NOVA: LIFE'S GREATEST MIRACLE (TV)
Summary
One in this series of science documentaries. This documentary details the process of human gestation and birth. All life on earth is driven by the desire to reproduce, compelled on a genetic level by replication of DNA in many forms, including sexual reproduction. Sexual reproduction encourages variety in traits, thus ensuring the survival of a species. The average adult human male produces over one thousand sperm every second, each containing a complete copy of his genetic information to pass on to potential offspring. Sperm and eggs are produced by a process of meiosis and are loaded with chromosomes containing the essential genes, 23 from each parent for a total of 46 in every cell. These chromosomes self-replicate and pass on information to each other as cells divide, thus creating complete genetic information inside a sperm or egg. Each month, a woman’s ovaries select one of her eggs (which have all been produced at birth) to bombard with nutrients before it is ejected through the fallopian tube into the uterus. However, without sperm to fertilize the egg, it dies in a matter of hours. Attraction in any species, including humans, is at least partially chemically based, which is a catalyst for sexual activity. In males, this includes the process of ejaculation, which releases sperm into the vagina. There, many of the sperm die while others continue swimming, trying to reach the woman’s egg. First they attempt to pass through the cervix into the uterus, which blocked by a layer of mucus except around the time of ovulation. They are then brought into the fallopian tube, although the egg may not be present if the woman is not at her time of ovulation. Many sperm are chemically altered by the cilia on the edges of the fallopian tube, allowing them to pass further on. Once they reach the egg they must bypass the support cells surrounding it, as well as the protein membrane surrounding the egg’s outer surface, called the “zona.” They accomplish this by interlocking proteins from the sperm’s outer shell with similar proteins on the zona. The sperm then releases enzymes allowing it to burrow through the zona and into the egg. The membranes of both egg and sperm fuse as it is finally drawn inside. The documentary follows a married couple, Melinda Tate Iruegas and Sergio Iruegas, expecting their first child, and they discuss the traits they hope to pass on, as well as their initial reactions to Melinda’s pregnancy. Although the sperm and egg have fused, only about half of all eggs fertilize properly, thus not ensuring success. Once the egg receives the sperm the zona prevents other sperm from entering, and the sperm releases its chromosomes into the egg to begin the process of meiosis. The cell begins to divide 24 hours after the sperm enters; all the while the egg travels down the fallopian tube as it continues to divide every few hours. Rarely, the cell cluster splits into two groups and creates identical twins. Once the cell has divided into a few hundred cells, it becomes a blastocyst, and breaks out of the zona in order to latch onto the walls of the mother’s uterus in order to derive nutrients. It produces chemicals to suppress the immune system inside the uterus so it will not be attacked as a foreign body before it burrows into the lining of the uterus, which can have an effect on the mother’s health, commonly known as “morning sickness.” Two weeks after conception, the cells begin to organize themselves into an embryo in a process called gastrulation. The cells begin to layer themselves, which eventually become specialized into different organs and tissues in the embryo. The cells continue to grow and coalesce in the coming days, forming recognizable human structures. Each parent’s DNA contains “instructions” as to what kinds of cells to form in an embryo via proteins, dependent upon which genes are active in which cells. Cells “communicate” on a molecular level via chemical releases, which ensures that the correct cells are appropriated and “activated” at the proper parts of the body, thus building correct proteins and determining traits, such as the gender of the baby. In the early development of the embryo, gender is not yet determined; a slight chromosomal activation determines gender. One gene, SRY, activates proteins that allow the embryo to produce or suppress testosterone for the determination of gender. The embryo continues to take form in the coming weeks, until it is two months old, when it becomes a fetus. It will grow four hundred times larger in the months to come, requiring constant nutrients from its mother. The Iruegases discuss how Melinda’s sense of smell and appetite heightened during her pregnancy, and she became particular about what she ate. The mother’s blood supplies nutrients to the placenta, which uses its villae to extract oxygen from the mother’s blood cells to supply to the fetus. Some organs in the fetus are functional immediately, while others do not activate until a late stage in the pregnancy. The fetus cannot see or hear until the fifth or sixth month of pregnancy. The fetus grows during the last trimester, and the brain begins to produce myelin, which allows for faster nerve activity. Eventually the fetus becomes too large to remain in the uterus, and the mother engages in the arduous task of giving birth to the child after it reaches nine months in growth. The cervix opens as the uterus contracts, widening to accommodate the baby’s head. Sometimes the opening is not wide enough and the baby must be born via caesarian-section, although this is a relatively recent development, and infant mortality rates were far higher in the past. Melinda gives birth successfully to a baby boy.
Details
- NETWORK: PBS
- DATE: November 20, 2001 8:00 PM
- RUNNING TIME: N/A
- COLOR/B&W: Color
- CATALOG ID: B:75402
- GENRE: Public affairs/documentaries
- SUBJECT HEADING: Public affairs/documentaries
- SERIES RUN: PBS - TV series, 1974-
- COMMERCIALS: N/A
CREDITS
- Bo G. Erickson … Executive Producer
- Paula S. Apsell … Executive Producer
- Melanie Wallace … Senior Producer
- Lisa D'Angelo … Supervising Producer
- Julia Cort … Producer, Writer
- Nathan Gunner … Associate Producer
- Bradley Smith … Animation
- Ethan Herberman … Researcher
- Ray Loring … Music by
- Mason Daring … Theme Music by
- Martin Brody … Theme Music by
- Michael Whalen … Theme Music by
- John Lithgow … Narrator
- Melinda Tate Iruegas … Interviewee
- Sergio Iruegas … Interviewee
- Lea Boysen … Cast
- Henrik Dahl … Cast