Chapter 6: Bones and Bone Tissue – Structure, Classification, and Function

Overview of the Skeletal System

Functions of the Skeletal System

The skeletal system is a vital organ system that provides the framework for the human body. It performs several essential functions necessary for survival and movement.

• Protection: Bones protect internal organs, such as the skull protecting the brain and the rib cage protecting the heart and lungs.

• Mineral Storage: Bones store minerals, primarily calcium and phosphorus, which can be released into the bloodstream as needed.

• Hematopoiesis: The process of blood cell formation occurs in the red bone marrow.

• Fat Storage: Yellow bone marrow stores fat as an energy reserve.

• Movement: Bones act as levers that muscles pull on to produce movement.

• Support: The skeleton supports the body and maintains its shape.

Classification of Bones by Shape

Main Types of Bones

Bones are classified according to their shapes, which relate to their functions and locations in the body.

• Long Bones: Longer than they are wide; primarily found in the limbs (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width; provide stability and support with little movement (e.g., carpals, tarsals).

• Flat Bones: Thin, flattened, and usually curved; protect internal organs and provide surfaces for muscle attachment (e.g., sternum, skull bones).

• Irregular Bones: Complex shapes that do not fit into other categories (e.g., vertebrae, pelvic bones).

• Sesamoid Bones: Small, round bones embedded within tendons; reduce friction and modify pressure (e.g., patella).

Bone Type	Shape	Examples
Long Bone	Longer than wide	Femur, Humerus
Short Bone	Cube-shaped	Carpals, Tarsals
Flat Bone	Thin, flat, curved	Sternum, Skull
Irregular Bone	Complex shapes	Vertebrae, Pelvis
Sesamoid Bone	Small, round, within tendons	Patella

Structure of a Long Bone

Major Components

Long bones have a specialized structure that supports their function in movement and weight-bearing.

• Diaphysis: The shaft of the bone, composed mainly of compact bone.

• Medullary Cavity: Central cavity within the diaphysis, containing bone marrow.

• Epiphyses: The ends of the bone, usually broader than the diaphysis and composed of spongy bone.

• Epiphyseal Line: Remnant of the growth plate, marking the site of longitudinal growth in childhood.

• Metaphysis: Region between the diaphysis and epiphysis, containing the epiphyseal plate in growing bones.

• Articular Cartilage: Hyaline cartilage covering the joint surfaces of the epiphyses, reducing friction and absorbing shock.

Bone Marrow

Red Bone Marrow (Hematopoietic Tissue)

Red bone marrow is responsible for the production of blood cells through hematopoiesis.

• Location: Found in the trabecular (spongy) bone of the epiphyses of long bones, flat bones, and vertebrae.

• Function: Produces red blood cells, white blood cells, and platelets.

Yellow Bone Marrow

Yellow bone marrow primarily serves as a storage site for fat.

• Location: Found in the medullary cavity of long bones.

• Function: Stores adipose tissue, which can serve as an energy reserve.

Microscopic Anatomy of Bone Tissue

Extracellular Matrix (ECM)

The bone matrix consists of inorganic and organic components that provide strength and flexibility.

• Inorganic Matrix: Mainly hydroxyapatite (calcium phosphate crystals) that give bone its hardness.

• Organic Matrix (Osteoid): Composed of collagen fibers and ground substance, providing tensile strength and flexibility.

Cells of Bone Tissue

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells that secrete osteoid.

• Osteocytes: Mature bone cells that maintain bone tissue.

• Osteoclasts: Bone-resorbing cells that break down bone matrix.

Additional info:

• Further details on bone development, growth, and repair are covered in subsequent sections of the chapter.

• Clinical scenarios and prefixes/suffixes related to anatomy are provided for context and application.