Perichondrium & Cartilage: Structure and Function

Structure and Function of the Perichondrium

• The perichondrium is a dense irregular connective tissue that surrounds cartilage, except at joints.
• It provides nutrients to cartilage, resists outward expansion during compression, and aids in growth and repair.

Hyaline Cartilage vs. Fibrocartilage

• Hyaline cartilage has a smooth, glassy appearance and is composed of fine collagen fibers.
• It provides support with some flexibility and reduces friction.
• It is located on articular surfaces of bones, nose, trachea, costal cartilage, and embryonic skeleton.
• Fibrocartilage has thick collagen fibers and is less firm than hyaline cartilage.
• It has high tensile strength, resists compression, and absorbs shock.
• It is located in intervertebral discs, pubic symphysis, and menisci of the knee.

Comparison of Cartilage and Bone

• Cartilage is flexible, avascular, contains chondrocytes in lacunae, and has a matrix of collagen and elastic fibers.
• Bone is rigid, vascularized, contains osteocytes in lacunae, and has a matrix of collagen fibers and calcium salts.

Seven Important Functions of Bone Tissue

• Support
• Protection (e.g., skull, rib cage)
• Movement (levers for muscles)
• Mineral storage (calcium, phosphate)
• Blood cell formation (hematopoiesis in red marrow)
• Triglyceride (fat) storage (yellow marrow)
• Hormone production (osteocalcin for insulin regulation)

Two Major Groups of Bones in the Skeleton

• Axial skeleton: skull, vertebral column, rib cage.
• Appendicular skeleton: limbs and girdles (pectoral & pelvic).

Four Bone Classes with Examples

• Long bones: longer than wide (e.g., femur, humerus).
• Short bones: cube-shaped (e.g., carpals, tarsals).
• Flat bones: thin, flattened (e.g., skull, ribs, sternum).
• Irregular bones: complex shapes (e.g., vertebrae, hip bones).

What Distinguishes Sesamoid Bones?

• Sesamoid bones develop within tendons and enhance leverage (e.g., patella).

Compact vs. Spongy Bone

• Compact bone is dense, smooth, and forms the outer layer.
• Spongy bone is porous, made of trabeculae, and is found inside bones.

Gross Anatomy of Short, Irregular & Flat Bones

• They lack a diaphysis and epiphysis, and a thin compact bone layer surrounds spongy bone.

Gross Anatomy of Long Bones

• Diaphysis (shaft), epiphyses (ends), medullary cavity (marrow)

Diaphysis (Medullary Cavity & Contents)

• The shaft of a long bone contains yellow marrow (fat storage).

Epiphyses & Epiphyseal Line

• The ends of long bones are covered by articular cartilage, with an epiphyseal line (remnant of growth plate).

Function & Location of Red Marrow

• Function: blood cell formation.
• Location: spongy bone of flat bones, epiphyses of long bones (in adults).

Periosteum Structure & Function

• Structure: Outer fibrous layer, inner osteogenic layer with osteoblasts/osteoclasts.
• Function: bone growth, repair, attachment for tendons/ligaments.

Endosteum vs. Periosteum

• Endosteum: thin membrane lining medullary cavity, contains bone-forming cells.
• Periosteum: outer covering of bone, provides structural support.

Osteon Structure of Compact Bone

• Haversian system: central canal surrounded by concentric lamellae, contains blood vessels & nerves.

Central Canal vs. Perforating Canal

• Central canal runs parallel and contains vessels/nerves.
• Perforating canal runs perpendicular and connects central canals.

Lacunae & Canaliculi Relationship

• Lacunae: small cavities housing osteocytes.
• Canaliculi: tiny canals connecting lacunae for nutrient exchange.

Interstitial vs. Circumferential Lamellae

• Interstitial lamellae are between osteons, remnants of old osteons.
• Circumferential lamellae are outer layers around the entire bone.

Five Bone Cell Types

• Osteogenic cells: stem cells.
• Osteoblasts: bone-forming cells.
• Osteocytes: maintain bone.
• Osteoclasts: break down bone.
• Bone lining cells: regulate calcium exchange.

Structure & Function of Osteoid

• Organic part of bone matrix (collagen & proteins), provides flexibility.

Inorganic Components of Bone

• Hydroxyapatite (calcium phosphate) provides hardness.

Bone Resorption (Cells & Process)

• Osteoclasts secrete enzymes & acids to break down bone.

Microscopic Structure of Spongy Bone vs. Compact Bone

• Similar: both have lamellae, osteocytes.
• Different: no osteons in spongy bone, contains trabeculae.

Osteogenesis vs. Bone Growth

• Osteogenesis is bone formation during embryonic development.
• Bone growth is lengthening & thickening after birth.

Two Osteogenesis Pathways

• Intramembranous: skull & clavicle (bone forms in connective tissue).
• Endochondral: long bones (cartilage template replaced by bone).

Steps in Long Bone Lengthening (Zones)

• Resting Zone → Proliferation Zone → Hypertrophic Zone → Calcification Zone → Ossification Zone.

Appositional Growth (When & How?)

• Thickening occurs throughout life via periosteum.

Growth & Thyroid Hormones in Bone Growth

• GH stimulates growth and TH regulates proportions.

Estrogen & Bone Growth

• Promotes growth spurt and closes growth plates.

Vitamins & Minerals for Bone Growth

• Calcium, phosphate, vitamin D, C, A, K.

Why Bone Remodeling Matters

• Prevents bone from becoming brittle and adapts to stress.

How Mechanical Stress Affects Bone Remodeling

• More stress = more bone deposition.

Blood Calcium Homeostasis (Feedback System & Hormones)

• Hormones: PTH (raises Ca²⁺) and Calcitonin (lowers Ca²⁺).

Types of Fractures

• Open (compound), closed (simple), greenstick, comminuted, spiral, compression, epiphyseal.

Four Stages of Bone Healing

• Hematoma formation → Fibrocartilaginous callus formation → Bony callus formation → Bone remodeling.

Paget's Disease

• Excessive bone remodeling results in weak bones.

Osteoporosis & Risk Factors

• Bone resorption > formation. Risk factors: aging, low estrogen, poor diet.

Osteomalacia vs. Rickets

• Osteomalacia: soft bones (adults).
• Rickets: soft bones (children, vitamin D deficiency).