The papillary pattern is perhaps the only kind of lines of our skin that everyone knows about. However, experts distinguish a great variety of other lines, patterns and folds. A brief review published a few years ago in the Clinical Dermatology Review describes them in dozens, from AA lines forming on the inside of the elbow to a “yellow line” running along the edge of the non-skin-contacting tip of the nail.
Some of them can be found on their own body, others show through only under certain conditions or violations. Some are determined by the structure of the skin or its flexion, others remain with us, like an echo of early embryonic development.
Hole lines
The most famous in this series are the lines described by the Austrian anatomist Karl Langer in the 1860s. It was his name that they received, although even Langer himself referred to earlier references that he met in the works of the outstanding French physician Guillaume Dupuytren, after whom many symptoms and medical techniques are named.
Conducting his own experiments in the dissecting room, Dupuytren made holes in the skin of the corpses with an awl, noting that they quickly stretch, acquiring an oval, elongated shape. In turn, Langer plotted their location on the body diagram, highlighting and tracing the lines associated with the structure of collagen fibers in the inner parts of the skin; in 1861 his work "On the splitting of the skin" was published.
The scientist found that, in general, they are oriented perpendicular to the muscle fibers, indicating lines of static stress on the skin. Wounds caused by Langer's lines heal faster and leave less scarred tissue, so surgeons often rely on them, making the incisions necessary for operations. This feature perfectly demonstrates the structuring role of collagen, which provides support - the matrix for the growth and reproduction of skin cells.
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Lines from cells
Unlike Langer, the lines described in 1901 by the Berlin physician Alfred Blaschko do not follow any known vascular, nervous, muscular, or connective structures. The dermatologist noticed them, drawing attention to the fact that various nevi (moles), pigmentation disorders, rashes, birthmarks and other skin abnormalities often follow a general pattern, diverging in wide V letters in the upper back, S-shaped lines on the lower back and U -shaped - around the chest and shoulders.
For Blashko, the appearance of the lines remained a complete mystery, and although today their formation is associated with the early stages of intrauterine development, this mechanism has not yet been properly studied. In general, everything happens like this: the cells of the embryo divide, forming various tissues. Some of them differentiate into skin cells. Growing out of certain areas and along certain directions, which are set by signaling substances, different cell lines form a complex pattern.
This process is sometimes compared to a pattern that baristas draw on the surface of coffee using milk. Its "shadow" is preserved in the hidden lines of the skin - and not only on it. Anatomical analogues of the Blaszko lines are found in other parts of our body, including the eyes and teeth.
However, it is unlikely that you will be able to consider them on your own, unless you have the corresponding dermatological diseases. It's easier to see lines on animals. Cell lines of slightly different genetics can determine the coat color of dogs and cats. Therefore, their spots often follow the directions given by the earliest stages of the development of the organism.
Roman Fishman