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Understanding The Skin

  • Basic Skin Physiology

    Human skin is our soft outer covering for our bodies. In humans, our skin is the largest ORGAN of the integumentary system. Our skin is made up of multiple layers ectodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs in humans(1). Our skin is our protection from the environment and reacts to our environment. Our skin is the first line of defense from external environmental factors. One of the most important roles the skin plays for us is the role in protecting the body against pathogens(2) and excessive water loss(3). Some other functions of the skin are:

    • Insulation
    • Temperature Regulation
    • Sensation
    • The production of Vitamin D folates.

    If a person’s skin becomes heavily damaged, the skin may become scars and discolored and/or depigmented.

    The main components of skin are:

    • Epidermis
    • Basement Membrane
    • Dermis
    • Hypodermis

    (1)”Skin care” (analysis), Health-Cares.net, 2007 Proksch E, Brandner JM, Jensen JM. (2008).
    (2) The skin: an indispensable barrier. Exp Dermatol. 17(12):1063–72.
    (3) Madison KC. (2003). Barrier function of the skin: “la raison d’etre” of the epidermis. J Invest Dermatol. 121(2):231-41. doi:10.1046/j.1523- 1747.2003.12359.x PMID 12880413

  • Epidermis Layer

    The outermost layers of the skin are composed of the epidermis layer. The epedermis forms a protective barrier over the body’s surface. This layer is responsible for keeping water in the body and preventing pathogens from entering. This layer is a stratified squamous epithelium,(1) composed of proliferating basal and differentiated suprabasal keratinocytes. The epidermis also helps the skin regulate body temperature.

    Keratinocytes in the stratum basale proliferate through mitosis and the daughter cells move up the strata changing shape and composition as they undergo multiple stages of cell differentiation to eventually become anucleated. During that process keratinocytes will become highly organized, forming cellular junctions (desmosomes) between each other and secreting keratin proteins and lipids which contribute to the formation of an extracellular matrix and provide mechanical strength to the skin. (2) Keratinocytes from the stratum corneum are eventually shed from the surface (desquamation).

    The epidermis layer contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis.

    The layers of the Epidermis:

    • Stratum Corneum
    • Stratum Lucidum (Palms and Soles)
    • Stratum Granulosum
    • Stratum Spinosum
    • Stratum Germinativum (also called the Stratum Basale)
  • Basement Membrane

    The thin sheet of fibers called the basement membrane is what separates the epidermis from the dermis. The basement membrane is made through the action of both tissues. The basement membrane controls the traffic of cells and molecules between the dermis and epidermis but also serves, through the binding of a variety of cytokines and growth factors, as a reservoir for their controlled release during physiological remodeling or repair processes.(1)

    The primary function of the basement membrane is to anchor down the epithelium to its loose connective tissue (the dermis) underneath. This is achieved by cell-matrix adhesions through substrate adhesion molecules (SAMs).

    The basement membrane acts as a mechanical barrier, preventing malignant cells from invading the deeper tissues.(2) Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called carcinoma in situ.

    The basement membrane is also essential for angiogenesis (development of new blood vessels). Basement membrane proteins have been found to accelerate differentiation of endothelial cells.(3)

    (1)Iozzo, RV (2005). “Basement membrane proteoglycans: From cellar to ceiling”. Nature reviews. Molecular cell biology 6 (8): 646–56. doi:10.1038/nrm1702. PMID 16064139.
    (2)Liotta LA, Tryggvason K, Garbisa S, Hart I, Foltz CM, Shafie S (March 1980). “Metastatic potential correlates with enzymatic degradation of basement membrane collagen”. Nature 284 (5751): 67–8. doi:10.1038/284067a0. PMID 6243750
    (3) Kubota Y, Kleinman HK, Martin GR, Lawley TJ (October 1988). “Role of laminin and basement membrane in the morphological differentiation of human endothelial cells into capillary-like structures”. J. Cell Biol. 107 (4): 1589–98. doi:10.1083/jcb.107.4.1589. PMC 2115245. PMID 3049626.

  • Dermis Layer

    The layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues is the dermis layer. The dermis layer consists of connective tissue and cushions the body from stress and strain.

    The dermis is divided into two specific layers:

    • The Papillary Region - The Papillary Region is the superficial area adjacent to the epidermis(1) . It provides s strengthened connection with the epidermis.
    • The Reticular Dermis - The Reticular Dermis is a deep thicker area (1). This area of the skin gives the skin its strength, extensibility and elasticity.

    The dermis is tightly connected to the epidermis through the basement membrane. Structural components of the dermis are:

      • Collagen
      • Elastic Fibers
      • Extrafibrillar Matrix (previously called ground substance).(2)

    The dermis layer also contains mechanoreceptors. These receptors provide:

    • Sense of touch and heat
    • Hair Follicles
    • Sweat Glands
    • Sebaceous Glands
    • Apocrine Glands
    • Lymphatic Vessels
    • Blood Vessels.

    These blood vessels are what provide both vital nourishment and waste removal for both dermal and epidermal cells.

    The three (3) major types of cells found in the dermis (3):

    • Fibroblasts
    • Macrophages
    • Adipocytes

    Other main components of the dermis (3):

    • Collagen (which provides strength)
    • Elastin (which provides elasticity)
    • Glycosaminoglycan’s.

    (1)James, William; Berger, Timothy; Elston, Dirk (2005). Andrews’ Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Pages 1, 11–12. ISBN 0-7216-2921-0.
    (2) Marks, James G; Miller, Jeffery (2006). Lookingbill and Marks’ Principles of Dermatology (4th ed.). Elsevier Inc. Page 8–9. ISBN 1-4160-3185-5.
    (3)3.^ a b The Ageing Skin – Structure

  • Hypodermis Layer

    The hypodermis is not part of the skin. The hypodermis lies below the dermis. The objective of the hypodermis is to attach our skin to underlying bone structure and muscle. Another main function is supplying it with blood vessels and nerves.

    The hypodermis consists of loose connective tissue and elastin. The main cell types are:

    • Fibroblasts
    • Macrophages
    • Adipocytes (the hypodermis contains 50% of body fat).

    Fat serves as padding and insulation for the body. Another name for the hypodermis is the subcutaneous tissue (2).

    More specifically the hypodermis contains the following (1):

    • Fibrous bands anchoring the skin to the deep fascia
    • Fat, except in the eyelid, scrotum, penis, nipple and areola
    • Blood vessels on route to the dermis
    • Lymphatic vessels on route from dermis
    • Hair follicle roots
    • Fine, flat sheets of muscle, in certain locations, including the scalp, face, hand, nipple, and scrotum, called the panniculus carnosus
    • The glandular part of some sudiferous glands
    • Nerves: all nerves identified as “cutaneous“
    • Nerves: free endings and Pacinian corpuscles
    • Bursae, in the space overlying joints in order to facilitate smooth passage of overlying skin


  • Skin Thickness

    The thickness of a person’s skin varies from location to location on the body. In humans for example, the skin located under the eyes and around the eyelids is generally considered the thinnest skin in the body at 0.5mm thick. This are of skin is generally one of the first areas to show the signs of aging. Such signs might be:

    • ‘Crow’s Feet’
    • Wrinkles
    • Dark Circles
    • Baggy Eyes

    The average thickness of skin on your face will be right around 1.3mm thick (1). The neck area usually has a general thickness of 2.0mm (2). The rest of the areas on the body will vary in thickness of skin. The thickness can range from 4 mm – 5mm in some areas.

    There are many factors to determine how quickly a person’s skin will age and become thinner. The two main areas to determine how a person’s skin will age and become thinner are:

    • Genetics
    • Environmental Conditions

    (1) http://wiki.answers.com/Q/How_thick_is_facial_skinProksch E, Brandner JM, Jensen JM. (2008).The skin: an indispensable barrier. Exp Dermatol. 17(12):1063–72.
    (2) http://www.chacha.com/question/how-thick-is-the-skin-on-a-humans-neck

  • Differences between young vibrant skin and older aged skin

    The aging of skin is a known as the cellular degenerative process. It is a result from genetics and environmental factors. The dermal layer of skin contains the structural elements and proteins necessary for maintaining skin thickness, elasticity, and vitality. With age, the rate of production of these proteins decreases, and results in wrinkling, laxity, dryness, and general thinning of the skin.

    Prominent wrinkling is mainly caused by the loss of dermal collagen content, and a decreased rate of collagen production(1). This is a result of decreased growth factor production.

    When your skin is young, the dermal layer of skin naturally contains more growth factors necessary for maintaining skin thickness, elasticity and vitality.

    Molecular Aspects of Dermatology, GC Priestley, ed. John Wiley & Sons, NY 1993

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