BONE HISTOLOGY

Histology of Bone Bone consists of widely separated cells

surrounded by large amounts of matrix

Four principal types of cells:1. Osteoprogenitor cells –

multipotent stem cells that can turn into other bone cells.

2. Osteoblasts – bone forming cells located in peri & endosteum. Synthesize collagen.

Histology of Bone Osteocytes – mature bone cell

(osteoblast surrounded by a calcium matrix). Maintain daily metabolism such as the exchange of nutrients and wastes with the blood.

Osteoclasts – cell that destroys or reabsorbs bone cells and are concentrated in the in the endosteum

Histology of Bone Matrix contains some calcium

carbonate, calcium phosphate but mostly hydroxyapatite, which is the PRIMARY salt that makes bone hard.

Matrix (Bone) composition = 25% water, 25% protein fibers and 50% minerals

What are the tissues that make up bones?

1. Compact Bone Tissue○ Outer layer of bone○ Dense in appearance○ Made out of water, collagen, and

crystalized mineral salts (Ca, P)2. Spongy Bone Tissue

○ Inner layer of bone○ Filled with red bone marrow○ Arranged in bars and plates called

Trabeculae○ Porous openings between trabeculae =

spongy appearance

What does compact bone look like at the microscopic level? Matrix organized into structural units called OSTEONS aka Haversian System Circular and tubelike Arranged into layers

(rings) called lamellae Lamellae are made up

of protein fibers, calcium, phosphorus and other minerals

Lamellae surround central canal which contains blood vessels, nerves and lymph

What separates the Lamellae circles? Rings of osteocytes

(mature bone cells) Osteocytes are found in

spaces called lacunae Tiny canals called

canaliculi radiate outward from the central canal to all lacunae making them connected

Blood vessels and nerves enter central canal from periosteum

Bone Growth Most bone is formed by Endochondral

ossification (IN- outward)

Occurs in all bones except flat bones.

Step 1 = Cartilage formsStep 2 = Cartilage growsStep 3 = Bone replaces the cartilage from the

inside center outward.

IntramembranousWithin membranes, no cartilage precursorForms flat bones

Bone Repair

What is cartilage?

• Special form of dense connective tissue that is comprised of collagen and elastin fibers.

• Cartilage is created by chondrocytes.

• No blood vessels so nutrients and waste are transported via diffusion. Very slowly.