The first organ to develop in the human body is the heart. Thus, the cardiovascular system is also the first system in the developmental phase of embryogenesis to be established, and it is very complex in the process. The first heartbeat of the embryo can be detected by ultrasound at about the sixth week of pregnancy. By then, however, quite a bit has already happened in embryonic heart development.
What is embryonic heart development?
The first organ to develop in the human body is the heart. The first heartbeat of the embryo can be detected by ultrasound at about the sixth week of pregnancy. From the third week, the process of heart formation begins. As long as only a few cells are present, each cell receives the necessary nutrients from its environment. However, as soon as the cells begin to divide, the nutrients no longer reach the cells without help. The substances must therefore be transported elsewhere. At the same time, degradation or waste products are produced and must be disposed of. This is the task of the cardiovascular system and the reason why it is formed first in the organism.
Function and task
The structure begins with the formation of the trifoliate cotyledon. This is a tissue cluster formed from the zygote (fertilized egg) after fertilization, after the cells have divided and cell migration begins. It consists of the inner cotyledon, also called the endoderm, and initially builds a two-layered structure that ends with the outer cotyledon, the ectoderm. Finally, the migration and displacement of all the cells forms the middle layer, the mesoderm, which is sandwiched between the other two layers by the process. These three layers look like a disk. The outer layer is attached to a fluid-filled bladder called the amniotic cavity. In turn, a yolk sac is present at the endoderm. The process of cotyledon division is called gastrulation. A chorda plate now forms within the middle layer, which at first acts like a gutter and then grows into a kind of tube. This, also called the ‘chorda dorsalis’, runs in axis of the embryo. To the side of this lies the endoderm. Above the ‘chorda dorsalis’ is the prechodal plate. Over the axis the endoderm advances and shifts the axis into the mesoderm. A neural bulge forms on the ectoderm at the same time, which then closes to form the neural tube. This is the phase where major cell rearrangements occur during embryogenesis. Vertical and lateral folding of the trifoliate cotyledon takes place, and an intraembryonic body cavity, also known as the celomic cavity, is formed, surrounded by mesoderm and ectoderm. The endoderm closes with the intestinal tube. The neck region in front of the prechodal plate is the starting point of the entire development of the heart and is located in the cardiogenic zone. The original cells of the cardiac anlagen are located in this zone, and the cardiac tube is also formed here. This is still primitive and is located at the bottom of the abdominal cavity, being surrounded by the mesoderm, which later becomes the myocardium. The heart tube now begins to curl and elongate, forming a loop-like structure from the fourth week. This gives rise to various spaces and the cardiac loop, which shifts to the left. In this state, the heart loop already looks like the later heart, but for the time being only one atrium and one single chamber exist. By separation, four heart chambers are then formed. Between the already existing atrium and the ventricle lies a transition. This is called the atrioventricular canal. The walls thicken and form endocardial cushions that fuse together to form left and right sections. Next to it, a muscle bar shifts, and the opening that is still present is covered by a cone bulge. Fusing with the endocardial cushions is the ‘septum primum’ which develops into the vestibular septum, which in turn grew from the primitive atrium. After the ventricles divide, the outflow tract also divides. This occurs through the ‘septum aorticopulmonale’. The blood flow now passing through the cardiac loops creates spiral pressures there, thus serving as a landmark for the ‘septum aorticopulumonale’. The ‘septum primum’ is joined by another ‘septum secundum’, likewise two openings are formed, which are necessary because the lungs are not yet formed and thus the blood circulation is maintained.Both septa fuse together and form a gap. The heart is now fully present.
Diseases and complaints
Throughout human life, the heart pumps blood through the organism. However, due to the complex process of heart development, malformations can occur and these in turn can cause various, even combined, defects. If the heart is affected by damage or malfunction over time, certain areas may not be able to heal completely. Therefore, researchers hope to replace heart cells that are irreparable, which would be an alternative to heart transplantation in the treatment of heart disease. For example, one line of research attempted to generate bone marrow cells to form new heart muscle cells, but was unsuccessful. Just as it was long assumed that the adult brain could not form new brain cells, which is not the case (see neurogenesis), there was also an assumption that the adult heart would not be able to form new heart cells. This, too, has been disproved. However, this ability decreases with age. The discovery that new heart cells are nevertheless produced, albeit in ever smaller numbers, has opened up a new field of research with the hope of being able to supply a damaged heart with new cells. To do this, researchers are trying to find out where the newly formed heart cells come from and how this formation can be controlled in the healthy organism. As in the brain, it is assumed that there may be heart stem cells that can form new cells. Researchers are trying to grow these in the laboratory. In this way, embryonic stem cells can be converted into heart cells. However, at the current state of research, the body still rejects the cells when they are reimplanted.
