Fetal Development: Cognitive Functioning and Learning
Fetal Development: Cognitive Functioning and Fetal Learning
Prenatal Development
The case for 9 months in a pattern that is not uniform. Throughout this period, changes of varying intensity and importance occur. The periods during which prenatal life is conventionally divided are: conception, zygote (development until the 2nd week), embryo (3rd-8th week), and fetus (9th to 38th week).
Phases of Development
Conception
Every 28 days, an egg leaves the ovary and travels to the uterus through the fallopian tubes. The egg is one of the largest cells of the human body and contains half of the necessary information to form a new human being. During ejaculation, millions of sperm are produced that move at a speed of 3 cm every 10 minutes. The sperm may be capable of fertilizing an egg even after 3 or 5 days of being deposited in the female vagina. Hence, the fertilization of an egg does not have to occur at the time intercourse takes place. However, when the egg leaves the ovary, it has only 24 to 48 hours for fertilization. If it is not fertilized, it will be shed in the next period along with the mucosa of the vaginal wall.
The sperm, in contrast to the egg, is minuscule in size but contains the other half of the information that the egg needs to become a human being. The egg and sperm are the only cells of the body that contain only half the chromosomes, 23 and not 46 like the rest. Each chromosome has hundreds of genes, which are composed of DNA molecules. DNA is the chemical instruction needed to build a new being.
Recent studies indicate that the meeting between the two gametes is not all due to the fate of the brave sperm: the egg is known to emit chemical signals to guide the sperm. Only those of better quality reach the egg, and only one of those few can penetrate inside. The cell formed from the union of an egg and sperm is called a zygote and begins to form approximately one hour after the sperm penetrates the egg.
When an egg is fertilized by a sperm, the sex of the future being is determined. We know that to form a new human being, we need to have 23 pairs of chromosomes. 22 are called homologous chromosomes because they are formed by the same DNA fragments and are responsible for the development of the new being. The last pair of chromosomes are the sex chromosomes, which support the combination of 2 types of chromosomes: XX in females or XY in males.
The X and Y chromosomes are very different. X is long and contains about 3,500 genes, while the Y chromosome is one of the shorter and has only 32 genes. In addition, in one of its arms, it has a considerable amount of non-coding DNA, i.e., it does not provide instructions for protein formation.
The future baby’s sex is determined by the sperm that fertilizes the egg, depending on whether it carries the X or Y chromosome. If it carries the Y chromosome, a gene called SRY will provoke, between the 5th and 8th week of gestation, the gonadal differentiation of the testes and all the other changes associated with males. By default, if the SRY gene is not present, the embryo is transformed into a female, and the gonad differentiates into an ovary.
The fertilized egg, the zygote, multiplies quickly, becoming first a solid mass called a morula. This compact morula then becomes a hollow sphere called a blastula. Then it sinks and folds by one of its hemispheres until it joins the other, becoming a bag or hollow sphere with two walls. Now it is ready to implant and secure itself to the wall of the uterus, which is enriched in blood, and the process of gastrulation begins. This implantation takes about 6 days.
Until recently, no one knew in detail how the embryo managed to implant in the uterine wall. Recent investigations reveal that there is first an unstable fixation and then a series of attempts until it stops completely. It is known that this adhesion occurs through the molecule L-selectin, which interacts with carbohydrates that are placed on the wall. This finding raised the hypothesis that a possible alteration in this process could be the cause of some natural abortions and infertility, i.e., the zygote simply cannot set in the uterus and, therefore, does not continue the process.
If implantation has been successful, then the specialization of certain cells begins; a few remain on the outside of that area, and others develop in the interior. The former will lead to the support of the embryo, and the latter will form the embryo itself.
We must distinguish between differentiation and morphogenesis when we speak of development, as both relate to recent processes. Differentiation is a process in which an undifferentiated cell, meaning that it can potentially become any specialized cell, is grouped with other cells to form an organ, tissue, or organs. Morphogenesis is a process at the morphological level in which the organs are configured and remodeled to make way for an organism with the morphological and functional attributes of its own species.
If, due to genetic or environmental causes, an alteration occurs in morphogenesis, the embryo can develop congenital malformations of varying severity for life development.
Embryo
This period is arguably the most important and delicate of pregnancy because all the major internal and external structures form in this phase. We noted the characteristic and common development is the morphogenesis of vertebrates, which share two characteristics that make us follow a hidden script: one is the cephalocaudal development, and the other is the proximodistal.
The first, cephalocaudal, means that the earliest morphological parts that begin to stand out are the head and trunk. This development script is accompanied by the proximodistal, i.e., growth is directed from the center of the body outward to the most remote parts.
In the zygote, some cells stayed outside, and others were inside. Some of these internal cells begin to differentiate into 3 germ layers. The process is also called gastrulation. At the end of the 2nd week, the embryo looks like a cylinder in which these three layers can be differentiated: ectoderm, mesoderm, and endoderm.
The fate of the germ layers will be as follows: the ectoderm layer will be related to the outside world and is responsible for forming the nervous system, eyes, nose, ears, tooth enamel, skin, and hair. The mesoderm will specialize in the muscles, cartilage, bones, heart, and sexual organs. The endoderm will form the internal organs and glands.
As the inner cells of the zygote develop into the embryo, the three major external support systems also evolve:
- Amniotic sac: a fluid-filled membrane that wraps around the embryo as it grows, protecting it and maintaining a stable temperature.
- Placenta: the tissue through which the fetus and mother exchange materials. If not for this system, the fetus could not receive any food or oxygen and could never develop.
- Umbilical cord: connects the embryo to the placenta and consists of tubes that carry the materials exchanged between the fetus and mother. The fetal blood does not mix with the mother’s, so it can be of a different blood type. This entire transaction occurs on the membrane of the placenta, which acts as a filter.
These 3 components are the support of the embryo, and without them, the embryo could not develop autonomously. It has not yet been possible to develop an artificial support system that enables a human being to develop outside the natural uterus. There are incubators where premature babies can complete their maturation stage to finish being completely autonomous. But if the fetus is born before 23 or 24 weeks, the chance of surviving outside the womb is very low.
Fetus
During this period, the fetus continues to develop and complete the structures that have already begun in the previous phase and gains weight, going down to 3 kg and approximately 50 cm long to complete its gestation period. Its growth rate is incredibly fast. However, upon reaching 7 to 8 months, this pace begins to hold.
At this stage, the fetus drastically changes its appearance by adopting a more human countenance. From now on, its whole body and face are very similar to those of a baby already born.
Third Month
The head grows less. The skin, which was transparent before, thickens. The eyes, which were on the side of the head, are now moving forward, providing a more human appearance to the fetus. The eyelids are closed and do not open until the 6th or 7th month. The brain takes on the basic organization of its body, which will later give rise to the control of complex functions such as hearing and seeing. The external sexual organs have begun to differentiate. From now on, you can see the differentiated sexual organs of the fetus. The fetus can form a fist, shake its feet, and swallow. We have seen that it can move around the body in response to tactile stimulation or when the mother laughs or coughs loudly. However, the mother still does not feel these movements.
Fourth Month
The toenails and fingernails develop. Fingerprints are also formed as the exclusive identification of the individual. Their eyes are sensitive to light through the eyelids. The sense of taste begins to develop. Regarding smell, until recently, it was thought that it did not develop inside the uterus because it depended on air and breath. However, it was discovered that there is a discrimination of odors. The fetus begins to respond to specific sound stimuli. The womb is a much noisier place than is usually supposed, and both internal sounds coming from the mother and some external sounds have been found.
Fifth Month
Hair appears on the head and eyelashes, and the whole body is covered by lanugo, which is shed one week after birth. Now the fetus should measure about 25 cm and weigh about 250 gr. The brain of the fetus already has the 100 billion cells that are in an adult. But we must not forget that the fetus is operational; the 14 billion neuronal connections are formed after birth, without which these neurons could not generate all the processes and phenomena that will be involved. A loud noise can startle the fetus, and it can swim effortlessly without kicking and turning its body. As momentum grows, it is limited by the size of the chest cavity. Also, in this month, sleep-wake rhythms can be observed.
Sixth Month
The fetus has a more upright posture to strengthen the bone structure. It measures 30 cm and weighs 800 gr.
Seventh Month
The fetus starts the sucking reflex if its lips feel some friction. Now it opens and closes its eyes, whose eyeballs are formed. It can sense light of a reddish color due to the maternal tissue and skin. Although the fetus keeps its eyelids closed, we know that it can react to certain luminous stimuli from the 4th month. The brain is developed enough to partially regulate breathing, swallowing, and maintaining body temperature. However, if born, it should remain in the incubator until its body has sufficient autonomy and defenses to face the outside world. Although significant progress has been made, physicians have rarely been able to save premature babies below 23 weeks, and before 7 months, the probability of subsequent disorders and physical and psychological sequelae is very high.
Eighth Month
Until the 8th month, fat does not accumulate under the skin, and the fetus begins storing the maternal nutrients in its body. Starting this month is when the mother provides the necessary antibodies for possible infections, even 6 months after birth, the age at which the baby can generate its own defenses. Everything is ready and prepared for this new being to be born and become an autonomous body. Any human being, during the first months of life, adapts, changes, and learns at an absolutely awesome rate.
Movements
The interest in knowing what happens during prenatal life is not new. In 1885, Preyer used two techniques to study the movement of fetuses at various stages of gestation. One was placing his hands on the mother’s abdomen, and the other was listening with his stethoscope. He concluded that the fetus spontaneously moved its arms and legs for at least 12 weeks of gestation. In addition, Preyer compared his notes on fetal movements with those of newborns and affirmed that they were very similar. Despite the rudimentary nature of his procedure, Preyer was quite right. Indeed, fetuses have spontaneous movements as well as reflex movements, which are similar to those we see in newborns.
Current technological advances allow us to observe and study in depth the movements of the fetus in utero and determine at what stage of gestation it begins to make them. One of the most widely used techniques to date is ultrasound. We know that until about the 7th week, it does not produce autonomous movements. After appearing only a few forms of thrill and until the 12th week, the following patterns of activity are found in the fetus:
- Phase of sleep and inactivity
- Phases of much agitation with movements around the body
- Sporadic kicks into the wall of the uterus
- Strong and regular movements of the trunk of the fetus
From the 12th week, common movement patterns begin to emerge in all fetuses, continuing throughout pregnancy and even after birth. Towards the 15th week, different patterns of movement are recognized. The sequence in which they appear is common to all fetuses, but with slight variations in the ages when they are first seen. These movements persist throughout prenatal life and may also be observed after birth.
From the first moments, spontaneous motility is observed, and as the neural and muscular structures evolve and become functional, movement patterns constantly arise. Together with data obtained by ultrasound are additional ones that come from aborted human fetuses or those born prematurely, as well as other animal species.
As for reflex movements, they appear ontogenetically at about the same time as spontaneous movements. The difference between the two types of movement is that most reflexes are associated with the survival of the baby at birth, while spontaneous movements seem to have a more functional mission in the structures that are forming in the fetus. A reflex is triggered inescapably in the presence of more or less specific internal or external stimuli. In utero, various reflexes can be seen, such as sucking or grasping. But undoubtedly, the reflexes developed in the early months of gestation are reflexes that will be available at birth and thus ensure the survival of the baby.
When the baby is born, it has a large and varied set of reflexes. Many seem to have a clear adaptive significance; in others, however, their function for survival is not clear. However, the absence of either can be an index of pathology or organic disorder of the newborn, caused by some adverse agent during gestation. Some of the reflexes disappear as the baby grows, and their retention is usually associated with some pathology of the nervous system. Many other reflexes remain for a lifetime, such as the patellar reflex or blinking, and in these cases, their disappearance or malfunction is also associated with some organ dysfunction. Finally, there are reflexes that disappear as such to become a behavior that is controlled voluntarily, ceasing to be controlled subcortically to move to the control of the cerebral cortex.