Anatomy of a Long Bone

Parts of a Long Bone

• A long bone has several parts: epiphysis (expanded end), diaphysis (bone shaft), metaphysis (widening part between diaphysis and epiphysis), articular cartilage (covers epiphysis), periosteum (encloses bone, dense connective tissue), compact (cortical) bone (wall of diaphysis), spongy (cancellous) bone (makes up epiphyses), trabeculae (branching bony plates, make up spongy bone), medullary cavity (hollow chamber in diaphysis, contains marrow), and endosteum (lines spaces and cavity).
• Bone marrow is found in the medullary cavity and spongy bone spaces, and can be either red or yellow.

Microscopic Structure of Bone

• Osteocytes are mature bone cells that occupy lacunae (chambers).
• Canaliculi are tiny passageways that allow cell processes of osteocytes to exchange nutrients and wastes.
• The extracellular matrix of bone is made up of collagen fibers (which give bone resilience) and inorganic salts (which make bone hard).

Compact and Spongy Bone

• Compact bone is strong, solid, and weight-bearing, and is made up of cylindrical units called osteons.
• Spongy bone is flexible and has spaces between trabeculae that reduce its weight.

Bone Development, Growth, and Repair

• Bone development begins in the first few weeks of prenatal development and continues to grow and develop into adulthood.
• Bones form when bone tissue replaces existing connective tissue in one of two ways: intramembranous bones or endochondral bones.
• Intramembranous ossification occurs in flat bones, such as the skull and clavicles, and involves bone formation between sheets of primitive connective tissue.
• Endochondral ossification occurs in long bones and most of the skeleton, and involves bone formation from hyaline cartilage models.

Skeletal Organization

• The adult skeleton has approximately 206 bones.
• Some people have extra bones, while others lack certain bones.
• The skeleton is divided into the axial skeleton (80 bones, including the skull, vertebral column, thoracic cage, and hyoid bone) and the appendicular skeleton (126 bones, including the pectoral girdle, upper limbs, pelvic girdle, and lower limbs).

Divisions of the Skeleton

• The axial skeleton includes the skull, middle ear bones, hyoid bone, vertebral column, and thoracic cage.
• The appendicular skeleton includes the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.

Vertebral Column Curvatures and Composition

• The vertebral column has four curvatures: cervical, thoracic, lumbar, and sacral.
• The vertebral column is composed of 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, 5 fused sacral vertebrae, and 4 fused coccygeal vertebrae.

Thoracic Cage

• The thoracic cage includes the ribs, thoracic vertebrae, sternum, and costal cartilages that attach the ribs to the sternum.
• The thoracic cage supports the pectoral girdle and upper limbs, protects the thoracic and upper abdominal viscera, and plays a role in breathing.

Upper Limb

• The upper limb bones form the framework of the upper arm, forearm, and hand, and provide muscle attachments for limb movement.
• The bones of the upper limb include the humerus, radius, ulna, carpals, metacarpals, and phalanges.

Hand

• The hand consists of the wrist, palm, and fingers (digits).
• The bones of the hand include the carpal bones (8), metacarpal bones (5), and phalanges (14).

Pelvic Girdle

• The pelvic girdle consists of 2 hip (coxal, pelvic, or innominate) bones.
• The pelvis is composed of the pelvic girdle, sacrum, and coccyx.
• The pelvic girdle supports the trunk of the body, protects the viscera, transmits weight to the lower limbs, and provides attachment for the lower limbs.

This quiz covers the different parts that make up a long bone, including the epiphysis, diaphysis, metaphysis, and more. Test your knowledge of the structure and function of each part.