1. Basic structures and functions of skin

Dermatology

1. Basic structures of the skin Dr. BIJAY KR YADAV

2. Introduction to skin: Largest organ of our body. It weighs an average of 4 kg Area- 2m 2 It acts as a barrier (external environment as well as preventing loss of important body constituents )

3. Structure of skin Composed of 3 layers: Epidermis, dermis and subcutaneous tissue. Epidermis: Outer layer. Is a continually renewing structure gives rise to derivative structures called appendages (pilosebaceous units, nails, and sweat glands). The epidermis ranges in thickness from 0.4 to 1.5 mm.

4. Epidermis composed of 4 layers St. corneum St. granulosum St. spinosum /pickle cell layer St. basalis St lucidum ( palms and soles) Composed of 4 cell types- . Keratinocytes Melanocytes Langerhans cells Merkel cells

5. Stratum corneum Outermost layer The epidermis is stacked layers of anucleate, flattened cornified cells It provides mechanical protection to the skin and a barrier to water loss and permeation of soluble substances from the environment

6. Stratum granulosum 1-2 cell layer thick Consists of keratihyaline granules consisting of profillagrin , keratin filaments, loricrin These are the precursors of lipids of cell envelop.

7. Stratum spinosum They are named for the spine-like appearance of the cell margins. As these cells differentiate and move upward through the epidermis, they become progressively flatter and develop organelles known as lamellar granules. These secretory organelles deliver precursors of stratum corneum lipids into the intercellular space.

8. Stratum germinativum/basalis – innermost layer in which cells undergo mitosis continually. This allows for replacement of upper layers that are sloughed and repair of damage. New cells move toward the surface and their cytoplasm is replaced by keratin – a protein that makes them tough and waterproof. 30% of basal cells are actively dividing.

9. Keratinocytes/ squamous cells Principal cells of the epidermis*(85%) Flattened dead cells Arranged like bricks and stuck together by lipids Ectodermal in origin Special function is to produce keratin.

10. Melanocytes: They are pigment producing cells Derived from neural crest Are dendritic cells Reside in basal layer at 1:10 every basal keratinocytes Contain melanosomes ( size and no determine the color)

11. Langerhans cells Found scattered among keratinocytes in st. spinosum Constitute 3-5% of cells Characterised by intracytoplasmic organelle Langerhans/ Birbeck granules Responsible for delayed type hypersensitivity( antigen presenting cells)

12. DERMAL-EPIDERMAL JUNCTION The dermal-epidermal junction (DEJ) is a basement membrane zone that forms the interface between the epidermis and dermis. The major functions of the DEJ are to attach the epidermis and dermis to each other and to provide resistance against external shearing forces

13. D-E junction…….. Junction is formed by basement memb zone. Ultrastructurally , composed of 4 components. 1. memb of basal cells with hemidesmosomes 2. lamina lucida 3. lamina densa 4. fibrous components ass with anchoring fibrils, dermal microfibrills , collagen fibres .

14. Functions of skin 1. Protection - against chemicals, particles, uv rays, microbes 2. Homeostasis - prevents loss of water, electrolytes, macromolecules 3. Shock absorber- by dermis & sc tissue. 4. Temperature regulation- bl.vs ,sweat glands. 5. Sensation- thru specialized nerve endings 6. Protection and prising - nails 7. Insulation and calorie reserve - sc fat 8. Vit D synthesis- keratinocytes 9. Body odour - apocrine sweat glands 10. Lubrication - sebaceous glands.

15. Disorder of the sebaceous glands Sebaceous glands are holocrine in association with the hair follicles and produced an oily secretion called sebum. The glands are present all over the body except the palm, the soles, the eyelids and the fingertips. These are most numerous on the scalp, the face, the upper middle portion of the chest and the back. The sebaceous glands are rudimentary at birth but start functioning at the age of puberty under the influence of sex hormones. Androgens increases the size of sebaceous glands, while estrogens reduces the size of the sebaceous glands.

16. Primary Lesions Macule : A circumscribed, flat, non palpable area of altered colour with variable size and shape. It can be either hyper, hypo or depigmented like café au lait macules in neurofibromatosis, tan brown in melasma . Papule : A palpable small, solid, elevated lesion of <0.5 cm, with well defined margins which projects above the surface of the surrounding skin like the lesions of molluscum contagiosum , miliaria , acne, scabies etc . Vesicle : It is a circumscribed, well defined, raised, fluid filled lesion, of size <0.5 cm in diameter. It is found in diseases like chicken pox, herpes simplex, herpes zoster, pemphigus etc . Wheal : An erythematous, edematous, evanescent, well circumscribed, raised, round to oval lesion which disappears within 24 hours. Wheal is a primary lesion of urticaria .

17. Secondary Lesions Scale : Scales are the flakes of lesion that are formed secondary to some infammatory process. They are of various types like silvery scales as seen in psoriasis, greasy yellow scales in seborrhoeic dermatitis, collarete scales in pityriasis rosea , fish like scales in icthyosis . Crust : Crust is formed due to any discharge like pus, serum or blood. It is seen in eczematous dermatitis, impetigo, pemphigus and pemphigoid group,etc Excoriation : A superficial excavation of epidermis which may be linear or punctate resulting from scratching. It is commonly seen in scabies, atopic dermatitis, lichen planus,etc . Lichenification : It is the thickening of epidermis with hyperpigmentation and loss of skin marking in response to prolonged itching . Ulcer: A skin defect where there has been loss of the epidermis and dermis

18. Macule: Non-palpable change in skin color with distinct borders

19. Morphology

20. Macule: Non-palpable change in skin color with distinct borders

21. Papule: Palpable, solid lesion less than 0.5 cm in diameter

22. Papule: Palpable, solid lesion less than 0.5 cm in diameter

23. Papule: Palpable, solid lesion less than 0.5 cm in diameter blue nevus

24. Vesicle: Fluid-containing, superficial, thin-walled cavity less than 0.5 cm

25. Vesicle: Fluid-containing, superficial, thin-walled cavity less than 0.5 cm

26. Vesicle: Fluid-containing, superficial, thin-walled cavity less than 0.5 cm varicella with vesicles and bullae

27. Ulcer: A skin defect where there has been loss of the epidermis and dermis

28. Ulcer A focal loss of epidermis and dermis, and heal with scarring Examples Decubitus Ischemic Stasis ulcers Neoplasms

29. Ulcer: A skin defect where there has been loss of the epidermis and dermis pyoderma gangrenosum

30. Crust Is a collection of dried serum and cellular debris- a scab Examples Acute eczematious inflammation Atopic on the face Impetigo- golden or honey colored Tinea capitis

31. Morphology

32. CRUSTING SCALING

33. Excoriation An erosion caused by scratching Are often linear Examples Scabies Atopic dermatitis Dry skin

34. Lichenification An area of thickened epidermis induced by scratching Skin lines are accentuated so it looks like a washboard Examples Atopic dermatitis, chronic eczematous dermatitis

35. LICHENIFICATION

36. FISSURE ULCER

37. ATROPHY LICHENIFICATION

38. Thank you Have a good day