Study Guide: The Integumentary System – Anatomy & Physiology

The Integumentary System

Introduction to the Integumentary System

The integumentary system is the body's outer covering, primarily consisting of the skin, hair, nails, and associated glands. It serves as a protective barrier and plays vital roles in sensation, thermoregulation, and metabolic functions.

• Key Structures: Epidermis, dermis, hypodermis, hair, nails, sebaceous and sweat glands.

• Main Functions: Protection, sensation, temperature regulation, excretion, and synthesis of vitamin D.

Section 5-1: The Epidermis

Layers and Functions of the Epidermis

The epidermis is a stratified epithelial tissue forming the outermost layer of the skin. It is composed of several layers, each with distinct cell types and functions.

• Classification: The epidermis is classified as stratified squamous epithelium.

• Layers: (from superficial to deep)

  1. Stratum corneum

  2. Stratum lucidum (only in thick skin)

  3. Stratum granulosum

  4. Stratum spinosum

  5. Stratum basale

• Thick vs. Thin Skin: Thick skin (palms, soles) contains all five layers; thin skin (most of the body) lacks the stratum lucidum.

• Cell Types:

  • Keratinocytes: Main cell type, produce keratin for protection.

  • Melanocytes: Produce melanin pigment, found in the stratum basale.

  • Langerhans cells: Immune cells, also called dendritic cells.

  • Merkel cells: Sensory receptors for touch.

• Hemidesmosomes: Structures that anchor epidermal cells to the basement membrane.

• Desmosomes: Junctions that connect adjacent keratinocytes, providing mechanical strength.

• Water Loss: The stratum corneum is the most important barrier to water loss.

Example: The skin on the palm is thick skin, containing all five layers, while the skin on the forearm is thin skin.

Section 5-2: The Dermis

Structure and Function of the Dermis

The dermis is the connective tissue layer beneath the epidermis, providing structural support, elasticity, and housing blood vessels, nerves, and accessory structures.

• Layers:

  1. Papillary layer: Superficial, contains loose connective tissue and dermal papillae.

  2. Reticular layer: Deep, dense irregular connective tissue, provides strength and elasticity.

• Dermal Papillae: Projections that increase surface area for attachment to the epidermis and contain capillaries and sensory receptors.

• Scarring: Scars form when the skin heals after injury; orientation of the scar depends on the direction of the wound.

• Accessory Structures: Hair follicles, sweat glands, sebaceous glands, and nails are embedded in the dermis.

Example: Stretch marks are caused by tearing of the dermal collagen fibers.

Section 5-3: The Hypodermis

Subcutaneous Layer and Its Functions

The hypodermis, or subcutaneous layer, lies beneath the dermis and consists mainly of adipose tissue. It anchors the skin to underlying tissues and provides insulation and energy storage.

• Functions: Insulation, energy storage, shock absorption, and anchoring skin to muscles.

• Clinical Importance: The hypodermis is the site for subcutaneous injections.

Example: The thickness of the hypodermis varies depending on body region and nutritional status.

Section 5-4: Skin Color and Circulation

Pigmentation and Blood Flow

Skin color is determined by the presence of pigments and the circulation of blood in the dermis.

• Main Pigments:

  • Melanin: Produced by melanocytes, gives skin its brown to black color.

  • Carotene: Yellow-orange pigment from diet, stored in the skin.

  • Hemoglobin: Red pigment in blood, visible in fair skin.

• Albinism: Genetic condition where melanin is not produced, resulting in pale skin and hair.

• Skin Color Changes:

  • Cyanosis: Bluish tint due to low oxygen.

  • Jaundice: Yellowing due to liver dysfunction.

  • Addison's disease: Bronze pigmentation due to adrenal insufficiency.

  • Tumor of the pituitary gland: May cause abnormal pigmentation.

Example: A person with anemia may appear pale due to reduced hemoglobin in the blood.

Section 5-5: Vitamin D Synthesis

Role of Sunlight and Epidermal Cells

Exposure to sunlight enables epidermal cells to synthesize vitamin D, which is essential for calcium absorption and bone health.

• Process: UV radiation converts 7-dehydrocholesterol in the skin to vitamin D3 (cholecalciferol).

• Importance: Vitamin D deficiency can lead to bone disorders such as rickets and osteomalacia.

• Clinical Note: Excessive sun exposure increases the risk of skin cancer, including basal cell carcinoma, squamous cell carcinoma, and melanoma.

Example: People living in northern latitudes may require vitamin D supplementation due to limited sunlight exposure.

Section 5-6: Hair Structure and Function

Types and Properties of Hair

Hair is a keratinized structure produced by hair follicles in the dermis. It serves protective, sensory, and thermoregulatory functions.

• Hair Types:

  • Lanugo: Fine, unpigmented hair on the fetus.

  • Vellus: Fine, pale hair on children and adults.

  • Terminal: Coarse, pigmented hair (scalp, eyebrows, eyelashes).

• Hair Structure: Shaft (visible part), root (embedded in skin), follicle (surrounds root).

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

• Hair Color: Determined by melanin type and amount.

• Clinical Note: Hair loss (alopecia) can result from genetics, disease, or medications.

Example: Straight or curly hair is determined by the shape of the hair follicle.

Section 5-7: Glands of the Skin

Sebaceous and Sweat Glands

The skin contains several types of glands that contribute to its protective and regulatory functions.

• Sebaceous Glands: Produce sebum, an oily substance that lubricates skin and hair.

• Sudoriferous (Sweat) Glands:

  • Merocrine (Eccrine): Widely distributed, produce watery sweat for thermoregulation.

  • Apocrine: Found in axillae and groin, produce thicker secretion, active after puberty.

• Other Glands: Ceruminous glands (earwax), mammary glands (milk).

• Thermoregulation: Sweat evaporation cools the body; homeostatic feedback mechanisms regulate sweat production.

Example: Excessive sweating during exercise helps prevent overheating.

Section 5-8: Nails

Structure and Growth of Nails

Nails are keratinized plates that protect the tips of fingers and toes and aid in manipulation of objects.

• Parts of the Nail: Nail plate, nail bed, nail matrix (growth area), cuticle (eponychium), lunula (whitish crescent).

• Growth: Nails grow from the matrix; growth occurs at the base under the cuticle.

• Clinical Note: Changes in nail appearance can indicate systemic diseases.

Example: Clubbing of nails may be a sign of chronic hypoxia.

Section 5-9: Skin Repair and Burns

Healing and Burn Classification

After injury, the skin undergoes a series of phases to repair itself. Burns are classified by depth and extent of tissue damage.

• Phases of Repair:

  1. Inflammation

  2. Migratory

  3. Proliferative

  4. Maturation

• Tattoo Removal: Permanent tattoos require destruction of pigment in the dermis.

• Burns:

  • First-degree: Affects epidermis only.

  • Second-degree: Affects epidermis and part of dermis.

  • Third-degree: Destroys epidermis and dermis; may require grafting.

• Rule of Nines: Used to estimate the percentage of body surface area affected by burns.

Example: A burn covering the entire arm is approximately 9% of total body surface area.

Section 5-10: Effects of Aging on the Skin

Age-Related Changes

Aging affects the skin by reducing its elasticity, thickness, and ability to repair itself. Melanocyte activity decreases, leading to paler skin and increased risk of injury.

• Common Changes: Wrinkling, thinning, slower healing, reduced sweat and oil production.

• Clinical Note: Elderly individuals are more prone to skin infections and pressure ulcers.

Example: Older adults may develop age spots due to accumulation of pigment.

Table: Comparison of Epidermal Layers

Layer	Location	Main Cell Type	Function
Stratum corneum	Outermost	Keratinocytes (dead)	Protection, water resistance
Stratum lucidum	Palms, soles (thick skin)	Keratinocytes (dead)	Extra protection
Stratum granulosum	Middle	Keratinocytes	Keratin formation
Stratum spinosum	Above basale	Keratinocytes, Langerhans cells	Strength, immune defense
Stratum basale	Deepest	Keratinocytes, melanocytes, Merkel cells	Cell division, pigment production, sensation

Key Equations

• Rule of Nines (Burn Assessment): $\text{Total Body Surface Area Burned} = \sum \text{(Area % for each region affected)}$

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

Additional info: Academic context and definitions have been expanded for clarity and completeness.