BY DR. JOSE MA. EDUARDO P. DACUDAO
AT THE STAGE that the product of conception is composed of several blastomeres, it is often referred to as an embryo. As yet, being essentially identical clones of the original zygote, blastomeres do not exhibit much diversity in relation to each other.
Thus far we have:
1. Zygote (from Greek zug?tos “joined”) – A single cell with 23 pairs of chromosomes (46 chromosomes) resulting from the joining of a sperm and an egg cell.
2. An embryo composed of several cells (blastomeres).
Succeeding stages of development are:
3. Morula (from Latin morum “mulberry”] – The embryo consists of a solid mass of about a hundred cells.
4. Blastula (from Latin and Greek blastos “bud, germ, sprout”) – A hollow sphere composed of a single layer of cells that results from the morula hollowing itself. Intercellular diversity starts blooming. Experiments in the early 1900s (by the great German zoologist Hans Spemann 1869-1941, winner of the 1935 Nobel Prize in Physiology or Medicine) indicate that the cells of the embryo at the late blastula stage are mapped or correspond to the body structures that they later form.
5. Gastrula – (from Latin and Greek gast?r “stomach”) – A sac composed of two layers of cells that in the human embryo arises from the invagination or inpouching of a portion of the blastula wall. The outer layer is called the ectoderm. The inner layer is called the endoderm. In most animal Phyla, including Phylum Chordata, the Phylum to which humans belong to, a third layer, called the mesoderm, forms between the ectoderm and the endoderm. These layers are called the primary germ layers.
From these three relatively simple germ layers arise all the complexities of the human body, including the human brain.
The endoderm forms the primitive gut, which eventually becomes the gastrointestinal tract or GIT (stomach and intestines) and its derivatives. This includes an evagination or outpouching that becomes the respiratory system (trachea, bronchi, lungs). Other derivatives include the liver, pancreas, and other organs and glands that secrete digestive juices into the GIT.
The mesoderm gives rise to most structures in between the GIT and the skin. Derivatives include the blood and blood vessels (cardiovascular system), the kidneys and reproductive glands (genitourinary tract), muscles and skeleton (musculoskeletal system), and connective tissues.
The ectoderm gives rise to the skin and the central nervous system, which is composed of the brain and the spinal cord.
The brain itself is an immensely complex system, the most complex single structure in the Universe that scientists know of. A complex system is a system composed of numerous interacting components and therefore very difficult to analyze. The brain’s components are highly complex systems by themselves.
The Universe is meant to be complex and diverse. The good theologian or the mystic might say that the world is meant to be complex (or diverse) by the Creator. He would be in complete agreement with the geneticist who would say that genetic diversity is good for a species, the ecologist who would say that biodiversity is good for an ecosystem, and the Federalist who would say that the cultural diversity fostered by Federalism is good for the country.
You the human reader, whose nature inherently bespeaks of the complexity and diversity of the Universe, should agree./PN
