Histology of Bone

Bone consists of widely separated
cells surrounded by large amounts of
matrix

Four principal types of cells:
1.
2.
Osteoprogenitor cells – multipotent
stem cells that can turn into other
bone cells.
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 forms
 Step 2 = Cartilage grows
 Step 3 = Bone replaces the cartilage from the
inside center outward.

Intramembranous
 Within membranes, no cartilage precursor
 Forms 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.