Bone Tissue

Bone tissue is a specialized form of connective tissue through which bone cells are embedded in an extracellular matrix rich in collagen, calcium phosphate, and ions.

It’s the major constituent of the skeleton.

Regardless of their rigid structure, bones are living and dynamic elements which might be continuously remodeling.

Types of Bone Tissue

Bone tissue may be categorized in accordance with its macroscopic (observed with the naked eye) and microscopic structure.

Concerning the macroscopic structure, bone tissue may be categorized into compact bone and spongy bone:

Compact Bone

It’s formed by parts with out visible cavities.

These bone types are associated to protection, support and resistance.

They’re often found within the diaphysis (long shaft of the bone).

Spongy Bone

It’s formed by parts with many intercommunicating cavities.

It represents a lot of the bone tissue of short, flat and irregular bones.

Most are discovered within the epiphyses (the enlarged ends of a long bone).

Regarding microscopic structure, bone tissue may be categorized as primary and secondary:

Primary bone tissue

Additionally known as non-lamellar or immature.

It presents an irregular arrangement of collagen fibbers; lamellae are usually not formed.

It has fewer minerals and a better quantity of osteocytes, in comparison with secondary bone tissue.

It’s the first type of bone to form, throughout embryonic development. This tissue is uncommon in adults, persisting in areas of intense remodeling, such because the dental alveoli and tendon insertion areas.

Secondary bone tissue

Additionally known as lamellar or mature, it’s present in adults.

It presents collagen fibbers organized in lamellae, that are parallel to one another. Osteocytes are arranged inside or on the surface of every lamella.

This type of tissue consists of a set of layers of circular, concentric lamellae with totally different diameters, known as Haversian systems or Haversian systems.

Composition of Bone Tissue

Bone tissue is formed by cells and calcified extracellular materials, the bone matrix.

The cells on this tissue may be of three types: osteoblasts, osteocytes and osteoclasts.

Osteoblasts are located on the periphery of the bone and have long cytoplasmic extensions that touch neighboring osteoblasts.

They’re responsible for producing the bone matrix that’s deposited around them. When trapped by the newly synthesized matrix, they’re known as osteocytes.

Osteocytes are essentially the most abundant cells in bone tissue. When they’re retained within the mobile matrix, the cytoplasmic projections of every cell decrease. Thus, the channels where these extensions had been positioned serve as communication between one gap and another.

It is usually via these channels that vitamins and oxygen reach the bone cells. The bone channels constitute a posh network, responsible for the maintenance and vitality of the bone matrix.

Osteoclasts are large, multinucleated cells (6 to 50 nuclei). They originate from the fusion of blood cells, monocytes. They change into active throughout the bone resorption phase, as they will move alongside bone surfaces and destroy broken or aged areas.

This enables the activity of osteoblasts, which proceed to produce bone matrix. The movement of osteoblasts and osteoclasts causes the bones to undergo continuous reworking.

Bone matrix

The bone matrix is ​​very resistant and has an organic portion and an inorganic portion. The inorganic portion represents roughly 50% of the weight of the matrix, and is shaped, in greater quantities, by phosphate and calcium. The organic part, in flip, is mainly composed of collagen, especially type I collagen.

Bone Coverings

Outer surface of bones is surrounded by a layer of connective tissue, the periosteum.

Bone tissue is highly vascularized. Within the periosteum there are blood vessels and nerves that penetrate the bones via small holes.

The interior surface of bones is lined by the endosteum, formed by osteoblasts and osteoclasts.

Bone tissue is a particular type of connective tissue, with considered one of its most striking characteristics being the presence of calcified extracellular materials (bone matrix). This matrix is ​​inflexible because of calcification however can also be elastic because of the presence of collagen fibers.

Bone tissue is a tough tissue that forms our bones.
Along with this matrix, bone tissue contains specialised cells: osteocytes, osteoblasts and osteoclasts. Osteocytes are cells situated inside the gaps within the matrix; osteoblasts are cells involved within the synthesis of the organic a part of the matrix and are situated on its periphery; and osteoclasts are mobile cells, due to this fact occurring in varied elements of the tissue.

Functions of Bone Tissue