Integumentary System

General Composition and Function

The integumentary system consists of the skin and its accessory structures, serving as the body's primary barrier and interface with the environment. It plays vital roles in protection, sensation, thermoregulation, and communication.

• Structure of Skin

  • Epidermis – Keratinized stratified epithelium

  • Dermis

  • Subcutaneous layer (Hypodermis)

• Accessory Structures

  • Sweat glands

  • Oil (sebaceous) glands

  • Hair

  • Nails

• Functions of Skin

  1. Protection – Prevents dehydration and infection (acid mantle, keratin, antimicrobial peptides)

  2. Synthesis of Vitamin D – Contributes to bone health

  3. Sensation – Largest sense organ; detects tactile, thermal, and pain stimuli

  4. Thermoregulation – Regulates body temperature via sweat and blood flow

  5. Nonverbal Communication – Expressive faces, general appearance of skin/hair

Microscopic and Gross Anatomy of Skin

The skin is composed of multiple layers and specialized cells, each contributing to its protective and sensory functions.

• Epidermis – Comprised of five cell types:

  1. Keratinized stratified squamous epithelium

  2. Keratinocytes – produce keratin

  3. Melanocytes – produce melanin

  4. Langerhans cells – immune function

  5. Merkel cells – tactile sensation

  Mnemonic: Come Let's Get Sun Burned (Stratum Corneum, Lucidum, Granulosum, Spinosum, Basale)

• Types of Skin

  • Thick Skin – Palms and soles; contains stratum lucidum; hairless

  • Thin Skin – Covers rest of body; lacks stratum lucidum; hairy

Dermis and Hypodermis

The dermis provides strength and elasticity, while the hypodermis anchors skin and stores energy.

• Dermis

  • Composed of collagen, elastic, and reticular fibers

  • Contains blood vessels, nerves, glands, hair follicles

  • Papillary Layer – Superficial, areolar tissue, forms fingerprints

  • Reticular Layer – Deeper, dense irregular connective tissue, contains hair follicles and sensory corpuscles

  • Produces stretch marks (striae) if collagen fibers tear

• Hypodermis (Subcutaneous Layer)

  • Loose connective tissue (adipose, areolar)

  • Well-vascularized

  • Connects skin to fascia, provides insulation and energy storage

Functions and Cells of the Epidermis

• Keratinocytes

  • 90% of epidermal cells

  • Produce keratin for toughness and water-proofing

• Melanocytes

  • Produce melanin pigment

  • Protect DNA from UV damage

• Langerhans Cells

  • Immune response, found in stratum spinosum and granulosum

• Merkel (Tactile) Cells

  • Receptors for touch, connected to nerve endings

Accessory Structures of the Integument

Hair

• Structure

  • Slender filament of keratinized cells

  • Hair shaft – above skin

  • Hair root – below skin

  • Hair bulb – base of hair root

  • Medulla, cortex, cuticle – layers of hair

  • Arrector pili muscle – contracts to produce "goosebumps"

• Functions

  • Scalp – insulation, UV protection

  • Eyebrows/Eyelashes – protection from particles

  • Sensory detection

• Hair Growth Cycle

  • Anagen – growth phase (6-8 years)

  • Catagen – regression phase (2-3 weeks)

  • Telogen – resting phase (1-3 months)

Nails

• Derivatives of stratum corneum

• Thin, dead cells packed with keratin

• Functions: protection, aid in grasping, manipulation

• Parts: free edge, nail body, nail root, nail bed, lunule, eponychium (cuticle)

Exocrine Glands

• Eccrine (Merocrine) Sweat Glands

  • Most abundant, found all over body

  • Function: cooling

• Apocrine Sweat Glands

  • Respond to stress/sexual stimulation

  • Found in axilla, groin, anal region

  • Thicker, more odorous secretion

• Sebaceous Glands

  • Produce oily sebum

  • Lubricates hair and skin

• Ceruminous Glands

  • Produce cerumen (earwax)

  • Waterproofs and protects ear canal

• Mammary Glands

  • Produce milk in females

  • Modified apocrine glands

Homeostatic Mechanisms

• Thermoregulation

  • Regulates body temperature by releasing sweat and adjusting blood flow

  • Vasodilation/vasoconstriction in dermis

• Integration with Other Systems

  • Renal: excretion of wastes via sweat

  • Muscular: shivering to produce heat

Disruption of Homeostasis

Burn Classifications

• First Degree – Epidermis only; redness, mild pain

• Second Degree – Epidermis and part of dermis; blisters, pain, may scar

• Third Degree – All epidermis and dermis; deeper tissues may be involved; requires skin grafts

• Fourth Degree – All layers plus bone/muscle; severe burns

Fluid Replacement and Infection Control

• Burns can cause significant fluid loss and risk of infection

• Debridement may be necessary to remove dead tissue

Skin Cancer

• Basal Cell Carcinoma – Most common, originates in stratum basale

• Squamous Cell Carcinoma – Originates in stratum spinosum, can metastasize

• Melanoma – Originates in melanocytes, aggressive, uses ABCD rule for diagnosis

Skeletal System

General Functions

The skeletal system provides the framework for the body, supports movement, protects organs, and serves as a reservoir for minerals and blood cell formation.

1. Blood Formation – Occurs in red bone marrow (epiphyses of long bones, axial skeleton, pelvis)

2. Support – Structural support for the body, attachment for tendons

3. Protection – Skull protects brain, vertebral column protects spinal cord, ribs/sternum protect thoracic organs, pelvis protects reproductive organs

4. Movement – Muscles attach to bones via tendons

5. Storage and Release of Minerals – Bones store calcium and phosphorus

Additional info: The notes have been expanded to include definitions, examples, and a summary table for clarity and completeness. All major topics from the original notes are covered and organized for exam preparation.