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Chapter 7

Chapter 7. Conception and Development of the Embryo and Fetus . Basic Concepts of Inheritance. Human Genome Project (1990) Chromosomes 23 matched pairs DNA Genes. Cellular Division. Gametes Ova — female gamete Sperm — male gamete Gametogenesis Meiosis Mitosis.

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Chapter 7

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  1. Chapter 7 Conception and Development of the Embryo and Fetus

  2. Basic Concepts of Inheritance • Human Genome Project (1990) • Chromosomes • 23 matched pairs • DNA • Genes

  3. Cellular Division • Gametes • Ova—female gamete • Sperm—male gamete • Gametogenesis • Meiosis • Mitosis

  4. Inheritance of Disease • Multifactorial • Genetic and environmental factors • Examples: cleft lip, neural tube defects • Unifactorial • Single gene inheritance • Examples: autosomal dominant, autosomal recessive, X-linked disorders

  5. Mendelian Inheritance • Autosomal Dominant • Affected person has affected parent • 50% chance of passing the trait • Males & females equally affected--dad can pass to son • Autosomal Recessive • Can have clinically normal parents, but both parents must be carriers • 25% chance of affected child • 50% chance child is carrier • Males & females affected equally

  6. X Linked Inheritance X-Linked Recessive • No male to male transmission • 50% chance carrier mom passes to son who will be affected • 50% chance carrier mom passes to daughters who become carriers • Affected dads cannot pass to sons, but all daughters are carriers X-Linked Dominant (Extremely rare) • Fragile X syndrome • Heterozygous females may be affected • No male to male transmission • Affected fathers will have affected daughters, but no affected sons

  7. Nursing Responsibilities • Assess for signs and symptoms of genetic disorders • Offer support • Assist in value clarification • Educate on procedures and tests

  8. Assessing for Genetic Disorders • Chorionic villi sampling (CVS) • Biopsy & chromosomal analysis of chorionic villi of placenta (transvaginal or abdominally) • 8-12 weeks (earlier than amnio) • Risks • Limb reduction syndrome • Excessive bleeding & pregnancy loss • Infection • Rh-Negative mom needs RhoGAM • Advantages: 1st trimester,highly accurate, quicker results than amnio

  9. Assessing for Genetic Disorders Ultrasound--best between 16-20 weeks • Detect head and craniospinal defects:anencephaly, microcephaly, hydrocephalus • GI malformations:omphalocele, gastroschisis • Renal malformations: dysplasia or obstruction • Skeletal malformations:caudal regression, conjoined twins • Fetal nuchal translucency:10-13 weeks

  10. Assessing for Genetic Disorders • Amniocentesis: 15 - 20 wks • Risks: miscarriage, bleeding, infection • Maternal age ≥ 35 • Hx of child with chromosomal abnormality • Parent carrying chromosomal abnormality • Mother carrying x-linked disease • Parent with in-born error of metabolism • Both parents carrying autosomal recessive disease • Family hx of neural tube defects

  11. Process of Fertilization • Oocyte and sperm meet in fallopian tube • Ovulation—cervical mucus changes • 200 sperm reach fertilization site • Capacitation • Penetrates zonapellucida—prevents fertilization by other sperm

  12. Implantation • Zygote propelled by • Cilia • Peristalsis • Reaches uterine cavity in 3 to 4 days

  13. Nidation • Occurs by 10th day after fertilization • Implantation bleeding • Blastocyst is buried beneath the endometrial surface

  14. Placenta • Develops from trophoblast cells • Lacunae • Chorionic villi • Intervillous spaces • Provides oxygenation, nutrition, waste elimination, and hormones • Protects fetus

  15. Placenta

  16. Embryonic and Fetal Structures • Placenta • Serves as the fetal lungs, kidneys and GI tract and as a separate endocrine organ throughout the pregnancy • Placental circulation established as early as 3rd week of pregnancy • Grows to 15-20 separate “lobes” called cotyledons • By wk 20, covers approx. 1/2 surface of internal uterus • No direct exchange of blood between the embryo and the mother during pregnancy--exchange is through selective osmosis

  17. Placental Circulation • Maternal blood from spiral arteries enters intervillous space of endometrium • Fetal chorionic villi reach into endometrium • Membrane of chorionic villi is 1 cell thick • Exchange of nutrients/substances

  18. Placenta

  19. Placenta

  20. Substance Transport Across Placenta • Diffusion • Active transport • Pinocytosis • Bulk flow and solvent drag • Accidental capillary breaks • Independent movement

  21. Placental Hormones • Human chorionic gonadotrophin (hCG) • Human placental lactogen (hPL) • Progesterone • Estrogen

  22. Development of the Embryo and Fetus

  23. Yolk Sac • Develops 8 to 9 days after conception • Essential for transfer of nutrients during second and third weeks of gestation • Hematopoiesis • Atrophies and is incorporated into umbilical cord

  24. Umbilical Cord • Usual location—center of placenta • 55 cm long (21 in); 1 to 2 cm diameter • Vessels: one vein, two arteries • Wharton’s Jelly: protects umbilical cord from compression

  25. Fetal Circulation • Heart begins to beat and circulate blood by end of third week • Umbilical vein: blood from placenta to fetus • Low Po2 important to maintain fetal circulation

  26. Fetal Circulation • Fetus derives oxygen and excretes carbon dioxide from oxygen exchange in the placenta, NOT lungs • Specialized structures in fetus shunt blood flow away from non-functioning lungs to supply important organs of the body, especially the brain • Foramen ovale (right to left atrium) • Ductus arteriosus (pulmonary artery to aorta) • Ductus venosus (umbilical vein to inferior vena cava, bypassing liver)

  27. Critical Thinking • During a prenatal examination, an adolescent client asks, "How does my baby get air?" The nurse would give correct information by saying: A) "The fetus is able to obtain sufficient oxygen due to the fact that your hemoglobin concentration is 50% greater during pregnancy." • B) "The lungs of the fetus carry out respiratory gas exchange in utero similar to what an adult experiences." • C) "The placenta assumes the function of the fetal lungs by supplying oxygen and allowing the excretion of carbon dioxide into your bloodstream."

  28. Fetal Membranes and Amniotic Fluid

  29. Embryonic Membranes • Early protective structures • Two separate membranes • Amnion—inner membrane, contains amniotic fluid • Chorion—outer membrane, forms fetal portion of placenta • Slightly adherent, form amniotic sac

  30. Purposes of Amniotic Fluid • Protects and cushions fetus • Maintains normal body temperature • Symmetrical fetal growth • Freedom of movement • Essential for normal fetal lung development

  31. Amniotic Fluid • Amount: 800 mL at 24 weeks • Fetal urine and lung secretions primary contributors • Slightly alkaline • Contains antibacterial, other protective substances

  32. Human Growth and Development

  33. Pre-Embryonic Period • First 2 weeks after conception • Rapid cellular multiplication and differentiation • Establishment of embryonic membranes and primary germ layers

  34. Embryonic Period • Begins third week after fertilization through end of eighth week • Organogenetic period: formation, differentiation of all organs • Germ layers: ectoderm, endoderm, mesoderm • Vulnerable to environmental insults

  35. Fetal Development

  36. Fetal Period • Beginning ninth week until birth or termination of pregnancy • Rapid body growth and differentiation of tissues, organs, and systems • Less vulnerable stage

  37. Weeks 17 to 20 • Growth slows • Quickening • Vernix caseosa • Lanugo • By 20 weeks—fetus 300 g and 19 cm (7.3 in)

  38. Weeks 21 to 25 • Gains weight • Skin pink • Rapid eye movements • Surfactant by 24 weeks

  39. Weeks 26 to 29 • If born, fetus may survive • Weeks 30 to 40 • Strong hand grasp reflex • Orientation to light • 38 to 40 weeks: 3000–3800 g and 45–50 cm (17.3–19.2 in)

  40. Nurse’s Role in Prenatal Evaluation • Initial prenatal visit • Assessment: cultural, emotional, physical, and physiological factors • Education • Genetic disorders • Prenatal tests

  41. Nursing Responsibilities • Assess for signs and symptoms of genetic disorders • Offer support • Assist in value clarification • Educate on procedures and tests

  42. Maternal Age and Chromosomes • Age 35 and above • Increased risk of chromosomal abnormalities • Down syndrome • Deletion • Translocation

  43. Multifetal Pregnancy • Monozygotic • Develop from one zygote • Division occurs at end of first week • Dizygotic • Develop from two zygotes • Separate amnions and chorions

  44. Identical Twins 1 Ovum Fraternal Twins 2 Ova

  45. Minimizing Threats to Embryo/Fetus • Nurse’s role • Assessment • Environmental and lifestyle risks • Knowledge • Physical and psychosocial well-being • Preconception counseling

  46. Chapter 8 Physiological and Psychosocial Changes During Pregnancy

  47. Hormonal Influences • Pituitary hormones • Influence ovarian follicular development • Prompt ovulation • Stimulate uterine lining • Corpus luteum • Estrogen: growth • Progesterone: maintenance

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