Chapter 47: Structure and Function of the Musculoskeletal System

Bone tissue consists of strong, mature lamellar bone, organized into functional units called osteons or Haversian systems, as well as temporary woven bone. Bone maintenance relies on four specialized cells: osteoprogenitor cells, bone-building osteoblasts, mature osteocytes that maintain the matrix, and large osteoclasts responsible for bone resorption and remodeling. Supporting structures include tendons (connecting muscle to bone) and ligaments (connecting bone to bone). The chapter emphasizes cartilage, noting the resilience of hyaline cartilage (found in articular surfaces) and the strength of fibrocartilage (found in menisci and intervertebral disks); cartilage is unique in that it is avascular and relies on fluid diffusion for nourishment. Mineral homeostasis is tightly controlled by the interplay of three hormones: Parathyroid Hormone (PTH) raises serum calcium by stimulating bone release and activating Vitamin D; calcitonin acts to lower serum calcium levels; and Vitamin D enhances intestinal absorption of calcium. Finally, articulations (joints) are classified as solid synarthroses (immovable) or freely movable synovial (diarthrodial) joints. Synovial joints are characterized by a fibrous joint capsule, an inner synovium that secretes lubricating synovial fluid, and specialized structures like bursae (to reduce friction) and fibrocartilaginous menisci.