3B Scientific 3B MICROanatomy™ Bone structure - 80 times enlarged - Manual (Page 4)

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Bone Structure Model
This model shows a section of a lamellar bone, as
found in the human skeleton as a basic structure of
a tubular bone (approx. 80 times enlarged).
Compared to other bone types, tubular bones
contain few bone trabeculae (spongy substance or
substantia spongiosa) (1) and a thick compact layer
(compact substance or substantia compacta) (2).
The bone is covered by a membrane, the perioste-
um (3). The inner layer of the periosteum (osteoge-
nic layer) consists of many cells and contains resting
precursor cells of the bone cells (osteoblasts) that
ensure regeneration in case of bone fractures. The
outer layer is made of firm, collagenous connective
tissue (fibrous layer). Bundles of collagenous fibers
pass directly from the periosteum into the connec-
tive tissue of the bone (perforating fibers, Sharpey
fibers) (4).
The next layer is the cortical layer (substantia corti-
calis) with its lamellar stratification of the intercel-
lular substance (thus lamellar bone). Located at the
very outside are the circumferential lamellae (5)
running parallel to the periosteum. The basic struc-
ture of the lamellar bone is formed by the osteons,
also referred to as Haversian systems (6). The lamel-
lae are layers of anorganic substance (approx. 65 %
of the complete substance), mainly hydroxyapatite,
and organic substance (over 90 % collagen). Since
the collagen fibers of the individual lamellae of
an oesteon run at various, respectively opposite
angles of inclination (7), the compound structure of
organic and anorganic components is additionally
stabilised against pull and push forces. The bone
cells (osteocytes) (8) are located between the lamel-
lae, held in lacunae. The cells are nourished by the
Haversian vessels (9), because all osteocytes are
linked to one another and with the Haversian canal
through canaliculi containing their cell extensions.
The intermediate lamellae are located between the
Haversian systems (osteons) without any connection
to blood vessels (10).
Their thickness and stratification corresponds to
that of former Haversian systems, however, the
Haversian systems have built up over them in
the course of the continuous restructuring of the
bone that also continues after the growth period.
Running from the periosteum, the Volkmann
canals contain vessels connecting the vessels of the
Haversian canals (11). The Volkmann canals are
bony canals that are not surrounded by circular
lamellae, as opposed to the Haversian canals. The
systematic order of the Haversian canals is not
disrupted by the transverse or oblique perforation
through the Volkmann canals. The cortical layer is
followed in a fluid transition by the trabecular layer
(spongy substance or substantia spongiosa), a spon-
gy trabecular structure consisting of thin plates and
rods (1). In the direction of the medullary cavity,
the bony substance is limited by the inner circum-
ferential lamella (12) and the inner membrane
called endosteum (13). The endosteum consists of
a connection of flat cells that can form new bones.
Red bone marrow (14) can be found between the
spongy trabeculae of the bone ends, and yellow
bone marrow or fatty marrow in the tubular part
of the bone. We thank Prof. Richard H. W. Funk,
MD, Director of the Institute of Anatomy of the Carl
Gustav Carus Medical Faculty, Dresden, Germany,
for his support in the development of this model.
Bone structure
1 Trabeculae of bone (spongy substance)
2 Compact substance or substantia compacta
3 Periosteum
4 Perforating fibers, Sharpey fibers
5 Outer circumferential lamella
6 Osteons
7 Lamellae of the osteons
8 Osteocytes
9 Haversian vessels
10 Intermediate lamellae
11 Volkmann canals
12 Inner circumferential lamella
13 Endosteum
14 Bone marrow (spongy substance)
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