Chapter 5: The Integumentary System – Study Guide Notes

The Integumentary System

Overview

The integumentary system consists of the skin and its associated structures, including hair, nails, and glands. It serves as the body's primary barrier against the external environment, regulates temperature, and provides sensory information.

Major Layers of the Skin

• Epidermis: The outermost layer, composed of keratinized stratified squamous epithelium. It is responsible for protection and contains distinct sublayers.

• Dermis: Located beneath the epidermis, it consists of two layers:

  • Papillary layer: Areolar tissue, contains capillaries, lymphatic vessels, and sensory nerve fibers.

  • Reticular layer: Dense irregular connective tissue, contains collagen and elastic fibers, and houses accessory organs.

• Hypodermis (Subcutaneous Layer): Deep to the dermis, composed of areolar and adipose tissue. It separates the skin from underlying fascia and organs. Note: Not considered part of the skin proper.

Layers of the Epidermis

• Stratum corneum: Top layer; consists of dead, keratinized cells. Provides water resistance (not waterproof).

• Stratum lucidum: Present only in thick skin (palms, soles); contains proteins keratin and keratohyalin.

• Stratum granulosum: Layers of keratinocytes producing keratin and keratohyalin; cells begin to die.

• Stratum spinosum: Keratinocytes bound by desmosomes; contains dendritic cells for immune response.

• Stratum basale: Deepest layer; attached to basement membrane. Contains melanocytes, keratinocytes, basal cells, and Merkel cells (touch sensation).

Cell Types in the Epidermis

• Keratinocytes: Primary cell type; produce keratin, a tough, waterproof protein. Originate in the stratum basale and found throughout all layers. Form a protective barrier.

• Melanocytes: Located in the stratum basale; produce melanin within melanosomes and transfer it to keratinocytes. Melanin protects DNA from UV damage.

Alive vs. Dead Epidermal Layers

• Alive: Stratum basale, stratum spinosum, stratum granulosum (cells are dying).

• Dead: Stratum corneum, stratum lucidum.

Dermis Layers

• Papillary layer: Areolar tissue; contains capillaries, lymphatic vessels, sensory nerve fibers, and dermal papillae (projections between epidermal ridges).

• Reticular layer: Dense irregular connective tissue; contains collagen and elastic fibers, and accessory organs.

Fingerprints

• Epidermal ridges: Formed by deeper layers of the epidermis; extend adjacent to dermal papillae. Increase surface area for attachment and create unique fingerprint patterns.

• Dermal papillae: Projections of the dermis that interlock with epidermal ridges.

Factors Affecting Skin Color

• Melanin: Produced by melanocytes; amount and distribution affect skin color.

• Carotene: Yellow-orange pigment from diet; accumulates in epidermal cells.

• Hemoglobin: Oxygenated blood gives skin a reddish tint.

• Other factors: Genetics, environmental exposure, and disease.

Sensory Perception in the Skin

• Merkel cells: Located in the stratum basale; detect touch.

• Dendritic cells: Immune response; found in stratum spinosum.

• Free nerve endings: Detect pain, temperature, and pressure; located throughout dermis and epidermis.

• Meissner's corpuscles: Detect light touch; found in papillary layer.

• Pacinian corpuscles: Detect deep pressure and vibration; found in reticular layer.

Degrees of Burns

• First degree: Affects only the surface of the epidermis; causes erythema (redness).

• Second degree: Damages entire epidermis and part of the dermis; causes blistering and swelling. Accessory structures usually not damaged.

• Third degree: Destroys epidermis, dermis, and extends into subcutaneous layer; sensory nerves destroyed, less pain. Requires skin grafting.

Rule of Nines

The rule of nines is used to estimate the percentage of body surface area affected by burns in adults.

Body Region	Percentage
Head	9%
Each Arm	9%
Each Leg	18%
Anterior Trunk	18%
Posterior Trunk	18%
Perineum	1%

Additional info: The rule of nines helps guide fluid resuscitation and treatment decisions.

Types of Skin Grafts

• Autograft: Skin from the patient's own body.

• Allograft: Skin from another human donor.

• Xenograft: Skin from another species (e.g., pig).

• Used for: Third degree burns and other injuries where skin cannot repair itself.

Anatomy of Hair and Hair Follicle

• Hair: Composed of dead, keratinized cells.

• Major structures:

  • Shaft: Visible part above skin.

  • Root: Embedded in follicle.

  • Medulla, cortex, cuticle: Cell layers of hair.

• Hair follicle: Surrounds the root; includes the bulb, papilla, and matrix (site of cell division).

Hair Growth Cycle and Types

• Anagen: Active growth phase.

• Catagen: Transitional phase.

• Telogen: Resting phase.

• Terminal hair: Thick, pigmented (scalp, eyebrows).

• Vellus hair: Fine, unpigmented (body surface).

Thermoregulation by Hair and Skin

• Hair: Insulates and protects.

• Skin: Regulates heat loss via sweat glands and blood flow.

Endocrine vs. Exocrine Glands

• Endocrine glands: Release hormones into the bloodstream (e.g., thyroid).

• Exocrine glands: Release secretions onto epithelial surfaces (e.g., sweat, sebaceous glands).

Sebaceous Glands

• Location: Associated with hair follicles.

• Function: Secrete sebum (oil) to lubricate skin and hair.

• Connection: Ducts open into hair follicles or directly onto skin surface.

Sweat Glands

• Types:

  • Eccrine (merocrine): Widely distributed; open directly onto skin surface; involved in thermoregulation.

  • Apocrine: Found in axillae, groin; open into hair follicles; produce thicker, odoriferous secretion.

• Function: Regulate temperature, excrete waste.

Anatomy of Nails

• Nail plate: Hard, keratinized structure.

• Nail bed: Underlying tissue.

• Nail matrix: Site of cell division.

• Lunula: Crescent-shaped area at base.

• Cuticle (eponychium): Protective fold.

Changes in Skin with Aging

• Thinner epidermis and dermis.

• Reduced collagen and elastic fibers.

• Decreased gland activity.

• Slower repair and increased risk of injury.

Skin Repair After Damage

• Step 1: Inflammation and bleeding.

• Step 2: Formation of a blood clot and scab.

• Step 3: Migration of epithelial cells and fibroblasts.

• Step 4: Formation of granulation tissue.

• Step 5: Remodeling and scar formation.

Scar Tissue

• Purpose: Restores structural integrity after injury.

• Presence: Composed of dense collagen fibers; lacks normal skin structures.

Additional info: Scar tissue is less flexible and may impair function depending on location and extent.