Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Name: Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.
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Description: Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Genetics and Fertilization
Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Objectives Define key terms listed. Define a chromosome and give the number in each human body cell. Compare a gene and a chromosome. Explain how the sex of an individual is determined. Describe human fertilization and implantation. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Genetics Our genes are programmed to use deoxyribonucleic acid (DNA) DNA is the master protein controlling development and functioning of all cells Spiral shaped strands found in nucleus of all human cells Genetic codes are programmed into the new individual’s cells by DNA Single mistake or variation in sequence can effect cell(s) development Can lead to mutations/disease Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Chromosomes Threadlike, spiral structure Occur in pairs; made up of long chains of DNA One from mother, one from father Each cell contains 46 chromosomes There are 22 arranged pairs known as autosomes The remaining pair are gametes, or sex cells, which determine the sex of the developing fetus Each chromosome is composed of genes; defined as segments of DNA controlling heredity (gene single bead; chromosome strand of beads) Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Cell Division and Gametogenesis
Division of a cell begins in its nucleus Contains gene-bearing chromosomes Two types of cell division Mitosis=body cell division Meiosis=reproductive cell division Review Figure 3-1 (p. 30). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Mitosis Continuous process Body grows, develops, and dead cells are replaced Each “daughter cell” contains same number of chromosomes as parent cell 46 chromosomes in a body cell are called diploid number Process of mitosis In sperm—spermatogenesis In ovum—oogenesis Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Meiosis Reproductive cells undergo two sequential divisions Number of chromosomes is reduced by half (23) Each cell contains only one sex chromosome, called haploid Process completed in sperm before traveling toward fallopian tubes; in ovum occurs after ovulation, if fertilization occurs Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fertilization When sperm and ovum unite New cell contains 23 chromosomes from sperm and same amount from ovum Chromosome number is returned to 46 (diploid) Traits from mother and father are inherited Formation of gametes by this type of cell division is gametogenesis Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Dominant Genes Dominant overpower recessive traits and are passed on to the offspring If only one parent has dominant trait, 50% of offspring will have it too If both parents carry a recessive trait, there is a chance that one of the offspring will display that trait Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Recessive Genes If each parent carries a recessive trait, there is a chance that one offspring will display that trait Review Figure 3-2 (p. 30). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Sex Determination Determined at time of fertilization Spermatozoon (sperm cell) has either an X or Y chromosome Female ovum only contains an X chromosome XX—female XY—male The male determines the sex of the fetus See Figure 3-3 (p. 31). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Beginning of Embryonic Development

Fertilization Conception: union of egg and sperm; also known as fertilization Normally occurs in outer third of fallopian tube After a single sperm enters ovum, a membrane forms to prevent the entry of more sperm Ovum can be fertilized from 6 to 24 hours after its release from the ovary Sperm can survive up to 5 days after ejaculation Once fertilized, the nucleus of the sperm and the ovum unite to form a zygote Refer to Did You Know? – Life Expectancy of Ovum and Sperm (p. 31). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Implantation Zygote starts a series of rapid cell divisions as it travels from the fallopian tube to the uterus Over several days various stages of development continue to occur See Figure 3-4 (p. 32). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Embryonic Period Trophoblastic cells aid in the implantation process and provide nutrients to the developing embryo Embryonic development is from the 2nd to 8th week after conception At this point teratogenic agents may exert profound and damaging effects on the developing embryo Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Period of Development
Lasts from the 8th week until birth Care must still be taken to prevent harm to the developing fetus Refer to Box 3-1 (p. 32). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Audience Response System Question 1
The placental transfer of gases, nutrients, waste materials and other substances can be increased by maternal: Hyperglycemia Hypoglycemia Answer: A Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Objectives Discuss fetal development. Explain the development and function of the placenta. Review the functions of amniotic fluid and the umbilical cord. Diagram fetal circulation to circulation after birth. Discuss multifetal pregnancy, and compare two types of twins. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Embryonic Cell Differentiation
Occurs during 2nd and 3rd week after conception All tissues and organs of the embryo or fetus come from three cell layers Ectoderm Mesoderm Endoderm Review Box 3-2 (p. 32). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Membranes and Amniotic Sac
Amnion—protects developing embryo Forms a cavity in which the embryo or fetus floats Expands to accommodate growing fetus Chorion is outer membrane that encloses growing amnion Both fuse together as fetus continues to grow, becoming amniotic sac (“bag of waters”) Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Amniotic Fluid Clear and slightly straw-colored Consists of 98% water Traces of protein, glucose, fetal lanugo (hair), fetal urine, and vernix caseosa Most derived from maternal blood with fetal urine contributing to the amount of fluid in later development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Amniotic Fluid (cont.) At term can be 800 to 1000 mL Hydramnios (excessive fluid) if greater than 2000 mL Associated with malformations of CNS Oligohydramnios (not enough fluid) if less than 300 mL Typically associated with renal abnormalities Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Functions of Amniotic Fluid
Allows embryo or fetus to move about freely Prevents amnion from adhering Cushions against injury from external sources Maintains a constant temperature surrounding the embryo or fetus Provides fluid homeostasis Prevents umbilical cord compression See Box 3-3 (p. 33). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Placental Circulation
The blood of the fetus flows through the umbilical arteries into the fetal capillaries in the villi and then back to the fetal circulation through the umbilical vein. Maternal blood is transported by the uterine spiral arteries to the intervillous space, and it leaves by the uterine veins to return to the maternal circulation. Metabolic and gaseous exchange occurs as the blood flows slowly around the villi. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Placenta Formation Begins at the outer layer of the blastocyst Trophoblastic cells multiply and develop the chorionic villi Villi penetrate the lining of the uterus (decidua) Uteroplacental circulation begins around 17 days postconception Allows for the absorption of nutrients and oxygen and the excretion of wastes Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Uteroplacental Blood Flow
50 mL/min at 10 weeks gestation 500 to 600 mL/min at term Maternal and fetal circulatory systems are separate See Figure 3-6 (p. 35). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Placental Transfer Movement of gases, nutrients, waste materials, drugs, and other substances across the placenta Can be modified by maternal nutritional status, exercise, and disease Can be increased by maternal hyperglycemia Can be decreased by reduced uteroplacental blood flow Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Immunologic Functions of the Placenta
Protects fetus from pathogens Prevents rejection by the mother Allows most viruses, some bacteria, pollutants, and drugs to cross the membrane Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Placental Blood Flow Can be reduced if uterine artery is constricted (e.g., maternal hypertension) Harm can come from substances that cross the placental barrier (e.g., alcohol, nicotine, carbon monoxide, some prescription and illicit drugs) Contractions of the uterus can decrease flow; therefore, important to monitor for uterine relaxation between contractions Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Progesterone First produced by corpus luteum, then by placenta Functions during pregnancy Maintain uterine lining for implantation of zygote Reduce uterine contractions to prevent spontaneous abortion Prepare gland of breasts for lactation Stimulate testes to produce testosterone, which aids the male fetus in developing the reproductive tract Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Estrogen During pregnancy Stimulates uterine growth Increases blood flow to uterine vessels Stimulates development of breast ducts Effects not directly related to pregnancy Increased skin pigmentation (mask of pregnancy) Vascular changes in skin and mucous membranes Increased saliva production Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Umbilical Cord Lifeline between fetus and the placenta Contains Two umbilical arteries One umbilical vein Embedded in Wharton’s jelly (prevents kinking of cord and interference with circulation) Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Umbilical Blood Vessels
Before birth Umbilical arteries carry deoxygenated blood Umbilical veins carry oxygenated blood Blood flows through the umbilical arteries to the placenta Carbon dioxide and other waste products are then released Umbilical vein carries oxygen and nutrients from placenta to fetus See Memory Jogger – Umbilical Vessels (p. 35). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Circulation Before and After Birth

Embryonic Circulation
Fertilized ovum derives nutrition first from its own cytoplasmic mass Then from the decidua by activity of trophoblastic cells By 4th week after conception, embryo gains circulation and nourishment from yolk sac Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Circulation After 4th week of gestation Blood circulation through placenta to fetus is well-established Fetus does not breathe, but does have breathing movements Liver does not process most waste products Refer to Figure 3-7 (p. 36). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Circulatory Shunts
Ductus venosus: diverts some blood away from liver as it returns from placenta Foramen ovale: diverts most blood from right atrium directly to left atrium Bypasses lungs Ductus arteriosus: diverts most blood from pulmonary artery into aorta Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Circulation Before Birth
Oxygenated blood enters fetal body through umbilical vein Half goes to liver through portal sinus Remainder enters inferior vena cava (IVC) through ductus venosus Blood in IVC enters right atrium, passes directly into left atrium through foramen ovale Rest of blood from right ventricle joins blood from left ventricle through ductus arteriosus Waste products are returned to placenta through umbilical arteries Review Table 3-1 (p. 36). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Circulation After Birth
Fetal shunts not needed after birth Foramen ovale closes when pressure in right side of heart falls as lungs become more fully inflated Little resistance to blood flow Blood oxygen level rises, causes ductus arteriosus to constrict Ductus venosus closes when flow from umbilical cord stops See Table 3-2 (p. 36). Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Closure of Fetal Circulatory Shunts
Foramen ovale closes functionally within 2 hours after birth Permanently by age 3 months Ductus arteriosus closes functionally within 15 hours Permanently in about 3 weeks Ductus venosus closes functionally when cord is cut Permanently in about 1 week After permanent closures, the ductus arteriosus and ductus venosus become ligaments. Refer to Chapter 16 to review newborn congenital cardiac problems. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Development Three basic developmental stages include Zygote: conception to 2nd week Embryo: 2nd to 8th week Fetus: 9th week to birth Review Table 3-3 (pp ) in class. What factors may affect fetal development? What should the nurse encourage the mother to do to prevent neural tube defects? Answer: folic acid supplements and prenatal care. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Fetal Development (cont.)
Factors that may affect development Quality of ovum and sperm Inherited characteristics Intrauterine environment Injury by exposure to teratogenic chemicals Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Most critical time in fetal development is the first 8 weeks This period is called the organogenesis period Review Figure 3-8 (p. 38), which discusses the sensitive or critical periods in human prenatal development. How can growth of the fetus be limited? Answer: by lack of nutrients and oxygen received from the mother. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

14th week: fetal movement 20th week: fetus may survive outside uterus Age of viability 28th week: surfactant is minimal and is needed to help keep alveoli in lungs open 40th week: full-term and ready to survive outside of uterus Refer to Table 3-3 (pp ). What is the term or terms used to describe a fetus who is born past 42 weeks gestation? Answer: postterm or postmature. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Multifetal Pregnancy More than one fetus is developing at the same time Monozygotic: identical twins From one egg and one sperm Dizygotic: fraternal twins (nonidentical) From two ova and two sperm Review Figure 3-9 (p. 40). What are the terms to describe a multifetal pregnancy where there are 3, 4, or 5 fetuses developing at the same time? Answer: triplets, quadruplets, quintuplets. Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

Audience Response System Question 2
Which fetal circulatory shunt closes functionally within 15 hours of delivery and permanently in about 3 weeks? Ductus arteriosus Foramen ovale Ductus venosus Answer: A Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc.

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