Anatomy of bone

Bone is the hardest part of the body which is covered by muscle.

Classification of bone

1. Long bone
2. Short bone
3. Flat bone
4. Irregular bone

Let's discuss the structure of the typical long bone

• In children, a typical long bone lets take an example of the femur has 2 ends which are also known as epiphyses, and an intermediary portion called the shaft, which is also known as diaphysis.

• The part of the shaft which joins the epiphyses is called metaphysis.

• Epiphyses and metaphyses are separated by a  thin plate of growth cartilage, one at each end.

• This plate is known as the epiphyseal plate.

• At maturity, the epiphyses are fuses with the metaphysis.

• The epiphyseal plate gets replaced by bone.

• Articular cartilage covers the articular ends of the epiphyses.

• Periosteum covers the rest of the bone and it provides attachment to the tendons, muscles, ligaments, etc.

• Sharpey's fibres are present which connects the bone to the periosteum & they are the strands of fibrous tissue.

Now, If we classify bone microscopically then the bone can be classified as woven and lamellar.

Woven bone(fibrous bone): Immature bone; and is characterized by random organisations of osteocytes (bone cells) and collagen fibres.

• At the initial stages of fracture healing, woven bone is formed at periods of rapid bone formation.
• Woven bone is mechanically more immature(weaker) bone.
• It can be found in the foetal skeleton.

Lamellar bone( mature bone): It has orderly arrangments of osteocytes (bone cells) and collagen fibres.

• Lamellar bone constitutes of both cortical and cancellous bone.
• But there is a difference between lamellae in these bones, i.e. the cortical bone lamellae are densely packed, and the cancellous bone lamellae are loosely packed.
• Osteon– a basic structural unit of lamellar bone. Central canal or Haversian the canal is surrounded by a series of concentric laminations or lamellae.
• These canals move longitudinally and join freely to each other and with volkmann's canal.
• The following runs horizontally from an endosteal to periosteal surfaces.
• The shaft of the bone is made up of cortical bone and the ends are mainly made up of cancellous bone. The junction between the cortical bone and the cancellous bone is termed as corticocancellous junction which is the most common site of fractures.

Haversian canal- series of minute tubes in the outermost zone of the compact bone or cancellous bone, that allows blood vessels and nerves to travel through them.

• Each Haversian canal usually contain one or two capillaries and nerve fibres.
• The channels are grown by concentric layers called lamellae.
• Envelops the blood vessels and nerve cells throughout the bones and communicates with bone cells through connections termed as canaliculi. This unique pattern is carried to mineral salt deposits & storage which gives bone tissue its strength.
  
• Most of the individual lamella form concentric rings around the larger longitudinal canal in the mature compact bone, within the bone tissue, these canals are called as Haversian canal.
• Osteons are present in the Haversian canal.

Volkmann's canals: tiny channels in the bone that transmit blood vessels from the periosteum into the bone and that interact with the Haversian canals.

• It provides energy and nourishing element for osteons.

Let discuss the composition of bone :

Bone is made up of:

• Bone cells

• Extracellular matrix (organic and inorganic)

Bone cells:

a) osteoblast

b) osteocytes

c) osteoclasts

Blood supply of bones

1. Nutrient artery

2. Metaphyseal vessels

3. Epiphyseal vessels

4. Periosteal vessels

Hope you all find this helpful for you, if you have any query related to this topic or any other topic then you all are free to contact me via contact us or you can also ask your doubts on the comment box. Thank you! 

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