The Beginning of the Life Cycle Parenthood has

The Beginning of the Life Cycle � Parenthood has many joys and satisfactions, but it is also stressful and involves a lot of hard work. � Parents must be prepared to give their child love and guidance throughout his or her life, not just as a baby. � Upon deciding to have a child, a couple may try to conceive, or get pregnant.

The Beginning of the Life Cycle � Think about Ch. 18 and the menstrual cycle. � During sexual intercourse, sperm from the man are deposited into the vagina. � Some of these sperm swim through the uterus to the fallopian tubes. � If the egg is on its way to the uterus, a sperm may fertilize it. � This moment of fertilization is called conception.

Fertilization � Only a few hundred sperm of the millions that enter the vagina usually make it to the egg, and only one can fertilize it. � Within seconds of fertilization, the surface of the egg changes so that no more sperm can enter the egg. � In the first week after fertilization, the fertilized egg undergoes many cell divisions and travels to the uterus.

The Zygote � The united egg and sperm is called a zygote. � Within 36 hours, while the zygote is still in the fallopian tube, it begins to divide.

Cell Division � The original cell divides to make two cells. � From the two-cell stage until about nine weeks after fertilization, the growing structure is called an embryo. � The two-celled embryo divides into four cells, and so on.

The Blastocyst � About five days after fertilization, the embryo reaches the uterus, where it floats free for a few days. � By this time, it is made up of about 50 -100 cells. � The structure, called a Blastocyst, is no longer a solid mass of cells, but a sphere of cells surrounding a hollow center.

Implantation � Once the blastocyst forms, it begins to attach itself to the wall of the uterus. � The process of the attachment is called implantation. � http: //www. tulsafertilitycenter. com/roadmap /conception. php