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Introduction to Dermatology Part-
(Skin Structure)
Course Objectives :
Below is a summary of the key objectives of the course. ➢ To understand the basics of skin anatomy. ➢ To be familiar with the language of dermatology by learning the primary and secondary skin lesions and to be able to describe various skin conditions. ➢ To enable medical students to recognize the most common skin diseases and to manage them. ➢ To be familiar with the diagnostic laboratory tests pertinent to dermatology. ➢ To help students to formulate decent differential diagnoses of skin diseases. ➢ To gain an overview of the skin manifestations of systemic diseases. ➢ To be able to deal very appropriately with different emergencies in dermatologic diseases
Sources : doctor’s slides and notes + FITZPATRICK color atlas +433team male and
female + 434team
Done by: Qusay Ajlan
Revised by: Khaled Al Jedia
[ Color index : Important | Notes | Extra ]
The Skin The human skin is the outer covering of the body.The skin is a complex, dynamic organ and is the largest organ of the body. Skin function : ★ Barrier to harmful exogenous substance & pathogens. ★ Prevents loss of water & proteins. ★ Sensory organ protects against physical injury. ★ Regulates body temperature. ★ Important component of the immune system. ★ Vit.D production by absorbing UVB. ★ Has psychological and cosmetic importance such as hair, nails.
Stratum corneum (cornified layer horny cell layer) ● Outermost layer ● The cells in this layer have No nucleus ● Its 25 cell layer ● The cells have a thick envelope that helps it resist external chemicals. Stratum granulosum (granular cell layer): ● Diamond shaped cells ● Cytoplasm is filled with keratohyalin organelles (the protein Keratohyalin forms dense cytoplasmic granules that promote dehydration of the cells well as aggregation and cross-linking of the keratin fibers. The nuclei and other organelles then disintegrate, and the cells die) ● The thickness of this layer is proportional to that of the stratum corneum ● In thin skin its 1-3 cell layers and 10 cell layers in thick (fingertips, hand and soles) Stratum spinosum ( Spinous cell layer ): ● In the spinous layer they are connected to each other by desmosomes and gap junctions which appear as spines thus called spinous layer ● Bone marrow derived Langerhans cells which are antigen presenting cells (MHC II) are found in this layer.(skin immune function) And they can be identified through birbeck granules. Abnormal proliferation of these cells is seen in Langerhans cell histiocytosis Basal cell layer (stratum basale) : ● This layer Rests on (above) the basement membrane ● Divides continuously and moves upwards. ● It takes 28 days to transmit cells from this layer to stratum corneum ● Melanocytes are dendritic cells lying between basal cells in a ratio of 1: ● Melanocytes are cells responsible for skin pigment and provide protection from UV light. They are mainly seen in this layer. ● The size of melanosomes and packaging differentiate white from dark skin. ● The number of melanocytes are equal in white and dark skin ● Melanocytes can also be found in the hair bulb, eye and brain.
Cornification (keratinization) : ● It is the cytoplasmic events that occur in the cytoplasm of epidermal keratinocytes during their terminal differentiation into dead horny cell (corneocyte) ● The total process takes approximately 2 months ● It involves the formation of keratin polypeptides. ● Abnormalities in this process lead to roughness and scaling of the skin like PSORIASIS (In psoriasis it takes 3 days which will result in a lot of scales) Basement Membrane : Between epidermis and dermis and Consists of two layers: ● Lamina Lucida (thin clear amorphus space) (above) (superficial) ● Lamia dense (an electron dense area) (below)(deep) Contains important proteins and proteinous structures which are important in bullous and autoimmune diseases ● Laminin ● Desmosomes : adheres keratinocytes to the basement membrane ● Anchoring filaments : connects lamina lucida to lamina densa ● Anchoring fibrils : connects lamina densa to papillary dermis Its the site of attack injury in blistering diseases Types of blisters : 1-Intraepidermal blisters (within the spinosum layer ) (like pemphigus vulgaris ) 2-subepidermal : between dermis and epidermis like(bullous pemphigoid)
Subcutaneous fat: ● lies below the dermis. ● Attach the skin to underlying bone ● and muscle as well as supplying it with blood vessels and nerves ● The main cell types are fibroblasts macrophages and adipocytes ● Inflammation of the subcutaneous fat is called panniculitus
Skin appendage are skin-associated structures that serve a particular function It includes : 1-eccrine/apocrine glands 2-hair follicles 3-sebaceous glands 4-nails Eccrine glands: ● Tubular structures open freely on the skin , not attached to hair follicles. ● Under the influence of cholinergic stimuli. ● Present everywhere except ● The vermilion border^1 ● Nailbeds ● glans penis ● Labia minora ● Abundant in palms and soles. (^1) is the normally sharp demarcation between the lip and the adjacent normal skin.
Hair follicles: ● Hair follicle has the hair shaft, hair bulb and the bulge. ● Pilosebaceous unit include: ○ hair follicle ○ sebaceous gland ○ arrector pili Muscle. nails: ● The nail plate is formed of hard keratin. ● Proximal nail fold morphology can be altered in connective tissue disease. ● The lunula is the visible part of the matrix. ● The matrix covers the mid-portion of the distal Phalanx. ● Fingernails grow 3mm/month. ● Toenails grow 1mm/month. ● Nails can be affected in systemic and skin diseases.
