Skin Anatomy: The Body's Protective Covering

1. Skin: The Integumentary System

2. Functions • Provides a barrier against hazardous materials and pathogens • Major receptor for the sense of touch • Waterproofs the body and prevents fluid loss • Helps the body synthesize vitamin D from ultraviolet light • Integument means “covering”

3. Structures • Skin • Largest organ of the body • Approx 5 kg in the average human • Dermat/o, cutane/o mean skin • Made up of two distinct tissue layers and an underlying layer of fatty tissue

4. Skin Layers

5. Structures • Epidermis • Outermost layer of skin • Consists of stratified squamous epithelium • Top layers are flat overlapping cells that contain soft keratin(fibrous, water-repellant protein) – form the waterproof barrier

6. Structures • Lower layer is the basal layer – produces the epithelial cells that get pushed toward the surface where they die and become filled with keratin • The dead cells slough off so new cells can take their place • The basal layer also contains melanocytes that produce melanin (the dark brown pigment that determines skin colour, produces freckles, and protects against ultraviolet light)

8. Structures • Dermis • AKA corium • Contains connective tissue, blood and lymph vessels, nerve fibers • Collagen– tough, flexible, fibrous protein • Mast Cells – respond to injury, infection, or allergy by releasing substances like histamine and heparin • Provides a living substrate for the epidermis, and contains the accessory structures, such as hair follicles, glands, and nerve endings

9. Structures • Subcutaneous Layer • Connects the skin loosely to the underlying muscles • Consists of loose connective tissue and adipose tissue • Subcutaneous means “below the skin” • Provides a cushion against shock, and insulation against temperature changes

10. Accessory Structures • Sebaceous Glands • Associated with hair follicles • Except on palms of hands and soles of feet (most concentrated in the scalp) • Secrete sebum – an oily substance which lubricates the skin and discourages bacterial growth (it is slightly acidic) • Also helps to prevent water loss

11. Accessory Structures • Sweat Glands • AKA sudoriferous glands • Tiny, coiled glands that secrete perspiration (sweat) to the body surface • Most numerous on the palms of the hands, soles of the feet, forehead, armpits • Perspiration is composed primarily of water and some salt and waste products • Functions to excrete excess water and cool the body • Hidr/o means sweat • Hidrosis is the production of sweat

12. Accessory Structures • Eccrine Sweat glands • Open onto the skin surface and secrete through openings called pores • Most numerous type

13. Accessory Structures • Apocrine Sweat glands • Open into hair follicles • Most numerous in armpit and external genitalia • Substance secreted also contains proteins and fatty acids which give it a yellow colour • Respond to pain, emotional stress, sexual arousal, etc

14. Accessory Structures • Hair (trich/o, pil/o) • Columns made of dead protein cells filled with hard keratin • Melanocytes in the follicle produce melanin which colours the hair • Follicle: sac that holds the root of the hair (its shape determines whether hair will be straight or curly) • Arrector pili – tiny muscle fibers that contract to make the hair stand erect (reduces heat loss through the skin)

15. Accessory Structures • Nails • Thin plates of keratinized cells that protect the end of the fingers and toes • Nail Body: translucent, closely molded to underlying tissues

16. Accessory Structures • Nail Bed: joins the nail body to the underlying tissue and nourishes the nail • Very vascularized – gives the nail its pink colour • Root: fastens the nail to the finger or toe by fitting it into a groove in the skin

17. Accessory Structures • Free Edge: portion of the nail body not attached to the nail bed (white portion of the nail) • Lunula: pale, half-moon shaped region at the root of the nail • Part of the nail body that covers the matrix (active area where new cells form)

18. Accessory Structures • Cuticle: Narrow band of epidermis attached to the surface of the nail just in front of the root • Protects the new cells as they grow • Onych/o, ungu/o mean nail

19. Medical Specialties • Dermatologist • Specializes in diagnosing and treating disorders of the skin

20. Pathology • Sebaceous Glands • Acne vulgaris • Chronic inflammation of the skin characterized by pustular eruptions caused by an overproduction of sebum • Most common type of acne

21. Pathology • Comedo • Non-infected lesion formed by the buildup of sebum and keratin in a hair follicle • Closed = whitehead • Open = blackhead • Deep = pimple (papule) • Very deep = cyst

22. Pathology • Seborrhea • Any condition that is characterized by an overproduction of sebum • Seborrheic dermatitis • Inflammation that causes scaling and itching of upper layers of skin • Ex extensive dandruff, cradle cap • Seborrheic keratosis • Benign growth • Has a waxy “pasted-on” look • Often occurs in the elderly

23. Pathology • Sweat Glands • Anhidrosis • Abnormal absence of sweating • Hyperhidrosis • Condition of excessive sweating • Diaphoresis • Profuse sweating • Due to specific cause such as menopause, shock, extreme emotion, eating spicy food, etc • Miliaria • AKA heat rash, prickly heat • Itchy rash caused by blockage of the sweat glands by bacteria and dead cells

24. Pathology • Hair • Folliculitis • Inflammation of the hair follicles • Especially common on the limbs and in the beard area • Hirsutism • Presence of excessive facial and body hair in women • May be hereditary or caused by hormone imbalance • Alopecia • AKA baldness • Partial or complete absence of hair from where it usually grows

25. Pathology • Nails • Clubbing • Abnormal curvature of the nails • Can be hereditary, but may also be related to oxygen deficiencies • Koilonychia • “spooning” of the nail • Often an indication of iron-deficiency anemia • Onychocryptosis • AKA ingrown toenail

26. Pathology • Onychomycosis • Fungal infection of a nail • May cause the nail to turn white, yellow, green, or black, and become thick or brittle • Onychophagia • AKA “nail biting” • Onycholysis • Loosening of the nail from the nail bed • Often due to infection • Paronychia • Inflammation and swelling of tissue around the nail

27. Pathology • Skin Pigmentation • Albinism • Inherited deficiency or absence of pigment in the skin, hair, and irises due to a missing enzyme necessary for the production of melanin

28. Pathology • Melanosis • Any condition of unusual deposits of black pigment in the skin • Vitiligo • Loss of melanin resulting in white areas of the skin, usually the face and hands (autoimmune disorder)

29. Pathology • Bruises • Petechiae • Pinpoint hemorrhages (less than 2 mm in diameter) • Sometimes result from severe fever Ecchymosis • Larger irregular area of purplish discolouration • Ex black eye, bruise

30. Pathology • Surface Lesions • Pathologic change of the tissue due to injury or disease • Described by: • Appearance • Location • Colour • size

31. Pathology • Crust • AKA scab • Collection of dried serum and cellular debris • Macule • Discoloured, flat spot that is less than 1 cm in diameter (ex freckles, flat moles) • Papule • Small, raised, red lesion that is less than 1 cm in diameter – does not contain pus

32. Pathology • Nodule • Solid raised lesion that is larger than 1 cm and deeper than a papule • Plaque • Scaly, raised area of closely spaced papules • Ex psoriasis • Scales • Flakes or dry patches of excess dead epidermal cells

33. Pathology • Verruca • AKA wart • Small, hard, skin lesion caused by the human papilloma virus • Wheal • AKA welt • Smooth, slightly elevated area that itches • Often a symptom of allergic reaction or insect bites

34. Pathology • Fluid-Filled Lesions • Abscess • Closed pocket containing pus • Caused by bacterial infection • Cyst • Closed sac just under the skin containing soft or semisolid material

35. Pathology • Pustule • Small, circumscribed lesion containing pus • impetigo, smallpox, etc • Vesicle • Small blister containing watery fluid • Less than 0.5 cm in diameter • Bulla • Large blister containing watery fluid • More than 0.5 cm in diameter

36. Pathology • Through the skin • Abrasion • Superficial layers of skin are scraped or rubbed away • Fissure • Groove or crack in the skin • Laceration • Torn and jagged wound or accidental cut • Puncture wound • Deep hole made by a sharp object

37. Pathology • Ulcer • Open lesion of the skin or mucous membrane resulting in tissue loss around the edges • Decubitous ulcer – pressure ulcer or bedsore • Area where prolonged pressure causes tissue death

38. Pathology • Dermatitis • Inflammation of the skin • Usually involves redness, itchiness (pruritus), swelling • Eczema • Form of dermatitis that occurs on the face, neck, elbows, and knees • Skin is red, blistered, or oozing • Eventually can become scaly, brown, and thickened • Contact Dermatitis • Localized allergic response caused by contact with an irritant or allergen

39. Pathology • Erythema • Redness of the skin due to dilated capillaries • Ex blush, inflammation, sunburn • Pyoderma • Any acute, inflammatory, pus-forming bacterial skin infection • Ichthyosis • Group of hereditary disorders characterized by dry, thickened and scaly skin • Ichthy/o means dry or scaly

40. Pathology • Lipedema • Chronic swelling due to accumulation of fat and fluid under the skin • Commonly occurs between the calf and ankle • Psoriasis • Skin disorder characterized by the occurrence of red papules covered by silvery scales on the elbows, knees, scalp, back or buttocks • Caused by an increase in the rate of basal cell growth

41. Pathology • Rosacea • Chronic, idiopathic condition • Produces redness, tiny pimples, and broken blood vessels, often on the face • Scleroderma • Autoimmune disorder • Connective tissues become thickened or hardened

42. Pathology • Urticaria • AKA hives • Wheals caused by an allergic reaction • Xeroderma • Dry skin

43. Pathology • Bacterial Skin Infections • Furuncles (Boils) • large, tender, swollen areas caused by infection around hair follicles or sebaceous glands • Cellulitis • Acute, rapidly spreading infection within the connective tissue • Symptoms include malaise, swelling, warmth, and red streaks

44. Pathology • Impetigo • Highly contagious pyoderma • Characterized by isolated pustules that become crusted and rupture • Necrotizing Fasciitis • AKA flesh-eating bacteria

45. Pathology • Fungal Skin Infections • Tinea • AKA ringworm • Grows on skin, hair or nails • Fungus spreads out in circle leaving normal-looking skin in the middle

46. Pathology • Parasitic Skin Infections • Scabies • Caused by infestation with the itch mite • Produces brown lines and an itchy rash • Pediculosis • Infestation with lice

47. Pathology • Skin Growths • Callus • Thickening of the skin caused by repeated rubbing • A corn is a callus that has developed a hard core • Cicatrix • Scar resulting from the healing of a wound • Forms from granulation tissue • Keloid • Abnormally raised or thickened scar that expands past the boundaries of the original incision

48. Pathology

49. Pathology • Nevus (nevi) • AKA mole • Small, dark skin growths that develop from melanocytes • Normally benign • Dysplastic nevi are atypical moles that may develop into skin cancer

50. Pathology • Skin Cancer • Most common form of cancer, but often curable • Basal cell carcinoma • Slow growing, rarely spreads • Lesions are pink, smooth, and raised with a depression in the center (tend to bleed easily)