The Integumentary System

Introduction

The integumentary system consists of the skin and its associated structures. It is the largest organ system in the human body, providing protection, sensation, and other vital functions necessary for homeostasis.

Structure of the Skin

General Characteristics

• Skin (cutaneous membrane) covers the entire body surface.

• It is the largest organ by surface area and weight.

• Total surface area: approximately 2 square meters (22 square feet).

• Weight: 4.5–5 kg (10–11 lb), about 16% of total body weight.

• Thickness: ranges from 0.5 mm (eyelids) to 4 mm (heels); average is 1–2 mm.

Major Layers of the Skin

• Epidermis: Outer, thinner layer composed of keratinized stratified squamous epithelial tissue.

• Dermis: Deeper, thicker layer made of connective tissue.

• Subcutaneous (subQ) layer / Hypodermis: Located beneath the dermis, not technically part of the skin but closely associated. Composed mainly of adipose and areolar tissue.

Overview of Skin Functions

Protective and Regulatory Roles

• Epidermis:

  • Resists mechanical damage

  • Decreases water loss (prevents dehydration)

  • Prevents penetration by microbes (barrier to infection)

• Dermis:

  • Provides sensory information (touch, pain, temperature)

  • Site of vitamin D synthesis (with UV exposure)

  • Regulates body temperature (via blood vessels and sweat glands)

Skin Structure Diagram

The skin is organized into distinct layers and contains various structures, as shown in the cross-sectional diagram:

• Hair shaft and hair follicle

• Papillary layer (upper dermis): contains dermal papillae, capillary loops, and Meissner's corpuscles (touch receptors)

• Reticular layer (lower dermis): contains dense irregular connective tissue, sweat (eccrine) glands, sebaceous (oil) glands, arrector pili muscles, nerves, and Pacinian (lamellated) corpuscles (deep pressure receptors)

• Subcutaneous tissue: contains adipose tissue and larger blood vessels

Additional info: The diagram also shows the cutaneous vascular plexus, sensory nerve fibers, and other appendages of the skin.