Chapter 56 - Structure & Function of Musculoskeletal System

• connective tissue structures (e.g., ligaments and tendons) connect the bones and join muscles to bone
• the axial skeleton is composed of the bones of the skull, thorax, and vertebral column
• the axial skeleton forms the axis of the body
• the appendicular skeleton consists of the bones of the upper and lower extremities, including the shoulder and hip
• the skeletal system serves as a framework for the attachment of muscles, tendons, and ligaments
• the skeletal system protects and maintains soft tissues in their proper position
• the skeletal system provides stability for the body
• the skeletal system maintains the body's shape
• the skeletal system acts as a storage reservoir for calcium
• the skeletal system contains hematopoietic connective tissue in which blood cells are formed
• bone is connective tissue in which the intercellular matrix has been impregnated with inorganic calcium salts
• bone has great tensile and compressible strength but is light enough to be moved by coordinated muscle contractions
• the intercellular matrix is composed of organic matter and inorganic salts
• approximately 1/3 of the weight of the intracellular matrix is composed of organic matter, primarily collagen
• the inorganic salt that composes the majority of the intercellular matrix is hydroxyapatite
• cancellous (spongy) bone is found in the interior and epiphyseal ends of long bones
• cancellous (spongy) bone is composed of trabeculae, or spicules, of bone that form a lattice-like pattern
• compact (cortical) bone forms the outer shell of a bone and the diaphysis of long bones
• compact (cortical) bone has a densely packed calcified intercellular matrix that makes it more rigid than cancellous bone
• long bones are found in the upper and lower extremities
• short bones are irregularly shaped and are located in the ankle and rist
• flat bones are composed of a layer of spongy bone between two layers of compact bone
• flat bones are found in areas such as the skull and rib cage
• osteoprogenitor cells are undifferentiated cells that differentiate into osteoblasts
• osteoprogenitor cells are found in the periosteum, endosteum, and epiphyseal growth plate of growing bones
• osteoblasts are bone-building cells that synthesize and secrete the organic matrix of bone
• osteoblasts participate in the calcification of the organic matrix
• osteocytes are mature bone cells that function in the maintenance of bone matrix
• osteocytes play an active role in releasing calcium into the blood
• osteoclasts are bone cells that are responsible for the resorption of bone matrix and the release of calcium and phosphate from bone
• cartilage is a firm but flexible type of connective tissue
• cartilage is composed of cells and intercellular fibers embedded in an amorphous gel-like material
• elastic cartilage (e.g., ear) is elastin-containing and located in areas requiring flexibility
• hyaline cartilage (e.g., nose) is articular cartilage in long bones
• fibrocartilage is found in the pubic symphysis and intervertebral discs
• collagen is an inelastic and insoluble fibrous protein that has great tensile strength
• tissues that contain large numbers of collagenous fibers generally appear white
• elastin is the major component of elastic fibers that allows them to stretch several times their length and rapidly return to their original shape when the tension is released
• intestinal absorption of calcium:

  • PTH: increases indirectly through increased activation of vitamin D
  • calcitonin: probably not affected
  • vitamin D: increases
• intestinal absorption of phosphate:

  • PTH: increases
  • calcitonin: probably not affected
  • vitamin D: increases