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

2. Which is the largest organ of the body

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

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

5. Skin Structure Three Layers a) Epidermis b) Dermis c) Subcutaneous adipose tissue Thickness of skin (for information only) Epidermis +dermis = 1.5-4.0 mm Epidermis only = 0.05-0.1 mm

6. Skin Structure Basement membrane Apocrine sweat gland

7. 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)

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

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

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

11. Dendritic melanocyte –keratinocyte unit

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

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

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

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

16. Skin Vasculature

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

18. Skin Appendages Apocrine sweat g l and

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

20. Normal Pilosebaceous Unit Hair follicle Sebaceous gland

21. 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.

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

23. 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

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

25. Keratinocytes Desmosome Desmosome Plaque Core

26. 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

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

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

29. Molecular Structure of Basement Membrane Zone For information only

30. Epidermal Changes: Correlate Pathology with Clinical Appearance

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

32. Acute dermatitis (Spongiotic dermatitis) Juicy papule Spongiosis

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

34. Psoriasis Acanthosis Plaque lesion with a silvery scale Hyperkeratosis Parakeratosis

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

36. Lichenification

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

38. 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

39. 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 ?

40. 1 2 Practice QUIZ 3

41. Thank You