Conception & Fetal Development PDF

Conception & Development of the Embryo and Fetus Objectives: Explain the basic concepts of inheritance Outline the process of fertilization, implantation and placental development Discuss threats to embryo/fetal well-being and development and explain the nurse’s role in minimizing threats to the dev...

Conception & Development of the Embryo and Fetus Objectives: Explain the basic concepts of inheritance Outline the process of fertilization, implantation and placental development Discuss threats to embryo/fetal well-being and development and explain the nurse’s role in minimizing threats to the developing fetus Basic Concepts of Inheritance Human Genome Project (1990–2003) Chromosomes 23 matched pairs DNA Genes Inheritance of Disease Multifactorial Genetic and environmental factors Examples: cleft lip, neural tube defects Unifactorial Single gene inheritance Examples: autosomal dominant, autosomal recessive, Xlinked disorders Autosomal Dominant Inheritance Single altered gene Mutation Parent who is heterozygous for the trait 50% chance of passing trait to offspring Examples: Huntington’s disease, achondroplasia, neurofibromatosis Autosomal Recessive Inheritance Each parent has the altered gene 25% risk of passing trait to offspring Specific populations Sickle cell anemia more frequent in African American populations Examples: phenylketonuria (PKU), cystic fibrosis X-Linked Dominant Inheritance Altered gene on X chromosome X-linked dominant in father None of sons will inherit the disorder All of daughters will inherit the disorder Female with X-linked dominant trait 50% chance of passing trait to daughters X-Linked Recessive Inheritance More common than X-linked dominant disorders Occurs more frequently in males Female carrier 50% chance of passing to offspring Examples: hemophilia A, Duchenne muscular dystrophy Cellular Division Gametes Ovum: female gamete Sperm: male gamete Gametogenesis Meiosis Mitosis Process of Fertilization Oocyte and sperm meet in fallopian tube Ovulation: cervical mucus changes ~200 sperm reach fertilization site Capacitation Penetrates zona pellucida; prevents fertilization by other sperm Cellular Multiplication Cleavage: rapid cellular division Morula: solid ball of cells Blastocyst: inner mass of cells Embryoblast Trophoblast Implantation Zygote propelled by Cilia Peristalsis Reaches uterine cavity in 3–4 days Nidation Occurs by 10th day after fertilization Implantation bleeding Blastocyst buried beneath the endometrial surface Placenta Develops from trophoblast cells Lacunae Chorionic villi Intervillous spaces Provides oxygenation, nutrition, waste elimination, and hormones Protects fetus Substance Transport Across Placenta Diffusion Active transport Pinocytosis Bulk flow and solvent drag Accidental capillary breaks Independent movement Placental Hormones Human chorionic gonadotropin (hCG) Human placental lactogen (hPL) Progesterone Estrogen Development of the Embryo and Fetus Yolk Sac, Umbilical Cord, Fetal Circulation Yolk Sac Develops 8–9 days after conception Essential for transfer of nutrients during 2nd and 3rd weeks of gestation Hematopoiesis Atrophies and is incorporated into umbilical cord Umbilical Cord Usual location in center of placenta 55 cm long (21 in.); 1–2 cm diameter Vessels: 1 vein, 2 arteries Wharton’s jelly: protects umbilical cord from compression Fetal Circulation Heart begins to beat and circulate blood by end of 3rd week Umbilical vein: blood from placenta to fetus Low Po2 important to maintain fetal circulation Fetal Circulation (cont’d) 3 unique shunts Ductus venosus: bypasses liver and enters inferior vena cava Foramen ovale: right and left atria to supply blood to head, upper and lower extremities Ductus arteriosus: returning blood bypasses lungs Fetal Membranes and Amniotic Fluid Embryonic Membranes, Purpose and Characteristics of Amniotic Fluid Embryonic Membranes Early protective structures 2 separate membranes Amnion: inner membrane, contains amniotic fluid Chorion: outer membrane, forms fetal portion of placenta Slightly adherent; form amniotic sac Purposes of Amniotic Fluid Protects and cushions fetus Maintains normal body temperature Promotes symmetrical fetal growth Allows freedom of movement Essential for normal fetal lung development Characteristics of Amniotic Fluid Amount: 800 mL at 24 weeks Fetal urine and lung secretions primary contributors Slightly alkaline Contains antibacterial, other protective substances Human Growth and Development Pre-embryonic, Embryonic, Fetal Periods Pre-embryonic Period First 2 weeks after conception Rapid cellular multiplication and differentiation Establishment of embryonic membranes and primary germ layers Embryonic Period From 3rd week after fertilization through end of 8th week Organogenetic period: formation, differentiation of all organs Germ layers: Ectoderm, endoderm, mesoderm Vulnerable to environmental insults Fetal Period From 9th week until birth or termination of pregnancy Rapid body growth and differentiation of tissues, organs, and systems Less vulnerable stage Fetal Period: Weeks 9 to 12 Body growth increases Ossification centers appear Intestines leave umbilical cord, enter abdomen External genitalia by week 12 Urine production begins Fetal Period: Weeks 13 to 16 Very rapid growth Coordinated movements of limbs Ossification of skeleton Ovaries differentiated Fetal Period: Weeks 17 to 20 Growth slows Quickening Vernix caseosa Lanugo By 20 weeks: fetal weight 300 g and length 19 cm (7.3 in.) Fetal Period: Weeks 21 to 25 Gains weight Skin pink Rapid eye movements Surfactant by 24 weeks Fetal Period: Weeks 26 to 40 Weeks 26 to 29 If born, fetus may survive Weeks 30 to 40 Strong hand grasp reflex Orientation to light 38–40 weeks: 3,000–3,800 g (weight) and 45–50 cm (17.3–19.2 in.) (length) Threats to Embryonic and Fetal Development Chromosomal abnormalities and teratogens Medications and other substances Vitamins, alcohol, tobacco, caffeine, drugs, radiation, and lead exposure TORCH infections Nurse’s Role in Prenatal Evaluation Initial prenatal visit Assessment: cultural, emotional, physical, and physiologic factors Education Genetic disorders Prenatal tests Heredity and Genetics Congenital anomalies Malformations Deformations Dysplasia Maternal Age and Chromosomes Age 35 and older Increased risk of chromosomal abnormalities Down syndrome Deletion Translocation Multifetal Pregnancy Monozygotic Develop from 1 zygote Division occurs at end of 1st week Dizygotic Develop from 2 zygotes Separate amnions and chorions Minimizing Threats to Embryo/Fetus Nurse’s role Assessment Environmental and lifestyle risks Knowledge Physical and psychosocial well-being Preconception counseling