Download NAME: GLORY P.A. BRIGGS MATRICULATION NUMER: 14/MHS06

NAME: GLORY P.A. BRIGGS
MATRICULATION NUMER: 14/MHS06/017
DEPARTMENT: MEDICINE AND SURGERY
COURSE: GENERAL HISTOLOGY
COURSE CODE: ANA 203
Histology of Haversian System
Histology according to the Medical dictionary is the science concerned
with the minute structure of cells, tissues and organs in relation to their
function. Hence from the definition above, we can infer two things: Firstly,
that in simple terms, histology of haversian system refers to the
microscopic study of the haversian system and secondly, the haversian
system comprises of cells and tissues, which brings us to the question,
“What is haversian system?”
Haversian system also known as osteon refers to the chief basic unit
of structure of each compact bone (found in the shafts of long bones) in
humans consisting of a small hollow passageway called HAVERSIAN
CANAL (named for Clopton Havers, a 17th-century English physician),
surrounded by a series of concentric bone layers called LAMELLAE of
which there may be 4 to 20, each 3 to 7 microns thick, in a single haversian
system. Osteons are several milimetres long and about 0.2 milimetre
(0.008 inch) in diameter; they tend to run parallel to the long axis of a bone
and are not present in many vertebrate animals.
It is also important to note that this microscopic canal system was first
noticed by ANTON VON LEEUWENHOEK in 1978 but later in 1691, an
English physician, Clopton Havers published and lectured about the
microscopic makeup of canals in the bone, hence these canals were
generally referred to as CANALS OF HAVERS. His theory was that they
provided the oils necessary to harden the bone around it.
As discovered during studies by the above researchers, down the
middle of each of these systems (i.e running longitudinally in the centre) is
a hollow tube-THE HAVERSIAN CANAL, a freely anastomosing channel
containing blood vessels, nerves, loose connective tissue and endosteum.
The blood vessels provide nutrients to the living bone tissue while the
nerves and lymph vessels help with immune response in the bones and
also pick up signals from various stimuli. The haversian canal also absorb
necrotic or dying bone tissue which leave empty lacunae so that they can
be replaced by new osteocytes.
Transverse vessels called VOLKMANN CANALS run perpendicular to
the long axis of the cortex. These Volkmann canals connect adjacent
osteons and also connect the blood vessels of the haversian canals with
the PERIOSTEUM, the tissue covering the bone’s outer surface.
Also, they consist of multiple EXTERNAL CIRCUMFERENTIAL
LAMELLAE (around the marrow cavity) and often some INNER
CIRCUMFERENTIAL LAMELLAE (immediately beneath the periosteum) as
stated earlier. Between successive lamellae are series of spaces called
LACUNAE, each with ONE OSTEOCYTE OR BONE CELL, interconnected
by CANALICULI containing the cells’ dendritic processes. Processes of
adjacent cells are in contact via GAP JUNCTIONS. The osteocytes give
rise to the OSTEOBLASTS and also work along with collagen and calcium
phosphate that make up the matrix of the lamellae to ensure that the
compact bone is very strong.
Scattered among the intact osteons are numerous irregular shaped groups
of parallel lamellae called INTERSTITIAL LAMELLAE, which are lamellae
remaining from osteons partially destroyed by OSTEOCLASTS during
growth and remodeling of bone. The outer boundary of each osteon is a
more-collagen rich layer called the CEMENT LINE.
Having known the histology of the haversian system, it is important to
know its function. The exact function of this system is not known but some
theories state that it repairs damaged bone tissue, reduce stress on the
compact bone and give muscle a place to anchor.