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Chapter 3 Fetal Development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 1.

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Presentation on theme: "Chapter 3 Fetal Development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 1."— Presentation transcript:

1 Chapter 3 Fetal Development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 1

2 Genetics and Fertilization Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 2

3 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. 3

4 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. 4

5 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. 5

6 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 6

7 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. 7

8 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. 8

9 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. 9

10 Genes  Segment of DNA chain  Coded for inheritance  Carry instruction for dominant and recessive traits Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 10

11 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. 11

12 Recessive Genes  If each parent carries a recessive trait, there is a chance that one offspring will display that trait Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 12

13 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 13

14 Beginning of Embryonic Development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 14

15 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 15

16 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 16

17 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. 17

18 Fetal Period of Development  Lasts from the 8th week until birth  Care must still be taken to prevent harm to the developing fetus Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 18

19 Audience Response System Question 1 The placental transfer of gases, nutrients, waste materials and other substances can be increased by maternal: A.Hyperglycemia B.Hypoglycemia Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 19

20 Fetal Development Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 20

21 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. 21

22 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 22

23 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. 23

24 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. 24

25 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. 25

26 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 26

27 Placenta  Two sections  Maternal  Fetal  Permits exchange of materials carried in the bloodstream between mother and fetus Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 27

28 Placental Circulation Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 28

29 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. 29

30 Uteroplacental Blood Flow  50 mL/min at 10 weeks gestation  500 to 600 mL/min at term  Maternal and fetal circulatory systems are separate Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 30

31 Placental Functions  Protection  Nutrition  Respiration  Excretion  Hormone production Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 31

32 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. 32

33 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. 33

34 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. 34

35 Placental Hormones  Progesterone  Estrogen  Human chorionic gonadotropin (hCG)  Human placental lactogen (hPL) Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 35

36 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. 36

37 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. 37

38 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. 38

39 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 39

40 Circulation Before and After Birth Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 40

41 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. 41

42 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 42

43 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. 43

44 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 44

45 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 45

46 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 46

47 Fetal Development  Three basic developmental stages include  Zygote: conception to 2nd week  Embryo: 2nd to 8th week  Fetus: 9th week to birth Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 47

48 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. 48

49 Fetal Development (cont.)  Most critical time in fetal development is the first 8 weeks  This period is called the organogenesis period Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 49

50 Fetal Development (cont.)  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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 50

51 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 Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 51

52 Audience Response System Question 2 Which fetal circulatory shunt closes functionally within 15 hours of delivery and permanently in about 3 weeks? A.Ductus arteriosus B.Foramen ovale C.Ductus venosus Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 52

53 Review Key Points Copyright © 2012, 2008 by Saunders, an imprint of Elsevier Inc. 53


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