SKIN : STRUCTURE AND FUNCTION Dr. M. Joseph Department of Pathology LHSC

Which is the largest organ of the body

Objectives Structure and function of various layers of skin Histologic changes in the epidermis - Spongiosis - Hyperkeratosis - Parakeratosis - Acanthosis - Lichenification - Acantholysis

Skin Functions 1) Protection 2) Thermoregulation 3) Sensation 4) Metabolic

Skin Structure Three Layers a) Epidermis b) Dermis c) Subcutaneous adipose tissue Thickness of skin (for information only) Epidermis +dermis = mm Epidermis only = mm

Skin Structure Basement membrane Apocrine sweat gland

Epidermis: Keratinized stratified squamous epithelium S. Corneum (4) S. Granulosum (3) S. Spinosum (2) S. Basalis (1) Merkel cell 4 layers >95% of epidermal cells are keratinocytes, keratinocyte replication and maturation - keratinization 3 specialized cells (Melanocyte, Langerhans cells, Merkel cells)

Epidermis:4 Layers Under the microscope Stratum Corneum Stratum Granulosum Stratum Spinosum Stratum Basalis

Skin Types/Mucosa Compact Thickened Stratum Corneum Thin skinThick skin, palm, sole Mucosa No stratum Corneum

Function of 3 Specialized Cells in Epidermis Merkel cell Melanocytes - melanin synthesis Langerhans cells - immunologic function Merkel cells -tactile function

Dendritic melanocyte –keratinocyte unit

Melanin production and Transfer Melanin in Melanosome Melanocyte Keratinocyte Melanosome caping keratinocyte nucleus- gives protection of DNA against UV injury

Melanocytes in dark and light skin Dark skinWhite skin The number of melanocytes per unit area of the skin are the same

Light skinDark skin Dark skin has increased production of melanosomes, and melanin More transfer of melanin to keratinocytes Slower rate of degradation of melanosomes

Dermis: upper papillary dermis and lower reticular dermis Collagen Elastic fibers Ground substance Nerves Blood vessels

Skin Vasculature

Skin Appendages (adnexal structures) Sweat glands Hair follicles Sebaceous glands Nail, hair

Skin Appendages Apocrine sweat g l and

Pilo-sebaceous unit ACNE - structure including histology of pilosebaceous unit - pathophysiology of acne - correlate clinical lesions with pathology

Normal Pilosebaceous Unit Hair follicle Sebaceous gland

Acne: a disease of pilosebaceous unit Open comedone Closed comedone The mouth of the dilated hair follicle is widely open in open comedone and closed in closed comedone. The lumen contains keratin, lipid and bacteria Rupture of closed comedones usually lead to inflammatory acne.

Open Comedones Closed Comedones (blackheads) (whiteheads) Inflammed acne (pustular)

Acne: pathogenesis Primary event: development of comedones Androgen dependent Abnormal desquamation of keratinocytes in the pilosebaceous unit Increase in sebum production Overgrowth of Proprionibacterium acnes Rupture of comedones and Inflammation

Skin Structure (molecular level) Epidermal Desmosome Epidermal Basement Membrane Zone

Keratinocytes Desmosome Desmosome Plaque Core

The molecular structure of thedesmosome Desmoplakin 1 (245 kd) Desmoplakin 2 (215 kd) Plaque Core Plakoglobin (85 kd) Plakophilin 1,2,3 (75 kd) Keratocalmin (250 kd) Desmoglein 1 (165 kd) Desmoglein 2 (Colon) Desmoglein 3 (130 kd) Desmocollins: 1a, b 2a, b 3a, b Other Plaque Components: Envoplakin, Perlplakin, and Corneodesmosin (Keratinocyte Envelops) Pemphigus vulgaris antigen is Desmoglein 3, in core

Basement Membrane Zone Hemidesmosome Lamina lucida LaminaAnchoring densafibrils Bullous Pemphigoid antigen is in Hemidesmosome

Basement Membrane Zone Bullous Pemphigoid antigens are BPAg1 and BP Ag2, in Hemidesmosome

Molecular Structure of Basement Membrane Zone For information only

Epidermal Changes: Correlate Pathology with Clinical Appearance

SPONGIOSIS: intercellular edema (1), may cause microvesicles (2) 2 1 Normal skin

Acute dermatitis (Spongiotic dermatitis) Juicy papule Spongiosis

1) Hyperkeratosis: thickening of the stratum corneum 2) Parakeratosis: nuclei preserved 3) Acanthosis: e pidermal hyperplasia (stratum spinosum thickened) 1&2 3 Normal skin

Psoriasis Acanthosis Plaque lesion with a silvery scale Hyperkeratosis Parakeratosis

Lichenification: thickening of the skin with increased skin markings Normal skin Thickening of all layers of skin

Lichenification

Pemphigus vulgaris Acantholysis: loss of desmosomal connection, keratinocytes round up and separate Flaccid bulla withIntraepidermal bulla focal erosion

Objectives Structure and function of various layers of skin Changes in the keratinocytes - Hyperkeratosis, parakeratosis - Acanthosis - Spongiosis - Lichenification - Acantholysis Post lecture reading: Interesting facts on structure & function….webCT Not examinable

QUIZ 1) Which cell produces melanin ? 2) Name the gland involved in acne ? 3) Name the odor producing gland ? 4) What is a desmosome ? 5) Function of Langerhan’s cell ? 6) Layers of basement membrane zone? 7) Where is vit D synthesized ?

1 2 Practice QUIZ 3

Thank You