Page 274 - Atlas of Histology with Functional Correlations

Osteons (Haversian Systems; Transverse Section,

Decalcified)

This illustration shows the primitive bone marrow (15) and developing osteons
in a compact bone. Vascular tufts of connective tissue from the periosteum or

endosteum invade and erode the bone and form primitive osteons. Bone
reconstruction or remodeling will continue as the initial osteons, and then later
ones, are broken down or eroded, followed by the formation of new osteons.

The new bone matrix (11) and bone spicule (12) of an immature compact
bone are stained deep red with eosin due to the presence of collagen fibers.

Numerous primitive osteons are visible in the transverse section, with large
central (Haversian) canals (2, 9) surrounded by a few concentric lamellae (9)
of bone and osteocytes in lacunae (10). The central (Haversian) canals (2, 9)

contain primitive osteogenic connective tissue (13) and blood vessels (2). Bone
deposition is continuing in some of the primitive osteons (2, 9), as indicated by
the presence of osteoblasts (1, 14) around the central (Haversian) canals (2, 9)
and the margin of the innermost bone lamella. In some osteons, the
multinucleated osteoclasts (6) have formed and eroded shallow depressions

called Howship lacunae (5) in the bone. Osteoclasts (6) continue to resorb and
remodel the bone as it forms.

Primitive osteogenic connective tissue (13) passes through the bone, from
which arise tufts of vascular connective tissue that give rise to new central

(Haversian) canals (2, 9). Osteoblasts (1, 14) are located along the periphery of
the developing central canals.

In the lower left corner of the figure is the primitive bone marrow (15), in
which hematopoiesis (blood cell formation) is in progress; this is the red

marrow. Also present in the bone marrow cavity (15) are developing
erythrocytes and granulocytes, megakaryocytes (4, 8), blood sinusoids
(vessels) (3, 7), and osteoclasts (6) in the eroded Howship lacunae (5). Some
megakaryocytes (4, 8) are adjacent to the blood sinusoids. Their cytoplasmic

processes protrude into these blood sinusoids, where they eventually fragment
and enter the bloodstream as platelets.

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