What Are the Layers of Human Skin?
Skin is an effective communicator between the outside environment and the brain (delicate touch, pain, pressure, hot and cold) Comprises 12-15% of an adult's body weight, One square centimeter has:
• 6 million cells
• 5000 sensory points
• 100 sweat glands
• 15 sebaceous glands
Skin formed from three layers:
• Epidermis (the outer layer)
• Dermis ('true skin')
• Subcutaneous (fat) layer
A skin cell starts its life at the lower layer of the skin (the basal layer of the dermis), which is supplied with blood vessels and nerve ending. The cell migrates upward for about two weeks until it reaches the bottom portion of the epidermis, which is the outermost skin layer. The epidermis is not supplied with blood vessels, but has nerve endings. For another 2 weeks, the cell undergoes a series of changes in the epidermis, gradually flattening out and moving toward the surface. Then it dies and is shed.
Epidermis the 'Outer Layer of the Skin'
The main function of the epidermis is to form a tough barrier against the outside world, while the dermis is a soft, thick cushion of connective tissue that lies directly below the epidermis and largely determines the way our skin looks. Both layers keep repairing and renewing themselves throughout or life, but the dermis does it more slowly than the epidermis. Under the dermis is a layer of fat cells, which is known as adipose tissue (or subcutaneous fat layer). It provides insulation and protective padding for the body. It also provides an emergency energy supply.
Dermis 'True Skin'
The dermis is the layer responsible for the skin's structural integrity, elasticity and resilience. Wrinkles develop in the dermis. Typical collagen and elastin creams, for example, never reach the dermis because collagen and elastin molecules are too large to penetrate the epidermis.
It is the thickest of the skin layers and comprises a tight, sturdy mesh of collagen and elastin fibers. Both collagen and elastin are critically important skin proteins: collagen is responsible for the structural support and elastin for the resilience of the skin.
The key type of cells in the dermis is fibroblasts, which synthesize collagen, elastin and other structural molecules. The proper function of fibroblasts is highly important for overall skin health.
The dermis also contains capillaries (tiny blood vessels) and lymph nodes which produce immune cells. Blood capillaries are responsible for bringing oxygen and nutrients to the skin and removing carbon dioxide and products of cell metabolism (what we call waste matter). Lymph nodes are engaged in protecting the skin from invading microorganisms.
Finally, the dermis contains sebaceous glands, sweat glands, hair follicles and a small number of nerve and muscle cells. Sebaceous glands, based around hair follicles, produce sebum, an oily protective substance that lubricates the skin and hair and provides protection by forming an acid mantle when mixed with sweat. When sebaceous gland produce too little sebum, as is common in older people, the skin becomes excessively dry and more prone to wrinkling. Too much of sebum, as is common in teenagers, often leads to acne.
Subcutaneous Tissue 'Fat Layer'
Subcutaneous tissue is the deepest layer of the skin located under the dermis and consisting mainly of fat cells. It acts as a shock absorber and heat insulator, protecting underlying tissues from cold and trauma. The loss of subcutaneous tissue in later years, leads to facial sag and makes wrinkles more visible.
What are skin functions?
1. Sensation - nerve endings identify touch, heat, cold, pain and pressure
2. Heat regulation – cooling – perspiration (evaporation), warming – shivering (closes pores) and Goosebumps (tiny erect hairs trap warm air)
3. Absorption - ultraviolet rays (forms vitamin D for bone formation), essential oils and medicines (e.g. HRT, anti-smoking patches)
4. Protection - produces melanin to protect from too much UV light, acid mantle (sebum and sweat) protects against bacteria and moisture loss
5. Excretion - waste products and toxins are eliminated via sweat glands
6. Secretion - sebum keeps the skin lubricated and soft, and the sweat combines with the sebum to form an acid mantle to fight off infection.