If we trace back all the ‘beginnings’ of our life, we’ll ultimately reach the point at which we were born. However, birth is not the first thing in our life. There are a million other major events that took place before we were even born, starting from when we were just a single cell. That, is the very first ‘beginning’ of our life. This article will explain the developments and events that took place in us in before our birth
First month– In the first week, the cells are arranged in two layers: an outer trophoblast and the inner cell mass. The inner cell mass is concentrated on one side of the sphere formed by the outer trophoblast, and this set up is often referred to as the ‘snow globe model’, as the outer trophoblast represents the glass, inner cell mass represents the ornament inside and the blastocoel (fluid) represents the liquid part of the snow-globe.
The inner cell mass is pluripotent, which means that they have the ability to differentiate into cells of any tissue such as muscles, brain, nervous tissues, etc.
The third week starts with the beginning of gastrulation. As we know, humans are triploblastic mammals with the three layers ectoderm, mesoderm, and endoderm. Gastrulation is the formation of these layers from the pluripotent cells.
The last event of the first month is Neurulation, which starts after gastrulation and concludes at the end of the first month. This is the process in which the neural plate converts into the neural tube. The neural crest, as seen in the picture, is sometimes considered as a fourth germ layer, as the cells differentiate to form the nervous system, bones and other connective tissues. This is an extremely sensitive process, and any minute defect may lead to significant malfunctions.
Second month- The second month covers most of the facial changes: hollow spaces for eyes, folds for ears, areas for nose and lips are created. Two bud like structures appear which ultimately develop into our hands. An interesting fact is that at this stage the embryo has a tail, which later on differentiates into our legs, while forming the tailbone or coccyx. There have been around 40 cases throughout history where the tail has not fused to form the coccyx, hence rendering the newborn with a vestigial tail.
Around the sixth month, pieces of the placenta appear and can be seen in sonographs.
The end of the second month marks the end of embryogenesis, and from now on the child is referred to as a fetus instead of embryo.
Third month– Most of the internal development takes place here. The circulatory system starts functioning as the heart has been beating since the first month itself. Erythrocytes and leucocytes flow through the blood stream. Digestive system rapidly develops and even starts secreting hormones, bile, etc. fingernails, toenails, and the basic structures of teeth under the gums are formed. The urinary system also starts functioning; the kidneys start filtering urine around the end of the month. The tail mentioned earlier disappears and in its place are two little leg like structures. The end of the third month also marks the end of the first trimester.
SECOND TRIMESTER
The fetus at this stage is often referred to as a peach, as it is now approximately the size of a peach and is covered by a layer of small soft hairs called lanugo, just like a peach.
In the fourth month, the skin changes drastically. Although the skin is almost transparent, it develops fingerprints, foldings on hands and legs for fingers and toes, eyelids, etc.
Rapid eye movement takes place, rods and cons come in place, and the beginning of the optical nerve can be seen. The fetus can detect light and move away or towards it depending on the situation. It is able to perform voluntary movement such as movement of hands and legs, scratching, and fluttering of eyelids.
The fetus receives oxygen from the placenta as even though the lungs are present, the alveoli are not. The third phase out of the five phase of lung development takes place at this stage, which is the ‘canalicular phase’, in which the surfaces for gaseous exchange is formed and vascularized.
Chromosome tests for down syndrome, color blindness and several other disorders can be performed at this stage.
THIRD TRIMESTER
The body gets covered by a layer of a waxy substance named vernix caseosa that acts as an anti-microbial, moisturizer, and anti-infective. It stays on until a few days after birth.
The fetus focuses on building its neural connections, forms a regular sleeping pattern and even dream. It can open and close its eyelids now, since the amniotic fluid is almost over. Many parents speak to the fetus as it can now hear and process sound. The calcium absorption increases in order for the bones to harden (except the ones in the skull).
The fetus goes from the size of a peach to the size of a little watermelon in the last few months. Just a week or so before birth, the fetus turns upside down, in a process called ‘lightening’. The last few events take place to prepare the child for the outside world.