Lesson 10

The Integumentary System

The integumentary system — skin, hair, nails, and associated glands — is the body's first line of defense. Skin is the largest organ, comprising about 16% of body weight. Dermatology covers conditions from common infections and inflammatory diseases to life-threatening cancers. Understanding skin lesion morphology is essential for clinical documentation.

50 min4 sections5 objectives

Learning Objectives

1Describe the three layers of the skin and their functions
2Identify combining forms for integumentary structures
3Classify primary and secondary skin lesions
4Recognize common dermatological conditions
5Describe skin cancer types and prevention strategies

1Skin Layers

Epidermis (outer, avascular):

Stratum basale: Deepest; contains stem cells and melanocytes (melanin production)

Stratum spinosum: Spiny appearance due to desmosomes

Stratum granulosum: Lamellar bodies release lipids → waterproofing

Stratum lucidum: Only in thick skin (palms, soles)

Stratum corneum: Dead, keratinized cells — continuous shedding

Dermis (inner, vascular):

Papillary layer: Dermal papillae (fingerprints), sensory receptors

Reticular layer: Dense collagen + elastin; sweat glands, hair follicles, sebaceous glands, Pacinian corpuscles

Hypodermis (subcutaneous tissue): Adipose + loose connective tissue; not technically skin

2Skin Functions and Appendages

Functions: Protection, thermoregulation, sensation, vitamin D synthesis, immunity, fluid balance

Sweat Glands (sudoriferous):

Eccrine: All over body; thermoregulation

Apocrine: Axilla/groin; puberty onset; bacterial breakdown → body odor

Sebaceous Glands: Secrete sebum (oil) → lubricates and waterproofs skin/hair; acne vulgaris when blocked

Hair Follicles: Each hair shaft surrounded by follicle + arrector pili muscle

Alopecia: Hair loss (androgenic alopecia, alopecia areata)

Nails: Keratinized plates protecting fingertips; useful diagnostic indicators

Clubbing: Chronic hypoxia

Koilonychia (spoon nails): Iron deficiency anemia

Beau's lines: Severe illness

3Skin Lesion Classification

Primary Lesions (initial):

Macule: Flat, color change, <1 cm (freckle)

Patch: Flat, color change, >1 cm (vitiligo)

Papule: Raised, solid, <1 cm (wart, acne)

Plaque: Raised, solid, >1 cm (psoriasis)

Vesicle: Fluid-filled, <1 cm (herpes, chickenpox)

Bulla: Fluid-filled, >1 cm (burn blister)

Pustule: Pus-filled (acne, impetigo)

Wheal: Transient, edematous (hives/urticaria)

Nodule: Solid, deeper, 1–2 cm

Secondary Lesions (from primary):

Crust, scale, erosion, ulcer, fissure, scar (keloid), excoriation

4Skin Cancers

Basal Cell Carcinoma (BCC): Most common cancer; arises from basal layer; rarely metastasizes; pearly nodule with rolled edges

Squamous Cell Carcinoma (SCC): Second most common; from squamous cells; can metastasize; scaly, red plaque or ulcer

Melanoma: Most dangerous; from melanocytes; ABCDE rule:

A: Asymmetry

B: Border irregularity

C: Color variation

D: Diameter >6mm

E: Evolution/change

Burns (classified by depth):

Superficial (1st degree): Epidermis only; redness, pain (sunburn)

Partial thickness (2nd degree): Epidermis + part of dermis; blisters

Full thickness (3rd degree): All layers; painless (nerve destruction); skin grafting needed

Clinical Connections

►Melanoma risk doubles for each blistering sunburn in childhood and adolescence
►Dermatological signs often reflect systemic disease (jaundice → liver disease, butterfly rash → lupus)
►Wound healing progresses through hemostasis, inflammation, proliferation, and remodeling phases

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L9: Special Senses: Eyes and Ears

L11: The Endocrine System