The Integumentary System

Overview

The integumentary system is the body's largest organ system, accounting for 10–15% of total body weight. It is not merely an outer covering, but a complex organ with multiple functions essential for maintaining homeostasis.

• Cutaneous membrane (skin): Consists of two main components: the epidermis and the dermis.

• Accessory structures: Include sweat glands, sebaceous glands, hair, and nails, all embedded within the cutaneous membrane.

Skin Structure

Main Layers of the Skin

• Epidermis: The superficial layer composed of keratinized stratified squamous epithelium resting on a basement membrane. It provides a protective barrier and is avascular (lacks blood vessels).

• Dermis: Located deep to the epidermis and basement membrane, it consists of loose connective tissue and dense irregular connective tissue. The dermis is highly vascular and supports the epidermis.

Accessory structures such as sweat glands, sebaceous glands, hair, and nails are embedded in the skin. The skin also contains sensory receptors and arrector pili muscles (small bands of smooth muscle associated with hair follicles).

Hypodermis (Superficial Fascia or Subcutaneous Fat)

• Location: Deep to the dermis; not technically part of the skin.

• Function: Anchors the skin to deeper structures such as muscle and bone.

• Composition: Made of loose connective and adipose tissues; contains abundant blood supply.

Cellulite

Cellulite is the dimpled or "orange peel" appearance of skin that occurs when collagen bands form around adipose tissue in the hypodermis.

• Commonly develops in the thighs, hips, and gluteal area.

• Influenced by genetics, gender, amount and distribution of adipose tissue, and age.

• It is a normal condition (not a disorder).

• There is little evidence that "cures" for cellulite are effective; the only proven ways to minimize it are healthy diet and regular exercise.

Vascularity and Nutrient Supply

• The epidermis is avascular and relies on diffusion of oxygen and nutrients from blood vessels in the deeper dermis.

• This diffusion limits the thickness of the epidermis (Gradients Core Principle).

• About 50% of epidermal cells are too far from adequate blood supply to sustain life, so the superficial layers are composed entirely of dead cells.

Basic Anatomy of the Skin (Diagram)

The skin consists of the following structures (as shown in the diagram):

• Epidermis

• Dermis

• Hypodermis (subcutaneous fat)

• Sweat pore

• Hair shaft and follicle

• Sebaceous gland

• Arrector pili muscle

• Blood vessels

• Sensory neurons

• Adipose tissue

Example: The arrector pili muscle contracts in response to cold or emotional stimuli, causing hair to stand up (goosebumps).

Summary Table: Main Layers and Features of the Skin

Additional info: The hypodermis is sometimes referred to as the superficial fascia and is important for thermal insulation and shock absorption.