The first organ to be created in the human body is the heart. This means that the cardiovascular system is also the first system in the developmental phase of embryogenesis, which is built up and is very complex. The first heartbeat of the embryo can be detected by ultrasound around the sixth week of pregnancy. Until then, however, there is a lot going on embryonic heart development happen.
What is embryonic heart development?
From the third week the process of heart formation begins. As long as there are only a few cells, each cell receives the necessary nutrients from its environment. But as soon as the cells start dividing, the nutrients can no longer reach the cells without help. The substances must therefore be transported elsewhere.
At the same time, degradation and waste products are created and must be disposed of. This is the job of the cardiovascular system and the reason why this is the first to be formed in the organism.
Function & task
The structure begins with the formation of the three-leaved cotyledon. This is a cluster of tissue that emerges from the zygote (fertilized egg cell) after fertilization, after the cells have divided and cell migration begins. It consists of the inner cotyledon, also called the endoderm, and initially builds up a two-layer structure that ends with the outer cotyledon, the ectoderm. Finally, the migration and displacement of all cells forms the middle layer, the mesoderm, which is pushed between the other two layers as a result of 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, there is a yolk sac on the endoderm. The process of forming the cotyledons is known as gastrulation.
A chordal plate is now formed within the middle layer, which initially acts like a channel and then grows into a kind of tube. This, also known as the 'chorda dorsalis', runs along the axis of the embryo. To the side of this is the endoderm.
The prechodal plate is located above the 'chorda dorsalis'. The endoderm advances over the axis and moves the axis into the mesoderm. At the same time, a neural bulge forms on the ectoderm, which then closes into the neural tube.
This is the phase in which large cell rearrangements occur during embryogenesis. A vertical and lateral folding of the three-leaved cotyledon takes place, an intraembryonic body cavity is formed, which is also known as the coelomial cavity and is surrounded by the mesoderm and ectoderm. The endoderm closes with the intestinal tube.
The neck region in front of the prechodal plate forms the starting point for the entire development of the heart and lies in the cardiogenic zone. This is where the original cells of the cardiac system are located, and the heart tube is also formed here. This is still primitive and is located on the floor of the body cavity, surrounded by the mesoderm, which later becomes the myocardium.
The heart tube now begins to bend and lengthen and forms a loop-like structure from the fourth week onwards. This creates different rooms and the loop of the heart that shifts to the left. In this state, the heart loop already looks like the future heart, but initially there is only one atrium and one chamber. Then four heart interiors are formed by separation.
There is a transition between the already existing atrium and the ventricle. This is called the atrioventricular canal. The walls thicken to form endocardial pillows that fuse together to form a left and right section.
A muscle bar moves next to it, the opening that is still present is covered by a conical bulge. The 'septum primum', which develops into the pre-septum and which in turn has grown out of the primitive atrium, fuses with the endocardial cushion.
After the chambers have split, the Austrombahn also splits. This happens through the 'septum aorticopulmonale'. The blood flow that now flows through the heart loops creates spiral pressure conditions there and thus serves as an orientation aid for the 'septum aorticopulumonale'.
The 'septum primum' is joined by another 'septum secundum', and two openings are also formed, which are necessary because the lungs have not yet formed and the blood circulation is maintained. Both septa grow together and form a gap. The heart is now complete.
Illnesses & ailments
During the entire human life, the heart pumps blood through the body. However, the complex process of heart development can lead to malformations and these in turn can trigger various, even combined defects.
If the heart is affected by damage or disturbances over time, certain areas can no longer heal completely. Therefore, researchers hope to replace heart cells that are irreparable, which would be an alternative to heart transplants in the treatment of heart diseases.
One research direction tried z. B. to produce bone marrow cells, which should form new heart muscle cells, but this did not succeed. Just as it has long been assumed that the adult brain cannot, which it cannot (see Neurogenesis), cannot make new brain cells, there was also the assumption that an adult's heart would not be able to make new heart cells. That too could be refuted. However, this ability decreases with age.
The discovery that new heart cells are still being produced, albeit in ever smaller forms, 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 a healthy organism. Similar to the brain, it is assumed that there may be heart stem cells that can form new cells. Researchers try to breed these in the laboratory. In this way, embryonic stem cells can be converted into heart cells. However, with the current state of research, the body still rejects the cells during re-implantation.
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