Compact Bone Structure and the Human Skeleton: Study Notes

Compact Bone Structure

Microscopic Anatomy of Compact Bone

Compact bone is a dense form of bone tissue that provides strength and structure to bones. Its microscopic anatomy reveals specialized structures that support its function.

• Osteon (Haversian System): The fundamental structural unit of compact bone, consisting of concentric layers (lamellae) of calcified matrix surrounding a central canal.

• Lamellae: Thin layers of bone matrix arranged in concentric circles around the central canal.

• Central (Haversian) Canal: A channel in the center of each osteon containing blood vessels and nerves.

• Perforating (Volkmann's) Canal: Canals that run perpendicular to the central canals, connecting them and allowing passage of blood vessels and nerves from the periosteum.

• Lacunae: Small spaces between lamellae that house osteocytes (mature bone cells).

• Osteocytes: Mature bone cells responsible for maintaining bone tissue.

• Trabeculae of Spongy Bone: The lattice-like network found in spongy bone, providing structural support and housing bone marrow.

Example: The osteon structure allows compact bone to withstand compressive forces, making it ideal for supporting the weight of the body.

Key Functions and Cell Types

• Osteoblasts: Bone-forming cells that secrete bone matrix. They are essential for bone growth and repair.

• Osteocytes: Former osteoblasts that have become trapped in the matrix they secreted; they maintain bone tissue.

• Bone Matrix: The intercellular substance of bone tissue, consisting of collagen fibers and inorganic mineral salts (mainly hydroxyapatite).

Example: During bone growth, osteoblasts lay down new bone matrix, which later becomes mineralized.

Long Bone Anatomy

• Diaphysis: The shaft or central part of a long bone, composed mainly of compact bone.

• Epiphysis: The ends of a long bone, usually wider than the shaft and composed of spongy bone covered by a thin layer of compact bone.

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

Definition: Long bones are bones that are longer than they are wide, such as the femur, humerus, and tibia.

Human Skeleton: Major Bones

Anterior View of the Skeleton

The human skeleton provides structural support, protects internal organs, and facilitates movement. The major bones of the body can be identified from an anterior (front) view.

• Clavicle: Also known as the collarbone, it connects the sternum to the scapula.

• Sternum: The breastbone located in the center of the chest.

• Humerus: The upper arm bone, connecting the shoulder to the elbow.

• Ulna and Radius: The two bones of the forearm. The ulna is on the side of the little finger, and the radius is on the thumb side.

• Ilium: The broad, upper part of the hip bone.

• Pubis: The anterior part of the pelvic bone.

• Femur: The thigh bone, the longest and strongest bone in the body.

• Tibia and Fibula: The two bones of the lower leg. The tibia is the larger, medial bone; the fibula is the thinner, lateral bone.

• Metacarpals: The bones of the hand between the wrist (carpals) and the fingers (phalanges).

• Tarsals: The bones of the ankle and proximal foot.

Example: The femur supports the weight of the body during standing and walking, while the tibia and fibula form the lower leg and contribute to movement and stability.

Classification of Bones by Shape

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

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

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

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

Table: Major Bones of the Human Skeleton (Anterior View)

Bone	Location	Function
Clavicle	Shoulder girdle	Connects arm to trunk
Sternum	Chest (midline)	Protects heart and lungs
Humerus	Upper arm	Arm movement
Ulna	Forearm (medial)	Forearm movement
Radius	Forearm (lateral)	Forearm rotation
Ilium	Pelvis	Supports abdominal organs
Pubis	Pelvis (anterior)	Supports pelvic organs
Femur	Thigh	Supports body weight
Tibia	Lower leg (medial)	Main weight-bearing bone
Fibula	Lower leg (lateral)	Stabilizes ankle
Metacarpals	Hand	Hand structure
Tarsals	Ankle/foot	Foot movement and support

Additional info:

• Bone tissue is highly vascularized, allowing for nutrient and waste exchange.

• Compact bone is primarily found in the diaphysis of long bones, while spongy bone is more common in the epiphyses.