Bone consists of mineralized tissue that contains four different kinds of cells. These are bone lining cells, osteocytes, osteoclasts and osteoblasts.
Bone has an important role within the body as it ensures locomotive activity can take place whilst offering protection and support for soft tissues, phosphate storage and calcium.
Bone also contains bone marrow which is incredibly important in regard to the overall functionality of the bones.
Despite the somewhat plain appearance of bone, it is a multifaceted organ that is often resorbed efficiently by osteoclasts and neoformed efficiently by osteoblasts.
There is also a breadth of evidence to suggest that osteocytes act as orchestrators within the bone remodeling process.
The primary function of bone lining cells is not overly clear, however, these particular cells do play an incredibly important part in both bone resorption and bone formation.
Bone remodeling is a complicated process whereby older bone is replaced with new bone. This remodeling process consists of three different phases.
Firstly, the bone enters into a resorption process by the osteoclasts. Next, there is a transition period that occurs from the resorption phase to the formation of new bones and lastly, the bone formation occurs by using the osteoblasts.
Thus, this overall remodeling process occurs because of the combined actions of osteocytes, osteoclasts, osteoblasts and bone lining cells.
A combination of these cells is essential to form an anatomical structure that is otherwise known as the multicellular unit. Bone remodeling is essential to heal any fractures and adapt the skeleton for mechanical use.
This is why an imbalance of bone resorption and errors in bone formation can result in a variety of bone diseases.
For instance, resorption by osteoclasts that becomes excessive without any correlating amount of nerformed bone using osteoblasts will contribute to overall loss of bone and osteoporosis by proxy.
Comparatively, an excess in nerformed bone that does not correlate to the resorption process by osteoclasts can result in osteopetrosis.
Therefore, it is essential to reach an overall equilibrium between bone resorption and bone formation and this process typically depends on systemic and localized factors that includes cytokines, chemokine, biochemical stimulation and hormones.
Recent studies have also indicated that the bones also influence other organs in regard to activity. Bone is also influenced by other organs and the systems within the body and thus, it is not a one-way street.
These studies have provided a breadth of new insight into the complexity of bone tissue.
Thus, bone tissue is one of the key components within the skeletal system. Other components within this system include marrow cavity, collagen and fibers.
As mentioned, bones consist of numerous specialized cells that serve a variety of purposes and functions.
Specialized Bone Cells In Depth
Osteoblasts consist of cells that form other aspects like collagen fibers. Osteoblasts derive from the osteoprogenitor cells and are used to build new bones.
They are also crucial in the rebuilding process in the eventuality that a bone breaks. This process involves the accumulation of osteoblasts that then form an osteoid which hardens when minerals are added.
Osteocytes can be defined as old osteoblasts that are no longer able to form new bones. Whilst new bone forms from osteoblasts, the osteocytes become enveloped in new bone.
Thus, osteocytes become embodied within the bone whilst the new bone forms and in this sense, they can be depicted as being the mature cells within the bone. Osteocytes also contain branches that ensure that they are able to connect to one another.
Osteoclasts are far larger cells when compared to the others and these cells play a key role in breaking down the bone through the phagocytosis process.
Although these cells become incredibly active whenever bone is broken, they also help to make sure that bone does not become degraded or excessively produced. Osteoclasts often contain multiple nuclei as they are larger cells.
Bone Lining Cells
These cells are not usually mentioned in regards to bone formations as they are located on the surface of the bone. However, they play a significant role in ensuring that the surface of the bone is appropriately covered.
Bone is primarily formed using two processes otherwise known as intramembranous ossification and endochondral ossification.
Intramembranous ossification involves the condensing of mesenchymal cells at centers of ossification whereas endochondral bones are formed where there is cartilaginous blastema.
Structure And Anatomy Of Bone Tissues
It is important to note that there are five varieties of bone that are usually identified on the basis of their overall shape and form. These bones include:
These bones are developed via the endochondral ossification process. These ones include those that are located within the appendicular skeleton (the femur and tibia bone).
They also include a shaft that ensures that the epiphysis is connected. The epiphysis is the spongy part of the bone that contains a thinner layer of compacted bone.
The metaphysis is the location between the epiphysis and the shaft which is usually the point that grows during the development process.
Short bones consist of a thinner layer of bone that has compacted and covers the spongy bone.
These bones are often shaped like cuboids as a result, and they provide essential stability and support to the body. These bones include the carpal and tarsal bones.
In contrast to short bones, flat bones consist of duplicity layers of compacted bone that covers the marrow and spongy bone contained within the flat bone. The ribs, skull and scapulae are all examples of flat bones.
Sesamoid bones are usually found at the end of the long bone and include the patella bones that are primarily located within the knee. These bones protect any tendons from excessive wear and tear.
Irregular bones consist of a thin layer of compacted bone that covers the spongier bone. A bone that is characterized as irregular is usually labeled in accordance to the content within the bone as opposed to the overall shape of the bone.
These bones also include bones that are located within the vertebrae and hip.
In regard to overall bone anatomy, the key parts of identify include the following:
The endosperm is a thin membrane that forms the lining of the cavity of the bone marrow. In this sense, the endosperm lines the internal surface of the bone, encompassing the marrow.
The periosteum is one of the toughest membranes and covers the entire length of the shaft. However, it doesn’t cover the cartilage.
This membrane also includes a layer of fiber and an osteogenic layer that ensures that the bones are appropriately nourished and repaired.
The compact bone is also known as the cortical bone. These bones are dense due to the matrix of calcification within them. They also contain small spaces that are called lacunas.
To an outside observer, this compacted bone has a solid layering that acts as an external layer. These bones are used to support the body’s weight due to their strength.
The spongy bone is otherwise known as the cancellous bone and includes porous tissue which contains bone marrow. These bones also encapsulate the spaces that include red bone marrow.
Whilst it may not be as tough and hard as a compact bone, a spongy bone does play a crucial role in protecting the marrow which inherently ensures that red blood cells can be produced efficiently.
Bones Under Closer Observation (Stereo Microscope)
Stereo microscopy is one of the easiest methods to observe the bone’s surface. This process involves a section of bone being placed under a microscope in order to view any specimens under the required level of magnification.
These bones are often observed by students who wish to understand the different varieties of bones in order to ascertain the individual differences between them.
For example, students will be able to compare bones that include an outer layer of membrane with those that do not contain an outer layer of membrane.
When observing bones under a stereo microscope, a student may observe the bone as being porous and including multifaceted chambers that come in a variety of sizes.
This observation process doesn’t require any extensive preparation of the bone itself.
In order to view bone tissue under a microscope, the sample of bone has to be very carefully prepared to ascertain which specimen will provide the observer with the most accurate and beneficial results.
As such, the preparation process requires the following aspects:
- Bone sample selection.
- A compound microscope
- Micro polishing pads
- Polishing paper
- Saw microtome
- Epoxy glue (clear)
- Take your saw microtome and cut the bone, reducing it to approximately 25mm in length. Leg bone is often the best bone to use for this.
- Clean your bones using warm water.
- Take your polishing paper and your micro polishing pad and polishing the part of the bone that will come into direct contact with the microscope slide. This will ensure that any scratches or uneven sections can attach properly onto the slide.
- Clamp down your bone in a vise, and cut it to obtain an appropriately sized slice if needed.
- The size of the sample that you are using should be approximately 5mm by 5mm.
- Then, using your epoxy glue, bind this narrowed sample onto the glass slide of the microscope. You should press the side of the bone onto the slide firmly to ensure that the layer of glue is as thin as possible.
- Once you have attached your sample to the slide, you can use your polish paper in order to reduce its thickness to approximately 25um. You should try to avoid thinning your bone too much as this may affect the observation process.
- Remove any outer layers of dust, carefully wiping your sample with water, before placing your cover slip over the top.
- View your sample under the relevant microscope setting.
When observing your sample under a compound microscope, the sample will show multifaceted patterns across the surface of the bone. Students will also be able to see a variety of concentric layers contained within the Osteons.
These layers may also include a number of spots or lacunas that contain conduit at the heart of these osteons and these are otherwise known as the Harversian canal.
Bones Under Closer Observation (Electron Microscope)
In order you prepare your sample for observation under an electron microscope, you will need to make the follow preparations:
- Ensure that you have Glutaraldehyde
- Osmium tetroxide
- Saccharose solution
- Epon B. Knife
- Alcohol oxide
- Propylene oxide
- A diamond knife
- Uranyl acetate
- Lead citrate
- Toluidine blue
- Fix your sample of glutaraldehyde for approximately two hours.
- Wash your sample using your saccharose solution and leave it overnight.
- Postfix your sample in osmium tetroxide for approximately 1 hour.
- Dehydrate your sample using the propylene oxide and alcohol.
- Embed in Epon B.
- Cut an appropriately sized section from your sample using a glass knife.
- Stain this section with toluidine blue.
- Take an ultramicrotome that comes equipped with a diamond knife and cut your section again in order to thin it even more.
- Strain this thinned section once more with uranyl acetate and lead citrate.
- View it via a transmission electron microscope.
When you view the bone section using a transmission electron microscope, you will be able to observe the collagen within the matrix of the bone. You will also be able to observe the osteoid tissue otherwise known as the uncalcified matrix.
Any students that are observing the sample will also be able to see the Osteons, which consist of concentric layers that can sometimes be referred to as lamellas.
As previously mentioned, conduits or Haversian canals can be observed at the center.
These are critical features within the bone as they hold essential vessels that enable blood and lymph to circulate, ensuring that the cells remain healthy and appropriately nourished.
Lacunas can also be observed and these contain the osteoblast cells that form the overall matrix and include fibers of collagen.
To summarize, the bone contains four different cell components that can be easily observed under a microscope using a thorough preparation process.
These cells consist of osteocytes, osteoclasts, osteoblasts and bone lining cells. Osteocytes, osteoblasts and osteoclasts are contained within the bone whilst the lining cells form an external layer.
Because of this, the bone lining cells are often overlooked when closely observing the bone.
However, each of these components synchronize to form a process that is imperative to ensure that the bones remain healthy and rejuvenated.
The remodeling process requires each of these cells to function appropriately in order to ensure that there is not an imbalance of cell growth with the restructuring process.
Long bones, short bones, spongy bones, flat bones and some examples of bone that require an extensive remodeling process in order to function appropriately.
Therefore, it is important to understand the individual functionality of each of these cells in order to ascertain where there may be an imbalance within the body and which organs may be causing unwanted changes.
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