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BIOD 331 Module 10 (Structure & Function of the
Skeleton and Bone,Joint Classification and Structure,
Osteoarthritis (OA), Gout Osteoporosis,
Module 10.1 Structure & Function of the Skeleton and Bone
Overview
The skeleton works closely with muscles and connective tissues for support and movement. The skeletal system gives the body structure, protects internal organs, allows movement, produces blood cells, and stores minerals like calcium. It includes bone tissue , cartilage , ligaments , and tendons. The skeleton is divided into: ● Axial skeleton – skull, thorax (ribs/sternum), vertebral column ● Appendicular skeleton – upper/lower extremities + pelvic/pectoral girdles
Types of Bone Tissue
Type Description Function Cortical (Compact) Bone Dense outer shell Strength, rigidity, structure Cancellous (Spongy) Bone Inner lattice-like trabeculae with marrow Weight-bearing, withstands tension/torsion Cancellous bone’s trabecular network contains bone-forming cells and marrow, resisting tensile and twisting stress.
Bone Shapes
Type Examples Notes Long bones Femur, humerus Shaft (diaphysis) + ends (epiphyses) Short bones Wrist, ankle Mostly spongy bone Flat bones Skull, ribs, scapula Protection + muscle attachment Irregular bones Vertebrae, pelvis Complex shapes Figure reference: Figure 10.2 shows long bone anatomy — diaphysis (shaft), epiphysis (ends), cortical outer layer, cancellous inner layer.
Bone Matrix Composition
Calcified matrix makes bone strong enough to support body weight. Bone is a connective tissue composed of cells + fibers + extracellular matrix. Component Contents Function
Organic matrix Collagen + ground substance Bone flexibility, repair & growth support Inorganic matrix Calcium phosphate, carbonate, magnesium, Hardness, mineral storage sodium
Laminar vs Woven Bone
Type Description Laminar bone Mature bone arranged in osteons (cylinders) Woven bone Immature, laid down rapidly, seen in growth & repair
Osteon Structure (Laminar Bone)
● Osteons → cylindrical pillars aligned with long axis ● Central (Haversian) canal → nerves + blood vessels ● Volkmann canals → connect periosteum to medullary cavity ● Lamellae → concentric rings ● Lacunae → house osteocytes ● Canaliculi → allow nutrient exchange Figure reference: Figure 10.3 shows tree-ring-like osteon structure with canals connecting vessels.
Bone Blood Supply
Structure Function Nutrient arteries Enter bone → supply medullary cavity + inner cortex Periosteal vessels Supply outer cortex Cancellous bone Nourished via diffusion through canaliculi
Bone Cells
Cell Type Function
Cancellous bone Trabecular inner bone, marrow-filled Osteon Structural unit of compact bone Osteoblast Bone-building cell Osteocyte Mature bone cell maintaining matrix Osteoclast Bone-resorbing cell PTH Raises blood Ca²⁺ Calcitonin Lowers blood Ca²⁺ Vitamin D Promotes Ca²⁺^ absorption & bone mineralization
🌟 Quick Memory Tricks
● OsteoBLAST builds bone ● OsteoCLAST crushes bone ● PTH = Pulls calcium To blood ● Compact = hard cortex , Cancellous = sponge/can-cell
🧠 Practice Check-In
Can you explain: ✔ Difference between cortical vs cancellous bone? ✔ Role of osteoblasts vs osteoclasts? ✔ How PTH & calcitonin affect calcium? ✔ Why bone heals slower than soft tissue? Module 10.2 — Joint Classification and Structure
Overview
Joints, or articulations , are the points where two or more bones meet. They enable movement and provide mechanical support for the skeleton. Joints are stabilized and supported by ligaments and tendons — both dense connective tissue structures made primarily of collagen fibers. ● Tendons connect muscle to bone
● Ligaments connect bone to bone Because collagen has a limited blood supply, these tissues heal slowly but have high tensile strength, maintaining joint stability.
Joint Classification
Joints are classified by structure and degree of movement allowed:
1. Synarthroses (Non-synovial joints) No joint cavity; allow little or no movement. Types: Type Description Example Synostoses Bones fused by dense connective tissue or bone Skull sutures Synchondroses Bones joined by hyaline cartilage , limited movement Ribs to sternum Syndesmoses Bones separated by fibrous tissue/disc; joined by ligaments Pubic symphysis, intervertebral joints Mnemonic: Syn- = together → little or no movement. 2. Synovial Joints (Freely Moving Joints) Have a joint cavity filled with synovial fluid , allowing greater mobility. They are categorized by the type of motion between the bones: Synovial Joint Type Motion Example Pivot joint Rotation Between cervical vertebrae (atlas/axis) Hinge joint Flexion/extension Knee, elbow Saddle joint Flexion/extension + side-to-side Thumb (carpometacarpal)
Joint Innervation and Proprioception
● Nerves supplying the joint arise from the same roots as muscles crossing that joint. ● The synovial membrane receives autonomic innervation (few pain fibers), while fibrous capsules and ligaments have pain receptors sensitive to stretch or torsion. ● Proprioceptive nerve fibers in tendons/ligaments sense movement and trigger reflexes to prevent injury during strain.
Clinical Correlation
● Synovial fluid analysis helps identify diseases like gout and rheumatoid arthritis. ● Limited cartilage vascularity explains chronic issues with cartilage repair (e.g., OA). ● Proprioceptive dysfunction can lead to instability or risk of injury.
✅ Key Terms & Definitions (10.2)
Term Definition Joint (Articulation) Point where two or more bones meet Tendon Connects muscle to bone Ligament Connects bone to bone Synarthroses Joints with little to no movement Synostoses Immovable joints (skull sutures) Synchondroses Slightly movable joints connected by cartilage (rib-sternum) Syndesmoses Slightly movable fibrous joints (pubic symphysis)
Synovial joint Freely moving joint with a cavity and synovial fluid Articular cartilage Hyaline cartilage on bone ends; reduces friction Synovium Inner membrane secreting synovial fluid Proprioception Body’s awareness of position and movement Pivot joint Rotational motion Hinge joint Flexion/extension motion Ball-and-socket Multidirectional motion
🌟 Summary & Memory Tips
● Synarthroses = Stiff , Synovial = Smooth ● Tendon = Muscle → Bone , Ligament = Bone → Bone ● Articular cartilage = no blood = slow to heal ● Synovial fluid = joint “oil” ● Proprioception = “body GPS”
🧠 Practice Check-In
✔ What are the three types of synarthroses? ✔ Why do cartilage injuries heal slowly? ✔ Which synovial joint allows movement in all planes? ✔ How does proprioception protect joints? Perfect — I’ll continue seamlessly through the rest of the modules. Here’s your next detailed section:
Proteoglycans Give stiffness, elasticity, and resistance to compression Collagen Provides tensile strength; forms supportive framework Ground substance Semi-solid gel supporting chondrocytes Water Provides lubrication and shock absorption The proteoglycans carry a negative charge , attracting water molecules and creating high osmotic pressure , which helps resist compression and lubricate joints. Chondrocytes constantly remodel cartilage by producing matrix-degrading enzymes and new matrix — this process becomes disrupted in OA.
Pathophysiology of OA
- Early changes: ○ ↑ Water content ○ ↓ Proteoglycan concentration ○ Weakening of the collagen framework due to imbalance of synthesis and breakdown
- Inflammatory mediators: ○ Interleukin- 1 β (IL- 1 β) ○ Tumor Necrosis Factor-α (TNF-α) → Trigger degradation of collagen and proteoglycans, leading to further cartilage loss.
- Structural changes: ○ Chondrocyte clusters enlarge and reorganize ○ Edema develops in matrix → rough cartilage surface ○ Microfractures form → filled with synovial fluid , which deepens fissures ○ Cartilage erodes → exposed subchondral bone thickens ○ Osteophytes (spurs) form along margins ○ Synovial membrane inflammation occurs (late-stage)
Figure 10.8 depicts OA changes: cartilage erosion, bone thickening, osteophyte formation, and narrowed joint space.
Contributing Factors
● Repetitive joint loading: from occupations or athletics (kneeling, lifting, pitching, running, dancing) ● Immobilization: lack of motion reduces synovial fluid flow → cartilage malnourishment ● Both lead to joint failure and degeneration.
Clinical Presentation
Symptom Description Pain Aching, worsens with activity, relieved by rest Crepitus Grinding sensation with movement Stiffness Brief morning stiffness (< 30 min) ROM limitation Follows capsular pattern (specific to affected joint) Common sites Hips, knees, cervical/lumbar spine, PIP/DIP joints, thumb base, first MTP (big toe) ● Can be unilateral or bilateral depending on compensatory strain. ● Example: right knee OA → altered gait → OA develops later in left knee.
Differentiating OA vs RA
Feature Osteoarthritis (OA) Rheumatoid Arthritis (RA) Type Degenerative Autoimmune, systemic
○ Corticosteroid injections for flare-ups (limit to ≤3/year due to cartilage damage risk)
- Surgery ○ Arthroscopic debridement: removes damaged tissue or osteophytes ○ Total Joint Replacement (TKA/THA): severe cases (hip/knee).
✅ Key Terms & Definitions (10.3)
Term Definition Osteoarthritis (OA) Degenerative joint disease causing cartilage breakdown Articular cartilage Hyaline cartilage covering bone ends; reduces friction Proteoglycans ECM molecules giving cartilage elasticity and stiffness Chondrocytes Cartilage cells responsible for matrix maintenance IL- 1 β / TNF-α Cytokines that promote cartilage destruction Osteophytes Bony projections (spurs) from joint degeneration Crepitus Grinding sensation from rough articular surfaces Subchondral bone Bone beneath cartilage; thickens in OA Synovial membrane Inner capsule layer producing joint fluid Rheumatoid Arthritis (RA) Autoimmune joint inflammation (systemic)
🌟 Summary
● OA = wear and tear → cartilage erosion → bone changes ● RA = immune attack → inflammation → systemic involvement ● OA pain increases with activity , RA pain improves with movement ● IL- 1 β + TNF-α = key inflammatory drivers of OA progression Module 10.4 — Osteoporosis
Overview
Osteoporosis is a metabolic bone disease that causes: ● Decreased bone mass and density ● Weakened bone structure ● Increased fracture risk Bone resorption exceeds bone formation, often due to aging or hormonal imbalance.
Etiology
Primary causes: ● Aging – loss accelerates after 35– 40 ● Postmenopausal estrogen decline ● Genetic predisposition Secondary causes: ● Elevated cortisol (Cushing’s or chronic steroid use) ● Prolonged immobilization ● Malnutrition / eating disorders ● Endocrine disorders (hyperthyroidism, DM, RA).
Diagnosis
Bone Mineral Density (BMD) measured via DEXA scan Results are reported as T-scores : T-Score Interpretation ≥ - 1.0 Normal
- 1.0 to - 2.5 Osteopenia (low bone mass) ≤ - 2.5 Osteoporosis Screening recommendations (NOF): ● Women ≥ ● Men ≥ ● Adults >50 with a fracture ● Postmenopausal women & men (50–69) with risk factors.
Risk Factors
Table 10.1 — Risk factors for osteoporosis: Personal Lifestyle Drugs/Disease Female, age, Sedentary, low Ca intake, Steroids, anticonvulsants, heparin, white/Asian, small smoking, alcohol, high Cushing’s, DM, COPD, hyperthyroidism, RA frame caffeine
Prevention and Treatment
Prevention: ● Adequate calcium and vitamin D intake ○ Premenopausal: 1000 mg Ca/day
○ Postmenopausal: 1500 mg Ca/day ○ Vitamin D: 400–800 IU/day ● Weight-bearing exercise ● Avoid smoking, alcohol, caffeine Treatment: ● Antiresorptive drugs: ○ Estrogen / SERMs (Raloxifene) – decrease bone loss ○ Bisphosphonates (Alendronate, Risedronate, Ibandronate) – inhibit osteoclasts ○ Calcitonin – inhibits osteoclasts ● Anabolic agents: ○ Teriparatide (PTH analog) – increases osteoblast activity ● Testosterone therapy for men.
✅ Key Terms & Definitions (10.4)
Term Definition Osteoporosis Loss of bone density → fragile bones BMD (Bone Mineral Density) Amount of mineral in bone tissue T-score Standardized comparison of BMD RANK/RANKL/OPG system Controls osteoclast formation and bone resorption OPG Osteoprotegerin; inhibits RANKL Bisphosphonates Drugs that block bone breakdown
Primary gout Overproduction or under-excretion of uric acid; linked to diet/alcohol/metabolic syndrome Secondary gout Due to medications or diseases causing hyperuricemia (e.g., renal failure, leukemia)
Purine Metabolism
● Uric acid = end product of purine metabolism ● Purines formed through:
- De novo synthesis (from non-purine precursors)
- Salvage pathway (recycling nucleic acid bases) Four causes of hyperuricemia (Fig. 10.10):
- Overproduction of purines
- Decreased salvage of purine bases
- Increased cell turnover → nucleic acid breakdown
- Decreased uric acid excretion.
Pathophysiology
● Uric acid poorly dissolves in synovial fluid , especially at <37°C. ● Crystals form in cooler joints (commonly the great toe ) → trigger inflammation. ● Macrophages engulf urate crystals → release inflammatory mediators → joint destruction over time. ● Chronic accumulation = Tophi (visible nodules). Figure 10.11: (A) Tophus on finger; (B) cross-section showing urate crystal accumulation.
Clinical Presentation
Stage Description
Asymptomatic hyperuricemia High uric acid, no symptoms Acute gouty arthritis Sudden intense pain, redness, swelling (1st MTP joint common) Intercritical phase Symptom-free interval between attacks Chronic tophaceous gout Repeated attacks → joint deformity, visible tophi
Diagnosis
● Confirm urate crystals in synovial fluid or tophi biopsy ● 24 - hour urine collection: determines overproduction vs under-excretion ● 90% of gout patients = under-excretors.
Treatment
Goals: relieve pain, stop attacks, prevent recurrence. Phase Treatment Acute attack NSAIDs, colchicine (anti-inflammatory), corticosteroid injection Maintenance Allopurinol (reduces uric acid production), Uricosurics (increase excretion) Lifestyle Reduce alcohol and purine-rich foods (fish, shellfish, bacon, liver); maintain healthy weight
✅ Key Terms & Definitions (10.5)
Term Definition
