The Beginning of the Life Cycle Did you know that your body is made of trillions of cells? Your heart, lungs, skin, bones, and other body organs all began as a single cell that is smaller than the period at the end of this sentence.

In this lesson, you will learn to: Lesson Objectives In this lesson, you will learn to: Identify the stages of fetal development from conception through pregnancy and birth Explain how a pregnant female transfers nutrients and other substances to her fetus

Conception and Implantation Fertilization The entire complex human body begins as one microscopic cell that is formed by fertilization. The resulting cell is called a zygote. Within a day after the zygote forms, it begins dividing as it travels down the fallopian tube.

Conception and Implantation By the time it reaches the uterus, the zygote has divided many times to form a cluster of cells. After implantation of the zygote, the cluster of cells is known as an embryo. Click image to view movie.

Conception and Implantation Embryo Click image to view movie.

Structures Formed During Embryonic Growth As the embryo grows, its cells continue to divide, forming three tissue layers that later become various body systems. During this time, two important structures form outside the embryo: Amniotic sac Umbilical cord

Substances Passed to the Embryo Embryonic Growth Substances Passed to the Embryo Although the blood supply of the mother and the developing embryo are kept separate, materials diffuse from one blood supply to the other through the umbilical cord. Nutrients and oxygen pass from the mother’s blood to the embryo, and wastes from the embryo diffuse into the mother’s blood. If a pregnant female uses harmful substances, they can cross the placenta and harm the developing embryo.

Trimesters Fetal Development The time from conception to birth is usually about nine full months. These nine months are divided into three 3-month periods called trimesters. During the period of growth in the uterus, the fetus develops in preparation for living outside the mother’s body.

First Trimester – 0-14 Weeks Fetal Development First Trimester – 0-14 Weeks In the first trimester, the fetus develops a human profile. By week 12 the fetus makes crying motions but no sound and may suck its thumb.

Second Trimester – 15-28 Weeks Fetal Development Second Trimester – 15-28 Weeks In the second trimester, the fetus can hear conversations and has a regular cycle of waking and sleeping. Weight increases rapidly.

Third Trimester – 29 Weeks to Birth Fetal Development Third Trimester – 29 Weeks to Birth In the third trimester, the fetus uses all five senses and begins to pass water from the bladder.

Changes Experienced During Labor Stages of Birth Changes Experienced During Labor Many females experience weak, irregular muscular contractions of the uterus for weeks or even months before the baby is born. As the time approaches for the baby to be born, however, these contractions become regular, stronger, and closer together. The stronger contractions induce labor.

Stage 2: Passage through birth canal Stages of Birth Stages of Labor Stage 1: Dilation Stage 2: Passage through birth canal Stage 3: Afterbirth

Quick Review Choose the appropriate option. Q. The union of a male sperm cell and a female egg cell is called _________. zygote implantation fertilization labor

A. 3. fertilization Quick Review - Answer The union of a male sperm cell and a female egg cell is called fertilization. Click Next to attempt another question.

Quick Review Choose the appropriate option. Q. The zygote attaches to the uterine wall in the process called _________. labor implantation fertilization cell division

A. 2. implantation Quick Review - Answer The zygote attaches to the uterine wall in the process called implantation. Click Next to attempt another question.

Quick Review Choose the appropriate option. Q. In a developing fetus, nutrients from the mother pass to the fetus through the blood in the umbilical cord. True False

Quick Review - Answer A. True. In a developing fetus, nutrients from the mother pass to the fetus through the blood in the umbilical cord. Click Next to attempt another question.

Quick Review Choose the appropriate option. Q. Harmful substances taken in by a pregnant female can be transferred to a developing fetus, but the fetus is too small to be affected negatively. True False

Quick Review - Answer A. False. Harmful substances taken in by a pregnant female can be transferred to a developing fetus, and the fetus can be affected negatively. Click Next to attempt another question.

End of Lesson 1 Click Home to view the Main menu.

Quick Review - Answer A. Correct! The union of a male sperm cell and a female egg cell is called fertilization. Click Next to attempt another question.

Quick Review - Answer You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

Quick Review - Answer A. Correct! The zygote attaches to the uterine wall in the process called implantation. Click Next to attempt another question.

Quick Review - Answer You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

Stage 2: Passage through birth canal Stages of Birth Stages of Labor Stage 1: Dilation Stage 2: Passage through birth canal Stage 3: Afterbirth

Stage 2: Passage through birth canal Stages of Birth Stages of Labor Stage 1: Dilation Stage 2: Passage through birth canal Stage 3: Afterbirth

Conception and Implantation Fertilization The entire complex human body begins as one microscopic cell that is formed by fertilization. The resulting cell is called a zygote. Within a day after the zygote forms, it begins dividing as it travels down the fallopian tube. Fertilization is the union of a male sperm cell and a female egg cell.

Conception and Implantation By the time it reaches the uterus, the zygote has divided many times to form a cluster of cells. After implantation of the zygote, the cluster of cells is known as an embryo. Implantation is the attachment of zygote to the uterine wall. Click image to view movie.

Conception and Implantation By the time it reaches the uterus, the zygote has divided many times to form a cluster of cells. After implantation of the zygote, the cluster of cells is known as an embryo. Embryo is the developing child from the time of implantation until about the eight week of development. Click image to view movie.

Structures Formed During Embryonic Growth The amniotic sac is a thin, fluid-filled membrane that surrounds and protects the developing embryo. As the embryo grows, its cells continue to divide, forming three tissue layers that later become various body systems. During this time, two important structures form outside the embryo: Amniotic sac Umbilical cord

Structures Formed During Embryonic Growth As the embryo grows, its cells continue to divide, forming three tissue layers that later become various body systems. During this time, two important structures form outside the embryo: Amniotic sac Umbilical cord The umbilical cord is a ropelike structure that connects the embryo and the mother’s placenta.

Substances Passed to the Embryo Embryonic Growth Substances Passed to the Embryo Although the blood supply of the mother and the developing embryo are kept separate, materials diffuse from one blood supply to the other through the umbilical cord. Nutrients and oxygen pass from the mother’s blood to the embryo, and wastes from the embryo diffuse into the mother’s blood. If a pregnant female uses harmful substances, they can cross the placenta and harm the developing embryo. The placenta is a thick, blood-rich tissue that lines the walls of the uterus during pregnancy and nourishes the embryo.

Trimesters Fetal Development The time from conception to birth is usually about nine full months. These nine months are divided into three 3-month periods called trimesters. During the period of growth in the uterus, the fetus develops in preparation for living outside the mother’s body. Fetus is the developing embryo in the uterus.

Changes Experienced During Labor Stages of Birth Changes Experienced During Labor Labor is the final stage of pregnancy in which the uterus contracts and pushes the baby out of the mother’s body. Many females experience weak, irregular muscular contractions of the uterus for weeks or even months before the baby is born. As the time approaches for the baby to be born, however, these contractions become regular, stronger, and closer together. The stronger contractions induce labor.

Quick Review - Answer A. Correct! In a developing fetus, nutrients from the mother pass to the fetus through the blood in the umbilical cord. Click Next to attempt another question.

Quick Review - Answer You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.

Quick Review - Answer A. Correct! Harmful substances taken in by a pregnant female can be transferred to a developing fetus, and the fetus can be affected negatively. Click Next to attempt another question.

Quick Review - Answer You have answered the question incorrectly. Go back to try again, or click Next to view the correct answer.