Growth, Repair, and Disorders of the Integumentary System

Jump to Multilingual Approach: Lesson Slides with translation

Introduction

The skin is a dynamic organ that constantly renews and repairs itself—a balance essential for maintaining homeostasis. This lesson explores the normal growth cycle of the skin, the four phases of wound healing, and several common disorders and injuries—from acne and eczema to skin cancer and burns.

Normal Growth and Renewal of Skin

Recall that in thin skin, the epidermis consists of four major layers of cells that are continually renewing:

Stratum basale — Stem cells rapidly divide to supply new keratinocytes.
Stratum spinosum — Daughter cells move outward, forming desmosomal connections.
Stratum granulosum — Cells accumulate keratin-filled vesicles as they mature.
Stratum corneum — Cells die, merging into a keratin barrier that sheds regularly.

As basal cell proliferation matches surface loss, the epidermis maintains a steady thickness. Damage triggers an accelerated, wound-repair response.

Skin Repair: Regeneration vs. Fibrosis

• Regeneration: Damaged skin is replaced by identical cell types, restoring basic function.

• Fibrosis: If tissue structure is altered, repair involves scar tissue formation (excess collagen) in the dermis. Over months to years, scars remodel—flattening and fading with improved function.

Phases of Wound Healing

Deep wounds—those involving both epidermis and dermis—progress through four overlapping stages: hemostasis, inflammation, proliferation, and remodeling. See Figure 1.

Hemostasis

• Damaged vessels expose collagen, triggering platelet aggregation and clot formation via positive feedback.

• Clots prevent blood loss and block pathogens. Macrophages begin clearing debris under the scab.

Inflammation

• Mast cells release histamine, increasing capillary permeability.

• Plasma proteins, antibodies, and white blood cells (neutrophils, lymphocytes) enter tissue via diapedesis.

• This response produces swelling, redness, heat, and pain—classic inflammatory signs.

Proliferation

• Granulation tissue forms: new capillaries (angiogenesis) + collagen laid down by fibroblasts.

• Epithelium regrows through keratinocyte migration and division, closing the wound.

Remodeling

• The epithelium restores all four normal layers.

• The dermal scar undergoes gradual remodeling: collagen is reduced and restructured, restoring flexibility and strength over months to years.

Common Integumentary Disorders

Acne

• Plugged hair follicles accumulate excess sebum and keratinocytes, which encourage Cutibacterium acnes colonization.

• Inflammation follows: red, swollen pustules and nodules, often driven by androgen-stimulated sebum production.

Eczema

• Chronic epidermal inflammation, edema, and spongiosis in the stratum spinosum.

• This leads to the thickened epidermis and keratin build-up, with vesicles and deep dermal inflammation, resulting in itchy, red, raised patches.

Skin Cancers

Uncontrolled proliferation due to UV-induced DNA mutations:

Basal-cell carcinoma — Arises in the stratum basale; most common but least dangerous.
Squamous-cell carcinoma — Originates in squamous keratinocytes; treatable if caught early.
Malignant melanoma — Develops in melanocytes; rare but deadly.

When detecting malignant melanoma, physicians use these ABCDE Warning Signs for moles:

• Asymmetry- the two sides are not symmetrical

• Border irregularity- the edges are irregular in shape

• Color variation- the color is varied shades of brown or black

• Diameter is greater than 6 mm

• Evolving shape or pigmentation- the color or shape of the mole has changed across time.

Burns and Degrees of Injury

Thermal, chemical, electrical, or UV damage leads to:

• Protein denaturation and cell death.

• Systemic impacts—inflammation, fluid loss, infection risk, electrolyte and immune disruptions.

Burn severity, see figure 4:

1. First-degree: Epidermis only – redness, swelling, pain; self-repairs.

2. Second-degree: Epidermis + superficial dermis – blisters form; painful; usually self-heals but slower.

3. Third-degree: Entire epidermis + dermis destroyed; painless due to nerve loss; requires grafting.

4. Fourth-degree: Involves hypodermis, muscle, bone; high risk; surgical intervention required. (not pictured)

Summary

In this lesson, we covered these key points:

1. The skin’s continuous renewal occurs through its four epidermal layers.

2. The four integrated phases of wound healing are hemostasis, inflammation, proliferation, and remodeling.

3. Common integumentary disorders—acne, eczema, skin cancers—and their disruption of homeostasis.

4. Burn types and systemic consequences.

Understanding these processes highlights the complexity of the integumentary system and its vital role in protection, regeneration, and balance.

Multilingual Approach Lesson Slides with translations

Use the interactive below to access the multilingual lesson slides.

Lesson Video

Watch this lesson video to hear an A&P instructor walk you through the lesson.

Practice Questions

Use these practice questions to assess your knowledge before you move on to the next section.

RETURN TO TOP