What is Histogenesis? What is it for? Which complaints or diseases can arise from misdirected histogenesis? These questions are to be answered in the following article.
What is the histogenesis?
Histogenesis describes the embryonic development of differentiated tissues with different tasks and functions through a genetically anchored program. This differentiated tissue arises from the undifferentiated fertilized egg cell.
Function & task
The fertilized egg cell is initially pluripotent: the cells contain the complete genetic information and the complete control program to develop a person. For this reason, identical twins can arise from an embryonic system that divides and drifts apart in the first few days after fertilization.
Once an egg cell has been fertilized, the morula is formed through many cell divisions. At the time of implantation in the uterine lining, the cells in the morula differentiate into "inside" and "outside" - the blastocyst is formed. From the eighth day after fertilization, the embryo develops. Another name is embryoblast or germinal disc. It first exists as a two-petalled germinal disc.
From the third week after fertilization, further remodeling work takes place. The three-leaved germinal disc emerged from the epiblast of the second-leaved germinal disc. It consists of the mesoderm (middle cotyledon), the endoderm (inner cotyledon) and the ectoderm (outer cotyledon). At this time there is already a right-left asymmetry in the primitive node in the middle of the germinal disc, which corresponds to the later asymmetry in the structure of the thoracic and abdominal organs.
Histogenesis plays a particularly important role in the embryonic period, as all organs are laid out in your blueprint in the first few weeks of pregnancy. Cots from cotyledons migrate to different places to form organs. Buds emerge on the trunk from which the extremities arise. In the face, different structures grow together internally and externally. This is how eyes, ears, nose, lips, jaw, palate and throat are formed.
Illnesses & ailments
If something goes wrong in the "building instructions", the asymmetrical orientation of the primitive knot can be incorrectly created during the development of the three-leaf germinal disc. As a result, the cells that are later to form the organs migrate in the wrong directions. The internal organs are then laid out in a different arrangement. This can affect all internal organs (situs inversus totalis) or some of them.
In Kartagener's syndrome, organs are redistributed randomly because the cilia, which usually move cells to places, are immobile. People with Kartagener syndrome can therefore have incorrectly designed internal organs. Sinusitis (inflammation of the paranasal sinuses) and Brochnial infections also occur due to the lack of ciliary function, as the airways do not clean themselves.
Severe disturbances in histogenesis end in intrauterine fetal death, miscarriage or premature birth. If the children are born alive, severe physical disabilities can result.
If the neural tube does not close properly during the embryonic period (22nd to 28th day of embryonic development), spina bifida can occur. Spina bifida can have various preliminary stages and manifestations. Affected people can have increased hair on the back, which adopts a typical pattern along the spine and extends to the sacroiliac joint. This can result in restricted mobility, paraplegia and walking problems. Control of the bladder and bowel can be impaired. Sometimes spina bifida is also associated with other disorders or disabilities, for example hydrocephalus.
A cleft lip and palate is caused by insufficient closure of the structures that make up the face. In the 5th to 7th week of pregnancy, the upper jaw bulges merge with the nasal bulges in the right and left halves of the face. If there are disorders here, the cleft lip develops. In the 10th-12th At the 1st week of pregnancy, the palatal processes merge with the maxillary bulges and at the front with the intermaxillary segment. If there are disorders - often associated with the cleft lip - the cleft palate arises. Depending on the severity, this can lead to drinking, swallowing, breathing and speech disorders. If the ventilation is poor, there is an increase in ear, nose and throat diseases.
Cleft formations, called colobomas, can also occur in the eyes during the embryonic period. In the 7th week of pregnancy, the eye vesicles are transformed into an eye cup. The coloboma arises from insufficient closure, usually towards the bottom of the nose. Colobomas of the eyelids, iris, lens, retina, choroid, and optic nerve are possible. In the case of a coloboma of the optic nerve (optic coloboma), visual function can be restricted. Squinting and eye tremors (nystagmus) occur.
In the 7th week of pregnancy, the germ cells are created, from which arms and legs, and later hands and feet, will develop. In the 8th week of pregnancy, the beginnings of the later legs and arms are visible. A week later, arms, legs, hands and feet are already formed, with the fingers and toes still connected by webbed feet. If the histogenesis is incorrectly controlled, deformities can occur in the extremities: for example, an arm may not be fully developed or redundant fingers and toes or club feet may develop.
Other damage in histogenesis is also known, for example through infectious diseases such as rubella, toxoplasmosis, alcohol, nicotine, medication or drug abuse during pregnancy. In areas with radioactive contamination, an increasing number of children were and are being born with genetic malformations. In the sixties of the last century, quite a few women took the sleeping pill Contergan during their pregnancy, which often resulted in severe deformities in their unborn children.
However, damage in histogenesis is often based on rare chronic diseases of a genetic nature. Information portals were created for those affected: at the European level these are 'Orpha Net' and 'Eurordis', on the German level the 'umbrella organization of the axis'.
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