Skin Structure, Function, and Assessment: Study Notes for Anatomy & Physiology

Skin Structure & Function

Overview

The skin is the largest organ of the human body, serving multiple essential functions for protection, sensation, and homeostasis. Its structure is adapted to provide a waterproof barrier and to interact with the environment.

• Protection from Environment: Prevents penetration of harmful substances and acts as a barrier against bacteria and viruses.

• Sensory Perception: Contains nerve endings that detect touch, pain, temperature, and pressure.

• Temperature Regulation: Regulates body temperature through sweat production and blood vessel dilation/constriction.

• Wound Repair: Facilitates healing through cell regeneration.

• Absorption and Excretion: Absorbs certain substances and excretes waste products via sweat.

• Production of Vitamin D: Synthesizes vitamin D when exposed to sunlight.

• Insulation: Subcutaneous fat provides thermal insulation.

Example: The skin's ability to produce vitamin D is crucial for calcium absorption and bone health.

Developmental Considerations

Infants, Children, and Adolescents

Skin structure and function change throughout development, affecting appearance and physiology.

• Newborn Infants:

  • Lanugo: Fine, downy hair present at birth.

  • Vernix caseosa: Thick, cheesy substance covering the skin at birth, providing protection.

  • Sebum: Holds water in the skin, may produce milia (small white bumps).

• Children:

  • Epidermis thickens, darkens, and becomes lubricated.

  • Hair growth accelerates.

• Adolescents:

  • Increased secretions from apocrine sweat glands.

  • Subcutaneous fat deposits increase.

  • Development of secondary sex characteristics.

The Aging Adult

With aging, the skin undergoes structural and functional changes that increase vulnerability to injury and disease.

• Elasticity: Degeneration of elastic fibers and collagen stiffening leads to loss of skin elasticity and sagging.

• Sweat and Sebaceous Glands: Decrease in number and function, resulting in dry skin.

• Senile Purpura: Discoloration due to increased capillary fragility and permeability, raising the risk of bruising.

• Skin Breakdown: Slower cell replacement and delayed wound healing; decreased subcutaneous fat.

• Hair Matrix: Reduced functioning of melanocytes, leading to gray hair.

Skin Assessment

Collection of Subjective Data

Subjective data involves gathering information from the patient about their skin health and history.

• Past history of skin disease, allergies, hives, psoriasis, or eczema

• Change in pigmentation or moles

• Excessive dryness or moisture

• Pruritus (itching)

• Excessive bruising

• Rash, sores, wounds, or lesions

• Medications

• Hair loss

• Changes in nails (soft, dry, cracked, clubbing)

• Environmental or occupational hazards

• Birthmarks

• Acne (adolescents)

• Falls (trauma, bruising)

Collection of Objective Data

Objective data is collected through physical examination and observation.

• Preparation: Carefully attend to skin characteristics to avoid missing abnormalities.

• Equipment Needed:

  • Strong direct lighting, gloves, penlight, centimeter ruler

  • Special procedures: Wood's light, magnifying glass

  • Laboratory tests: potassium hydroxide (KOH) and glass slide

Inspection and Palpation

• Moisture: Assess for diaphoresis (excessive sweating) or dehydration.

• Texture: Normal skin should feel smooth and firm.

• Thickness: Observe for thickened areas, such as callus formation.

• Oedema: Assess for fluid accumulation in the interstitial space.

• Mobility and Turgor: Evaluate skin elasticity.

• Vascularity or Bruising: Assess for tattoos, bruising, or other variations.

Inspection and Palpation - Nails

• Shape and Contour: Profile sign—angle of nail base should be 160 degrees.

• Consistency: Nails should be smooth, regular, not brittle or splitting, with uniform thickness.

• Colour: Translucent nail plate with pink nail bed below; note ethnic variations.

• Capillary Refill: Depress nail edge to blanch, then release and note return of color (should be rapid, indicating good peripheral circulation).

ABCDE(F) Skin Assessment

Promoting Health and Self-Care

Patients should be taught to perform skin self-examinations using the ABCDE(F) rule to detect suspicious lesions, especially for early identification of melanoma.

• A: Asymmetry – One half of the lesion does not match the other.

• B: Border Irregularity – Edges are ragged, notched, or blurred.

• C: Color Variation – Presence of multiple colors (brown, black, red, white, blue).

• D: Diameter – Greater than 6 mm (about the size of a pencil eraser).

• E: Elevation or Evolution – Raised surface or changes over time.

• F: Funny Looking – "Ugly duckling" sign; looks different from other moles.

Example: A mole that is asymmetric, has irregular borders, and is larger than 6 mm should be evaluated by a healthcare professional.

Abnormal Findings

Common Skin Disorders

• Psoriasis: Chronic autoimmune condition characterized by red, scaly patches.

• Dermatitis: Inflammation of the skin, often presenting as redness, swelling, and itching.

• Alopecia: Loss of hair from the scalp or body.

• Clubbing of Nails: Bulbous enlargement of the ends of fingers or toes, often associated with chronic hypoxia.

Shapes and Configurations of Lesions

• Primary Lesions: Initial, direct result of a disease process (e.g., macule, papule, vesicle).

• Secondary Lesions: Result from changes in primary lesions (e.g., crust, scale, scar).

Example: A vesicle (primary lesion) may rupture and form a crust (secondary lesion).

Pharmacology

Topical Steroids

Topical steroids, such as hydrocortisone, are commonly used to treat inflammatory skin conditions.

• Mechanism: Reduce inflammation and suppress immune responses in the skin.

• Indications: Used for conditions like dermatitis, eczema, and psoriasis.

• Adverse Effects: May cause burning, stinging, or irritation at the application site; prolonged use can lead to skin thinning.

• Contraindications: Avoid use on untreated skin infections or severe skin damage.

Example: Hydrocortisone cream is applied to reduce itching and inflammation in eczema.

References

• Brady, A., Tinghe, J. (2022). Medical-surgical nursing for Australian students - a systems approach. Wiley Asia.

• Bryant, B., Knights, K., Darroch, J., & Rowland, A. (2019). Pharmacology for health professionals (4th ed). Elsevier Australia.

• Brown, H., Edwards, H., Buckley, T., & Aitken, L. (2019). Lewis's medical surgical nursing: Assessment and management of clinical problems (5th ed). Elsevier Australia and New Zealand.

• Watt, E., & Forbes, H. (2021). Health assessment & physical examination (3rd ed). Elsevier Australia and New Zealand.