Chapter 6: Bone and Skeletal Tissues – Study Notes

Bone and Skeletal Tissues

Overview of the Human Skeleton

The adult human skeleton consists of 206 named bones, which are organized into two major groups based on their location and function.

• Axial Skeleton: Forms the long axis of the body and includes the skull, vertebral column, and rib cage. It primarily supports and protects the organs of the head, neck, and trunk.

• Appendicular Skeleton: Comprises the bones of the upper and lower limbs, as well as the girdles (pectoral and pelvic) that attach the limbs to the axial skeleton. This division is essential for movement and manipulation of the environment.

Classification of Bones by Shape

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

• Long Bones: Longer than they are wide; found in limbs (e.g., humerus, femur). They act as levers for movement.

• Short Bones: Cube-shaped; found in the wrist (carpals) and ankle (tarsals). Sesamoid bones (e.g., patella) are a subtype that form within tendons.

• Flat Bones: Thin, flat, and slightly curved; include the sternum, scapulae, ribs, and most skull bones. They provide protection and broad surfaces for muscle attachment.

• Irregular Bones: Have complicated shapes; examples include vertebrae and hip bones (os coxae).

Example: The ribs and most skull bones are classified as flat bones.

Functions of Bones

Bones perform several vital functions in the human body:

• Support: Provide a framework for the body and support soft tissues.

• Protection: Shield vital organs such as the brain, spinal cord, and thoracic organs.

• Movement: Serve as levers for muscles to act upon, enabling movement.

• Mineral and Growth Factor Storage: Store minerals (mainly calcium and phosphorus) and growth factors.

• Blood Cell Formation: Hematopoiesis occurs in red marrow cavities of certain bones.

• Triglyceride Storage: Fat is stored in bone cavities as an energy reserve.

• Hormone Production: Bones secrete osteocalcin, which helps regulate insulin secretion, glucose levels, and metabolism.

Additional info:

• Bone tissue is dynamic and constantly remodeled throughout life.

• Bone health is influenced by nutrition, hormonal balance, and mechanical stress.

Table: Classification of Bones by Shape

Bone Type	Description	Examples
Long Bones	Longer than wide, mostly limb bones	Humerus, femur, radius, ulna
Short Bones	Cube-shaped, found in wrist/ankle	Carpals, tarsals, patella (sesamoid)
Flat Bones	Thin, flat, slightly curved	Sternum, ribs, scapulae, skull bones
Irregular Bones	Complex shapes	Vertebrae, hip bones