Study Guide: The Integumentary System – Structure and Accessory Organs

The Integumentary System

Basic Structure of the Skin

The integumentary system is composed primarily of the skin and its accessory organs. The skin is the largest organ of the body and serves as a protective barrier, regulating temperature and providing sensory information.

• Superficial region (epidermis): The outermost layer of the skin, composed of stratified squamous epithelial tissue.

• Deeper region (dermis): Located beneath the epidermis, composed of connective tissue.

• Layers of the dermis:

  • Papillary dermis: Composed of areolar connective tissue.

  • Reticular dermis: Composed of dense irregular connective tissue.

• Functions of the skin:

  • Protection

  • Regulation of body temperature

  • Sensation

  • Excretion

Layers of the Epidermis

The epidermis consists of several distinct layers, especially prominent in thick skin (such as the palms and soles). Each layer has unique characteristics and functions.

• Stratum basale: Deepest layer, site of cell division and new cell generation.

• Stratum spinosum: Layer containing several rows of keratinocytes; provides strength and flexibility.

• Stratum granulosum: Layer where keratin filaments and granules appear; cells begin to die.

• Stratum lucidum: Present only in thick skin; translucent layer of dead cells.

• Stratum corneum: Outermost layer; many layers of dead, keratinized cells providing a tough, protective barrier.

Key Terms:

• Keratinocytes: Main cell type in the epidermis, responsible for producing keratin.

• Melanocytes: Cells that produce melanin, contributing to skin color and protection from UV radiation.

• Tactile (Merkel) cells: Sensory cells involved in touch sensation.

• Dendritic (Langerhans) cells: Immune cells that help protect against pathogens.

Functions and Sensory Structures of the Skin

The skin contains specialized structures for sensation and immune defense.

• Tactile corpuscles: Located in the dermal papillae; detect light touch.

• Lamellar (Pacinian) corpuscles: Located deep in the dermis; detect pressure and vibration.

• Dendritic cells: Epidermal cells that play a role in the immune response.

• Vitamin D synthesis: The skin produces vitamin D when exposed to sunlight, which is important for calcium absorption elsewhere in the body.

Accessory Organs of the Skin

Accessory organs include hair, nails, and glands, each contributing to the skin's protective and regulatory functions.

• Hair follicles: Structures that produce hair; associated with arrector pili muscles that cause hair to stand up (goosebumps).

• Arrector pili muscles: Smooth muscles attached to hair follicles; contract in response to cold or fright.

• Sebaceous glands: Oil glands that secrete sebum, lubricating skin and hair.

• Sudoriferous (sweat) glands: Glands that produce sweat for temperature regulation; include eccrine (widely distributed, regulate temperature) and apocrine (associated with hair follicles, found mainly in axillary and genital areas).

• Nails: Protective coverings for the tips of fingers and toes.

Mechanisms of Body Temperature Regulation

The integumentary system helps regulate body temperature through several mechanisms:

• Sweating: Evaporation of sweat cools the body.

• Vasodilation: Blood vessels in the dermis widen to increase heat loss.

• Vasoconstriction: Blood vessels narrow to reduce heat loss.

• Arrector pili muscle contraction: Causes hair to stand up, trapping air and providing insulation.

Table: Layers of the Epidermis and Their Features

Layer	Location	Main Features
Stratum basale	Deepest	Single row of dividing cells; melanocytes and tactile cells present
Stratum spinosum	Above basale	Several layers of keratinocytes; dendritic cells present
Stratum granulosum	Middle	Keratin granules appear; cells begin to die
Stratum lucidum	Only in thick skin	Translucent layer of dead cells
Stratum corneum	Superficial	Many layers of dead, keratinized cells

Table: Accessory Organs and Their Functions

Accessory Organ	Function
Hair follicle	Produces hair; protection and sensation
Arrector pili muscle	Contracts to raise hair; insulation
Sebaceous gland	Secretes sebum; lubricates skin and hair
Sudoriferous gland	Produces sweat; regulates temperature
Nail	Protects tips of fingers and toes

Key Equations

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

Additional info: Some details, such as the specific names of cell types and mechanisms of temperature regulation, were inferred from standard Anatomy & Physiology knowledge to provide a complete study guide.