of Embryology PRENATAL DEVELOPMENT 3  Terminology  Prenatal  Before birth  Embryology  The study of prenatal development.  Primordium  The earliest indication of a tissue or an organ during prenatal development.  Gestation  The amount of time spent in the womb  Overview of Embryology 5  Prenatal development  Begins at the start of pregnancy and continues until the birth of the child  Debate as to “when” pregnancy starts  Pregnancy starts on the first day of your last menstrual cycle  Pregnancy is not usually detected until implantation and pregnancy hormones are triggered (Usually 3-4 weeks after the “start” of pregnancy)  9 months of gestation is usually divided into trimesters or 3- month time spans. Periods of Prenatal Development Table 3-1 Overview of Prenatal Development PREIMPLANTATION PERIOD 7  Preimplantation Period  Preimplantation period  Fertilization/Conception:  Ovum is united with sperm Figure 3-1  Preimplantation Period Zygote  fertilized egg During fertilization, the final stages of meiosis occur in the ovum.  Creation of 4 sex cells Mitosis 2 identical Chromosomal mutations, Accessed 2010 at http://www.ncbi.nlm.nih.gov/ cells are created  Karyotype  Karyotype  A complete set of a person’s chromosomes  XX chromosomes for females  XY for males. Figure 3-2  Preimplantation Period  After fertilization, the zygote then undergoes mitosis, or individual cell division or cleavage.  After initial cleavage, the solid ball of cells is known as a morula.  Once the cells start to migrate within the cell, a blastocyst (or blastula) is formed. Applegate EJ. The Anatomy and Physiology Learning System, ed 3, Elsevier, 2006  Preimplantation Period  By the end of the first week, the blastocyst stops traveling and undergoes implantation and thus becomes embedded in the prepared endometrium, the innermost lining of Figure 3-3 the uterus on its back wall.  Preimplantation Period Implantation: A, Blastocyst approaches endometrium. B, Trophoblast: outer layer of blastocyst and forms attachment to uterine wall. C, Endometrial tissue grows over blastocyst to complete implantation. Applegate EJ. The Anatomy and Physiology Learning System, ed 3, Elsevier, 2006  Preimplantation Period After a week of cleavage, blastocyst consists 0f:  trophoblast layer:  peripheral cells  Support cells  embryoblast layer: Figure 3-4  small inner mass of embryonic cells  Gives rise to embryo  Preimplantation Period Summary of events during the first week of prenatal development. Applegate EJ. The Anatomy and Physiology Learning System, ed 3, Elsevier, 2006  Potential Issues During Early Stages of Pregnancy  Downs syndrome:  Disturbances during meiosis  10% of cases.  An example of this is Down syndrome (or trisomy 21), where an extra chromosome number 21 is present after meiotic division. Genetics Home Reference, U.S. National Library of Medicine, Accessed 2010 at http://ghr.nlm.nih.gov/ Figure 3-5  Oral Risks Relating to Downs Syndrome Increased risk of:  periodontal disease  Microdontia  Enlarged tongue  Other oral malformations  GERD  Dimentia/alzheimers Fehrenbach, MJ, Weiner J. Saunders Review of Dental Hygiene, ed 2. Saunders, Philadelphia, 2009 Overview of Prenatal Development EMBRYONIC PERIOD 18  Embryonic Period embryonic period of prenatal development  Second period  Beginning of the second week of development to the end of the eighth week.  Embryonic Period These physiological processes  Induction  Proliferation  Differentiation  Morphogenesis  Maturation  Induction First physiological process involved during prenatal development The action of one group of cells on another Chemical precursors initiate actions on other cells Process of Induction  Embryonic Period  Following induction is proliferation  Appositional growth  Tissue enlarges its size by the addition of layers on the outside of a structure.  interstitial growth  Tissue enlarges its size by the addition of layers from deep within a tissue or organ  Embryonic Period Differentiation Embryonic tissues specialize and create diverse tissue types. systems.  Differentiation Cytodifferentiation is the development of different cell types. Histodifferentiation is the development of different tissue types within a structure. Morphodifferentiation is the development of the differing structure or shape, or morphology, for each organ or system. Cells, tissues and structures  Maturation Maturation:  Involves proliferation, differentiation and morphogenesis Example:  The development of the ectoderm cells into the tooth germ and eventually into a tooth. https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fnrg1380/MediaObjects/ 41576_2004_Article_BFnrg1380_Fig2_HTML.jpg Developmental Processes in the Embryo Embyronic Period SECOND WEEK 28  Second Week Bilaminar embryonic disc:  Developed from the blastocyst  Appears as a flattened, essentially circular plate of bilayered cells. Figure 3-6  Second Week  The bilaminar embryonic disc has a superior and an inferior layer.  The superior epiblast layer is composed of high columnar cells  The inferior hypoblast layer is composed of small Figure 3-6 cuboidal cells. Embyronic Period THIRD WEEK 31  Third Week Primitive streak  forms within the bilaminar embryonic disc. Marks the start of Gastrulation  Formation of 3 germ layers Bilaminar embryonic disc Figure 3-7  Third Week  This furrowed, rod‑shaped thickening in the middle of the disc results from an increased proliferation of cells in the midline area.  The primitive streak causes the disc to have bilateral symmetry, with a right half and left half. Figure 3-7  Third Week  Migration of cells creates mesoderm.  Bilaminar disc now a trilaminar embryonic disc. Figure 3-8  Third Week  The trilaminar disc has three embryonic cell layers, or germ layers.  With the creation of this new embryonic cell layer of mesoderm, the epiblast layer is now considered ectoderm, and the hypoblast Figure 3-9 layer is now endoderm. 3 Embryologic Cell Layers Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone  Third Week  The disc now has a cephalic end, or head end.  At the cephalic end, the oropharyngeal membrane (or buccopharyngeal membrane) forms, consisting of only ectoderm externally and endoderm internally without any intermediate Figure 3-9 mesoderm.  Third Week During the later part of the third week, the central nervous system (CNS) begins to develop in the embryo. Nanci A. Ten Cate’s Oral Histology, ed 7. Mosby, St. Louis, 2008  Third Week  First, a specialized group of cells differentiates from the ectoderm and is now considered neuroectoderm.  These cells are localized to the neural plate of the embryo, a central band of cells that extends the length of the embryo, from the cephalic end to the caudal end.  This plate undergoes further growth and thickening, which cause it to deepen and invaginate inward, forming the neural groove and then on to the neural tube Neuroectoderm 41  Development of Central Nervous System  A, The neuroectoderm forms from the ectoderm and is located at the neural plate.  B, The neural plate then thickens to form the neural groove, surrounded by the neural folds.  C, Then these folds meet and fuse, forming the neural tube. Figure 3-10  Third Week  neural crest cells (4th embryonic layer)  Develop from neuroectoderm  Specialized cells  These cells migrate from the crests of the neural folds and then disperse within the mesenchyme.  Will develop into certain oral structures later. Figure 3-11  Third Week Nanci A. Ten Cate’s Oral Histology, ed 7. Mosby, St. Louis, 2008 Development of Embryonic Layers  Third Week By the end of the third week, the mesoderm additionally differentiates and begins to divide on each side of the tube into 38 paired cuboidal segments of mesoderm, forming the somites which will become the vertebral plate.  Development of Somites Figure 3-12 Differentiated mesoderm gives rise to the somites that are located on the sides of the developing central nervous system. Embyronic Period FOURTH WEEK 48  Fourth Week During the fourth week of prenatal development, within the embryonic period, the disc undergoes embryonic folding, establishing for the first time the axis, which places forming tissue types into their proper positions for further embryonic development as well producing a somewhat-tubular embryo.  Folding of Embryo Figure 3-15 The trilaminar disc has folded into the embryo as a result of extensive growth of the ectoderm. The endoderm is thus inside the ectoderm, with the mesoderm filling in the areas between these two tissue types, except at the two embryonic membranes. 4th week of embryonic development Development of Pharynx Figure 4-10 The foregut gives rise to the primitive pharynx, which will form the oropharynx.  Fourth Week Finally, during the fourth week, the face and neck begin to develop, with the primitive eyes, ears, nose, oral cavity, and jaw areas. Figure 4-2  Developmental Disturbances During Embryonic Period Because the beginnings of all essential external and internal structures are formed during the embryonic period, this is considered the most critical period of prenatal development. Thus developmental disturbances occurring during this period may give rise to major congenital malformations of the embryo.  Developmental Disturbances During Embryonic Period  ectodermal dysplasia  Involves the abnormal development of one or more structures from ectoderm.  Involves skin, hair, eyes, nails, and glands (all from ectoderm)  Anodontia (partial or complete)  Hereditary Figure 3-13  Known Teratogens Involved in Congenital Malformations  Developmental Disturbances During Embryonic Period  Treacher Collins syndrome (or mandibulofacial dysotosis)  Failure of migration of the neural crest cells to the facial region  Failure of full facial development Figure 3-14  Developmental Disturbances During Embryonic Period infective teratogen is the virus of rubella (German Measles) can result in cataracts, cardiac defects, and deafness. Centers for Disease Control and Prevention, Accessed 2010, http://www.cdc.gov/rubella/  Developmental Disturbances During Embryonic Period  Infective teratogen  bacterial spirochete of syphilis, Treponema pallidum,  (Hutchinson’s incisor)  Molars (mulberry molar)  Blindness, deafness, and paralysis. Figure 3-16  Developmental Disturbances During Embryonic Period Fetal alcohol syndrome Teratogenic drug effect during the embryonic period Ethanol ingestion crosses placenta Figure 3-17 Overview of Prenatal Development FETAL PERIOD 60  Fetal Period  1) Zygote 2) Embryo 3) Fetus  Starts at the:  9th week of development or the 11th week of pregnancy  Most major structures have been developed and will now mature  This process involves:  Proliferation  Differentiation  morphogenesis  Fetal Period Fetus in utero, between fifth and sixth months. Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone  Developmental Disturbances During Fetal Period Amniocentesis  amniotic fluid is sampled during the fourteenth to sixteenth week of pregnancy  Most common invasive test  May detect some congenital malformations  Developmental Disturbances During Fetal Period  Systemic tetracycline antibiotic therapy of the pregnant female can act as a teratogenic drug during the fetal period.  tetracycline stain  Antibiotic chemically bonds with dentin  Amoxicillin overuse Figure 3-18 linked to surface changes on enamel  Tetracycline Stain Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009