Study Guide: Integumentary, Skeletal, Joints, and Muscular Systems

The Integumentary System

Structure and Roles of the Skin

The skin is the largest organ of the human body and serves as a protective barrier. It consists of multiple layers and specialized structures that contribute to its various functions.

• Protection: Shields underlying tissues from mechanical damage, pathogens, and dehydration.

• Thermoregulation: Sweat glands and blood vessels help regulate body temperature.

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

• Excretion: Sweat glands excrete waste products.

• Vitamin D Synthesis: Initiates synthesis when exposed to UV light.

Layers of the Skin

• Epidermis: Outermost layer; avascular; composed mainly of keratinocytes.

• Dermis: Middle layer; contains connective tissue, blood vessels, nerves, glands, and hair follicles.

• Hypodermis (Subcutaneous Layer): Deepest layer; composed of adipose tissue for insulation and energy storage.

Layers of the Epidermis

• Thick Skin: Found on palms and soles; has five layers:

  • Stratum basale

  • Stratum spinosum

  • Stratum granulosum

  • Stratum lucidum

  • Stratum corneum

• Thin Skin: Covers most of the body; lacks stratum lucidum.

Cells of the Epidermis

• Keratinocytes: Produce keratin, a protein that strengthens the skin.

• Melanocytes: Produce melanin, which protects against UV radiation.

• Langerhans Cells: Immune cells that detect and fight pathogens.

Skin Glands and Receptors

• Sebaceous Glands: Secrete sebum for lubrication and waterproofing.

• Sudoriferous (Sweat) Glands: Eccrine (thermoregulation) and apocrine (odor production).

• Sensory Receptors: Detect touch, pressure, pain, and temperature.

Factors Affecting the Skin

• Wounds: Cuts, abrasions, and lacerations disrupt skin integrity.

• Chemicals: Can cause burns or allergic reactions.

• UV Radiation: Leads to sunburn, DNA damage, and increased cancer risk.

• Burns: Classified by depth (first, second, third degree).

Rule of Nines

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

• Body is divided into sections, each representing 9% (or multiples) of total body surface area.

The Skeletal System

Structure of Cartilage and Bone

• Cartilage: Flexible connective tissue; types include hyaline, elastic, and fibrocartilage.

• Bone: Rigid connective tissue; supports and protects organs, stores minerals, and houses marrow.

Osteon Structure

An osteon (Haversian system) is the structural unit of compact bone.

• Cylindrical structure with concentric lamellae around a central canal containing blood vessels and nerves.

Types of Bones

• By Development:

  • Membranous (intramembranous ossification): Flat bones like skull.

  • Endochondral (endochondral ossification): Most bones, including long bones.

• By Shape:

  • Long bones (e.g., femur)

  • Short bones (e.g., carpals)

  • Flat bones (e.g., sternum)

  • Irregular bones (e.g., vertebrae)

Structure of Long Bones

• Diaphysis: Shaft of the bone.

• Epiphyses: Ends of the bone.

• Metaphysis: Region between diaphysis and epiphysis; contains growth plate.

• Medullary Cavity: Central cavity containing marrow.

• Periosteum: Outer membrane covering bone.

Endochondral Ossification

Process by which most bones form from a cartilage template.

1. Bone collar forms around diaphysis.

2. Cavitation of cartilage in the center.

3. Primary ossification center develops in diaphysis.

4. Secondary ossification centers form in epiphyses.

5. Epiphyseal plate allows for longitudinal growth.

Bone Cells and Remodeling

• Osteoblasts: Build new bone matrix.

• Osteoclasts: Break down bone matrix.

• Osteocytes: Mature bone cells maintaining bone tissue.

Joints

Categories and Classifications

• Structural Classification:

  • Fibrous (e.g., sutures in skull)

  • Cartilaginous (e.g., intervertebral discs)

  • Synovial (e.g., knee, shoulder)

• Functional Classification:

  • Synarthroses (immovable)

  • Amphiarthroses (slightly movable)

  • Diarthroses (freely movable)

Examples of Joint Types

Structural Type	Example	Functional Type
Fibrous	Sutures (skull)	Synarthrosis
Cartilaginous	Pubic symphysis	Amphiarthrosis
Synovial	Shoulder joint	Diarthrosis

Synovial Joints: Structure and Features

• Articular cartilage covers bone ends.

• Joint (synovial) cavity contains synovial fluid.

• Articular capsule encloses the joint.

• Ligaments reinforce the joint.

• Special features: Menisci, bursae, and tendon sheaths in select joints.

Special Synovial Joints

• Shoulder: Ball-and-socket; greatest range of motion.

• Elbow: Hinge joint; flexion and extension.

• Hip: Ball-and-socket; stable, weight-bearing.

• Knee: Modified hinge; menisci and ligaments provide stability.

Types of Joint Movement

• Flexion/Extension/Hyperextension

• Abduction/Adduction

• Rotation

Muscle Tissue

Types of Muscle

• Skeletal Muscle: Voluntary, striated, attached to bones.

• Cardiac Muscle: Involuntary, striated, found in heart.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs.

Muscle Fiber Structure

• Sarcoplasmic Reticulum (SR): Stores and releases calcium ions.

• Triad: T tubule flanked by two terminal cisternae of SR.

• T Tubule: Invagination of sarcolemma; conducts impulses.

• Myofilaments: Actin (thin) and myosin (thick) filaments.

• ATPase: Enzyme on myosin head; hydrolyzes ATP for contraction.

• Cross-bridge: Connection between actin and myosin during contraction.

Levels of Muscle Organization

• Myofibril: Contractile threads within muscle fiber.

• Muscle Fiber (Cell): Surrounded by endomysium.

• Fascicle: Bundle of muscle fibers; surrounded by perimysium.

• Muscle: Bundle of fascicles; surrounded by epimysium.

Sliding Filament Mechanism

Muscle contraction occurs as myosin heads pull actin filaments toward the center of the sarcomere.

• A Band: Length of thick filaments; remains constant.

• I Band: Region with only thin filaments; shortens during contraction.

• H Zone: Center of A band; shortens during contraction.

• M Line: Center of sarcomere; anchors thick filaments.

Types of Skeletal Muscle Fibers

Type	Contraction Speed	Fatigue Resistance	Color
Slow Oxidative	Slow	High	Red
Fast Glycolytic	Fast	Low	White
Fast Oxidative	Fast	Intermediate	Red/Pink

Effects of Aging and Exercise on Muscle

• Aging: Decrease in muscle mass and strength; increased fibrosis.

• Exercise: Increases muscle size (hypertrophy), strength, and endurance; can delay effects of aging.

Example: Endurance training increases the proportion of slow oxidative fibers, while resistance training increases muscle hypertrophy.