1. CHAPTER 4 PRENATAL DEVELOPMENT Section 1- The Developing Baby

2. THE FEMALE REPRODUCTIVE SYSTEM

3. THE MALE REPRODUCTIVE SYSTEM

4. WHEN CAN CONCEPTION OCCUR?

5. CONCEPTION About once every 28 days, an ovum - an egg cell- is released by one of a woman’s two ovaries. This occurs as part of a woman’s menstrual cycle and is called ovulation. At the same time, a woman’s body of releases specific hormones. These prepare the uterus in the event that the ovum is fertilized. The uterus is the organ in a woman’s body in which a baby develops during pregnancy. It is a pear-shaped muscle able to expand during pregnancy. During ovulation, the inner lining of the uterus grows and thickens. If the over me is not fertilized, aligning breaks down and passes out of the body. This is the bleeding that women experience as a menstrual period.

6. CONCEPTION (CONTINUED…) When an ovum is released from ovary, it moves through the Fallopian tube, which connects the ovary to the uterus. The journey from the ovary to the uterus takes about two or three days. When the ovum reaches the uterus, it usually disintegrates and leaves the body with the menstrual flow. When a sperm, or male cell, reaches the Fallopian tube, it may penetrate and fertilize the ovum. This process is called conception. Pregnancy begins at that time. An ovum usually lives 12 to 24 hours, while a sperm is capable of fertilizing along for approximately 48 to 72 hours. During a woman’s menstrual cycle, there are approximately three or four days during which intercourse could lead to conception.

7. CONCEPTION (CONTINUED…)

8. THE GERMINAL STAGE The baby’s development during pregnancy is called prenatal development. It is often grouped into three stages called the germinal stage, embryonic stage, and fetal stage. The germinal stage is the first stage in a baby’s development. It includes the formation of the as the zygote, or fertilized egg. This stage lasts only about two weeks, but includes the key steps in establishing a pregnancy.

9. THE GERMINAL STAGE (CONTINUED…) Cell division. While the zygote is still in the Fallopian tube, it begins to grow by cell division. This single cell splits into two cells, then the two cells rapidly multiply to four, then to eight, and so on. After about four days of growth and slow movement, the zygote reaches the opening to the uterus. Implantation. By this time, the lining of the uterus has thickened enough to provide a place for the zygote to attach itself and continue to grow. The zygote usually implants in the lining of the uterus and is covered by that lining. Despite the rapid growth of the zygote during the two weeks after fertilization, is only the size of the head of a pin.

10. THE EMBRYONIC STAGE The second stage of pregnancy is the embryonic stage. The embryo is what the developing baby is called from about the third week of pregnancy through the eighth week. During this time, the embryo grows rapidly. It is also during this stage that several important and amazing changes occur. Organs and body systems. First, the cells begin to separate and develop into major systems of the human body- heart and lungs, bones and muscles. These internal organs and their systems are not ready to function yet, however. They continued to develop throughout the pregnancy. Approximately 27 days after conception, the neural tube, a tube in the back of the developing baby that will become the brain and spinal cord, has closed. At this point, the brain systems begin to take control of the various body systems.

12. THE EMBRYONIC STAGE (CONTINUED…) Organs and body systems (continued…). By about the sixth the week after conception, the connections between the brain and the spine allow the first movements of the embryo. The developing brain is sensitive to damage from any drugs or alcohol the mother might take, especially at this crucial stage. It is vital that a pregnant woman avoid these substances throughout her pregnancy. Amniotic sac. Second, a sac filled with fluid forms around the embryo. This amniotic fluid protects the developing baby. (At the peak of pregnancy there is approximately 1 quart of amniotic fluid in the amniotic this point in development, the embryo is still verysac). The amniotic sac is formed from special layers of cells in the uterus. It cushions the embryo from any bumps or falls that the mother might have. At small (about 1 inch or 2.5 cm long) and can float freely in the in the amniotic fluid.

13. THE EMBRYONIC STAGE (CONTINUED…) The placenta and umbilical cord. Third, a tissue called the placenta develops. The placenta is also formed from special layers of cells in the uterus. It is rich in blood vessels and attached to the wall of the uterus. The mother’s bloodstream carries food and oxygen to the placenta. The placenta’s job is to absorb oxygen and nourishment from the mother’s blood to be transmitted to the baby through the umbilical cord, which connects the baby to the placenta. In addition, the umbilical cord takes carbon dioxide and other waste products away from the baby and to the placenta, which releases those wastes into the mother’s bloodstream.

14. THE EMBRYONIC STAGE (CONTINUED…) The umbilical cord is usually stiff and firm, like a garden hose filled with water. It is generally not flexible enough to loop around the fetus, although this may occur in rare cases. The placenta and umbilical cord provide everything a baby needs until birth.

15. THE FETAL STAGE The third and final stage of development, the fetal stage, is also the longest time. It begins around the eighth or ninth week of pregnancy and lasts until birth. During this stage, the developing baby is called a fetus. At this time, the buds for all 20 “baby” teeth appear. The vocal cords develop, and the digestive system and kidneys begin to function. By the end of the third month, spontaneous movements are possible. Making movements. Sometime during the fourth or fifth month, the kicks and other movements of the fetus touch the wall of the uterus. These movements are faint and infrequent at first. These are usually the first fetal movements that the mother can feel. She may feel her baby’s movement as a kind of fluttering, like a butterfly. Gradually, these sensations become stronger and more frequent, telling the mother that she is indeed carrying the a live child within her.

16. THE FETAL STAGE (CONTINUED…) A pregnant woman’s doctor usually asks her when she first felt these movements. This information helps the doctor estimate the baby’s age and makes sure the baby is developing normally. This information can also be used to help project an accurate due date. Completing development. During the last few months of pregnancy, development continues, preparing the fetus to live independently. By the seventh month, the baby is capable of living outside of the uterus, but not without a great deal of medical help. The body’s major organs become ready to function without any help from the mother’s body. The fetus also gains weight rapidly. Fat deposits, which will help the baby maintain body heat after delivery, are formed under the skin. The fetus, which had been thin and wrinkled, takes on a smoother, rounder appearance of a baby. During this time, the fetus also stores nutrients and builds immunity to diseases and infections.

17. THE FETAL STAGE (CONTINUED…) Staying active. The fetus can do a surprising number of things- suck its thumb, cough, sneeze, yawn, kick and hiccup. A fetus can even cry. Even though the uterus is crowded, the fetus is still very active and change positions. Growing bigger. As the fetus grown, so does the amount of surrounding amniotic fluid. The uterus also expands, causing the woman’s abdomen to grow. When the fetus grows large during the last few months of pregnancy, it no longer has room to stretch out. It curls up inside the uterus in what is called the fetal position.

19. PREPARING FOR BIRTH The common length of pregnancy is about 40 weeks or 280 days, from the first day of the last menstrual cycle. By this time, the fetus is fully developed and can usually survive outside the mother’s body without a great deal of medical assistance. Some babies are born either a few weeks early or a few weeks late. This is generally not a problem.

20. PHYSICAL CHANGES FOR THE MOTHER Toward the end of the 40 weeks, the baby’s weight seems to shift downward, and most mothers feel more comfortable in their upper abdomen. This shift is called lightening. Sometimes there is a visible change in the shape of the mother’s abdomen, giving signs that the baby has dropped into the birth canal- the channel through which the baby passes during birth. In the majority of births, the fetus is usually upside down at this point, with the head nestled in the mother’s pelvis. This is the easiest and safest position for birth because the baby’s head is the largest part of the body. If the head can be expelled from the mother’s body easily, the rest of the body usually delivers easily as well. The baby is generally less active because there is very little space to move.

21. PHYSICAL CHANGES FOR THE MOTHER (CONTINUED…) In some cases, the fetus does not turn to the head-down position in the last few weeks. Instead, the fetus is in a seat-down or a feet down position in the mother’s pelvis. This is called a “breech presentation”.

22. PHYSICAL CHANGES FOR THE MOTHER (CONTINUED…) In many of these instances, a doctor uses a surgical procedure called a cesarean section to deliver the baby.

23. PHYSICAL CHANGES FOR THE MOTHER (CONTINUED…) The skin of the mother’s abdomen appears stretched to capacity. The muscles of the uterus and abdomen can be stretched to many times their original capacity during pregnancy. At the end of the pregnancy, the muscles of the uterus contract to expel the baby during delivery. The mother’s abdominal and uterine muscles generally return to near- normal sizes approximately six weeks after delivery.

24. SECTION 4-1 REVIEW 1)What cells join together to cause conception? 2)What happens during the germinal stage? How long does this stage last? 3)What changes might a pregnant woman feel in the germinal and embryonic stages? 4)What major changes take place in the developing baby during the embryonic stage? 5)What are some characteristics of a fetus at five months’ development? 6)Why do babies born at full term have a better chance of survival than babies born a few months early? 7)When a mother feels lightening, what does this tell her about the fetus?