BSC2086 A P II Final Exam Study Guide Lesson 23 Introduction to Development Lesson 23 Development Development Gradual modification of anatomical structures and physiological characteristics from fertilization to maturity Fertilization Conception When male female gametes fuse development Differentiation Creation of different types of cells required in development o Occurs through selective changes in genetic activity o As development proceeds some genes are turned off while others are Embryological Development Occurs during first two 2 months after begins turned on fertilization o Embryology Study of the events that occur during embryological development Fetal Development Begins at start of 9th week o Continues until birth Prenatal Development Embryological fetal development stages Postnatal Development Commences at birth o Continues to maturity state of full development or completed growth Capacitation must occur before spermatozoa can fertilize secondary oocyte o Contact with secretions of seminal glands o Exposure to conditions in female reproductive tract Fertilization occurs in the uterine tube within a day after ovulation o Secondary oocyte travels a few centimeters o Spermatozoa must cover distance between vagina ampulla Covers 5 inches hour Takes 2 hours for sperm to reach ampulla Fertilization Fertilization produces zygote containing 46 chromosomes o Occurs upon fusion of two haploid gametes each contain 23 chromosomes Spermatozoon travels relatively large distance to deliver paternal chromosomes to fertilization site Secondary Oocyte provides cellular organelles inclusions nourishment genetic programming necessary to support development of embryo for a week Acrosome of Sperm Cells o Releases Hyaluronidase Enzyme that breaks bonds between adjacent follicle cells Acrosin Proteolytic enzyme o Penetrate corona radiata zona pellucida toward oocyte surface Sperm binds to receptor found on zona pellucida Activates acrosome Releases enzymes to digest path through zona pellucida 1 BSC2086 A P II Final Exam Study Guide Lesson 23 Oocyte Activation Changes in oocyte metabolism triggered by contact and fusion of sperm oocyte cell membranes o Causes 1 Cortical Reaction oocyte plasma membrane depolarizes releases exocytosis enzymes that Inactivate sperm receptors Harden zona pellucida o Both prevent polyspermy 2 Completion of meiosis II formation of 2nd polar body 3 Activation of enzymes to increase cell s metabolic rate After oocyte activation completion of meiosis II o Amphimixis Fusion of male female pronuclei Female Pronucleus Nuclear material remaining in ovum after oocyte activation Male Pronucleus Swollen nucleus of spermatozoon o Now zygote has 46 chromosomes o Fertilization is complete Cleavage Series of cell divisions o Produces daughter cells o First cleavage occurs 30 hours after fertilization Produces 2 daughter cells each size of original zygote Daughter cells called blastomeres Differentiation Involves changes in genetic activity of some cells but others Influenced by cytoplasmic content o o As the blastomeres divide each receives a portion of cytoplasm that may differ in composition o Oocyte receives many molecules nutrients RNA from granulosa cells 2 BSC2086 A P II Final Exam Study Guide Lesson 23 Gestation Induction Cells release chemical substances that affect differentiation of other embryonic cells o Can control highly complex processes o Not error free can disrupt normal development Gestation Time spent in prenatal development o Consists of three 3 integrated trimesters each three 3 months long First Trimester Period of embryological and early fetal development o Rudiments of all major organ systems appear Second Trimester Development of organs organ systems o Body shape proportions change Third Trimester Rapid fetal growth deposition of adipose tissue o Most major organ systems are fully functional First Trimester First Trimester most dangerous period in prenatal life o 40 of conceptions produce embryos that survive past first trimester Includes Four 4 Major Stages o Cleavage Implantation o o Placentation o Embryogenesis 3 BSC2086 A P II Final Exam Study Guide Lesson 23 1 Cleavage o Sequence of cell divisions begins immediately after fertilization o Zygote becomes a pre embryo develops into multicellular blastocyst o Ends when blastocyst contacts uterine wall o Blastomeres Identical cells produced by cleavage divisions mitosis Subsequent divisions faster every 10 12 hours o Morula Stage after three 3 days of cleavage Pre embryo is solid ball of cells resembling mulberry Reaches uterus on day 4 o Blastocyst Hollow ball formed by blastomeres with an inner cavity blastocoele Blastomeres no longer identical in size shape Trophoblast Outer cells o Develop into structures that provide nutrients to o Secrete enzyme that erodes zona pellucida hatching Inner Cell Mass Located on one side inside trophoblast embryo the blastocyst Insulated from outside o o Will form embryo 4 BSC2086 A P II Final Exam Study Guide Lesson 23 2 Implantation o Occurs seven 7 days after fertilization o Begins with attachment of blastocyst to endometrium of uterus o Blastocyst adheres to uterine lining Inner cell mass side faces the endometrium o Trophoblast cells divide rapidly at contact point creating several layers Cellular Trophoblast cells closest to interior of blastocyst remain intact Cells next to endometrium fuse forms multinucleated syncytial trophoblast hyaluronidase o Erodes path through uterine epithelium by secreting o Maternal epithelial cells divide migrate to enclose the blastocyst by day 10 5 BSC2086 A P II Final Exam Study Guide Lesson 23 o Erosion of endometrium by syncytial trophoblast releases nutrients for blastocyst Erosion occurs at capillary walls destroys them releasing blood Blood pools in trophoblastic channels called o Villi extend away form the trophoblast into lacunae endometrium Accelerating breakdown of endometrial blood vessels blood flow to lacunae Increase in size complexity until day 21 o Sets stage for formation of vital embryonic structures 3 Placentation o Occurs as blood vessels form around periphery of blastocyst o Placenta develops 4 Embryogenesis o Formation of viable embryo o Establishes foundations for all major organ systems Formation of the Amniotic Cavity o Amniotic Cavity A fluid filled chamber Inner cell mass organized into an oval sheet two 2 layers thick Superficial layer faces amniotic cavity 6 BSC2086 A P II Final Exam Study Guide Lesson
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