[Biology Class Notes] on Periosteum Pdf for Exam [2024]

The Periosteum meaning and role can be drawn to similarities to that of skin. Just like the skin covers the outer surface of the body, the periosteum is a thick layer that is the outer covering of bone. The Periosteum of bone covers the outer surfaces but not the joint spaces which are called articular surfaces which are lined by synovial membrane. Bones are very crucial as it protects our bodies, organs and even carries our entire weight. And the periosteal layer of the periosteum of bone protects this important part of our body. Now that we are aware of the periosteum meaning let us understand the anatomy and functions of the periosteum of bone.

Anatomy of the Periosteum

The periosteum meaning clearly justifies the membranous tissue that is the periosteum covers the bone surface and does not cover the articular surfaces as there are ligaments and tendons attached to this and the areas the cartilage surrounds the bones. The periosteum of bone is made up of two layers of which one is a fibrous membrane made up of connective tissue and the other has osteoblast cells. Let us understand further about these two layers.

The outer fibrous layer of the periosteum is the fibrous layer which is further divided into two parts. The outer or superficial layer of this fibrous membrane has very few elastic fibres and is predominantly made up of a collagenous matrix with interspersed elongated fibroblasts. This layer also has blood vessels which can be referred to as the periosteal vessels and the nerves and are the most highly vascularized substratum hence the primary contributor to the blood supply to the skeletal muscle and even the bones. The deeper layer of the outer layer is more elastic because of many fibroelastic cells and is not very vascularised.

The inner layer of the periosteum is the highly cellular cambium layer can. It contains osteoblast cells and mesenchymal progenitor cells. Due to its cellular nature, it is responsible for appositional growth. In the fetus stage, it has a lot of significance and even in the early years due to its osteoblastic potential and it decreases with age, most of it reduced during childhood itself. In adults, the fibroblasts in the inner layer are elongated with a configuration essentially indistinguishable from the fibroblasts adjacent to it that lie in the outer layer.

Periosteum and Endosteum

The two layers that protect the bones are the periosteum which is the outer layer and the endosteum the inner layer in bone and often they are used interchangeably because of their similarities like both are made up of connective tissue, both contain fibroblasts, osteoblasts, and osteoprogenitor cells and even play a key role in bone remodelling but they have a lot many differences.

Differences Between Periosteum and Endosteum

Periosteum	Endosteum
A layer of connective tissue that lines the bones leaving space for joints and tendons and ligaments attachments,	Endosteum lines the bones along with the medullary cavities as well.
The periosteum is a dense and thick layer of cells forming tissues.	The endosteum which is also made up of connective tissue is a very thin layer.
The thickness of this thick layer is around 100 micrometres.	The thickness of this thin layer is 0.1 to 0.5 micrometres.
The periosteum thickness is unique and crucial which can further be divided into the outer fibrous layer and the inner cambium layer and each layer serves a specific function.	Endosteum consists of a single cellular layer of loose connective tissue that lines the cavities.
Lines the outer surface of the bone.	Lines the inner surface of the bone.
The outer layer is elastic which also helps in smooth movements of the bones.	This inner layer does not have elasticity properties.
Only lines the bones everywhere and not the joints or cavities and also excludes the areas that are covered by cartilage and the sesamoid bones.	The inner surface is entirely lined by the endosteum without leaving space for anything else even on the medullary canals, the Haversian canal, Volkman’s canal and even in the spongy tissue of bones.
Osteoblasts cells with great osteoblastic potential are present in the periosteum.	The cells found in the endosteum are hematopoietic cells and many fibroblasts cells.
It nourishes the compact bones.	Important in remodelling and growth and repair of bones.

Periosteum Functions

The periosteal vessels of the periosteum in the outer layer enter perpendicularly through Volkmann canals and enter another group of canals that run along the bones called Haversian canals, and thus are highly sensitive to any function occurring in the bones.
The periosteal vessels easily identify if any tissue is injured or damaged. It is because of these vessels one is able to register the pain.
When the nerves then send a signal of the pain to the brain the healing stage and process begins.
The osteoblasts cells in the cambium layer play an important role in bone formation.
The periosteum without covering the tendons and ligaments joining the bones provides attachment sites.
This layer even provides nourishment to the compact bones.
Provides a medium through which muscles are also attached to the bones.
The periosteum is also called the limiting layer as the outer fibrous la
yer prevents the bone tissue from spilling out into neighbouring tissues that are into the ridges and tubercles and even the waste removal process is also carried within the periosteum layer boundaries.

Damage of Periosteum

Often the periosteum damage of the bones is due to inflammation and the condition is called periostitis. And the damage can also be due to an infection. People who experience this kind of condition are often athletes. It can be acute periostitis or chronic periostitis.

Acute Periostitis	Chronic Periostitis
It is a painful condition that is caused by an infectious consequence of an autoimmune disease like osteomyelitis or even leukaemia.	It is caused when the bone is overused and when it is under stress continually for a prolonged period.
The results of infection can also be seen in people with diabetes, sexually transmitted diseases and even in ones suffering from urinary tract infection. This also leads to necrosis which is cell death where the infection is caused.	Inflammatory changes are mostly seen in athletes and the more common reason is lifting heavy weights, jumping and running.
Risk factors include systemic infection, orthopaedic surgery like joint replacement surgery, open fracture, ulcers and atherosclerosis.	The risk factors here include high-intensity exercises that are physically extremely demanding and Osgood-Schlatter disease that is more common in children.
Symptoms in acute condition include intense pain, difficulty bearing weight on the affected limb, pus formation, fever and chills and swelling of the tissue surrounding the bone.	In chronic periostitis the bones over time become extremely tender to touch and ache, temporary bouts of shin splints and similar injuries, also causes swelling and inflammation.
Can be diagnosed easily with the help of an x-ray and one needs to visit when they feel uneasiness. Bone scanning and counting blood count also reveals information about any signs of infection.	A detailed diagnosis is required through MRI (Magnetic resonance imaging) scan. The chronic condition can also result in periosteal chondroma which is a noncancerous tumour and that needs a depth diagnosis.
Treatment for pus and swelling is a medication mostly antibiotics and draining of it and in case of necrosis, surgical debridement is a very effective method.	The treatments, in this case, are resting the affected area, applying ice to the area, while healing one only needs to engage in low-impact activities and one can even take anti-inflammatory drugs like ibuprofen.

Ways to Avoid Periostitis

The recovery period depends on the severity of the injury and it usually lasts 2-4 weeks to 6-8 weeks one must be regular with medication and in case of chronic condition keep applying ice packs.
The acute condition can be managed once you reduce the risk factors that cause the diseases leading to acute periostitis.
If you are diabetic manage your blood sugar level and if advised also take the insulin from an external source.
Stay healthy by exercising but avoid high impact exercises.
Stay active and manage your weight.
Reduce cholesterol levels by avoiding oily and unhealthy foods.
Blood pressure also needs to be maintained by reducing the intake of salty foods
Dietary changes can do wonders for the body
Alcohol and smoking only worsen the condition of the pain and infection so avoid at all costs.

Conclusion

Even though the periosteum does not contribute to bone growth in adults it does a great job in supplying blood and nourishment and the inner layer protects it from injuries and damage and even aids in the healing processes of fractures of any sort. And one must be careful as any damage to the periosteum be it through overuse or infection the consequences only makes the bones more prone to fractures. And as one ages fracture healing is more painful and if one has an infected and damaged periosteum the healing is not up to mark. Hence periosteum must be very well protected and taken care of because it provides a cushion for the bones that carry our body.