GENERAL DERMATOLOGY
1. Epidermis, dermis, subcutis - anatomy, histology and ultrastructural features.
The skin - the interface between humans and their environment - is the largest organ in the body. It weighs an average of 4 kg and covers an area of 2 m2. It acts as a barrier, protecting the body from harsh external conditions and preventing the loss of important body constituents, especially water. Layers of the skin:
- The epidermis – the outermost layer of the skin - which is firmly attached to, and supported by connective tissue in the underlying dermis. It provides a waterproof barrier and creates our skin tone. The skin’s color is created by special cells called melanocytes, which produce the pigment melanin.
- Dermis - beneath the epidermis - contains tough connective tissue, hair follicles and sweat glands.
- Subcutis/Hypodermis – loose connective tissue found beneath the dermis. It usually contains abundant fat.
EPIDERMIS
The epidermis is composed of keratinized, stratified squamous epithelium. It is made of four or five layers of epithelial cells, depending on its location in the body. It does not have any blood vessels within it (i.e., it is avascular). Skin that has four layers of cells is referred to as “thin skin.” The four layers are stratum basale, stratum spinosum, stratum granulosum and stratum corneum. “Thick skin” is found only on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum,
located between the stratum corneum and the stratum granulosum The cells in all of the layers except the stratum basale are called keratinocytes. A keratinocyte is a cell that manufactures and stores the protein keratin. Keratin is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from the deeper layers
The layers are: