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33 Home Science Unit 02

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  15 Home Science - Class XI INTRODUCTION TO HUMANDEVELOPMENT   C H A P T E R 2 You know that life begins with the union of ovum and sperm. Observe Figure 2.1. Whathappens to the ovum and sperm after theirunion?The growth from a singlemicroscopically smallcellto a body abouttwo hundred billion cells is phenomenal. Thisphase is known asthepre-natal stage. Afterbirth till death all human beings pass throughvarious phases known as post-natal life. Theknowledge about pre-natal and post-natallife helps you to understand yourself and to develop parental skills.Let usbegin this chapterwiththe concept ofpre-natal development.  Fig. 2.1 Union of sperm and ovum Ovum Sperm K EY  C ONCEPTS 2.1Stages of Development -Pre-natal and Post natal2.2Growth and Development2.3Areas of Development.2.4Factors Affecting Growthand Development Do you know ! Size of ovum: one of the largest cells of the body-approximately 0.1 millimeterin diameter.Size of sperm: one of the smallest cellsof the body-approximately 0.05millimeter in diameter.  16 INTRODUCTION TO HUMAN DEVELOPMENT 2.1Stages of Development Pre-natal and Post- natal A.Pre-natal Period Observe the video presentation on the topic ‘pre-natal period’ and prepare a brief note on the changes that go on during the pre-natal period. The followingindicators can be used. ã What are the characteristic features of the pre-natal period? ã What is the significance of lunar month with regard to pregnancy?It is customary for layman to think of pregnancy in terms of nine calendar months. But scientists use, as their measuring rod, ‘lunar months’ of 28 days each. These coincide with the periods of the female menstrual cycle. The ten lunar months of the pre-natal period may be marked off into three subdivisions. They are the periodof ovum, the period of embryo and the period of foetus. The highlights of eachof these developmental periods are given below. aPeriod of ovum (conception to the end of the second week) ãPractically unchanged in ‘size’ because of the lack of outside source of  nourishment ã Rapid internal development ã Implantation in the uterine wall about 10 days after fertilization becoming aparasite. bPeriod of embryo (end of the second week to the end of the secondlunar month) ã All important external and internal features start to develop and function ã Sex organs develop well enough to distinguish the sex of the embryo ã By the end of the period, embryo measures 1 ½ to 2 inches in length andweighs about 28.350 gms ã Growth in the head region is proportionately much greater than the rest of the body ã Accessory apparatus-placenta, umbilical cord and amniotic sac-develops. cPeriod of foetus (end of the second lunar month to birth) ã External and internal features continue growth and development ã Internal organs assume nearly adult positions by the fifth lunar month ã The nerve cells present since the third week, increase rapidly in numberduring the second, third and fourth months.. ã Foetal activity begins in the second and third months. Do you know! The sex of the child isdetermined at the timeof fertilization itself andnothing can change it.  17 Home Science - Class XI Human growth processes pass through various stages. The stages in thepre-natalperiod are summarised in Table 2.1 Table 2.1 Age Span for Human Developmental Stages-Prenatal Period  Observe Table 2.2 and prepare a note on the growth of foetus during the pre - natalperiod Sl No. a.b.c. Stages of life Period of the ovumPeriod of the embryoPeriod of the foetus Age Span Conception to the end of the second week End of the second week to end of the second lunar monthEnd of the second lunar month to birth armfaceamniotic sacplacentaumbilicalcorduterine cavityuterine liningyolk sacembryoamnioticsacprimitiveplacentabrainamniotic sacplacentaumbilicalcordfingersyolk sac Period 1 month2 months3 months Growth of Foetus Embryo consisting of twolayers of cellsSize of a kidney bean,constantly moving withdistinct, slightly webbedfingers.3 inches long and weighsnearly 28.35gms with uniquefingerprints, now in place.  18 INTRODUCTION TO HUMAN DEVELOPMENT fatcervixplacentaumbilicalcorduteruseyesmouthplacentaumbilicalcorduterusuterusumbilicalcordplacentaskinlipseyes   earlegumbilical cordplacentablood vesselscervixplacentaumbilicalcorduterusskullhairplacentaumbilicalcorduterus Period 4 months5 months6 months7 months8 months9 months Growth of Foetus 5 inches long and weighs141.75gms, skeleton startshardening from cartilage tobone.More than 10 inches long,eyebrows and eyelids arenow in place.Weighs 680gm andwrinkled skin starts tosmooth outWeighs about 1.36 Kgand is more than 15 incheslong, open and close eyesand follow light.Weighs about 2.15kg,lungs are well developedMore than 19 inches longand weighs nearly 3kg now. head  Table 2.2 Stages of Pre-natal Development

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Apr 15, 2019
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