DVT - Prenatal Development Lesson

 

Prenatal Development

Prenatal development begins at conception, the joining of a single egg and sperm, and occurs in three distinct phases: zygotic, embryonic, and fetal.

Zygote

Once a sperm has penetrated an egg, the single celled organism is called a zygote, and it is about the size of a period at the end of a sentence in a textbook. The zygote's cells rapidly divide, at first replicating themselves exactly and later creating cells that form various body parts. During this rapid cell division, some of the structures that house and protect the developing fetus form, and it eventually becomes implanted in the mother's uterine wall. Less than half of all zygotes survive these first two weeks, most exiting the mother's body during her next menstrual cycle, leaving the mother unaware that an egg was ever fertilized.

Embryo

Once it is attached to the uterine wall, the zygote begins to produce hCG, the pregnancy hormone that tells the mother's body to stop producing eggs. At this point, the embryonic period begins. An amniotic sac forms and is connected to the mother through the umbilical cord, which acts as a lifeline and a filter; through it the baby receives nourishment and oxygen.

The brain, spinal cord, and circulatory system begin development in the embryonic stage, and by the fifth week, when the embryo is about the size of a sesame seed, the heart begins to beat. The nervous system, legs, arms, eyes, ears, and teeth start to take shape during this stage. Genes on the sex chromosomes trigger the development of sex organs around week five.

Fetus

At nine weeks the baby is the size of a grape, and begins the fetal stage of development, which lasts until the end of the pregnancy. As neurons in the brain and spinal cord create new connections to one another, reflexes begin. The same reflexes that doctors look for in healthy babies (the rooting, sucking, Babinski, and Moro reflexes) can all be observed in a fetus at the 12-week mark. By 15 weeks, the fetus has its own set of unique fingerprints, although the fingers are very tiny, nicely in proportion to a baby that is about the size of an apple. It can also suck its thumb and grimace by 15 weeks. By 20 weeks, when the fetus is about the size of a banana, the nerve cells that specialize in taste and smell have developed so that the fetus can use these senses. Some babies born as early as 21 weeks after conception have survived, although the likelihood of survival is low. At 25 to 27 weeks, the fetus begins to respond to sound as these nerve cells complete development. About 80% of babies born after 26 weeks will survive. At this point, the fetus begins to gain the fat necessary to maintain body temperature outside the womb. At full term birth at 40 weeks, most US babies are about 20 inches and 6.6 pounds.

Flip through the slides to see the stages of prenatal development:

Timeline of prenatal development (in weeks):

While most prenatal development takes place without interference from the mother, it is important to consider the impact a mother can have. Proper nutrition, activity levels, and rest certainly help the fetus develop normally. Avoiding possible dangers to the developing life inside is vital.

Teratogens are harmful agents that can pass through the placenta and negatively affect the child, leading to developmental delays and birth defects. Earlier exposure to a teratogen leads to more severe effects because in earlier stages of prenatal development the nervous system and organs are being developed, while in the later stages the baby is mostly growing and gaining fat.

Complete the teratogens activity below:

 

IMAGES CREATED BY GAVS OR OPENSOURCE