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DERMATOLOGY. Dr.Pawana Kayastha. FUNCTIONAL ANATOMY,& PHYSIOLOGY OF SKIN. INTEGUMENT : skin( epidermis,dermis ) and associated appendages (sweat glands,sebaceous glands,hairs,nails ). Largest organ in the body.abt. 16% of total body weight. EPIDERMIS : Outermost layer of the integument

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functional anatomy physiology of skin


  • skin(epidermis,dermis) and associated appendages

(sweat glands,sebaceousglands,hairs,nails).

  • Largest organ in the body.abt. 16% of total body weight.


  • Outermost layer of the integument
  • Stratfiedsquamous epithelial layer of ectodermal origin
  • Devoid of vessels
approach to the patient


  • time course of rash
  • distribution of lesions
  • symptoms (e.g. itch or pain)
  • family history (especially of atopy and psoriasis)
  • drug/allergy history
  • past medical history
  • provocating factors (e.g. sunlight or diet)
  • previous skin treatments.
  • looking at and feeling a rash
  • assessment of nails, hair, and mucosal surfaces, even if these are recorded as unaffected.
  • The following terms are used to describe distribution: flexural, extensor, acral (hands and feet), symmetrical, localized, widespread, facial, unilateral, linear, centripetal (trunk more than limbs), annular and reticulate (lacy network or mesh like).
  • A glass slide is pressed firmly on the skin lesion. If a red lesion blanches, it implies that the red colour is secondary to blood within the vessels. By contrast, blood outside the vessels, such as that from a bruise or from vasculitis, will not blanch.
  • Success in blanching is a more useful physical sign than failure to blanch.
  • Granulomatous lesions a glass slide reveals an appearance commonly referred to as 'apple jelly nodule'.
epiluminescence microscopy dermatoscopy dermoscopy
  • This refers to surface microscopy using an illuminated lens with oil immersion directly on to the skin's surface. The presence of oil reduces specular reflection and reduces 'errors' due to the different refractive indexes of the various superficial layers of skin.
wood s light
  • This involves irradiation with a UV light source that causes normal skin, particularly dermis, to fluoresce (in the visible light range).
  • The basis for this is that in the ultraviolet A wavebands used by Wood's light, pigmentation has a greater degree of absorption than at longer wavebands, resulting in a greater degree of difference in fluorescence between pigmented and depigmented skin.
  • Wood's light also enhances the examination of cutaneouspigmentary abnormalities such as in patients with vitiligo, where areas of subtle depigmentation are more easily seen.
mycology samples
  • Cutaneous scale, nail clippings and plucked hairs can be examined by light microscopy when mounted in 20% potassium hydroxide.
  • The keratin is dissolved, allowing fungal hyphae to be identified.
  • Bacterial swabs Bacterial swabs taken in an appropriate culture medium are sometimes useful.
prick tests
  • Prick tests are a way of detecting cutaneous type I (immediate) hypersensitivity to various antigens such as pollen, house dust mite or dander. The skin is pricked with a dilution of the appropriate antigen solution. After 10 minutes a positive response is indicated by a weal and a flare. The weal is due to a local increase in capillary permeability and the flare a result of activation of the axon reflex.
  • . In individuals with a clear history of particular type I hypersensitivity a systemic reaction may follow a prick test and resuscitation facilities should be available. As an alternative, specific IgE levels to antigens can be measured in serum by a specific radioallergosorbent test (RAST).
patch tests
  • Patch tests detect type IV (delayed or cell-mediated) hypersensitivity. It is common practice for a 'battery' of around 20 common antigens, including common sensitisers such as nickel, rubber and fragrance mix, to be applied to the skin of the back under aluminium discs for 48 hours. The sites are then examined for a positive reaction 24 hours later and possibly again a further 24 hours later. An eczematous reaction, in the absence of an irritant reaction, suggests a type IV hypersensitivity to that particular allergen.
  • A negative patch test does not exclude a pathogenic role for a particular antigen nor does the presence of a particular response to an antigen mean that this antigen is causing the clinical disease.
  • Skin biopsies for routine histological examination are usually fixed in 10% formalin and stained with haematoxylin and eosin. Immunocytochemistry may also be performed on formalin-fixed sections but may require frozen sections . Immunocytochemistry is particularly useful for tumour diagnosis.

A portion of the skin biopsy can be frozen in liquid nitrogen for direct immunofluorescence (IF). This involves visualising antigens that are present in skin by identifying them with fluorescein-labelled antibodies. Similarly, indirect immunofluorescence can identify circulating antibodies in the serum by an additional step of adding the serum to a section of normal skin or other substrate. Immunofluorescence plays a major role in the diagnosis of the autoimmune bullous disorders.

electron microscopy

This investigation has played an important role in the diagnosis of some of the rare blistering disorders such as epidermolysisbullosa, although the availability of a range of antibodies to basement membrane zone antigens has in part replaced it.


Phototesting involves exposing skin (often on the back) to a graded series of doses of ultraviolet radiation (UVR) of known wavelength, either on one occasion or repeatedly.


In many photodermatoseserythema will occur at a lower dose of UVR than occurs in the normal population (e.g. drug-induced photosensitivity), or the time course of erythema may be prolonged (as in xerodermapigmentosum). Alternatively, UVR will provoke lesions with the morphology of the underlying photodermatosis, such as may occur in lupus erythematosus or solar urticaria. Diagnostic phototesting is an essential component of the investigation of patients with presumed photosensitive drug reactions and idiopathic photodermatoses such as solar urticaria.