Unit 6: Bone Tissue and Physiology

Introduction to the Skeletal System: Bone Tissue

The skeletal system is a vital organ system that provides structural support, protection, and facilitates movement. Bone tissue is specialized connective tissue that forms the rigid framework of the body. In adults, the skeleton consists of 206 bones, each serving multiple functions.

• Protection: Bones shield vital organs such as the brain, heart, and lungs.

• Storage: Bones store minerals (e.g., calcium, phosphorus) and fat (yellow marrow).

• Blood Cell Formation: Hematopoiesis occurs in red bone marrow.

• Movement: Bones act as levers for muscles.

• Support: Bones maintain body shape and posture.

Types of Osseous Tissue

Bone tissue is classified into two main types based on structure and function:

• Compact Bone: Dense tissue located deep to the periosteum, composed of osteons (Haversian systems). Provides strength and support.

• Spongy Bone: Found deep to compact bone, composed of trabeculae. Houses red bone marrow and resists compression.

Osteocytes are mature bone cells that reside in small cavities called lacunae within the calcified matrix. Bone tissue is highly vascularized, allowing for nutrient and waste exchange.

Types of Bones

Bones are classified by shape, which relates to their function:

• Long Bones: Longer than wide (e.g., humerus).

• Short Bones: Approximately equal length and width (e.g., tarsals).

• Flat Bones: Thin and broad (e.g., scapula).

• Irregular Bones: Complex shapes (e.g., vertebrae).

• Sesamoid Bones: Embedded in tendons (e.g., patella).

Anatomy of Long Bones

Long bones have distinct anatomical regions that contribute to their function:

• Diaphysis: Shaft of the bone, composed mainly of compact bone.

• Epiphyses: Proximal and distal ends, containing spongy bone and red marrow.

• Medullary Cavity: Central cavity containing yellow marrow (fat storage).

• Periosteum: Dense connective tissue covering the bone surface.

• Articular Cartilage: Hyaline cartilage covering joint surfaces.

Examples of long bones include the humerus, ulna, radius, femur, and tibia.

Microscopic Structure of Compact Bone

Compact bone is organized into repeating structural units called osteons:

• Osteons (Haversian Systems): Cylindrical structures that run parallel to the bone's long axis.

• Lamellae: Concentric rings of mineralized extracellular matrix (ECM) that provide strength. Types include circumferential, concentric, and interstitial lamellae.

• Central (Haversian) Canal: Runs down the center of each osteon, containing blood vessels and nerves.

Additional Features of Compact Bone

• Lacunae: Small cavities housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae, allowing communication and nutrient exchange between osteocytes.

• Perforating (Volkmann's) Canals: Perpendicular canals that connect central canals of adjacent osteons.

• Sharpey's Fibers: Collagen fibers anchoring the periosteum to the bone.

Microscopic Structure of Spongy Bone

Spongy bone is composed of a network of trabeculae:

• Trabeculae: Lattice-like structures that resist compression and house red bone marrow.

• Function: Reduces bone weight and provides space for hematopoiesis.

Summary Table: Types of Bone Tissue

Key Terms and Definitions

• Osteon: The basic structural unit of compact bone.

• Lamella: A layer of bone matrix in an osteon.

• Lacuna: A small cavity containing an osteocyte.

• Canaliculus: A microscopic canal connecting lacunae.

• Trabecula: A supporting strand of spongy bone.

Relevant Equations

Bone strength is related to its mineral content and structure. While there is no single equation for bone strength, the following formula relates to the density of bone:

Additional info: Academic context and definitions have been expanded for clarity and completeness. Images referenced in the original slides have been described and their content incorporated into the notes.