The Skeletal System: Bone Tissue Overview

• Bones facilitate movement by assisting skeletal muscles.
• Major minerals, especially calcium and phosphorus, are stored and released by bones to maintain mineral balance.
• Hemopoiesis, or blood cell formation, occurs in the red marrow of bones.

The Skeletal System: The Bone Tissue

• Bone comprises multiple tissues, including bone, cartilage, dense connective tissue, epithelium, blood-forming tissues, adipose tissue, and nervous tissue.
• Each bone is categorized as an organ, collectively forming the skeletal system along with cartilages.

Functions of Bone and the Skeletal System

• Bones support soft tissues and provide muscle attachment sites, serving as the body's structure.
• Internal organs are protected by bony coverings.

Yellow marrow serves as a triglyceride storage site in adults.

Structure of Bone

• Long bones consist of several parts: the diaphysis (shaft), epiphyses (ends), and metaphyses (areas between).
• The epiphyseal plate is critical for bone elongation during growth.
• Hyaline cartilage at the ends minimizes friction and absorbs shock.
• The periosteum covers the bone, promoting growth and repair and anchoring ligaments and tendons.
• The marrow cavity within the diaphysis contains yellow marrow or adipose tissue.

Histology of Bone Tissue

• Osseous tissue consists of widely spaced cells and significant extracellular matrix.
• Four principal bone cell types:
  • Osteoprogenitor cells develop into osteoblasts.
  • Osteoblasts are responsible for bone formation.
  • Osteocytes maintain mature bone tissue.
  • Osteoclasts break down bone tissue.
• The bone matrix includes inorganic salts (like hydroxyapatite and calcium carbonate) and collagen fibers, which confer hardness and tensile strength.
• Bone regions are classified as compact (dense) or spongy (lightweight with open spaces for marrow).

Blood and Nerve Supply of Bone

• Bones receive a rich blood supply through various vessels.
• Endochondral ossification involves transforming a cartilage model into bone, with six stages:
  • Cartilage development and growth.
  • Formation of primary and secondary ossification centers.
  • Development of a medullary cavity and articular cartilage.
• Bone growth in length occurs at the epiphyseal plate, which has zones for resting, proliferation, hypertrophy, and calcification.

Growth and Remodeling of Bone

• Appositional growth allows bone thickness increase via osteoblast activity in the periosteum.
• Bone remodeling is the continuous process of replacing old bone tissue with new tissue, influenced by factors like dietary intake and hormonal regulations.
• Acute hormonal signals are required for bone growth during childhood and major growth spurts.

Fracture and Repair of Bone

• A fracture represents any break in bone integrity.
• Fracture repair involves several stages, from clot formation to restoration of the bone structure.
• Common fracture types include open, comminuted, and stress fractures.
• Treatment requires realignment and immobilization to facilitate healing.

Bone’s Role in Calcium Homeostasis

• Bones act as the primary reservoir for calcium, regulating blood calcium levels through parathyroid hormone (PTH) and calcitonin.
• PTH increases blood calcium levels, while calcitonin decreases them.

Exercise and Bone Tissue

• Mechanical stress strengthens bone through increased mineral deposition and collagen production.
• Lack of stress leads to demineralization and reduced collagen.
• Weight-bearing exercises, like walking, promote bone mass retention.

Aging and Bone Tissue

• Aging primarily results in the loss of minerals (demineralization) and decreased protein synthesis, heightening fracture risk.

Disorders: Homeostatic Imbalances

• Bone scans serve as a diagnostic tool for identifying bone abnormalities.
• Osteoporosis involves decreased bone density and strength due to hormonal changes.
• Rickets and osteomalacia are conditions characterized by poor bone mineralization.

Medical Terminology

• Familiarity with medical terms related to skeletal tissue is essential for effective communication in the field.