Structure Of Bone
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Bone is a hard, living connective tissue that provides support, protection, and movement to the body. Structurally, a bone consists of an outer compact (cortical) bone, which is dense and strong, and an inner spongy (cancellous) bone, which is porous and lightweight. The outer surface is covered by a fibrous membrane called the periosteum, while the inner cavity is lined by the endosteum. Long bones have a central medullary cavity filled with bone marrow. Microscopically, compact bone is made up of osteons (Haversian systems) that provide strength and nourishment to bone cells.
STRUCTURE
OF BONE
Bone is the hardest connective tissue and
exists in two structural forms:
- Compact
(cortical) bone —
dense, forms the outer shell of most bones and the shafts of long bones;
about 80% of adult skeleton mass. Provides strength for
weight-bearing.
- Cancellous
(trabecular or spongy) bone
— porous, made of a lattice of trabeculae; lighter and more
flexible than compact bone; found at bone ends (epiphyses), inside flat
bones and vertebrae.
Bones also contain marrow spaces: red
marrow (hematopoietic) and yellow marrow (fatty).
MICROSCOPIC STRUCTURE OF BONE (COMPACT
BONE)
Compact bone is organized into repeating
structural units called osteons (Haversian systems):
- Haversian
(central) canal —
runs longitudinally through each osteon and houses blood vessels, nerves
and lymphatics.
- Lamellae — concentric rings of mineralized
matrix around the Haversian canal.
- Lacunae — small cavities between lamellae
that contain osteocytes.
- Canaliculi — tiny channels radiating from
lacunae that connect osteocytes to each other and to blood supply; permit
nutrient and waste exchange.
- Volkmann’s
canals — transverse
channels that interconnect Haversian canals.
This organized microstructure gives compact
bone its mechanical strength and ability to remodel.
