The articles about the structure and the functions of skin and its components
Thermoregulation is the maintenance of a relatively constant core body temperature.
A stem cell is a cell of multicellular organisms able to self-renew and to differentiate into different specialized cell types. It may be totipotent, pluripotent, multipotent, or unipotent. According to their origin, we can distinguish embryonic, fetal, amniotic, or adult (=somatic) stem cells. More recently, differentiated cells have been re-programmed into induced pluripotent stem (iPS) cells or directly transdifferentiated into another type of differentiated cell (= induced differentiated cell).
The skin is a complex organ organized in three layers, the epidermis (and its associated appendages, pilosebaceous follicles and sweat glands), the dermis and the subcutis or hypodermis . Its development is a fascinating process that has been progressively better and better understood and that has been the subject of a large number of publications. You will find below a selection of papers that could help to discover this research domain.
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The nail is mainly composed of the hard nail plate arising from a matrix. The shape of the nail is very variable in different persons; it is roughly rectangular and flat in shape; The nail bed has a pink color that can be seen because of the transparency of the plate and its extensive vascular network.
A whitish crescent -shaped lunula projecting from under the proximal nail folds is observed in the thumbs, uncommonly in the other fingers and in the large toenails. The lunula is the more distal portion of the matrix and determines the shape of the free edge of the nail plate. Its color is due in part to the effect of light scattered by the nucleated cells of the matrix and in part to the thick layer of the epithelial cells making up the matrix.
As the nail plate emerges from the matrix, its lateral and proximal borders are enveloped by folds of skin termed lateral and proximal nail folds. The skin underlying the free end of the nail is referred to as the hyponichium and is contiguous with the skin on the tip of the finger.
In humans, nails grow at an average rate of 3 mm a month. The growths of fingernails and toenails have different speeds. Complete regrowth of fingernails require 3 to 6 months while complete toenail regrowth needs 12 to 18 months. The growth rate is related to the length of the terminal phalanges; the nail of the little finger grows slower than the nail of the index finger. They grow faster in summer than in the other season. Contrary to popular belief, they do not continue to grow after death; it is the severe postmortem drying and shrinking of the soft tissue around the nail plate that give the illusion of a nail growth.
The main functions of the nails are to protect the end of the digit and to help in grasping objects.
The origin of the blood vessels in a skin graft after transplantation has been subjected to debate for long time. It is not entirely clear whether the vascularization of adult skin grafts is achieved by penetration of new vessels from the host into the transplant (neovascularization), by anastomosis of host blod vessels with preexisting graft vessels, or by combination of these processes.
It is well known that nude mice maintain lifetime skin grafts from a large variety of mammals, including man, and from bird. These grafts of heterologous skin onto nude mice retain all the morphological and ultrastructural features associated with normal skin. Human skin grafted onto the nude mouse appears to be able to preserve not only its structural and immunological identity but also most of its functional properties. Wound healing is one major property of skin. It was already suggested that human skin transplanted onto nude mice had the potential to regenerate since, as example, the human epidermis appears able to be completely regenerated from the surviving epidermal cells of the basal layer.
In the present article, we are going to successively describe the results of studies of the wound healing process of cutaneous full thickness wounds when the three cutaneous compartments, namely the epidermis, the dermal-epidermal junction and the dermis have been injuried. In other articles, we will analyse the healing of cutaneous partial thickness wound when the epidermis, and only a superficial part of the dermis is removed by mechanical dermabrasion and, eventually, cutaneous wound caused by a strong acid trichloro-acetic acid.