Friday, January 31, 2014

Embryo to Fetus

Few narratives compare with the startling sequence of events leading to the birth of a fully-formed human baby during a nine month time interval. Obstetricians are specialists in pregnancy and the care of women before and after birth. Their medical skills interconnect with experts in many other fields of medicine. For example, an embryologist is familiar with the formation and development of early prenatal life. In humans, the child is termed an embryo up until eight weeks. Thereafter, it is known as a fetus. The event sequence of the first few weeks of pregnancy is fascinating almost beyond imagination. The mysteries of embryology still puzzle scientists.

Several decades ago one author noted, “Nothing so puzzles embryologists as the way in which cells outfit themselves and trek about to settle different regions of the embryo.” Their puzzlement still persists, not as ignorance about what happens, but as ignorance about the how of certain prenatal phenomena. For example, as I write this post, the startling news broke that adult stem cells are capable of transforming to pluripotent stem cells (capable of forming virtually all of the 220 cell types of the human body). Surprisingly, a simple acid bath under various types of stress in the lab does the “trick” of transforming adult stem cells into any type of cell.

As development slowly proceeds during the first few weeks of pregnancy there are several astonishing events taking place in the tiny embryo. One event is the production of proteins, the building blocks from which body substance is composed. The well-known DNA molecule contains the instructions for countless protein building blocks. Many inquirers marvel with astonished wonder at the body-building processes of protein construction directed by the DNA code. More than 100,000 different proteins comprise the human body. There is, however, far more to this barely beginning story.

The earliest embryo’s pluripotent stem cells set themselves to the task. After the new cells are formed they must settle in the appropriate regions of the embryo to begin the formation of primordia, forerunners of body organs. For example, after only four weeks, the miniature heart inside the grain-of-rice-sized embryo, can be seen to pump blood through tiny arteries and veins. Other masses of cells are already forming, forerunners of nerves, muscles, and the skeleton. The complex detail of how precisely this tiny embryonic entity is assembled in order to lay the correct early foundation for birth of a fully-formed human in less than nine months is beyond our ability to describe.

Chemical triggers insure that the body assembly process goes “according to plan.” Research reveals dozens of chemical triggering events without which embryo integration would fail. The most wondrous and crucial embryonic development may be described under the banner of epigenetics, defined as heritable changes in gene activity that are not caused by changes in the DNA sequence. One example of epigenetic changes in higher forms of life such as humans is the process of cellular differentiation into the hundreds of different cell types we have mentioned in previous posts. The body’s ability to produce a fully functioning new person exceeds application of the wonders of the DNA code, marvelous as it is. Embryologists have assembled substantial knowledge of what happens. The knowledge of how the marvels occur is a source of even greater wonder. As we discover more answers to what happens, our Creator gifts scientists with slow accumulation of answers to the how questions.

When the embryo transitions to a fetus after the eighth week, sheer physical growth of the new human overtakes the complex wonder of the early, nascent physical bio-construction. Parents and their doctors may look ahead to viewing an ultrasound of the baby in which “humanity now covers the embryo’s countenance,” even though at twelve weeks the baby will be only about four inches long and weigh less than three ounces. Our wonderment and fascination at the oncoming arrival of a new human soul with the potential to achieve active consciousness soon after birth overwhelms us.

The Creator who brought the universe into existence brings new human life into existence approximately 370,000 times per day worldwide.