UCF Pathophysiology II Exam 4 (Chapters 50 + 51 + 52)

Functions of Skeletal System

• Protection: Shields vital organs (e.g., skull protects brain, ribs protect heart and lungs).

• Support & Movement:

  • Provides attachments for muscles and ligaments.

  • Acts as rigid levers so muscles can move the body.

• Storage: Stores minerals like calcium and phosphorus.

• Blood Cell Production: Bone marrow makes new blood cells (red, white, and platelets).

Bone Characteristics

• Highly vascular → has lots of blood vessels.

• Metabolically active → constantly breaking down and rebuilding (remodeling) from birth to death.

Fibroblasts/Fibrocytes

Needed for collagen production.

Osteoblasts

Lay down bone, formed from osteoprogenitor cells.

Think: blasts build bone

Osteocytes

Mature bone cells.

Osteoclasts

Responsible for bone resorption.

think: clasts clash with bone (they break it down)

Ground substance

Extracellular fluid, proteoglycans, chondroitin sulfate,
hyaluronic acid

– Minerals: magnesium, phosphorus, calcium

Collagen Fibers

Compose around 95% of the extracellular matrix. Provide stability, strength, and tensile stiffness; tolerate tension but not compression.

Osteon (Haversian System)

Basic unit of the bone.

Cancellous (Trabecular Bone)

Laid down in response to stress and shape to accommodate loads placed on the bone.

Compact Bone

Resistant to compression and dense in structure.

Functional Properties of Bone

Bone is capable of altering it's shape and density in response to mechanical stress.

Absence of bone stress due to immobility or altered weight bearing leads to demineralization.

Endochondral Ossification

Involves cartilage replacement by bone (embryonic development, fracture healing, and some bone tumor growth)

Why is bone’s ability to remodel important?

Remodeling lets bone repair after injury and adapt to stress.

Wolff's Law

Response of bone to stress.

Bone is laid down where it’s needed and resorbed where it’s not.

Think: Use it or lose it— bones grow stronger with stress, weaker without it.

What happens to bone without stress or external forces?

Osteoclast activity > Osteoblast activity  = bone loss

Think: No load = Clasts win → bone mass drops

Why are fractures through the epiphyseal plate serious in children?

May cause limb length discrepancy after healing.

Think: Epi = End of growth. Damage it, you end growth early

What happens to bone mass with age or disease?

Decreases — because bone resorption exceeds formation

Think: Old bones = More clasts, fewer blasts

5 Stages of Bone Healing

- Hematoma Formation (1-3 Days)– Inflammatory phase

- Fibrocartilage Formation (3 Days-2 Weeks)– Reparative phase begins

- Callus Formation (2-6 Weeks)

- Ossification (3 Weeks - 6 Months)

- Consolidation / Remodeling (6 Weeks - 1 Year)– Remodeling phase

Think: He Forgot Cold Old Coffee

Hematoma formation

Blood vessels break → hematoma forms → inflammation starts

Think: H = Hurts and Heals start here.

What happens during fibrocartilage formation?

Fibroblasts and chondroblasts create a soft callus (temporary patch).

Think: Fibro = Fibers form the first Fix

What happens during callus formation?

Hard callus begins replacing soft tissue with woven bone.

Think: Cushion turns to Concrete

What happens during ossification?

New bone replaces callus; mineralization increases

Think: Official bone formed

What happens during consolidation/remodeling?

Bone regains shape, strength, and structure

Think: Remodel = Return to normal

What is a joint (articulation or arthroses)?

A point of contact between bones where movement occurs

Think: Junction where bones meet

How does joint complexity relate to movement?

The more complex the movements → the more complex the joint structure

Think: Big moves need big designs

Synarthroses (Nonsynovial) Joints

Two Types: Fibrous and Cartilage

Fibrous Joints

Some Guys Stay Firm

• S – Suture (skull)

• G – Gomphosis (teeth)

• S – Syndesmosis (tibia/fibula)

• Firm = little movement (fibrous joints)

What are fibrous joints (synarthroses)?

bones are connected by fibrous tissue with no joint cavity — little to no movement.

Think: Syn = stuck

Suture Joint

Bones united by a thin, dense layer of fibrous tissue, found only in the skull

Think: Suture = Sewn shut

Gomphosis Joint

A peg-in-socket type joint; the only example is the joint between teeth and mandible/maxilla.

Think: Gum-phosis = in the gums

Syndesmosis Joint:

Two bones joined by a ligament or interosseous membrane, e.g., between tibia and fibula.

Think: Syn-desmosis = Side-by-side bones tied

Cartilaginous Joints

Soft Cartilage Structures

• S – Symphysis = Fibrocartilage plate (symphysis pubis)

• C – Synchondrosis = Hyaline cartilage (growth plate)

• S – Slight movement

What are cartilaginous joints?

Joints where bones are connected by cartilage, with limited movement and no joint cavity

Think: Cartilage = cushion,

Symphysis Joint

Two bones joined by a fibrocartilaginous plate or disk — e.g., symphysis pubis or intervertebral discs.

Think: Sym = together

Synchrondrosis Joint

Bones are connected by hyaline cartilage, often found at growth sites, like the epiphyseal plate or the first sternocostal joint

Think: Chondro = cartilage

Diarthroses (Synovial Joints)

• Joints designed for mobility and movement

• The most common and most movable type of joint in the body

Think: Dia = Dynamic, Dressed, and Damp

What covers a synovial joint?

A joint capsule or synovial sheath encloses the joint, providing protection and structure.

Think: bubble wrap that surrounds and protects the moving part

How is movement produced in synovial joints?

By muscle-tendon contractions; movement is controlled by ligaments and the joint capsule.

Think: Muscles move, ligaments limit

Muscles move, ligaments limit

Soft tissue structures—such as ligaments, tendons, and the capsule—enhance stability while still allowing movement.

Think: seatbelts that keep the joint safe while moving

What produces synovial fluid, and what is its function?

• Produced by fibroblast-like cells lining the joint capsule.

• Lubricates the joint, reduces friction, and nourishes cartilage.

Think: Synovial = Slick + Nourish

What are the 5 main features of a synovial (diarthrodial) joint?

• Fibrous joint capsule

• Joint cavity enclosed by the capsule

• Synovial membrane lining the capsule

• Synovial fluid lubricating the joint

• Hyaline cartilage covering the bone ends

What is the fibrous joint capsule and what does it do?

A tough outer layer that encloses the joint cavity and provides strength and protection.

Think: ziplock bag that keeps all the joint parts together.

What does the synovial membrane do?

It lines the inner surface of the capsule and produces synovial fluid

Think: Membrane Makes Moisture

What’s the purpose of synovial fluid?

Acts as a lubricant and shock absorber, reduces friction, and nourishes cartilage

Think: Joint Juice = Smooth Moves

What is the function of hyaline cartilage in joints?

Covers the ends of bones to reduce friction and absorb shock during movement.

Think: Hyaline Helps Glide

What are accessory structures in some synovial joints?

Include menisci, ligaments, tendons, and bursae, which provide support, cushioning, and stability.

Think: Extras = Stability + Comfort

What are the three categories of synovial joints based on the number of movement axes?

• Uniaxial – movement around 1 axis

• Biaxial – movement around 2 axes

• Triaxial (Multiaxial) – movement around 3 axes

What type of movement does a uniaxial joint allow?

Movement in one plane (like a door hinge)

Examples:

• Hinge joint (elbow, knee) → flexion and extension

• Pivot joint (neck, forearm) → rotation

Think: Uni = Uno = One Direction

What type of movement does a biaxial joint allow?

Movement in two planes (forward–backward and side-to-side).

Examples:

• Condyloid joint (wrist, knuckles)

• Saddle joint (thumb)

Think: Biaxial = Bike = Two Wheels, Two Directions

What type of movement does a triaxial joint allow?

Movement in three planes – flexion/extension, abduction/adduction, rotation.

Examples:

• Ball-and-socket joint (shoulder, hip)

Think: Triaxial = Triple Freedom

What is cartilage primarily made of?

• Water (main component)

• Inorganic salts

• Proteins, glycoproteins, and lipids

What composes the extracellular matrix (ECM) of cartilage?

• Collagen fibers: give tensile strength

• Elastin: provides elasticity

• Ground substance: proteoglycans + collagen fibrils

What cells produce the organic component of cartilage matrix?

Chondrocytes: secrete collagen, proteoglycans, and glycoproteins

Think: Chondro = Cartilage Cell Maker

How does cartilage reduce wear and friction in joints?

• Spreads loads over a large surface area of articulating bones

• Decreases contact stress during movement

Think: shock absorber & friction reducer

What provides stability and tensile strength in cartilage?

Collagen fibers: tolerate tension, resist stretching, but not compression

Think: Collagen = strong rope fibers, good for pulling but not squishing

What gives cartilage compression tolerance and rigidity?

Proteoglycan aggregation: absorbs compressive forces, keeps structure firm

Think: spongy support, resists being squashed

Ligaments

Connect bone to bone, provide mechanical stability to joints, and guide joint movements— but don’t move themselves (non-contractile).

Think: L for Link

Tendons

Attach muscle to bone and assist in generation movement.

Think: T for Tug

Joint Capsules

Work with ligaments to stabilize joints and limit excessive motion

Skeletal Muscle

• Makes up about 40% of total body weight

• Attached to bones and controlled voluntarily (you can choose to move it)

Functions of Skeletal Muscle

1. Movement:

   • Pulls on bones to create motion at joints

2. Strength & Stability:

   • Supports posture and keeps the skeleton steady

3. Protection:

   • Helps distribute loads and absorb shock, reducing stress on bones and joints

Skeletal Muscle: Composition

• Structural unit: the muscle fiber (muscle cell)

• Each fiber is wrapped in a membrane called the sarcolemma

• Fibers are grouped into bundles called fasciculi

Endomysium

Surrounds each muscle fiber—Connective Tissue Around Sarcolemma

Function: Provides support & protection

Perimysium

Surrounds each muscle fiber—Connective Tissue Around Fasciculi

Function: Groups fibers together

Epimysium

Surrounds each muscle fiber—Connective Tissue Around Entire Muscle

Function: Holds everything together & connects to tendons

Fiber Arrangements

• Parallel (strap or spiral): fibers run in the same direction → allow greater movement

• Oblique (unipennate, bipennate, multipennate): angled fibers → allow more strength

Striation

Organized structure of myofibrils of the contractile apparatus.

• Thick filaments → made mostly of myosin 🧱

• Thin filaments → made mostly of actin, with troponin and tropomyosin as regulatory proteins

Think: MATT

→ Myosin = thick
→ A + TT = thin

Muscle Contraction

• Function: Muscle pulls on bone → produces movement

• Mechanism: Sliding filament (cross-bridge) theory

  • Myosin heads attach to actin filaments → pull → shorten sarcomere → contraction

Mechanics of Muscle Contraction

• Muscle shortens → actin & myosin overlap more

• Z-lines move closer together as filaments slide

• Cross-bridge formation: Myosin head binds actin → pulls → releases → repeats

• ATP required for each cross-bridge cycle

Think: ZAP for Contraction

• Z-lines move closer

• Actin & myosin overlap

• Power stroke = ATP used

Regulation of Actin-Myosin Binding

• Tropomyosin blocks actin binding sites at rest

• Troponin controls tropomyosin position

• No calcium → troponin keeps tropomyosin covering actin → no contraction

• Calcium present → troponin moves tropomyosin → binding sites exposed → cross-bridges form

Think: Calcium Clears the Way

Calcium present → Clears tropomyosin → Actin binding sites exposed → Muscle contracts

Muscle Response to Use & Disuse

• Disuse → ↓ muscle mass, ↓ oxidative enzyme activity

• Early activity after injury → faster recovery, less atrophy, better circulation

Disorders of the Musculoskeletal System

• Bone Disease

•  Soft Tissue Injuries

• Diseases of Skeletal Muscle

Bone Disorders Overview

Alterations in Bone Mass & Structure

• Scoliosis – lateral curvature of the spine

• Osteoporosis – ↓ bone mass, ↑ fracture risk

• Rickets / Osteomalacia – defective mineralization (vitamin D deficiency)

Bone Infections

• Osteomyelitis – bacterial infection of bone

Bone Tumors

• Multiple myeloma – malignant plasma cell proliferation in bone

Scoliosis

• Lateral curvature of the spine → S- or C-shaped deformity
  

Causes:

• Idiopathic: 70–85% of cases

• Congenital disorders

• Connective tissue disorders

• Neuromuscular disorders

Nonstructural Scoliosis

• Resolves when bending to affected side

• No vertebral rotation or bony deformity

• Causes: postural problems, inflammation, leg length discrepancy

• Not progressive

Think: Nonstructural = Non-permanent, bends away

Structural Scoliosis

• Does not correct on bending

• Vertebral rotation present

• Vertebrae deformity → asymmetric hip, shoulder, rib cage

• Progressive

Think: Structural = Stays rigid, rotates

Scoliosis: Treatment

1. Bracing – Prevents progression in growing children
2. Exercises – Strengthen muscles, improve posture and flexibility
3. Surgery – Spinal fusion or instrumentation for severe curvature

Osteoporosis

Most common metabolic bone disease where bone resorption > bone formation

Effects:

• Disrupted balance between osteoblasts (build) and osteoclasts (break down)

• ↓ Mineral and protein matrix

• Bones become fragile → prone to fractures

Think: Porous bones break easily

Hormones That Affect Bone – Estrogen

Estrogen protects bone by:

• Preventing loss of osteoblasts (bone builders)

• Inhibiting osteoclasts (bone breakers)

↑Osteoclast activity → ↑Bone breakdown → ↓Bone density → Osteoporosis risk

Think: Estrogen Encourages bone

Osteoporosis: Risk Factors

FEMALES CAN FALL

F – Family history
E – Estrogen low
M – Menopause early
A – Asian/Caucasian
L – Little frame
E – Excess steroids
S – SLE/RA
C – Chronic kidney disease
A – Age
N – No hormones (postmenopause)
FALL – reminds you of fractures!

Osteoporosis Treatment

• Calcium and vitamin D supplements
• Exercise
• Estrogen replacement therapy

Rickets

Deficits in the mineralization of newly formed bone matrix in the growing skeleton.

Think: R = Rising bones

Osteomalacia

Deficits in mineralized of newly formed bone matrix in the mature skeleton.

Think: O = Old bones

Vitamin D (Calcitriol)

acts like a hormone that keeps calcium and phosphate levels balanced for strong bones.

Main Targets & Actions:

1. Intestines → 🍽
   ➤ Increases calcium and phosphate absorption from food.

2. Kidneys → 💧
   ➤ Reduces calcium loss in urine (helps keep calcium in the body).

3. Osteoclasts (Bone Cells) → 🦴
   ➤ Works indirectly to stimulate bone breakdown (resorption) when calcium is low — releases calcium into the blood.

Think: D = Digest, Deposit, Draw

What are the main causes of decreased Vitamin D?

Dark Clothes Stop Sun’s Delicious Nutrients

Dark skin
Clothing (covering)
Sunscreen > SPF 8
Sunlight (lack of)
Nutrition (poor)

What are the results of Vitamin D deficiency?

• Rickets in children (soft bones, bowed legs)

• Osteomalacia in adults (bone pain, fractures)

Think: D Down → Deformed bones

Why are the elderly at higher risk for Vitamin D deficiency?

They often have less sunlight exposure, thinner skin, and reduced dietary intake.

Think: E for Elderly → End of Sun time

Rickets and Osteomalacia Treatment

vitamin D

calcium

phosphorus supplementation

Osteomyelitis

Severe pyogenic infection of bone and local tissue.

How can organisms reach the bone?

1. Hematogenous – via bloodstream from infection elsewhere
2. Adjacent soft tissue – from burns, trauma, sinus disease, tumors
3. Direct introduction – open fractures, wounds, surgery, prosthetics

What is the most common pathogen in osteomyelitis?

Staphylococcus aureus

How is osteomyelitis treated?

ABC

Antibiotics: 4–6 weeks

Bone debridement: if abscess forms

Chronic infection: may require long-term management

What is multiple myeloma and how does it present?

• Definition: Slowly growing bone marrow malignancy; proliferation of a single clone of plasma cells

• Lab finding: Homogeneous immunoglobulin in urine & serum (“M-protein”)

• Symptoms: Bone pain is predominant

• Treatment: Aggressive combination chemotherapy or local radiation

Think:

• My = Multiple

• Painful = Predominant symptom is bone pain

• Plasma = Malignant plasma cells producing M-protein

Ligament Injuries

Occurs when loading exceeds physiologic range of motion.

Soft Tissue Injuries

• Ligament injuries
• Tendon injuries

What are ligament injuries and how are they classified?

• Cause: Loading exceeds physiologic range → microfailure → total failure

• Classification: Mild, moderate, severe (based on extent of tear)

• Symptoms: Pain with weight bearing, acute swelling

• Treatment: Depends on severity; severe cases may need surgical restoration

Tendon Injuries

• Severity: Range from mild strain to complete tear

• Causes:

  • Direct injury

  • Repetitive motion (overuse)

  • Infection

• Mechanism: Stress exceeds tendon fiber tolerance → injury

• Possible complication: Tendinitis

Diseases of skeletal muscle

• Muscular Dystrophy
    – Duchenne muscular dystrophy
• Myasthenia Gravis

Muscular Dystrophy

• Definition: Genetically determined myopathies → progressive muscle weakness & degeneration

• Pathophysiology: Muscle tissue replaced by fat & fibrous connective tissue

• Classification:

  • Pattern of inheritance (X-linked, autosomal, etc.)

  • Age of onset

  • Distribution of muscular weakness