The Skin Dr. D. Czarnecki MD MBBS

The Skin The skin is a BARRIER: physical – immunologicalThe skin is a BARRIER: physical – immunological WATER LOSSIt prevents WATER LOSS BODY TEMPERATUREIt controls BODY TEMPERATURE HORMONESIt produces HORMONES VITAMIN DIt produces VITAMIN D ELECTRICAL CURRENTSIt protects against low voltage ELECTRICAL CURRENTS

The Skin The main layers of the skin are:The main layers of the skin are: The epidermis The epidermis The dermis The dermis The epidermis is the cellular layer and lacks blood vessels or lymphatics. It can be divided, from bottom to surface, into the:The epidermis is the cellular layer and lacks blood vessels or lymphatics. It can be divided, from bottom to surface, into the: The basal layerThe basal layer Stratum spinosumStratum spinosum Stratum ganulosumStratum ganulosum Stratum corneumStratum corneum

The epidermis The dermis Fibroblasts Collagen elastin Stratum corneum Sweat gland Hair follicle with a sebaceous gland Blood vessels and lymphatics Langerhans cell melanocyte Basement membrane keratinocyte

The Skin The epidermis is separated from the dermis by the basement membrane. This is an anchoring layer and a barrier.The epidermis is separated from the dermis by the basement membrane. This is an anchoring layer and a barrier. The dermis containsThe dermis contains Blood vessels and lymphaticsBlood vessels and lymphatics NervesNerves Collagen and elastinCollagen and elastin FibroblastsFibroblasts Immune cellsImmune cells

THE STRATUM CORNEUM Lipid is synthesized within it It is a barrier, the main barrier between the skin and the environment It absorbs Ultra Violet Light The stratum corneum consists of dead keratinocytes within a lipid matrix

The skin immune system The skin is a major part of the immune systemThe skin is a major part of the immune system Langerhans cells migrate from the bone marrow to the epidermis.Langerhans cells migrate from the bone marrow to the epidermis. Langerhans cells phagocytose antigens, process the antigen, and migrate to the regional lymph node.Langerhans cells phagocytose antigens, process the antigen, and migrate to the regional lymph node. The Langerhans cell presents processed antigen to a helper (CD4) lymphocyte and this triggers an immune responseThe Langerhans cell presents processed antigen to a helper (CD4) lymphocyte and this triggers an immune response

Langerhans cells (from the bone marrow) Migrate to the epidermis Phagocytose antigen CD4 The antigen is degraded, transported to the regional lymph node where it is presented to HELPER LYMPHOCYTES Cytokines boost the immune response

The skin immune system Other products that protect the skinOther products that protect the skinDEFENSINS Peptides produced by the keratinocytesPeptides produced by the keratinocytes Inhibit the growth of bacteria and yeastsInhibit the growth of bacteria and yeasts Psoriatic skin produces thesePsoriatic skin produces these

Ultraviolet light 200nm nm UVCUVBUVA ozone Glass sunscreen opaque material

Ultraviolet Light That part of the sun’s rays between 200 and 400 nmThat part of the sun’s rays between 200 and 400 nm It is divided into UVC, UVB, and UVA UVC is the strongest but does not penetrate through ozoneUVC is the strongest but does not penetrate through ozone UVB is attenuated by ozone but does not penetrate through glass or sunscreenUVB is attenuated by ozone but does not penetrate through glass or sunscreen UVA does not penetrate through opaque materials. It is the weakest component of ultraviolet lightUVA does not penetrate through opaque materials. It is the weakest component of ultraviolet light

Ultraviolet light keratinocyte CYTOKINES GROWTH FACTORS VITAMIN DHORMONES Produces:

Melanocortin receptor 1 αMSH tyrosinase Eumelanin (brown) Phaeomelanin (yellow) Mutations in the MCR1 are associated with red hair Mutations are associated with an increased risk of melanoma, independent of hair colour Skin pigment is a mixture of eumelanin and phaeomelanin αMSH induces the enzyme These are produced by tyrosinase – αMSH induces the enzyme

Melanocytes produce melanin and it is transferred to the keratinocytes in contact with the melanocyte. Melanin is contained in melanosomes. In whites the melanosomes are small and grouped in membrane bound organelles. In blacks they are large and individual White skin Black skin A melanocyte and keratinocytes