What accounts for the majority of bone (osseous) tissue matrix:
a. collagen fibers b. bone marrow c. calcium salts d. osteoid
The Correct Answer and Explanation is:
The correct answer is: c. calcium salts
Explanation:
Bone, or osseous tissue, is a specialized connective tissue that serves structural, protective, and metabolic functions in the body. It primarily consists of two components: cells and a matrix, which is the extracellular material that provides bones with their strength and rigidity. While bone cells such as osteocytes, osteoblasts, and osteoclasts are critical for bone health and remodeling, it’s the matrix that gives bones their distinct properties.
The matrix of bone tissue is composed mostly of calcium salts, specifically in the form of calcium phosphate, which accounts for about 65% of bone’s dry weight. The mineralized component of the matrix, primarily hydroxyapatite (a form of calcium phosphate with the chemical formula Ca(_{10})(PO(_4))_6(OH)(_2)), provides bones with their characteristic hardness and the ability to withstand compressive forces. This mineralization process occurs when osteoblasts secrete an organic matrix known as osteoid, which is initially made up of collagen fibers and other proteins. Calcium salts then crystallize within the osteoid, transforming it into a hardened matrix. This calcified matrix is crucial for the bone’s load-bearing capacity and resistance to deformation.
Though collagen fibers (answer a) are present in the matrix and contribute to about 25-30% of the bone’s composition, their role is different. Collagen provides flexibility and tensile strength, preventing bones from being overly brittle. However, collagen alone does not provide the rigidity needed for bones to support the body’s weight, which is why calcium salts are critical.
Bone marrow (answer b) is housed within the bone cavities and is responsible for producing blood cells, but it does not constitute the majority of the matrix. Similarly, osteoid (answer d) is the organic precursor of the calcified matrix but represents only the initial, unmineralized phase before calcium salts are deposited. Therefore, calcium salts are the primary contributors to the matrix’s volume and functional properties, making them the majority component in bone matrix.