tissue is one of the main components of the skeletal system (other components
include bone marrow/marrow cavity, collagen fibers etc). Like other tissues in
the body, bones are made up of specialized cells that serve different
main types of cells that make up bone tissue include:
Osteoblasts - are the type of cells that form the matrix and
collagen fibers. They are derived from osteoprogenitor cells and are
responsible for building new bones as one grows. They are also important in
that they help rebuild bones in the event that they break. These processes
involve the cell (osteoblasts) accumulating at a give spot to form osteoid
(flexible material) that hardens when material (minerals) are added to it.
Osteocytes - are old osteoblasts that no longer serve to form new
bone. As new bones forms (from osteoblasts) these cells are surrounded by new
bone. Therefore, Osteocytes remain embedded inside the bone as new bone
continues to form. As such, they may be described as the principle/mature cells
have branching arms (looking like a star fish) that allow Osteocytes to attach
to each other
Osteoclasts - Osteoclasts
are larger cells compared to the others and play the role of breaking down and
reabsorbing the bone through phagocytosis. Although they are very active when
bones are broken, they also help ensure that bones are not overly produced or
are fused to monocytes and usually have more than one nucleus given that they
are large cells
type of bones cells that are not often mentioned are the lining cells that are
located on the surface of all types of bones. Lining cells form from
osteoblasts and play the role of covering the surface of bones.
are primarily formed through two processes namely; intramembranous ossification
and endochondral ossification. Whereas intramembranous ossification involves
the condensation of mesenchymal cells at ossification centers, endochondral
bones are formed in the presence of cartilaginous blastema.
Bone Tissue Anatomy and Structure
going into detail, it's worth noting that there are primarily five types of
bones that can be generally identified based on their forms (general shape).
Long Bones - Long bones develop through the endochondral
ossification process and include those located in the appendicular skeleton
such as the tibia and femur. They have a shaft part that connects the two ends referred
to as epiphysis (mostly spongy bone with a thin layer of compact bone).
metaphysis, which is the point between the shaft and epiphysis, is often the
point of growth during development.
Short Bones - Short bones are largely composed of a thin
layer of compact bone that covers vast spongy bone and marrow. This causes them
to appear cuboid in shape. They serve to provide support and stability and
include such bones as the carpal and tarsal bones.
Flat Bones - Unlike short bones, two layers of compact
bone cover the spongy bone and marrow in flat bones. Examples of flat bones
include ribs, scapulae and skull bones.
Sesamoid Bones - These bones are largely found at the end of
long bones and include such bones as the patella bone located in the knee. They
primarily serve to protect tendons from excess wear.
Irregular Bones - With irregular bones, a thin layer of the
compact bone cover the spongy bone. This category is largely categorized by the
content of the bone rather than the shape. It includes such bones as the hip
With regards to bone anatomy, some of the parts that can be easily
The endosteum - This is a thin membrane that lines the cavity of the bone
marrow. As such, the endosteum lines the inner surface of the bone (such as
long bones) thus surrounding the marrow.
Periostem - This is a tough membrane that can be seen covering the length
of the bone shaft. However, it does not cover the cartilage part. The membrane
also consists of a fibrous layer and osteogenic layer that makes nourishment
and repairs possible.
Compact Bone - Compact bone is also commonly referred to as
cortical bone. It is dense (because of calcified matrix) with tiny spaces known
as lucanas. To the naked eye, the compact bone is a solid layer present as the
external layer of all bones. Because of its strength, the compact bone makes it
possible for the bone to support weight.
Bone - Also referred to as cancellous bone, spongy bone is composed of porous tissue and contains the bone
marrow (it surrounds spaces filled with red bone marrow). While it is not as
hard as compact bone, spongy bone plays an important role of protecting the
marrow where blood cells are produced.
is one of the simplest methods to view the surface of a bone. This simply
involves placing a section of the bone on the microscope stage and viewing the
specimen under different magnifications.
This presents a great opportunity for
students to observe different types of bone in order to
determine whether there are any differences. For instance, students can compare a
bone that has a covering outer membrane and those without the membrane.
stereo microscope (and depending on the section of the bone under investigation)
the student may see the bone as porous with various chambers that vary in size.
method does not require significant preparation of the bone
To view a
bone tissue under the microscope, the bone sample has to be carefully prepared
in order to produce a specimen that will provide the best possible results.
This will require the following:
A bone section/sample
A compound microscope
Micro-Mesh polishing pads
Clear epoxy glue
Using a saw microtome cut
the bone section to reduce it to about 25mm in length (this could be a leg
Clean the bone using some
Using the grinding/polish
paper and then a micro-mesh polishing pad, polish the side that will be in
contact with the microscope glass slide - This removes any protruding sections
or scratches allowing the sample to attach to the slide appropriately
Clamp the section in a vise
and carefully cut it to obtain a narrow slice
Cut the section to dimensions
of about 5mm by 5mm chip
Using clear epox glue, bind
the section to the microscope glass slide
Try pressing the section on
the slide to ensure that the layer of glue is as thin as possible
Once the section is firmly
attached to the slide, use the polish paper to reduce its thickness to about
25um - while the section has to be sufficiently thin to get a good view of its
features, it should not be too thin given that this would affect the features
To remove the dust, wipe
the preparation with water and
place a cover slip on top
View the sample under the
viewed under the compound microscope, the section will show various patterns
across the surface. In particular, students will see various concentric layers
that make up the Osteons. These layers may contain numerous spots (lacunas)
with conduit at the center of each osteon known as the Harversian canal.
Fix the sample in
glutaraldehyde for about 2 hours
Wash the bone sample using
saccharose solution overnight
Postfix in osmium tetroxide
for about 1 hour
Dehydrate the sample using
alcohol and propylene oxide and embed in epon B.
Cut the section using a
glass knife to produce thin slices
Stain the section using toluidine
Using a ultramicrotome that
is equipped with a diamond knife, cut the section again to obtain ultrathin
Stain the section again
using uranyl acetate
View the section on
transmission electron microscope
bone section is viewed under transmission electron microscope, it is possible
to see collagen that makes up most of the organic matrix. In addition, students
can see the osteoid tissue, which is uncalcified matrix.
light microscope, students can see Osteons, which consist of concentric layers
that are also referred to as lamellas.
As mentioned, conduits referred to as
Haversian canals are at the center of these layers. These are important
features of the bone in that they hold vessels through which blood and
lymph are circulated. This ensures that the cells are continually nourished and
The small, dark spots (lacunas) that can also be seen contain
osteoblast cells that form matrix and collagen fibers. The lacunas can also be
viewed as connected to each other through what seems like very thin lines.
These systems are known as canaliculi and allow for gaseous and metabolite
view a spongy bone under the microscope, it will be possible to see the numerous
pores across the surface. These pores serve to hold not only some marrow, but
also nerves and vessels that transport blood to the cells delivering
nourishment and gas exchange.
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