Layers of the Skin

The Epidermis

The epidermis is the outermost layer of the skin, and protects the body from the environment. The thickness of the epidermis varies in different types of pare; information technology is only .05 mm thick on the eyelids, and is ane.5 mm thick on the palms and the soles of the feet. The epidermis contains the melanocytes (the cells in which melanoma develops), the Langerhans' cells (involved in the allowed system in the skin), Merkel cells and sensory nerves. The epidermis layer itself is made up of five sublayers that work together to continually rebuild the surface of the skin:

The Basal Cell Layer

The basal layer is the innermost layer of the epidermis, and contains small round cells called basal cells. The basal cells continually divide, and new cells constantly push older ones upward toward the surface of the pare, where they are somewhen shed. The basal cell layer is also known equally the stratum germinativum due to the fact that it is constantly germinating (producing) new cells.

Illustration of the layers of the skin

The basal cell layer contains cells called melanocytes. Melanocytes produce the skin coloring or pigment known every bit melanin, which gives pare its tan or brown color and helps protect the deeper layers of the skin from the harmful effects of the lord's day. Sunday exposure causes melanocytes to increase product of melanin in gild to protect the peel from damaging ultraviolet rays, producing a suntan. Patches of melanin in the pare cause birthmarks, freckles and age spots. Melanoma develops when melanocytes undergo malignant transformation.

Merkel cells, which are tactile cells of neuroectodermal origin, are also located in the basal layer of the epidermis.

The Squamous Cell Layer

The squamous jail cell layer is located above the basal layer, and is besides known as the stratum spinosum or "spiny layer" due to the fact that the cells are held together with spiny projections. Within this layer are the basal cells that take been pushed upward, however these maturing cells are at present chosen squamous cells, or keratinocytes. Keratinocytes produce keratin, a tough, protective protein that makes up the bulk of the structure of the skin, hair, and nails.

The squamous cell layer is the thickest layer of the epidermis, and is involved in the transfer of certain substances in and out of the body. The squamous cell layer also contains cells called Langerhans cells. These cells adhere themselves to antigens that invade damaged skin and alert the immune system to their presence.

The Stratum Granulosum & the Stratum Lucidum

The keratinocytes from the squamous layer are then pushed up through 2 thin epidermal layers chosen the stratum granulosum and the stratum lucidum. As these cells move further towards the surface of the skin, they become bigger and flatter and adhere together, and then somewhen go dehydrated and die. This process results in the cells fusing together into layers of tough, durable material, which continue to migrate up to the surface of the peel.

The Stratum Corneum

The stratum corneum is the outermost layer of the epidermis, and is made up of 10 to 30 thin layers of continually shedding, dead keratinocytes. The stratum corneum is likewise known as the "horny layer," considering its cells are toughened like an animal's horn. As the outermost cells age and wearable downwards, they are replaced by new layers of strong, long-wearing cells. The stratum corneum is sloughed off continually as new cells take its place, but this shedding process slows downwards with historic period. Complete cell turnover occurs every 28 to thirty days in immature adults, while the aforementioned process takes 45 to 50 days in elderly adults.

The Dermis

The dermis is located beneath the epidermis and is the thickest of the three layers of the skin (one.5 to 4 mm thick), making upwards approximately 90 percentage of the thickness of the skin. The master functions of the dermis are to regulate temperature and to supply the epidermis with nutrient-saturated claret. Much of the trunk'due south water supply is stored within the dermis. This layer contains most of the skins' specialized cells and structures, including:

  • Blood Vessels
    The claret vessels supply nutrients and oxygen to the pare and take abroad cell waste material and cell products. The blood vessels also transport the vitamin D produced in the pare back to the residual of the body.
  • Lymph Vessels
    The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.
  • Hair Follicles
    The hair follicle is a tube-shaped sheath that surrounds the role of the hair that is under the skin and nourishes the hair.
  • Sweat Glands
    The boilerplate person has almost 3 million sweat glands. Sweat glands are classified co-ordinate to 2 types:
    1. Apocrine glands are specialized sweat glands that can be plant only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body scent.
    2. Eccrine glands are the truthful sweat glands. Found over the unabridged body, these glands regulate body temperature past bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands tin produce up to two liters of sweat an 60 minutes, nonetheless, they secrete generally water, which doesn't encourage the growth of odor-producing leaner.
  • Sebaceous glands
    Sebaceous, or oil, glands, are attached to hair follicles and can be found everywhere on the torso except for the palms of the easily and the soles of the anxiety. These glands secrete oil that helps continue the pare smooth and supple. The oil also helps keep pare waterproof and protects confronting an overgrowth of leaner and fungi on the pare.
  • Nerve Endings
    The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, pressure and information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating trunk rut.
  • Collagen and Elastin
    The dermis is held together by a protein called collagen, made by fibroblasts. Fibroblasts are skin cells that give the skin its forcefulness and resilience. Collagen is a tough, insoluble protein institute throughout the torso in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible.

The dermis layer is made up of two sublayers:

The Papillary Layer

The upper, papillary layer, contains a sparse organization of collagen fibers. The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are achieved with a thin, all-encompassing vascular system that operates similarly to other vascular systems in the torso. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.

The Reticular Layer

The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and it strengthens the skin, providing construction and elasticity. Information technology as well supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.

The Subcutis

The subcutis is the innermost layer of the skin, and consists of a network of fat and collagen cells. The subcutis is too known as the hypodermis or subcutaneous layer, and functions as both an insulator, conserving the torso'due south heat, and equally a daze-absorber, protecting the inner organs. Information technology also stores fat as an energy reserve for the torso. The blood vessels, nerves, lymph vessels, and hair follicles as well cross through this layer. The thickness of the subcutis layer varies throughout the torso and from person to person.