Structure, Function, and Disorders of the Integumentary System

Aging and Skin Integrity

As the body ages, the skin undergoes significant physiological changes driven by both genetic and environmental factors. These changes can impact the skin's protective capabilities and overall appearance.

Key changes include:

• Texture and Appearance: Skin becomes thinner, drier, and more prone to wrinkling.
• Pigmentation: Changes in pigmentation occur due to a decrease in the number of melanocytes and Langerhans cells.
• Glandular Atrophy: There is a notable atrophy of the sebaceous, eccrine, and apocrine glands.
• Hair Changes: Hair becomes thinner, and there is a reduction in the number of hair follicles and changes in hair color.

Skin Lesions

Clinicians classify skin lesions based on their size, shape, and whether they are raised, flat, or fluid-filled. This classification is vital for accurate diagnosis.

Flat Lesions

• Macule: A flat, discolored area less than 1 cm (e.g., a freckle).
• Patch: A flat area of discoloration larger than 1 cm (e.g., a birthmark).

Raised Lesions

• Papule: A small, solid, raised lesion less than 1 cm (e.g., a small wart).

• Plaque: A raised, flat-topped lesion larger than 1 cm, commonly seen in psoriasis.

• Wheal: A temporary, raised area caused by localized edema (e.g., a hive).

• Nodule: A firm, solid lesion that extends deeper into the skin than a papule.

• Tumor: A large solid mass caused by abnormal tissue growth; it may be benign or malignant.

Fluid-Filled Lesions

• Vesicle: A small, elevated lesion filled with clear fluid (e.g., a herpes blister).
• Bulla: A fluid-filled blister larger than 1 cm.
• Pustule: A raised lesion filled with pus, often seen in acne or infection.

Other Manifestations

• Cyst: An enclosed sac beneath the skin containing fluid or semisolid material.
• Telangiectasia: Small, visibly dilated blood vessels near the skin's surface.
• Scale: Flakes of dead epidermal cells accumulating on the surface.
• Lichenification: Thickened, leathery skin with prominent lines caused by chronic rubbing.
• Erosion vs. Ulcer: An erosion is a superficial loss of the epidermis that usually heals without scarring, whereas an ulcer is a deeper loss involving the dermis and potentially subcutaneous tissue, which can produce scarring.
• Fissure: A narrow, linear crack in the skin.

Exam Tip: When distinguishing between a macule and a patch, always look at the size. If it is $< 1$ cm, it is a macule; if it is $> 1$ cm, it is a patch.

Pressure Injuries

Pressure injuries, also known as decubitus ulcers, result from unrelieved pressure on the skin, which causes underlying tissue damage. Common contributing factors include pressure, shearing forces, friction, and moisture.

Pressure injuries are staged based on the depth of tissue involvement:

• Stage I: Non-blanchable erythema of intact skin.
• Stage II: Partial-thickness skin loss involving the epidermis or dermis.
• Stage III: Full-thickness skin loss involving damage to or loss of subcutaneous tissue.
• Stage IV: Full-thickness skin loss with damage to muscle, bone, or supporting structures.

Keloids

While most wounds heal by forming a standard scar (fibrous tissue that replaces normal skin), some individuals experience abnormal healing.

Keloids are elevated, rounded, and firm scars characterized by clawlike margins that extend beyond the boundaries of the original injury site. This occurs due to excessive collagen formation during the dermal connective tissue repair process. Keloids are particularly common in individuals with darkly pigmented skin types and in those with burn scars.