Module 4
1. Module 4
1.8. Lesson 2
Module 4—From Fertilization to Birth
Lesson 2—Fetal Development, Trimester Events, and Environmental Factors
Get Focused
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The process of prenatal development continues after the embryonic period. In Lesson 1, you learned how in embryonic development, an offspring progresses from a single cell to an organism of millions of cells in a period of just two months. At the beginning of the ninth week of prenatal development, the name embryo is dropped, and the developing offspring is now called a fetus. As the embryo went through morphogenesis, the bases of all of the organ systems were formed. During the fetal stage, the organ systems develop further or mature. The placenta and umbilical cord are almost completely formed by the ninth week, and will soon take over hormonal control of maintaining the pregnancy.
Even though prenatal development is divided into the embryonic and fetal development periods, the full pregnancy is divided into three trimesters—each
trimester is three-months in duration. The first trimester consists of the embryonic development period and the beginning of fetal development. The first three months are the most critical because the bases of all of the organ systems are formed during this time. The heart begins beating; blood cells flow through blood vessels; limbs are formed; genitals are now present; and the brain, sense organs, and nervous tissue are formed.
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trimester: one-third of the gestational period
There are three trimesters of pregnancy.
The second and third trimesters also have significant developmental events consisting of further system development and maturation. A timeline of some major developments follows.
End of Month 4
- The baby is developing reflexes, such as sucking and swallowing, and may begin sucking his or her thumb in utero.
- Tooth buds are developing.
- Sweat glands are forming on the baby’s palms and soles.
End of Month 5
- Hair begins to grow on the baby’s head.
- Eyebrows, eyelids, and eyelashes appear.
End of Month 6
- The baby’s skin is covered with a protective coating called vernix.
- The baby is able to hiccup.
vernix: a cheesy, oily substance covering the fetus; has antibacterial properties
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End of Month 7
- Taste buds have developed.
- Fat layers are forming.
End of Month 8
- Tremendous brain growth occurs at this time.
- The baby’s fingernails may now extend beyond the fingertips.
- Most body organs are now developed, except for the lungs.
End of Month 9
- The lungs are mature.
- The baby is now fully developed and can survive outside the mother’s body.
teratogen: a substance that can cause deformities during fetal development; can be chemicals, viruses, or radiation
Substances and circumstances can affect prenatal development at any time. However, it is during the first trimester when the developing offspring is most vulnerable to teratogens, which are substances or other factors that can alter normal development. Some examples of teratogens are cigarette smoke, alcohol, drugs, and x-rays. There are a host of others.
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In addition to harmful agents that may be transferred to the embryo and fetus, there are also substances that are essential for proper growth and development. Proper nutrition, which includes the right amounts of vitamins and minerals, is fundamental to the healthy development of the embryo and fetus. For example, sufficient amounts of Vitamin B9, also known as folate or folic acid, help prevent neural tube defects during embryonic and fetal development. One of the activities you will be asked to do in this lesson will help you understand why it is important for a woman to consume a high amount of folate in her diet before conception.
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folic acid (folate): Vitamin B9; ingestion prior to and during pregnancy prevents neural tube defects, such as spina bifida
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Case Study Update:
Although Jane and John did not have to undergo hormone therapy or other reproductive enhancement technologies discussed in Module 3, you did advise them on the significance of knowing when ovulation was taking place. Ovulation is the time when the egg is most receptive to fertilization. Jane’s urine and blood tests now indicate a high level of hCG. This high hormone level is the basis of the pregnancy test and is what confirms a pregnancy. Fertilization has thus been successful and the embryo has begun development.
In Lesson 2 you will examine the following focusing questions:
- What are the major events of each trimester?
- What is the significance of the first trimester?
- What is the significance of the effects of teratogens on embryonic and fetal development?
This lesson will take approximately 40 minutes.
Module 4: Lesson 2 Assignment
Your teacher-marked Module 4: Lesson 2 Assignment requires you to submit a response to questions regarding genetic, hormonal, and environmental factors and their effects on embryonic and fetal development.
Download a copy of the Module 4: Lesson 2 Assignment to your computer now. You will receive further instructions on how to complete this assignment later in the lesson.
You must decide what to do with the questions that are not marked by the teacher.
Remember, that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.
While you are completing this lesson, there will be many opportunities for you to acquire, understand, and practise the concepts that are presented to you. As you complete these activities, as well as your summary notes, you will file everything in your course folder to reference when you are preparing for exams.
Remember you also have the option of trying additional questions from the textbook for further practice. Consult with your teacher for the answers to these questions. The Key will also provide you with many Diploma Exam-style multiple-choice, numerical-response, and written-response questions that will be an excellent review of the module. Practising your responses to these types of questions is good preparation for the Diploma Exam.