The Three Main Layers of Skin:
1. Epidermis: The first layer of skin is called the Epidermis. It is composed of stratified squamous epithelium that is keratinized. It contains the keratinocytes and melanocytes, it is avascular, and is the tissue layer above skin. It is the BARRIER Layer. The Epidermis is made up of five different layers:
Stratum Corneum: known as the “horny” layer, dead, stratified squamous, and it looks rough. This layer can become thick (callus) from constant irritation or use. Keratin is present in this layer. Keratin is a water repellent protein.
Stratum Lucidum: known as the “clear” layer with dead cells.
Stratum Granulosum: known as the “granular” layer. Is thin, and contains dying cells, and begins keratinization (cells move up).
Stratum Spinosum: known as the “spiny” layer, and acts as a protein synthesis with RNA to generate keratin, and contains living cells.
Stratum Basale: known as the “base” layer, or otherwise known as the Stratum Germinativum. This is the deepest layer and the only epidermal layer that receives adequate nourishment via diffusion from the dermis. It is the layer where rapid mitosis occurs, and has the youngest cells, and where melanin is located (pigment protects the skin from UV light)
2. Dermis: The middle layer of the skin is called the Dermis. It is composed of dense fibrous connective tissue. It contains sensory receptors for pain, pressure, touch, and temperature. It’s the vascular layer, and forms the basement membrane. It is made up of the following layers:
Papillary Layer: thin, and projects collagen and elastin into the basement membrane, contains areolar tissue and elastic fibers. (example: fingerprints) Thin,superficial areolar connective tissue with collagen and elastin fibers are found in the papillary layer. The superior surface appears as “peg-like” projections called dermal papillae that indent the epidermis. The House Meissner’s corpuscles or touch receptors, pain receptors, and capillary loops are located in this layer.
Reticular Layer: the “skin network”, which is thick, dense, fibrous connective tissue; has elastic fibers (stretchable); and contains the arrector pili muscle which attach to hair follicle and contract when cold. 80% of the dermal thickness is composed of dense and irregular tissue. It contains the blood vessels, sweat, and oil glands. The deep pressure receptors (pacinian corpuscles) are located here. It contains phagocytes, which prevent bacteria from penetrating to deeper body layers.
3. Hypodermis or Superficial Facia: The third layer of the skin is called the Hypodermis ( or Superficial Facia). It is composed as subcutaneous tissue and adipose tissue. It anchors the skin to underlying organs. It acts as a shock absorber and insulator.
Other Structures and Functions of the Integumentary System:
Sweat glands: The structure and function of sweat glands consists of a secretory coil that secretes an isotonic NaCl solution and contains a duct that reabsorbs Na+ and Cl−- to produce the hypotonic sweat that flows on to the surface of the skin.
Subcutaneous gland: Subcutaneous gland produces sebum (an oil) to keep hairs free from dust and bacteria. Sebum (oil) and sweat make up the 'surface film'. The