Bone and Cartilage Anatomy Quiz

Bone Storage and Blood Cell Production

• Bones store minerals vital for cellular function, especially calcium (Ca++) and phosphate (PO4-), crucial for muscle cells.
• Yellow bone marrow stores lipids.
• Bones contain stem cells capable of differentiating into cartilage, fat, or bone cells.
• Red bone marrow generates blood cells (hemopoiesis), harboring stem cells that produce erythrocytes, leukocytes, and thrombocytes.

Cartilage and Bone Characteristics

• Mechanical Properties: Cartilage is rigid yet flexible; bone is hard and strong.
• Mature Cell Type: Cartilage: chondrocytes; Bone: osteocytes.
• Matrix Composition: Cartilage: primarily protein; Bone: protein and calcium phosphate (Ca3(PO4)2).
• Vascularity: Cartilage: avascular (lacks blood vessels); Bone: vascular.
• Innervation: Cartilage: lacks nerve innervation; Bone: innervated.
• Growth/Repair: Cartilage: slow; Bone: fast.
• Membrane: Cartilage: perichondrium; Bone: periosteum. The periosteum has an outer fibrous and inner cellular layer, anchored by perforating fibers. The endosteum lines the internal bone surfaces and contains osteoprogenitor cells, osteoblasts, and osteoclasts.

Bone Classification and Structure

• Human bones are classified into four types based on shape.
• Compact bone: The basic functional unit is the osteon, with osteocytes arranged in concentric lamellae around a central canal.
• Spongy bone: The structure is a network of trabeculae

Endochondral Ossification

• A process of bone formation from a hyaline cartilage model.
• Stage 1: Mesenchymal cells differentiate into chondroblasts, which secrete cartilage matrix, forming a cartilage model. Chondroblasts mature into chondrocytes. A perichondrium forms.
• Stage 2: Cartilage calcifies, and a periosteal bone collar forms around the diaphysis (shaft). Chondrocytes hypertrophy, resorb matrix, and die, allowing blood vessels to invade. The perichondrium converts to periosteum, and osteoblasts secrete osteoid.
• Stage 3: A primary ossification center develops in the diaphysis. Osteoid is deposited onto cartilage remnants, extending towards the epiphyses (ends of the bone). Bone replaces calcified cartilage.
• Stage 4: Secondary ossification centers form in the epiphyses. Osteoclasts resorb bone matrix in the diaphysis, forming a medullary cavity.
• Stage 5: Cartilage remains only at articular cartilages and epiphyseal plates (growth plates).
• Stage 6: Epiphyseal plates ossify, forming epiphyseal lines, marking the end of growth (ages vary depending on the bone and sex; provided table gives examples).

Bone Growth

• Interstitial growth: Lengthening occurs at the epiphyseal plate.
• Appositional growth: Growth in diameter involves new bone formation on the exterior surface and bone resorption on the inner surface (endosteum) enlarging the marrow cavity.

Factors Influencing Bone Growth

• Mechanical Stress: Exercise strengthens bones.
• Hormones: Growth hormone, thyroid hormone, estrogen, and testosterone regulate bone growth during different stages of development. Calcitonin and parathyroid hormone control calcium homeostasis.
• Vitamins: Vitamin A (activates osteoblasts), Vitamin C (collagen production), and Vitamin D (calcium and phosphate absorption) are essential for bone health.

Bone Remodeling

• Bone is constantly remodeled throughout life, maintaining calcium and phosphate levels. The rate of remodeling varies greatly, with spongy bone replaced more frequently than compact bone.

Bone Fractures and Healing

• Stage 1: A fracture hematoma (blood clot) forms within 4-8 hours.
• Stage 2: A fibrocartilaginous (soft) callus forms (2-7 days) consisting of cartilage and osteoid.
• Stage 3: The soft callus is replaced by a bony (hard) callus through endochondral ossification (2+ weeks).
• Stage 4: Bone remodeling occurs over months to years, with compact bone replacing spongy bone.

Skeletal Structures

• Paranasal sinuses: Air-filled spaces that lighten the skull, warm and humidify air, and contribute to sound resonance.
• Orbital complex: Bony sockets protecting the eyes and containing eye movement muscles.
• Auditory ossicles: Three tiny bones (malleus, incus, stapes) in the temporal bone, essential for hearing.
• Hyoid bone: Unique bone not articulating with any other; supports the tongue and larynx.
• Fetal skull: Cranial bones are connected by fontanelles (soft spots) of connective tissue.
• Vertebral column: Composed of 26 bones (24 vertebrae, sacrum, coccyx).
• Ribs: 12 pairs; true ribs connect directly to the sternum, false ribs indirectly, and floating ribs do not connect to the sternum.
• Pelvis: Significant sex differences exist, primarily due to childbearing requirements.
• Arches of the foot: Medial, lateral, and transverse arches provide support and distribute weight.