Download Bone tissue

Bone tissue
Macroscopic features
Diaphysis – bone shaft – sight of compact bone
 Epiphyses – sight of spongy bone
 Bone marrow

– Red is sight of hematopoiesis (red blood cell
formation)
– Yellow is fat stores
 Periosteum – outer surface
Endosteum – lines inner surfaces
 Compact bone
 Spongy bone

Microscopic features

Lacunae
– Small pockets containing osteocytes

Lamellae
– Narrow layers of calcified matrix

Canaliculi
– Small channels that radiate through the
matrix, interconnecting lacunae and
connecting them to nearby blood
vessels.
Compact bone (microscopic)
Osteon or Haversian system – basic unit
 Osteocytes are arranged in circular layers
around a Haversian canal that contains
blood vessels and nerves.
 Layer of compact bone covers bone
surfaces everywhere except inside joint
capsules
 Compact bone usually found where
stresses come from a limited range of
directions.

Spongy bone (microscopic)

No osteons and different lamellar
arrangement than compact bone.
 Lamellae form plates called trabeculae.
 Spongy bone is found where bones are
not heavily stressed or where stresses
arrive from many directions.
 Spongy bone is much lighter than
compact.
Cells in bone
Osteocytes
- mature bone cells
- maintain normal bone structure by
recycling calcium salts and by
assisting in repairs
Cells in bone
Osteoclasts
- giant cells with 50 or more nuclei
- acids and enzymes secreted by
osteoclasts dissolve bony matrix and
release stored minerals.
Cells in bone
Osteoblasts
- produce new bone matrix and
promote deposition of calcium salts
in matrix.
- immature, matrix-depositing bone
cells, responsible for production of
new bone (osteogenesis).
Bone formation and growth
Skeletal growth begins about 6
weeks after fertilization and
continues until about age 25.
 Ossification – during development,
cartilage or other connective tissues
are replaced by bone.

Endochondral ossification

Most skeletal bone forms through this
process
 Ossification of existing hyaline cartilage
 Cartilage between shaft and epiphysis
does not completely fill with bone because
the epiphyseal plates (growth plate) on the
ends continue to enlarge, increasing the
length of developing bone.
Requirements for normal bone
growth

Must have a reliable source of minerals,
especially calcium salts.
 Diet must provide adequate amounts of
calcium and phosphate and the body must
be able to absorb and transport these
minerals to sites of bone formation.
 When blood calcium levels drop,
parathyroid hormone is released causing
calcium to be released from bone.
 Vitamin
D
–plays a role in normal calcium
metabolism
–Can be obtained from dietary
supplements or manufactured
by epidermal cells exposed to
UV radiation.
 Vitamin
A and C
–Essential for normal bone
growth and maintenance.
–Vitamin C deficiency can lead
to Scurvy with weak brittle
bones.