Embryogenesis involution is a basic movement of gastrulation. In addition, in involution in medicine often stands for the natural regression of a tissue with age. In pathophysiology, pathological regression of abilities and tissues is associated with this term.
What is involution?
In medicine, the term involution is used to describe a degenerative process in which individual tissues or organs “shrink.” This is true, for example, of the female uterus. In medicine, the term involution is used to describe a degenerative process in which individual tissues or organs “shrink.” Involution is an age-physiological process. For example, various organs are only active for a limited time and naturally regress after their active phase. This is true, for example, of the female uterus and female mammary glands, which naturally regress after the birth of a child. This definition differs from the embryological definition. In embryology, involution is understood to be a phase of gastrulation. During gastrulation, the so-called blastula inverts so that the three cotyledons form. Previously, the blastula germ formed in the so-called blastulation. Involution is the second of a total of five basic movements of gastrulation. The prospective endoderm, a portion of the inner cotyledon, curls up during involution.
Function and task
Involution has different meanings in medicine. The main meaning in applied medicine is that of natural and intended degeneration. In this context, involution is the regression of a tissue that physiologically needs to be active only for a certain period of time. For example, in the involution of the voice, the female voice lowers after postmenopause because of the now higher level of testosterone. Testosterone causes the larynx to enlarge, lowering the basic intonation when speaking. From about the age of 40, the eyes are affected by involution. Age-related defective vision in the sense of presbyopia is the result, which is particularly noticeable when reading without glasses. Another form of involution is hearing loss, which sets in gradually from the age of about 20. In aging humans, involution of speech also occurs. Due to natural cell losses in the extrapyramidal nervous system, the voice lowers during pronunciation and articulation becomes weaker. After cell losses in the pyramidal nervous system, there is also a slowing of pronunciation. Word-finding disorders and mild dementia are also age-physiologically natural involution. Embryogenetic involution, on the other hand, is a basic movement of gastrulation. During invagination, the prospective endoderm invaginates into the inner cavity of the blastula, known as the blastocoel, as part of gastrulation. Part of the outer wall is invaginated due to cell deformation. This process is followed by involution, in which the prospective endoderm curls in. Subsequently, ingression takes place in the sense of cell invagination of the prospective entoderm. In the subsequent delamination, blastula cells slough off cells of the entoderm into the blastocoel. In the final movement, epiboly, the prospective ectoderm overgrows the prospective endoderm in yolk-rich eggs.
Diseases and ailments
Disturbances in embryogenetic involution may result in malformations or even cause the child to abort. From the onset of gastrulation, the embryo is extremely sensitive to harmful substances. Gastrulation disorders may correspond to sirenomelia or coccygeal teratomas, for example. In addition, fused extremities, spinal anomalies, missing kidneys, or malformed genital organs may be due to gastrulation disorders. Gastrulation disorders are often associated with neurulation disorders, as the two phases sometimes overlap each other toward the end of gastrulation. Involution has many other associations from pathophysiology and need not necessarily be meant in the embryological sense in the context of disease. One association from pathophysiology is, for example, pathological dementia, as it can occur in the context of Alzheimer’s disease, but also in the context of alcoholism or Parkinson’s disease.Aphasia in the sense of a pathological loss of speech is also typical for these diseases and corresponds in the broadest sense to a pathological involution. Since all the symptoms mentioned are to some extent natural age phenomena of involution, diagnosis is more or less difficult. In order to distinguish a natural involution of speech and memory from a pathological phenomenon, different diagnostic tools are available. The most reliable and standard diagnostic tool in this case is a so-called screening by means of comprehensive standard tests. In German-speaking countries, the most common test for such screening is the Cognitive Minimal Screening. In addition, the CAMDEX from the English-speaking world is now available in Germany. This standard test was developed in Cambridge and measures not only the linguistic but also the non-verbal intelligence of older people in order to better assess involution. Early diagnosis of degenerative diseases such as Alzheimer’s and Parkinson’s should not be underestimated for several reasons. Exercise-based procedures, for example, can delay the progression of Alzheimer’s or Parkinson’s disease if detected. In addition, medications are now capable of approximately halting or at least slowing the progression of the disease over many years.
