LESSON 2 PRENATAL.pdf

Introduction to Human Development LESSON 2 “PRENATAL DEVELOPMENT ” By Nurul Husna  Mechanisms of Heredity: Chromosomes 1. Mechanisms of heredity:  Human eggs contain 23 chromosomes selected from the mother’s 46  Human sperm contain 23 chromosomes sele...

Introduction to Human Development LESSON 2 “PRENATAL DEVELOPMENT ” By Nurul Husna  Mechanisms of Heredity: Chromosomes 1. Mechanisms of heredity:  Human eggs contain 23 chromosomes selected from the mother’s 46  Human sperm contain 23 chromosomes selected from the father’s 46  Think of it as mixing two hands of cards (1 from mother and 1 from father), shuffling this mix, and then dealing a hand of cards  The dealt hand is your 23 pairs of chromosomes  Mechanisms of Heredity: Egg and Sperm United 1. The human egg and sperm unite, resulting in a zygote that contains a complete set of 23 paired chromosomes (46 in total) 2. The 46 chromosomes contain around 25,000 genes 3. Sex chromosomes: 23rd pair determines the child’s sex  Mechanisms of Heredity: Sex Chromosomes 1. Sex chromosomes (23rd pair)  Males: XY chromosomes  X from mother and Y from father  Females: XX chromosomes  X from mother and X from father  Two Types of Genetic Disorders 1. Inherited disorders: genetic problem  Example: Huntington’s disease (brain disorder that caused uncontrolled movement, emotional problem and loss of thinking ability) 2. Abnormal chromosomes: extra, missing, or damaged chromosomes that result in abnormal development  Examples: Down syndrome  Behavioral Genetics: Mechanisms and Methods 1. Dizygotic or fraternal twins: result from two different eggs fertilized by two different sperm  No more genetically similar than other siblings 2. Monozygotic or identical twins: result from the union of one egg and one sperm that splits in two soon after conception  Are genetically identical PRENATAL DEVELOPMENT  Periods of Prenatal Development 1. Prenatal development takes an average of 38 weeks  Time measured from date of conception  Usually occurs about two weeks after woman’s last menstrual period 2. Divided into three periods:  Period of the zygote (weeks 1-2)  Period of the embryo (weeks 3-8)  Period of the fetus (weeks 9-38)  Periods of Prenatal Development: The Zygote 1. Period of the zygote (weeks 1-2):  After fertilization, the zygote travels down the fallopian tube and is implanted in the uterine wall  Implantation triggers hormonal changes to prevent menstruation  Other cells form the placenta, which supports the baby’s development Events of the Period of the Zygote  Periods of Prenatal Development: The Embryo 2. Period of the embryo (weeks 3-8):  Body structures, internal organs, and the three layers of the embryo develop:  Ectoderm (outer layer: becomes hair, skin, nervous system)  Mesoderm (middle layer: becomes muscles, bones, circulatory system)  Endoderm (inner layer: becomes digestive system and lungs)  The amniotic sac fills with fluid; the umbilical cord connects the embryo to the placenta  The umbilical cord’s blood vessels join the placenta to the embryo  Allow exchange of nutrients, oxygen, vitamins, and waste products between mother and embryo  Periods of Prenatal Development: The Fetus 3. Period of the fetus (weeks 9-38):  Begins at week 9 and ends at birth  Fetus becomes much larger and bodily systems begin to function  Final development of many systems essential to human life occurs  All regions of the brain grow, particularly the cerebral cortex  Week 9: differentiation of the ovaries and testes  Week 12: circulatory system begins to function  Week 16: movements felt by mother  Week 20: eyebrow, eyelashes, scalp hair  Skin thickens and is covered by protective greasy substance (vernix)  Weeks 22-28: age of viability (can survive)  Weeks 22 and beyond: senses active; fetus can remember voices, music, tastes ENVIRONMENTAL INFLUENCES ON PRENATAL DEVELOPMENT The developing fetus is subject to many environmental hazards:  Nutrition|Stress|Age of parents  Teratogens  Environmental hazards  General Risk Factors 1. Nutrition  A pregnant woman should increase both her caloric and nutrient intake 2. Stress  Causes greater harm when experienced early in pregnancy 3. Mother’s age  Prenatal development is most likely to proceed normally when women are between 20 and 35 years of age  Teratogens: Drugs and Diseases  Teratogens: drugs, diseases, or environmental hazards causing abnormal prenatal development  Drugs (Examples: alcohol, aspirin, caffeine, and nicotine)  Nicotine use increases likelihood of miscarriage, low birth weight, birth defects  Diseases (Examples: AIDS, genital herpes, rubella (German measles), syphilis)  Some (rubella, syphilis) attack the fetus directly through the placenta; others (AIDS, genital herpes) attack the fetus during birth  Medications that may help treat a woman after she becomes ill do not prevent damage to the fetus  Teratogens: Environmental Hazards  Environmental Hazards (Examples: air pollution, X rays)  Exposing the fetus to environmental hazards such as polluted air can affect both physical and mental development of the fetus before birth and of the child after birth  Can also lead to the child’s developing health issues such as leukemia after birth