Test 1 Study Guide Chapter 3 The First Nine Months o Some of the most rapid and dramatic developments in the human lifespan occur in the o Gestation the period from conception to birth takes about 280 days counting the first nine months mother s last menstrual period o Three main stages Zygote first 2 weeks Development of a new human being starts when a male s sperm pierces the membrane of a woman s ovum or egg After puberty a woman experiences ovulation every 28 days an egg is released During puberty a male s body begins to produce an average of 2 million sperm every day After one sperm penetrates an ovum the egg develops a protective coating to shut out other sperm o winner take all competition natural selection that eliminates weak or damaged sperm o Fertilization is most likely to occur if a man and woman have intercourse on or a few days before ovulation Development begins almost instantaneously when conception occurs o Within hours the sperm and egg combine to form a zygote 23 chromosomes from the mother and 23 chromosomes from the father combine to create a genotype the unique genetic makeup of an individual Development of the phenotype physical characteristics has only just begun As the zygote travels toward the uterus the original cell divides and multiplies By the end of the first week differentiation has begun o The original stem cells begin to assume specialized roles o The zygotes outer cells will become a support system including the placenta which provides food and oxygen to the developing child and carries away waste products via the umbilical cord o The inner cells will become the embryo During the second week implantation occurs o The zygote embeds itself into the uterine wall which is nutrient rich AKA endometrium o When implantation is successful the pregnancy has begun Infertility and Reproductive Technology o Every year around 2 million couples seek help for infertility the failure to conceive a child after 12 months of sexual intercourse without birth control o The risk on infertility depends on a variety of factors Couples overall health Infections STDs Malnutrition obesity Alcohol smoking drugs Lifestyle Age Woman s fertility decreases around age 32 Man s decreases around age 35 o Infertility is not sterility permanent inability to conceive o Infertility is often treatable First step to treatment is to identify the cause Simplest treatments are giving a woman hormone based fertility drugs to stimulate ovulation or performing surgery to repair a damaged part of the man or woman s reproductive system Most common treatment for male infertility is artificial insemination inserting sperm directly into the woman s uterus with a syringe More advance technology is available for couples with complex problems Best known and most common is in vitro fertilization IVF where the woman first takes fertility drugs and then her ova and a male s sperm are combined in a petri dish and eventually implanted back into her uterus Prenatal adoption enables a couple to experience pregnancy and birth even though the developing child may not share their genes o Couples usually use their own gametes A surrogate mother gestational carrier may be arranged for if a woman cannot sustain a pregnancy o Reproductive technology does not increase the danger of birth defects Main risk is a multiple pregnancy which is linked to pregnancy complications premature birth low birth weight and infant death Another risk is the failure of IVF to succeed leading to psychological stress repeated cycles of hope and disappointment Embryo weeks 3 8 Begins about 2 weeks after conception when the zygote is firmly connected to the uterine wall Embryo s cells have formed specialized layers o Ectoderm outer layer which will become skin nerves and sense organs o Mesoderm middle layer which will become muscle bones and the circulatory system and some organs Fetus weeks 8 40 connected o Endoderm inner layer which will become the digestive system lungs urinary tract and glands Amniotic sac is a protective membrane filled with warm liquid that cushions the tiny embryo During the next 6 weeks the basic structure for a human being appears and organs begin to function The first visible development is the appearance of the primitive streak a thin line down the center of the embryo that will become the CNS o A portion of the ectoderm folds over to form a neural tube the beginning of the spinal cord o At 3 5 weeks the brain starts to develop at the top of the neural tube o Neurogenesis the production of neurons or nerve cells begins Almost all of the neurons in the human brain are generated during prenatal development An average of 250 000 neurons must be generated each minute although the rate is not constant over the 9 month period 2 months after conception the embryo is about one inch long and weighs just 0 04 ounces about one gram but all of the major organs and body parts have formed Organs muscles and the nervous system become more organized and Over the next 7 months the size of the fetus increases twentyfold The Brain and Behavior o Brain development accelerates and nuerogenesis is nearly complete by the end of the 6th month o Key point is that the CNS becomes active and responsive in midpregnancy o The 4th month is the time of quickening the first fetal movements the mother can feel o Development of brain and behavior is bidirectional Genetically determines brain development permits new behavior and interactions with the environment that shapes further brain development o Fetal development becomes increasingly organized At 3 months the fetus swallows urinates kicks curls its toes blinks hiccups and occasionally yawns At 6 months fetuses have been observed breathing and crying brain waves show distinct patterns of waking and sleeping states The fetus heart rate is ties to its body movement which tells that the fetus is tuning into its environment At 7 8 months the fetus is less active and more vigorous Quarters are cramped Brain can now inhibit and initiate activity Responds to sounds and vibrations As the brain develops fetuses are capable of simple learning Start to recognize familiar sounds and rhythms Research shows only that the fetuses recognize repeated familiar sounds o Learning o Individual Differences Already apparent in the fetal period Children with higher heart rate variability in the womb are more advanced in language and in play Also developed motor skills earlier explored more and were more upset