Page 584 - Concise Pathology for Exam Preparation ( PDFDrive )

21

Musculoskeletal System

BONE
Bone is the basic unit of the human skeletal system which is responsible for weight
bearing, protection of visceral organs, locomotion and haematopoietic cell production.
Bones can be classified based on their location, size and structure:

Location
Based on location, bones can be classified as follows:
• Axial skeleton: Bones of the skull, vertebral column, sternum and ribs
• Appendicular skeleton: Bones of the pectoral girdle, pelvis girdle and limbs

Size
Based on size, bones can be classified as follows:
• Long bones: They are tubular and hollow with two ends, eg, bones of the limbs.
• Short bones: Cuboidal in shape, located only in the foot (tarsal bones) and wrist (carpal
bones)
A long bone can further be divided into several regions (Fig. 21.1):
• Epiphysis: Region between the growth plate and the expanded end of bone, covered by
articular cartilage.
• Metaphysis: Region where the growth plate and the diaphysis meet.
• Diaphysis: The shaft of long bones located between the two metaphyses.
• Physis (epiphyseal plate, growth plate): Separates the epiphysis from the metaphysis
and is the zone of endochondral ossification in an actively growing bone.

Structure
1. Based on texture of cross sections, bone tissue can be classified as follows:
(a) Compact bone (dense bone, cortical bone): Compact bone is ivory like and
dense in texture without any spaces or cavities. It consists mainly of Haversian
systems or secondary osteons.
(b) Spongy bone (trabecular bone, cancellous bone): Spongy bone is so named
because it is sponge like with numerous cavities. It is located within the medullary
cavity and consists of extensively connected bony trabeculae that form a sponge
like network. Mature trabecular bone exhibits lamellae and osteocytes between the
lamellae. Inactive flattened osteocytes are also present on the bone surface.
2. Based on matrix arrangement, bone tissue can be classified as follows:
(a) Lamellar bone: Lamellar bone is mature bone in which the constituent collagen
fibres are arranged in lamellae. In contrast to spongy bone, the lamellae are ar-
ranged parallel to each other, in compact bone, the lamellae are organized concen-
trically around a vascular canal (Haversian canal).

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