16.24 System: reproductive system  
     
  The organs of the reproductive system enable men and women to have children. Human beings reproduce sexually. Sexual reproduction involves the union of sex cells. A new human being begins to develop after a sex cell produced by the father unites with a sex cell produced by the mother. The father's sex cells are called sperm, and the mother's are called eggs. The union of a sperm and an egg results in fertilization. The fertilized egg has all the information necessary for the development of a new human being.  
 
 
  The male reproductive system includes two testicles, which hang between the legs in a pouch called the scrotum. The testicles are glands that produce sperm. The sperm travel through tubes to the penis, an organ in front of the scrotum. Sperm leave a man's body through the penis.  
 
 
  Most of the female reproductive system lies inside the woman's body. Deep within the body are two glands called ovaries, each of which contains about 400,000 eggs. Only about 400 eggs will mature during a woman's childbearing years. About once a month, one of the ovaries releases an egg. The egg travels down a narrow duct called the Fallopian tube. The female body has two Fallopian tubes, one leading from each ovary. The Fallopian tubes open into the top of the uterus, a hollow, muscular organ. The other end of the uterus leads to a canal called the vagina. The vagina extends to the outside of the body, opening between the legs.  
  During sexual intercourse, sperm from the penis enters the vagina. Each sperm has a tiny tail and can swim. The sperm swim from the vagina to the uterus and into the Fallopian tubes. If an egg is present in one of the tubes, a sperm may fertilize it.  
  The fertilized egg cell continues its journey to the uterus, where it becomes attached to the wall of the organ. The cell divides over and over, forming the beginning of a developing baby. Soon, a complex organ called the placenta forms. The placenta enables the developing baby to obtain food and oxygen from the mother's bloodstream.  
  After about nine months, the baby is ready to be born. Powerful contractions of the uterus push the baby out through the mother's vagina, which widens to allow the baby to pass through.  
  Let us now look at the human body sensory system.  
 

 

  
 
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