Anatomy and Physiology I – Chapter 5: The Integumentary System

Chapter 5: The Integumentary System

Introduction

The integumentary system is the body's largest organ system, primarily composed of the skin and its accessory structures. It serves as the first line of defense against environmental hazards and plays a vital role in maintaining homeostasis.

Chapter Objectives

• List functions and characteristics of the skin.

• Discuss types of cells and tissues found in the skin.

• Describe the structure and function of the three layers of the skin.

• Describe the accessory structures (hair, nails, glands) associated with the skin, along with the functions of each.

• Explain how the skin functions in regulating body temperature.

• Discuss sense of touch and receptors involved.

• Discuss common disorders of the skin.

Functions of the Integumentary System

Overview of Skin Functions

• Protection: Shields tissues and organs from mechanical damage, pathogens, and chemical exposure.

• Excretion: Removes salts, water, and organic wastes through sweat.

• Temperature Regulation: Maintains body temperature via sweat production and blood flow regulation.

• Vitamin D Synthesis: Produces vitamin D3 (a steroid) when exposed to sunlight, which is converted to calcitriol for calcium metabolism.

• Storage of Nutrients: Lipids are stored in adipocytes located in the dermis and subcutaneous layer.

Major Parts of the Integumentary System

Cutaneous Membrane

• Epidermis: The outermost layer, composed of stratified squamous epithelium. It does not contain blood vessels.

• Dermis: The underlying area of connective tissue, which contains a dense network of blood vessels and nerves. It consists of dense irregular connective tissue.

• Subcutaneous Layer (Hypodermis): A deeper layer beneath the dermis, primarily composed of adipose tissue. It is not considered part of the cutaneous membrane but is important for insulation and energy storage.

Accessory Structures

• Hair

• Nails

• Exocrine Glands: Four types associated with the skin (e.g., sweat glands, sebaceous glands).

Structure of the Skin

Layers of the Skin

• Epidermis: Composed mainly of keratinocytes, the body's most abundant epithelial cells.

• Dermis: Contains connective tissue, blood vessels, nerves, and accessory structures.

• Hypodermis (Subcutaneous Layer): Consists mainly of adipose tissue, providing insulation and energy storage.

Skin Layering: Thick vs. Thin Skin

• Thick Skin: Found on palms of hands and soles of feet. Contains five layers:

  1. Stratum germinativum (deepest)

  2. Stratum spinosum

  3. Stratum granulosum

  4. Stratum lucidum (not found in thin skin)

  5. Stratum corneum

• Thin Skin: Covers the rest of the body. Contains four layers:

  1. Stratum germinativum (deepest)

  2. Stratum spinosum

  3. Stratum granulosum

  4. Stratum corneum

Cells and Tissues of the Skin

Key Cell Types

• Keratinocytes: Produce keratin, a protein that provides strength and waterproofing.

• Melanocytes: Produce melanin, which gives skin its color and protects against UV radiation.

• Langerhans Cells: Immune cells that help protect against pathogens.

• Merkel Cells: Sensory cells involved in touch sensation.

Accessory Structures of the Skin

Hair

• Function: Protection, sensation, and regulation of body temperature.

• Structure: Composed of keratinized cells; includes hair shaft, follicle, and bulb.

Nails

• Function: Protects the distal phalanges, aids in grasping objects.

• Structure: Hard plates of keratinized cells.

Exocrine Glands

• Sebaceous (Oil) Glands: Secrete sebum to lubricate skin and hair.

• Sudoriferous (Sweat) Glands: Two types:

  • Eccrine glands: Widely distributed, regulate temperature.

  • Apocrine glands: Found in specific areas, produce thicker secretions.

• Ceruminous Glands: Produce earwax.

• Mammary Glands: Produce milk.

Regulation of Body Temperature

Mechanisms

• Sweat Production: Evaporation of sweat cools the body.

• Blood Flow Regulation: Vasodilation increases heat loss; vasoconstriction conserves heat.

Sensation and Receptors

Sense of Touch

• Mechanoreceptors: Detect pressure, vibration, and touch (e.g., Meissner's corpuscles, Pacinian corpuscles).

• Thermoreceptors: Detect changes in temperature.

• Nociceptors: Detect pain.

Common Disorders of the Skin

Overview

• Acne: Inflammation of sebaceous glands.

• Psoriasis: Chronic autoimmune condition causing rapid skin cell turnover.

• Dermatitis: Inflammation of the skin due to various causes.

• Skin Cancer: Includes basal cell carcinoma, squamous cell carcinoma, and melanoma.

Summary Table: Layers of the Skin

Layer	Main Components	Functions
Epidermis	Keratinocytes, melanocytes, Merkel cells, Langerhans cells	Protection, waterproofing, sensation, immune defense
Dermis	Connective tissue, blood vessels, nerves, hair follicles, glands	Support, nourishment, sensation, thermoregulation
Hypodermis	Adipose tissue, larger blood vessels	Insulation, energy storage, shock absorption

Summary Table: Types of Skin Glands

Gland Type	Location	Secretion	Function
Sebaceous	Associated with hair follicles	Sebum (oil)	Lubricates skin and hair
Eccrine Sweat	Throughout skin	Watery sweat	Temperature regulation
Apocrine Sweat	Axillae, groin	Thicker, milky sweat	Activated at puberty, scent
Ceruminous	Ear canal	Cerumen (earwax)	Protects ear
Mammary	Breasts	Milk	Nourishes infants

Key Equations

• Vitamin D Synthesis: $\text{7-dehydrocholesterol} + UV \rightarrow \text{Vitamin D}_3$

Additional info: Some details, such as the specific cell types and functions, were expanded for academic completeness.