In The Womb National Geographic Answer Key Pdf

[Nell Barreto]

Writtenproduced, and directed by Toby Mcdonald, the 2005 National Geographic Channel film In the Womb uses the most recent technology to provide an intricate glimpse into the prenatal world. The technologies used, which include advanced photography, computer graphics, and 4-D ultrasound imaging, help to realistically illustrate the process of development and to answer questions about the rarely seen development of a human being. The following description of the images and narrative of the film captures the major points of In the Womb, and of embryonic and fetal development, as they are seen at the outset of the twenty-first century, depicted in only 100 minutes.

In the Womb opens with a glimpse of the mature fetus moments before she is ready to emerge into the outside world. The narrator explains that at this final stage, she is equipped with all of the faculties necessary for full function outside the womb. The main focus of the film, however, is the journey leading up to these final moments, a journey that begins with just a single cell. This journey is viewed intermittently throughout the film using 3-D and 4-D ultrasound scanning techniques which show the baby moving. 4-D refers to a string of 3-D images taken in real time (time is the fourth dimension), thus creating a movie of in utero events. In addition, the process is simulated by computer imaging based on observations, giving a vivid portrayal of embryonic and fetal development.

Three weeks into gestation, In the Womb simulates the embryo folding inward and elongating as the basic body plan is determined. An actual embryo at this stage is shown and a basic spine is visible. The top of the embryo, destined to become the head and brain, is indicated; this region has already begun to generate nerve cells by the fifteenth day of the pregnancy. These nerve cells will proliferate and eventually become the brain and the central nervous system. The heart forms soon after this, and twenty-two days after conception, begins to beat. This movement is initiated by a single heart cell which begins to beat and induces the cells around it to beat to the same rhythm. Close-up filming shows this pulse as heart cells proliferate and the organ continues to form. With the formation of the heart come thin veins and early blood cells responsible for transporting oxygen and nutrients; the blood in these veins moves to the beat of the heart. During the early stages of development the heart beats relatively independently, though its function will later be carefully regulated by the brain.

By the time the embryo is four weeks old, preliminary eyes have appeared on her head. These look like dark spots on a pale landscape of surrounding tissue on which the early contours of the forehead, nose, mouth, and other parts of the mature face can be seen. In addition, arm and leg buds emerge. The narrator mentions that even though thirty days have passed since conception, the embryo is almost indistinguishable from the embryos of other mammals.

By nine weeks, the nervous system has developed dramatically and starts to allow the fetus to move. Although this movement, shown through computer simulation, is not yet connected to the brain, it promotes agility and further growth. After this point, the body will gradually come under the control of the brain. This change also has the effect of regulating heart rate, which may increase to more than 150 beats per minute before cerebral regulation.

In the Womb also notes that, as well as providing a preliminary basis for diagnosis of complications, ultrasound scans also promote the development of parental attachment to the yet-unborn child. Ultrasound is thought to enhance the relationship of the child with the parents, both in infancy and later in life. At twenty-four weeks, this relationship could begin prematurely, for it is at this point that a baby could survive outside of the womb; though still small and underdeveloped, with appropriate intensive care, she could be considered viable. The greatest complications may arise due to the premature lungs, since the lungs only fully develop near the conclusion of the pregnancy and are filled with amniotic fluid until breathing begins.

But as ordinary as it seems, creating a new human being is no simple feat.Just think of it. No matter who you are, once upon a time you looked like this.From a single cell you built a body that has one hundred trillion cells. Youmade hundreds of different kinds of tissues and dozens of organs, including abrain that allows you to do remarkable things.

This program is funded in part by the Northwestern Mutual Foundation. Somepeople already know Northwestern Mutual can help plan for your children'seducation. Are you there yet? Northwestern Mutual Financial Network.

NARRATOR: You might think all the people on this beach are just workingon their suntans. But beneath all that sunscreen, under the skin, there's afrenzy of activity. Without even thinking about it, almost all the adults hereare busy trying to reproduce. They can't help themselves. The urge to procreateis a fundamental part of life, not just for us but for all life.

Fortunately, there's sex, the method of choice for 99.9 percent of theorganisms on Earth more complex than bacteria. With sexual reproduction, twoindividuals each provide some DNA. Most animals put it into sperm or eggs. Ifthe two can get together, a new being will be created, one that's differentfrom its parents and everybody else.

It's packed with tiny tubes coiled into bundles. Stretched out they couldcover half a mile. Inside all this tubing, the average man is churning out athousand new sperm every second. That's about a hundred million new sperm everyday and more than two trillion over a lifetime. And here's the tricky part:each and every sperm is one of a kind, carrying a unique genetic package.

In almost every cell of your body you have thirty thousand or more differentgenes, spread out on very long strands of DNA called "chromosomes." Most cellshave two versions of every gene on a total of 46 chromosomes. Exactly half ofthose, 23, came from your mom, and 23 came from your dad. They come in pairswhere the partners are very similar but not quite the same. The only time theyget together is during meiosis.

Here's how it works inside a testicle that's making sperm. First, eachchromosome makes an exact copy of itself, keeping it attached at one point.They condense, creating an X-shape. Now the chromosome partners get togetherand the two, or actually four, will embrace. They cling so closely, big chunkscarrying whole bunches of genes get exchanged between the partners. The cellthen divides twice, each time pulling the pairs apart. The final result is asperm or an egg cell with 23 chromosomes, half the normal number.

All this gene shuffling means that within a single species, there can be anenormous amount of diversity. And the more diversity, the better the odds arethat someone will survive to create a new generation.

SERGIO IRUEGAS: Because here you are and this is what our little girlmight look like. I wonder if the baby will have the characteristic eyebrowsthat come from my father's side of the family. We call them the Iruegaseyebrows.

But Melinda created all her eggs when she looked like this, a fetus in hermother's womb. Within a couple of months, she created several million eggs. Andthen, the eggs began to die. At the age of 31, Melinda may only have a fewthousand left. But that's okay, because inside an ovary, as opposed to atesticle, it's quality, not quantity, that counts.

Waiting for them is the open end of the Fallopian tube, which leads to theuterus. Its tentacles capture the egg and pull it inside. The egg is sweptalong by muscular contractions of the tube, as well as the constant swaying oftiny cilia. The egg has everything it needs to start a new life, except for onething: DNA from a sperm. And it has to get it fast. If the egg is notfertilized within a few hours it will die.

With sex, there will always be pressure to meet and impress a mate. When itcomes to actually choosing a partner, there's a lot to consider. For us, itmight be somewhat more complicated than picking the one that smells best, butthere's no doubt that the process can be heavily influenced by chemistry,natural drugs that flood the brain.

When love is in the air, the body can undergo some dramatic changes. Signalsfrom the brain speed up the metabolism of glucose. As a result, bodytemperature rises, skin sweats, heartbeat and breathing get faster. In a man,hormones cue blood vessels to relax, allowing the spongy tissue in the penis tofill with blood. At the height of sexual excitement, millions of sperm aresqueezed out of storage and swept up by fluid gushing from several glands,including the prostate. The flood carries them into a fifteen-inch-long tubelooping into the abdomen and then out through the penis. It's only about ateaspoon of liquid, but it typically contains about three hundred millionsperm.

They are immediately in peril. The vagina is acidic, so the sperm must escapeor die. They start to swim, at least some of them. Even in a healthy man, 60percent of the sperm can be less than perfect. Like this one with two tails.For these guys, the journey is over.

But what about the rest? What are the chances that one tiny sperm will reachand fertilize an egg? Sperm are often portrayed as brave little warriorsforging their way through hostile terrain to conquer the egg. Nothing could befurther from the truth.

Take the sperm's first obstacle, the cervix, passageway to the uterus. Most ofthe time, it's locked shut, plugged with mucous that keeps bacteria and spermout. But for just a few days a month, around ovulation, the mucous becomeswatery and forms tiny channels that guide the sperm through.

It's the slowpokes, caught up in the cilia lining the tube, who may have abetter chance. It's probably here that chemicals in the woman's body alter thesperm's outer coating. Only those sperm that are altered can get a date withthe egg. The sperm are released gradually, over the course of a few days, so atany given time only a couple hundred sperm will move on.

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