Chapter 5: The Integumentary System – Study Guide

Integumentary System Overview

Definition and Components

The integumentary system is the organ system that forms the external covering of the body, protecting it from the environment and aiding in various physiological functions. It consists of the skin, hair, nails, and associated glands (sweat and sebaceous glands).

• Skin: The largest organ of the body, serving as a barrier and interface with the environment.

• Hair: Filamentous structures that provide protection and sensory input.

• Nails: Hard keratinized plates protecting the tips of fingers and toes.

• Glands: Sweat (sudoriferous) and oil (sebaceous) glands with roles in thermoregulation and lubrication.

Functions of the Skin

• Protection: Acts as a physical, chemical, and biological barrier against pathogens, UV radiation, and mechanical injury.

• Body Temperature Regulation: Sweat glands and blood vessel dilation/constriction help maintain homeostasis.

• Cutaneous Sensation: Contains sensory receptors for touch, pain, temperature, and pressure.

• Metabolic Functions: Synthesizes vitamin D precursor when exposed to sunlight.

• Blood Reservoir: Stores up to 5% of the body’s blood volume.

• Excretion: Eliminates wastes such as urea, salts, and water through sweat.

Structure of the Skin

Layers of the Skin

• Epidermis: The superficial, avascular layer composed of keratinized stratified squamous epithelium.

• Dermis: The deeper, vascular layer made of connective tissue, containing nerves, blood vessels, and glands.

• Subcutaneous Tissue (Hypodermis): Not technically part of the skin, but lies below the dermis; consists mainly of adipose tissue for insulation and energy storage.

Epidermis

• Description/Location: Outermost layer; provides waterproofing and protection.

• Makeup: Composed of four or five layers (strata) of keratinocytes.

• Cells:

  • Keratinocytes: Produce keratin, a tough protective protein.

  • Melanocytes: Produce melanin pigment for UV protection.

  • Langerhans (Dendritic) Cells: Immune defense.

  • Merkel (Tactile) Cells: Sensory receptors for touch.

• Function: Protection, water resistance, and sensation.

Dermis

• Description/Location: Beneath the epidermis; thickest skin layer.

• Makeup: Two layers:

  • Papillary Layer: Areolar connective tissue with dermal papillae (fingerprints).

  • Reticular Layer: Dense irregular connective tissue with collagen and elastic fibers.

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

• Function: Provides strength, elasticity, and houses blood vessels, nerves, and glands.

Subcutaneous Tissue (Hypodermis)

• Description/Location: Deep to the dermis; not a true skin layer.

• Makeup: Adipose and areolar connective tissue.

• Function: Insulation, shock absorption, and energy storage.

Skin Pigments

• Melanin: Brown-black pigment produced by melanocytes; protects against UV radiation.

  • Imbalance: Overproduction can cause freckles/moles; underproduction leads to albinism.

• Carotene: Yellow-orange pigment from diet (carrots, etc.); accumulates in stratum corneum and hypodermis.

  • Imbalance: Excess can cause carotenemia (yellowish skin).

• Hemoglobin: Red pigment in red blood cells; gives pinkish hue to fair skin.

  • Imbalance: Cyanosis (bluish skin) indicates low oxygen; erythema (redness) from increased blood flow.

Hair

• Description: Flexible strands of dead, keratinized cells.

• Location: Covers most of the body except palms, soles, lips, nipples, and parts of external genitalia.

• Function: Protection (scalp, eyes, nose), sensation, and thermoregulation.

Structure of Hair

• Shaft: Part above the skin surface.

• Root: Part embedded in the skin.

• Medulla, Cortex, Cuticle: Three concentric layers of the hair shaft.

Hair Follicle

• Structure/Location: Extends from epidermis into dermis; surrounds the hair root.

• Associated Structures: Arrector pili muscle (causes "goosebumps"), sebaceous glands.

Hair Growth

• Anagen: Active growth phase.

• Catagen: Transitional phase.

• Telogen: Resting phase.

Hair Thinning and Baldness

• Alopecia: General hair thinning with age.

• Male Pattern Baldness: Genetically determined, sex-influenced condition.

• Imbalance: Can be caused by hormonal changes, stress, or disease.

Nails

• Description: Hard plates of keratin on the dorsal surface of fingers and toes.

• Structure: Nail plate, nail bed, nail matrix (growth area), lunula (white crescent), cuticle (eponychium).

• Function: Protects distal phalanges, aids in grasping and manipulation.

• Location: Tips of fingers and toes.

• Imbalance: Disorders include fungal infections, clubbing (hypoxia), and spoon nails (anemia).

Sweat (Sudoriferous) Glands

• Description: Exocrine glands producing sweat for thermoregulation and excretion.

• Structure: Coiled tubular glands in the dermis.

• Types:

  • Eccrine Glands: Widely distributed; secrete watery sweat directly onto skin surface.

  • Apocrine Glands: Found in axillary and anogenital areas; secrete thicker sweat into hair follicles.

• Function: Regulate body temperature, excrete wastes, and (apocrine) may play a role in scent.

• Location: All over body (eccrine); armpits and groin (apocrine).

Sebaceous (Oil) Glands

• Description: Exocrine glands that secrete sebum (oil) into hair follicles.

• Structure: Simple branched alveolar glands.

• Function: Lubricates skin and hair, prevents water loss, and has antibacterial properties.

• Location: All over body except palms and soles; most abundant on face and scalp.

• Imbalance: Overactivity can cause acne; underactivity leads to dry, cracked skin.

Types of Skin Cancer

• Basal Cell Carcinoma: Most common, least malignant; arises from stratum basale.

• Squamous Cell Carcinoma: Arises from keratinocytes of stratum spinosum; can metastasize if not removed.

• Melanoma: Cancer of melanocytes; most dangerous due to rapid metastasis.

Burns

• First-Degree Burns: Only epidermis is damaged; redness, swelling, pain.

• Second-Degree Burns: Epidermis and upper dermis damaged; blisters form.

• Third-Degree Burns: Entire thickness of skin destroyed; area appears gray-white, cherry red, or blackened; not painful (nerve endings destroyed).

Developmental Aspects of the Integumentary System

• Embryo to Fetus: Epidermis develops from ectoderm; dermis and hypodermis from mesoderm. Vernix caseosa (protective coating) covers fetus.

• Infancy to Adulthood: Skin thickens, sweat and sebaceous gland activity increases at puberty.

• Aging Skin: Epidermal replacement slows, skin thins, elasticity decreases, increased risk of injury and infection.

Layer	Main Cell Types	Key Functions
Epidermis	Keratinocytes, Melanocytes, Langerhans, Merkel	Protection, waterproofing, sensation
Dermis	Fibroblasts, Macrophages, Mast cells	Strength, elasticity, houses vessels/glands
Hypodermis	Adipocytes	Insulation, energy storage

Example: A sunburn is a first-degree burn affecting only the epidermis, while a severe burn from a fire may be third-degree, requiring skin grafts.

Additional info: The skin’s ability to synthesize vitamin D is crucial for calcium absorption and bone health.