Osseous Tissue and Development

Learning Objectives

• Identify the tissues and organs of the skeletal system

• Describe the histology of osseous tissue

• Explain bone development

• Discuss calcium balance

• Recognize bone fractures and disorders

Overview of the Skeletal System

Organization of the Skeleton

The human skeleton consists of 206 named bones, which are organized into two main groups:

• Axial skeleton: Forms the long axis of the body and includes the skull, vertebral column, and rib cage.

• Appendicular skeleton: Comprises the bones of the upper and lower limbs, as well as the girdles (shoulder and pelvic) that attach the limbs to the axial skeleton.

Like all organs, bones are composed of more than just osseous (bone) tissue; they also contain dense regular and irregular connective tissues, cartilage, and other components.

Functions of Bones

Major Functions

Bones perform several essential functions in the body:

• Support: Bones form the framework that supports the body and cradles soft organs.

• Protection: Bones provide a protective case for the brain, spinal cord, and vital organs.

• Movement: Bones serve as levers for skeletal muscles, enabling movement at joints.

• Storage: Bones act as reservoirs for minerals, especially calcium, magnesium, and phosphorus, which are involved in acid-base homeostasis. Yellow bone marrow stores fat (triglycerides).

• Blood cell production: Hematopoiesis, the formation of blood cells, occurs in the red bone marrow.

Illustrative Summary of Bone Functions

• Protection: The skeleton protects vital organs such as the brain.

• Mineral storage and acid-base homeostasis: Bones store minerals such as Ca2+ and PO43-, which are necessary for electrolyte and acid-base balance.

• Blood cell formation: Red bone marrow is the site of blood cell formation (hematopoiesis).

• Fat storage: Yellow bone marrow stores triglycerides (fat).

• Movement: Muscles produce body movement via their attachment to bones.

• Support: The skeleton supports the weight of the body.

Key Terms

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

• Acid-base homeostasis: The regulation of pH in the body, in which bone minerals play a crucial role by acting as buffers.

• Triglycerides: A type of fat stored in yellow bone marrow, serving as an energy reserve.

Example: Calcium Homeostasis

Calcium stored in bones can be released into the bloodstream to maintain stable blood calcium levels, which is vital for muscle contraction, nerve function, and blood clotting.

Additional info:

• Bone tissue is dynamic and constantly remodeled in response to mechanical stress and metabolic needs.

• Disorders of bone function can lead to diseases such as osteoporosis (loss of bone density) or osteopetrosis (abnormally dense bones).