How You Began
by Daniel James Devine
The majority of us don’t spend too much time thinking about how we were made. After all, people are born every day. Looking at the rounded belly of new mother, perhaps we acknowledge that something amazing and magical is happening inside her; but . . . well—embryonic development isn’t exactly dinnertime conversation.
If we only knew.
For thousands of years, people have been amazed by what goes on inside a mother’s womb, but no one could ever actually see what was happening. With today’s imaging technology we can; but few have looked. Are you ready for your breath to be taken away?
On that fateful day when you took your first gulp of fresh air, people in some countries, such as South Korea, say you were already one year old, not zero. Makes perfect sense too, because birth doesn’t create a baby—it simply moves him to a new environment. A baby is perfectly alive and human all of the nine months in his mother’s womb, from the moment of fertilization. A human’s development during this time is so complex and multi-faceted that to completely describe it all would require volumes. So, we’ll content ourselves now to look only at the period of most rapid growth and radical change: The first three weeks.
This miracle begins when conditions are precisely right, allowing a sperm and egg to meet. One spermatozoon (from the father) must find and penetrate a newly released ovum
(the mother’s egg) before time runs out. Once a month a delicate ovum
descends from one of the two female ovaries and has only about 24 hours
before it begins to weaken and disintegrate. Intercourse must occur
around this time to create a pregnancy. Of some 300,000,000 sperm, only
500 or less may survive the miles-long journey into the uterus and up
one of the two fallopian tubes that hides the ready egg. [1] After
penetrating the ovum’s protective barriers, only one sperm, if any,
will be fortunate enough to burrow completely through the wall.
Thankfully only one is needed. Upon the sperm’s entrance, an electrical
reaction in the egg causes all other sperm to drop off. [2] The
winning sperm releases its genetic material, which migrates towards the
nucleus of the ovum. They meet, they bond—and information from Dad and
Mom unite in one cell. Baby.
At this stage the baby is called a zygote.
Already, it has been determined if the new person is a boy or girl,
depending on what type of sperm (Y or X) fused with the egg. Bundled
inside this zygote is all the genetic information needed to make this
one miniscule cell into an unbelievably complex adult, distinct from
any other animal and unique among billions of other humans. Humble
beginnings have we all.
Amazingly, after about 12 hours, this zygote divides itself in half without any outside help, forming into two cells—each with its own copy of the original genetic blueprint. During this time the whole package is slowly descending the remaining length of the fallopian tube towards the uterus, the mother’s cozy womb. It may take three days to reach its destination, and meanwhile the cells continue to divide every 12 hours, multiplying from two to four to eight to 16 to 32 to—well, you get the idea. Only three days old, the baby has doubled his mass 4 or 5 times. Division happens in concert: Every cell splits at the same time as the others. When the baby has grown to 16 or 32 cells he is called a morula—Latin for mulberry, a fruit the cluster of cells now resembles. At 64, he’s called a blastocyst.
Hopefully by day 4 the child, smaller than a pen point, will have safely arrived in the uterus. (If not, the embryo may have gotten stuck in the crevices of the fallopian tubes and resulted in a dangerous tubal pregnancy.) Feeling quite at home, the child is ready to make a landing. The blastocyst slips out of a transparent, confining shell, and implants itself in a suitable spot on the uterine wall. Baby and Mom finally connect. Although she doesn’t feel it quite yet, a furious exchange of chemicals and hormones alert Mom’s body to the new dependant. Since the child contains genetic information from the father, a woman’s body would normally reject and kill this alien material, as it would a transplanted organ. But a special chemical message prevents this from happening. Around this time the child’s cells begin to act differently from one another—each one somehow knowing where to go, what to become. One group of cells huddles together and prepares to become the embryo. The others form the placenta, the baby’s nutritious nest for the next nine months. The yolk sac (much different from an egg yolk) develops not to feed but to manufacture blood cells for the embryo until he can make his own. In adults, blood cells are churned out of bone marrow; the flexibility integrated into the embryo allows the liver (developed by six weeks) to take over this job until the baby’s bones are mature enough to handle mass blood production.
Attached to his mother, the baby absorbs food and oxygen through the young placenta organ at an astounding rate. The still-dividing cells are given a boost of energy and for a while the embryo begins doubling its size every day. If he continued growing at this pace, the baby would be bigger than the sun at birth. [3] The umbilical cord forms and creates a lifeline from baby to placenta. Cells in the embryo have grouped into three specialized layers: The ectoderm, the mesoderm, and the endoderm. The ectoderm is the “outer layer” and will eventually develop into such things as the brain, nerves, and skin. The “inner layer,” or endoderm, will give rise to the stomach, intestines, and even the lungs, leaving the middle mesoderm to form muscles, the skeleton, and other organs. [4] Exactly how these cells know what to become is still a scientific mystery, and a good one.
No longer content as a meandering crowd of mission-minded cells, the embryo must take on a more efficient shape to allow the rapid production of all the complex apparatus that will be needed to run a postnatal (“after birth”) body. As the cells multiply, they act not only in interest of their own destinies, but begin working together to form major body features. During their stint as a blastocyst, the cells form a sphere. As cell differentiation occurs, the embryo cell group assumes a disk shape, which rapidly thickens as the baby grows. Finally, the embryo balloons into the figure of a lumpy egg—larger at the head end. Now it’s time for reconstructive surgery. Like Swiss cheese, our bodies have plenty of holes—hollow spots, like our throat, lungs, and a tangled digestive system. So, similar to a clay jar when the potter pushes a hole down through it, the cells perform the strange process of pulling an indentation into the embryo, forming a noticeable groove. As the groove advances, cells on the gulf’s brink send out filaments which grab cells on the opposite side, as if they were stuntmen, and pull them over the chasm like a roof to enclose the groove as quickly as it came. The entire performance creates somewhat of a cave that will become the full-length digestive tract the baby will need when he is born. [5] Another groove is created and becomes the neural tube, for housing the central nervous system. This tube will manufacture the brain and spinal cord. By now the embryo’s shape has been so stretched and restructured it resembles something akin to the zigzagged Quarter Note Rest, though still miniscule in size. The army of cells continues to reproduce and sends squad after squad to a host of projects—such as development of the brain, nerves, heart, blood, veins, muscles, and skeleton. Other small cell clusters grow out of either side of the neural tube on the embryo’s back. As these formations, called somites, stack neatly in place they look like a 1.0 version of the to-be-formed spinal column. Actually, the somites are powerhouses which are assuming position to construct the body’s skeleton and major muscles. [6] There is much work yet to be done.
At this point Mom probably knows what’s going on, either from an absent menstrual period or from morning sickness. Nausea is caused by a deluge of hormonal changes that will fortify her body to nourish the new child through the placenta and umbilical cord, and later with milk. The placenta operates as an exchange organ between mother and child. It allows the mother’s blood to trade oxygen and nutrients for carbon dioxide and waste from the baby, without ever letting their blood mix together. The rejuvenated blood is pumped to the baby through the umbilical cord at high-speed rates—eventually up to 4 mph (6.4 kph). [7] In the sixteenth century, the genius Leonardo Da Vinci wrote that a human fetus did not need a beating heart since it was completely nourished by its mother. [8] Of course he was mistaken. After 21 days, two seemingly primitive muscle structures fuse. With a gentle swoosh the first half contracts, the second half expands, and a heart is born. Blood circulation is not yet complete, but veins growing like vines are rapidly branching throughout the baby, anticipating where areas of major growth will need a heavy supply of nutrient-laden blood. As if trumpeting the success of the first three weeks of creation, the heart begins beating a rhythm that will last for a lifetime.
All this in a human the size of a freckle.
Even though every embryo will become a unique individual, all grow
at the same rate. It doesn’t take nine months for one baby to fully
develop and ten months for another; they grow according to schedule.
That schedule has been carefully designed by a Creator, who isn’t
hiding his masterpieces. Like a skyscraper skillfully crafted and built
step-by-step by an architect, a human doesn’t come together by himself.
He is the art of One greater. Clay, from a Potter.
Selected Links: The Visible Embryo ~ The Multi-Dimensional Human Embryo ~ University of New South Wales Embryology
[1] Alexander Tsiaras & Barry Werth, From Conception to Birth, Doubleday, New York, 2002, pg 42.
[2] Ibid, pg 42.
[3] Ibid, pg 61.
[4] Lennart Nilsson & Lars Hamberger, A Child is Born, trans. to English by Clare James, Delacorte Press/Seymour Lawrence – Bantam Doubleday Dell Pub. Group Inc., New York, 1990, pg 77.
[5] Tsiaras & Werth, pg 62.
[6] Microsoft Encarta Encyclopedia Standard 2003, version 12.0, Vertebrate Embryos illustration, 1993-2002 Microsoft Corporation.
[7] Geraldine Lux Flanagan, The First Nine Months of Life, Simon and Schuster, New York, 1962, pg 63.
[8] Ibid., pg 8.