The outermost layer of skin is the epidermis. It is made of stratified squamous epithelium. This epithelial tissue has been keratinized to prevent water loss. Remember that all epithelial tissue is avascular, which means it must depend on an underlying layer of tissue for its blood supply.
Below the epidermis lies the dermis, a layer of dense connective tissue. The dermis provides the epidermis with not only its blood supply, but is also the location of other skin accessories such as oil glands, sweat glands, hair and nerve supply.
Deep to the dermis is a layer of subcutaneous adipose connective tissue. The subcutaneous tissue is technically not part of the skin. It functions to anchor skin to the underlying organs and provide insulation and shock absorption. This layer of adipose (fat) tissue stores energy, regulates body temperature and provides protective cushioning.
Appendages & Components of the Skin
This is the structure that produces hair. The root is situated below the epidermis while the hair shaft reaches up beyond the epidermis. The root of the hair is the site of growth: cells multiply and are pushed up through the hair canal. As the hair moves up the canal towards the surface, they keratinize and eventually dehydrate and die.
These glands produce sebum (oily & waxy material). Sebum lubricates and waterproofs the skin, prevents brittle hair and kills bacteria. Sebaceous glands are commonly found connected to the hair follicles and spread the sebum to the surface of the skin by traveling up the hair shaft. Other sebaceous glands open up directly onto the skin. Glands are activated at puberty.
Arrestor pili muscle
Arrector pili muscles are tiny smooth muscles that connect to hair follicles. When they contract, they cause the hair to stand up (piloerection).
Eccrine sweat gland
Eccrine sweat glands connect to the surface of the skin using a pore. These glands are found all over the skin and are used to regulate temperature. The highest density of eccrine sweat glands are found in the palmar surface of the hands, plantar surface of the feet, and on the head. The type of sweat is mostly water, it does not generate strong body odor. Besides water eccrine sweat may also contain salts and vitamin C as well as some metabolic waste. Its acidic nature inhibits bacterial growth.
Apocrine sweat gland
Apocrine sweat glands connect to the hair follicle and secrete sweat rich in fatty acids and some proteins. They are only located in specific areas of the skin like the axillary & pubic regions. They begin to function at puberty. These are the sweat glands associated with strong body odor.
Blood vessels are found only in the dermis and hypodermis. They supply blood to all parts of the skin, including the epidermis through diffusion.
Mechanoreceptor that responds to sustained touch and pressure as well as stretch. They are found in high concentrations in the fingernails where they can detect pressure while gripping to allow for adjusting the grip to prevent slippage of the object being held.
Krause end bulb
Thermoreceptor that detects cold temperatures.
Mechanoreceptor that responds to changes in texture and slow vibrations. They are most sensitive to light touch and are found in high concentrations in the fingertips and lips.
Mechanoreceptor that responds to deep pressure and slow vibrations.
Mechanoreceptor that responds to changes in position & sustained pressure - it defines shapes and edges.
Free nerve endings
Detect pain, touch, pressure, temperature and itch - many individual free nerve endings can detect more than one sensation.
Keratinocytes make up at least 90% of cells of the epidermis. They produce the protein, keratin. They take on melanin via phagocytosis from surrounding melanocytes so that skin tone is evenly distributed.
Melanocytes produce melanin, a dark pigment. The more melanin produced, the darker the skin color appearance. The amount of melanin produced depends on genetics and exposure to sunlight. Melanin protects the skin from the harmful effects of ultraviolet radiation.
Antigen-presenting cells that take in foreign antigens by phagocytosis and process them to be presented to immune cells to activate the immune system.