Integumentary System (Skin)

THE INTEGUMENT

•         The integument is the body’s most massive organ.

•         Integumentary system is composed of skin that covers   the entire body, together with certain accessory organs which are derivatives of the skin, such as nails, hair, sweat glands, sebaceous glands and mammary gland.

ESSENTIAL FUNCTIONS

•         Acts as a barrier

•         Provides immunologic information

•         Participates in homeostasis

•         Conveys sensory information

•         Performs endocrine functions

•         Functions in excretion

Layers of Skin

a. Epidermis

1. STRATUM BASALE/ STRATUM GERMINATIVUM

•         Single layer of cells

•         Cuboidal / Columnar cells

•         Closely spaced nuclei

•         Basophilic cytoplasm

•         Contains melanin

•         Cell junctions(desmosomes,hemidesmosomes)

•         Contains stem cells

•         Provides epidermal cell renewal

2. STRATUM SPINOSUM

•         Several cells thick

•         Larger cells

•         Cytoplasmic processes or spines

•         Desmosomes

Node of Bizzozero(thickened desmosome site)

•         Prickle cells

•         Flattening of cells with elongated nuclei towards surface

3. STRATUM GRANULOSUM

•         Most superficial layer of nonkeratinized portion of epidermis

•         One to three cell layers thick

•         Keratohyalin granules

•         Irregular in shape

•         Variable in size

•         Intense basophilic staining

•         Contain cystine rich and histidine rich proteins (precursors of filaggrin)

4. STRATUM LUCIDUM

•         A subdivision of stratum corneum

•         Normally well seen in thick skin

•         Refractile appearance

•         Stains poorly

•         Eosinophilic cells

5. STRATUM CORNEUM

•         Cells are flattened, desiccated, anucleated

•         Most differentiated cells in the skin

•         Filled almost entirely with keratin filaments

•         Thick plasma membrane

•         Water barrier in epidermis

•         Variation in the thickness of layer

b. Dermis

•         Dermis varies from 0.2 to 4 mm in thickness

•         Composed of dense, irregularly arranged C.T.

•         Contains three types of C.T. fibres plus fibroblasts and macrophages

•         Two layers can be distinguished

•         Junction between dermis and epidermis

DERMAL RIDGES & DERMAL PAPILLA

•         True dermal ridges are present in thick skin in addition to dermal papillae

•         Dermal ridges have a parallel arrangement with the dermal papillae located between them

•         Distinctive pattern of dermal ridges

•         Most prominent in palmar and plantar surfaces

•         Hemidesmosomes strengthen the attachment of epidermis to the underline connective tissue

LAYERS OF DERMIS

1.  THE PAPILLARY  LAYER

•         Consists of loose C.T.

•         Thickness of collagen fibres

•         Contains type I and type III collagen

•         Irregular network of elastic fibres

•         Includes dermal papillae and ridges

•         Blood vessels

•         Nerve processes

2. THE RETICULAR LAYER

•         Always considerably thicker and less cellular than the papillary layer (although its thickness varies)

•         Characterized by thick irregular bundles of mostly type I collagen and by coarse elastic fibres

•         Langer’s lines

(formed by regular arrangement of collagen and elastic fibers

HYPODERMIS / SUBCUTANEOUS FASCIA

•         Panniculus adiposus

•         Arrector pilli muscles(connect hair follicle to more superficial dermis

•         Goose flesh

•         Panniculus carnosus

•         Thick in people living in cold climates and in wel nourished people.

CELLS OF EPIDERMIS

1. KERATINOCYTES

2. MELANOCYTES

3. LANGERHAN’S CELLS

3. MERKEL’S CELLS

KERATINOCYTES

•         Predominant cell type of epidermis

•         Originate in basal epidermal layer

•         Have two essential activities:

o        Produce keratin

o        Participate in epidermal water barrier

•         Structure of keratinocytes

MELANOCYTES

•         Neural crest derived

•         Scattered among the basal cells of S. basale

•         Epidermal – melanin unit

•         Dendritic cell

•         Cell junctions

•         Ratio of melanocytes to keratinocytes

•         In H & E preparations

•         With TEM

•         Capacity to replicate

•         Produce and distribute melanin into keratinocytes

•         Most important function of melanin

•         Production of melanin

•         Premelanosomes

•         Sites of concentration

•         Pigment donation

LANGERHAN’S CELLS

•         Dendritic appearing, antigen presenting cells in the epidermis

•         Mesenchymal origin and are derived from CD34+ stem cells in bone marrow so part of MPS system

•         In routine H & E preparation

•         Cell junctions

•         With special techniques such as gold chlorite impregnation

MERKEL’S CELLS

•         Modified epidermal cells

•         Located in stratum basale

•         Most abundant in skin where sensory perception is acute

•         Cell junctions

•         Lobed nucleus

•         Contain keratin filaments

•         Melanosomes

•         Cored neurosecretory granules

•         Merkel corpuscle

•         Mechanoreceptors

View histological slides here.