HUMAN REPRODUCTION - INTRODUCTION

STD-12      UNIT-6     CHA-3

HUMAN REPRODUCTION

INTRODUCTION   

• Humans are sexually reproducing and viviparous (give birth to young ones) organisms.  The reproductive units in sexual reproduction are specialized cells called gametes (sperms in males and ova in females).  
• The union of sperm and egg cell produces a fertilized egg, or zygote, that develops by mitotic division into a new multicellular organism.  
• Man is unisexual and reveals distinct sexual dimorphism.  Male visibly differs from the female in physical standards, external genital organs and accessory sex characters.  
• The reproductive systems of human males and females are made of two types of sex organs, primary and secondary.  
• Primary sex organs are those sex organs which produce gametes.  They are also called gonads.  
• Primary sex organs or gonads of males are called testes while those of females are known as ovaries.  
• They also produce steroid hormones essential for reproduction as well as the growth and development of the entire body.  
• Sex organs, glands and ducts which do not produce gametes and hormones but are otherwise essential for sexual reproduction are known as secondary sex organs.  
• These include the prostate, seminal vesicles, vas deferens and penis in male, and the fallopian tubes, uterus, vagina and mammary glands in females.  
• Accessory or external or secondary sex characters are those external features which provide distinctiveness the two sexes. 
• The secondary or the external sex characters have no direct role in sexual reproduction.  
• Puberty is the period when primary sex organs become functional and start secreting sex hormones which bring about development of secondary sex organs and appearance of secondary sex characters.  As a result sexual maturity is attained.
• It is characterized by rapid growth.  The average age of Onset for girls is 10 to 12 years old and for boys, 12 to 14 year old
• In boys pubertal changes occur in response to testosterone and in girls in response to estrogen .

SECONDARY SEX CHARACTERS IN MALE AND FEMALE

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