Integumentary System

Organs of the Integumentary System

The integumentary system consists of the skin and its associated appendages, which play vital roles in protection, sensation, and regulation.

• Skin

• Skin appendages:

  • Hair

  • Nails

  • Glands:

    • Sudoriferous (sweat) glands: eccrine, apocrine

    • Sebaceous glands

Layers of the Skin

The skin is composed of multiple layers, each with distinct functions and structures.

• Epidermis: Outermost layer, provides barrier and protection

• Dermis: Middle layer, contains connective tissue, blood vessels, nerves

• Subcutaneous layer (hypodermis): Deepest layer, primarily adipose tissue (not always considered part of skin)

Structure of Skin

Epidermis

The epidermis is a keratinized, stratified squamous epithelium that serves as the primary protective barrier.

• Keratinocytes: Produce keratin, provide strength and waterproofing

• Melanocytes: Synthesize melanin, protect against UV radiation

• Dendritic cells (Langerhans cells): Immune defense

• Tactile (Merkel) cells: Sensory receptors for touch

Differences Between Epidermal Layers

The epidermis is organized into distinct layers, each with unique cell types and functions.

• Stratum basale: Deepest layer, single row of rapidly dividing keratinocytes, contains melanocytes and tactile cells

• Stratum spinosum: Keratinocytes appear spiked, contains dendritic cells

• Stratum granulosum: Keratinocytes contain keratohyaline granules, lamellated granules of glycolipids

• Stratum lucidum: Thin, clear layer found only in thick skin (palms, soles)

• Stratum corneum: Outermost layer, dead keratinocytes, provides waterproof barrier

Dermis

The dermis is a connective tissue layer that supports and nourishes the epidermis.

• Cells: Fibroblasts, macrophages, mast cells, white blood cells

• Ground substance: Semi-fluid matrix containing collagen, elastin, and reticular fibers

• Blood vessels, lymph vessels, nerves

• Dermal layers:

  • Papillary layer: Areolar connective tissue, dermal papillae

  • Reticular layer: Dense irregular connective tissue

Skin Color

Factors Affecting Skin Color

Skin color is determined by several pigments and external factors.

• Carotene

• Hemoglobin

• Melanin

• Sun exposure and damage can alter pigmentation

Skin Appendages

Hair and Hair Follicle Structure

Hair is a filamentous structure composed of keratinized cells, growing from follicles embedded in the dermis.

• Hair structure:

  • Shaft

  • Root

  • Layers:

    • Medulla – soft keratin

    • Cortex

    • Cuticle – hard keratin

• Pigment: Melanin

• Hair follicle: Epidermal fold into dermis, contains hair bulb and papilla

• Arrector pili: Smooth muscle causing hair to stand (goosebumps)

Types of Hair

• Vellus hair: Fine, pale body hair

• Terminal hair: Coarse, long hair (scalp, eyebrows)

• Growth cycles: Anagen (growth), catagen (regression), telogen (resting)

• Clinical note: Male pattern baldness (androgenic alopecia)

• Hirsutism: Excessive hair growth

Nail Structure

Nails are protective coverings composed of hard keratin.

• Free edge

• Body

• Root

• Bed

• Matrix: Site of nail growth

• Lunula: Crescent-shaped area

• Eponychium: Cuticle

• Hyponychium: Under free edge

Glands of the Skin

Skin contains several types of glands with distinct functions.

• Sudoriferous (sweat) glands:

  • Eccrine glands: Widely distributed, open into pores, produce hypotonic filtrate

  • Apocrine glands: Found in axillary/genital areas, open into hair follicles, produce odor

• Ceruminous glands: Produce earwax (cerumen)

• Mammary glands: Secrete milk

• Sebaceous glands: Secrete sebum (oily substance), lubricates skin and hair

Functions of the Integumentary System

The integumentary system provides multiple protective and regulatory functions essential for homeostasis.

• Protection:

  • Chemical barrier: Acid pH, defensins, melanin

  • Physical barrier: Keratin, waterproofing

  • Biological barrier: Dendritic cells, macrophages

• Body temperature regulation: Sweat glands, blood vessel dilation/constriction

• Cutaneous sensation: Touch, pressure, pain, temperature

• Metabolic functions: Synthesis of vitamin D

• Blood reservoir: Dermal blood vessels

• Excretion: Nitrogenous wastes (urea, ammonia, uric acid)

Clinical Aspects and Pathology

Common Disorders

• Skin cancer:

  • Benign tumor: Wart, callus

  • Malignant:

    • Basal cell carcinoma

    • Squamous cell carcinoma

    • Melanoma

• Burns: Classified by degree (first, second, third), risk of fluid loss and infection

• Acne: Inflammation of sebaceous glands

Developmental Aspects of Skin

Skin development and aging involve changes in structure and function over the lifespan.

• Embryology: Epidermis from ectoderm, dermis from mesoderm

• Birth: Vernix caseosa (protective coating), lanugo (fine hair)

• Adolescence: Sebaceous glands become active

• Aging: Skin thins, becomes dry, bruises easily, wrinkles form

Summary Table: Epidermal Cell Types and Functions

Key Equations

• Vitamin D Synthesis (simplified):

Additional info: Some details, such as the stages of hair growth and the embryological origins of skin layers, were expanded for academic completeness.