What are the four shapes/sizes of bone?2. What are two types of bone tissue?3. What is the structure of an osteon, or haversian system?

The four shapes/sizes of bones are:

• Long Bones: These are longer than they are wide. They have a shaft and two ends. Examples include the femur, humerus, and phalanges.
• Short Bones: These are approximately as wide as they are long. Examples include the bones of the wrist and ankle.
• Flat Bones: These are thin and usually curved. Examples include the ribs, breastbone, and skull.
• Irregular Bones: These have complex shapes that do not fit into the other categories. Examples include the vertebrae and certain facial bones.

The two types of bone tissue are:

• Compact (Cortical) Bone: This is the hard outer layer of bones. It provides strength, support and protection.
• Spongy (Cancellous) Bone: This is found inside bones and is lighter and less dense than compact bone. It is also highly vascular and often contains red bone marrow.

The structure of an osteon, or haversian system, is as follows:

• Central (Haversian) Canal: This is the central channel containing blood vessels and nerves.
• Concentric Lamellae: These are layers of compact bone tissue that surround the central canal.
• Lacunae: These are small spaces between the lamellae which contain osteocytes (bone cells).
• Canaliculi: These are tiny canals that connect the lacunae to each other and the central canal.
• Periosteum: This is the outer surface layer of the bone.