WEBVTT

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Once inside the cervix, the sperm continue on their journey.

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Some remain here, perhaps to provide a back-up

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for those that continue on.

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The rest proceed up through the cavity of the uterus

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in search of the egg.

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Their number is noticeably reduced.

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Here from inside the uterus,

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we see the openings to the two fallopian tubes.

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The sperm swim toward them.

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One leads to the waiting egg.

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The other to an empty tube.

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Only half of the few remaining sperm

00:39:04.588 --> 00:39:10.769
will swim up the tube that holds the egg.

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The tubes are lined with millions of tiny cilia,

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the same cilia which helped draw the egg

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from the ovary toward the uterus at ovulation.

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These cilia sway constantly,

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creating a gentle downward current

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that the sperm must swim against.

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Some sperm get stuck in among the cells

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lining the walls of the tube.

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Others lose their sense of direction.

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During this part of the sperm's journey

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the layer of enzyme inhibitors, at the tips of their heads

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is slowly being worn away.

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The sperm are fully capacitated and able to fertilize

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the egg, if they ever encounter it.

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Of the two hundred million sperm that begin

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this long journey

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only about 50 ever reach the egg.

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The egg is surrounded by 2 layers of the nutritive

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cells which have nourished it on its journey

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in the fallopian tube.

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The sperm immediately release their digestive enzymes

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to break through these protective, nutritive layers

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in order the reach the egg itself.

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At best, only one will eventually enter and

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fertilize the egg.

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The joint force of their exertions starts the egg

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rolling around, like a mysterious, celestial body.

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All the while, the sperm are dissolving their way

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through the egg's outer layers.

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The first sperm to reach the egg's membrane

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is immediately drawn inside.

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This is the tail of the penetrating sperm

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seen from the surface of the egg at enormous

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magnification.

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And this is a picture from inside the egg itself.

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It has been fertilized now for only a fraction of a second.

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Here is the penetrating sperm with a circle

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around it

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from a wider perspective.

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Only this single sperm will be allowed inside the egg.

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A rapid, biochemical change took place in the

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egg's membrane.

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It is now impermeable to all other sperm.

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Once inside the sperm too undergoes a

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dramatic transformation.

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It loses its mid-piece and tail.

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The tailless head spells up almost like rising bread.

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This hole in the sperm head's covering

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is the first indication that it's about to rupture

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and release its precious genetic material.

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Here, the first strand of genes is making its way

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out of the sperm into the egg.

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The genetic material continues to spill out

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from the sperm head.

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Its tightly packed molecules contain the father's

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hereditary message.

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They almost seem to have been dispersed by

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an explosive force.

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This is an extreme close-up of the genetic material itself.

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The magnification on the television screen is over

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half a million times.

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The genetic material of the mother's egg

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and the father's sperm

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combine.

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Two cells have joined to make a single new cell.

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And within 24 hours that new cell begins to divide.

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These early cell divisions of the human embryo

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have never before been filmed.

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The fertilized egg now has 2 nuclei,

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the small indentations at the center of the cell.

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The first division of the egg is beginning.

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Now there are 2 identical cells,

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still within the same nourishing material

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of the original egg.

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No growth has occurred,

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but, rather, a distinction between cells.

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Once it has begun to divide

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the fertilized egg is called a zygote.

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Now there are 4 cells.

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The divisions happen at such an accelerated pace

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that there's little opportunity for the new cells

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to grow before they divide again.

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Now there are 8 cells.

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Each new generation of cells of the zygote is

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smaller than the one before it.

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Another division,

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and another.

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As the zygote divides, it moves along the tube

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toward the uterus.

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Now it has become a dense, compact cluster

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of many cells.

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And after 5 days it is called a blastocyst.

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It is still no bigger than the original egg.

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Its center is filled with liquid.

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Within 10 days of fertilization,

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the blastocyst implants itself firmly

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in the lining of the uterus.

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Already the mother's hormones are directing

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changes in her body

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to prepare it to support the growing embryo.

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Barely visible to the naked eye,

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the embryo will be nourished by the lining of the uterus,

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and then by the placenta.

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After 2 weeks, the embryo is elongated.

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It is barely one tenth of an inch long.

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At the top, what will become its head and brain.

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Below, at the tail, the embryo is firmly attached

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to the placenta, which will nourish it.

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At 4 weeks, the embryo has arm buds and

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is distinctly curled.

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It has the beginning of eyes.

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At 5 weeks, the nose begins to take shape.

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At 6 weeks, leg buds are apparent.

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The embryo is less than half an inch long.

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It floats inside the fluid-filled amniotic sac.

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Its spine is clearly visible.

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At 7 weeks, the embryo is three quarters of an inch long.

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It can move its hands on which there are

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clearly defined fingers.

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Its internal organs are visible.

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The eyelids are formed.

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The skull bones, rich in blood vessels,

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are growing together at an angle at the

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crown of the head.

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At 8 weeks, the fingers of the hand are

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well defined.

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And the toe joints of the feet are clearly visible.

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At about 10 weeks, the embryo is considered a fetus.

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It can move actively.

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There is a suggestion of an ear.

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It is two inches long.

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And it still has the stub of a tail.

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At 11 weeks, it is two and a half inches long.

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At 12 weeks, it is 3 inches long.

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Here-the umbilical cord-connecting the fetus

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to its food supply.

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By 14 weeks, it can bring its hands together.

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And suck its thumb.

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By 15 weeks, the sensory organs are nearly

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completely formed.

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And by 16 weeks, it is actively turning inside the mother.

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This fetus is 18 weeks old.

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It is five and a half inches long.

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And is here shown, 15 times larger than its

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actual size.

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Its mouth and lips are fully formed.

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And it has the strange nasal plugs

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whose purpose is not yet understood.

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The eyes of the fetus are closed,

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but it can see.

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(pulsing sound)

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This sound is made by the fetus as it

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breathes in the amniotic fluid

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in what is known as fetal respiration.

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It brings the fluid in through its mouth,

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and then breathes it out again.

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The umbilical cord is the fetus' link to its

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source of life, the mother.

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Here are the fetus' sex organs.

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All its important physiological systems have developed.

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But it will be at least another 8 weeks before the

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fetus has even a remote chance of surviving

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outside its mother's womb.

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Whatever signals the beginning of birth

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is till a mystery.

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But when the fetus is ready to be born,

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the uterus begins its powerful contractions.

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And the process of birth begins.

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"Pull your legs right in.

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Keep it coming.

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Take another quick breath.

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Hold it.

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Push.

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Don't stop.

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One more.

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Deep breath.

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Push....push.

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That a girl.

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Can you see this baby's head?"

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"Ok, now, stop pushing.'

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"Oh, beautiful job."

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"Here he is...

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suck out his little nose and mouth

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so he can take his nice, clean, first breath.

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Nothing's little about this baby."

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(baby cries)

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"Congratulations!"

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"Another girl!"

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(baby cries)

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"Happy birthday."