Essential Information: What Are the Types of Bone Tissue?

The human skeletal system consists of varying bone types that each play a special role in our bodies. They help with movement and to support our bodies. There are two types of bone tissue; compact and spongy (also called. Their density differs by how closely the cells they contain are packed.

Over 75% of all bone tissue is compact bone. Compact bone cells, also called cortical bone, look as if they are a solid mass. They are cells that are tightly packed and not solid at all. Small canals can be found running through bone tissue which contains blood vessels that penetrate the bone. The outside layer of bone is made up of compact bone. This hard layer gives bone its appearance. Spongy bone, known as cancellous bone, looks like a sponge with large spaces throughout its structure.

 

Bone Heal Thyself

When a bone is broken, a splint can be used to support and immobilize the injured area which aids in healing the bone tissue. Splints are usually made of fiberglass or steel and are stabilized with velcro straps to secure them. As the bone is healing, ultrasound if often used to aid in the process.

 

Physiology of Bones

Bones store the body's essential minerals such as iron and calcium and newly created blood cells. The skeletal system allows the body to move by using a range of motion.

 

The Two Types of Bone Tissue

Most bones in the body are comprised of compact and trabecular, or spongy, bone tissue. The outer bones are of the compact type as they provide protection and the trabecular bone tissue is on the inside. The amount of tissue of each type that the body has depends on the function and location of the bone. Both types of bone are made up of collagen fibers in a meshwork design. This meshwork contains phosphate and calcium in a mixture of water that forms a hard substance known as hydroxyapatite. Potassium, magnesium, and sodium are also present in small amounts.

As a living tissue, bone tissue serves as a collector of minerals used by the body. These minerals are continually being replaced and distributed as needed. Bone tissue is always changing, unlike other tissues in the body.

 

Types of Bones

There are five main types of bones in the human anatomy, they include sesamoid, irregular, flat, short, and long. These different types of bones have varying amounts of spongy and compact bone tissue depending on their function.

Sesamoid Bones

Irregular Bones

Flat Bones

Short Bones


Other Types of Bones

Sutural bones are located between the cranial bones and within sutural joints. They are tiny and the number of them varies from person to person.

 

Bone Function

Bones provide a skeletal structure to our bodies. They provide areas of attachment for most of the skeletal muscles and support soft tissue. They protect the body's internal organs so they are not at risk of injury. Examples of this would be the skull which protects the brain, the ribs that protect the lungs and heart, and the vertebrae that protect the spinal cord.

As skeletal muscle is connected to the bone,  a contracting muscle will cause the associated bone to move. Bone tissue also releases minerals into the bloodstream, balancing the body's mineral content. Among these minerals are phosphorus and calcium.

Blood cells are produced in the red bone marrow of some larger bones. As we age, red bone marrow turns to yellow bone marrow.

 

Compact Bone

Compact bone, also called cortical or lamellar bone (meaning plate), is made up of tightly packed plates wound into tubular shapes called osteons. These resemble a rolled newspaper. Each osteon contains a capillary that provides blood flow through the central channel. Their stacked form creates a protective shell-like membrane.

 

Structure of Compact Bone

The outer layer of bone tissue, or compact bone, is found in all bones but particularly in long bones. This layer is very dense and serves as support and protection. It can tolerate stress from the weight of the body and can be found in the arms and legs. The basis of what bones are made of is a substance called osteon, also known as the Haversian System. Each Haversian System is made up of a four-part cylindrical structure. This structure includes:

  • Canaliculi: the tiny channels that provide nutrients to osteocytes and remove waste material
  • Lacunae: the spaces between lamellae which is where bone cells, or osteocytes, reside
  • Lamellae: created from mineral salts forming a matrix of concentric rings that make bone hard
  • Haversian canals: contain nerves and blood vessels in a central tube surrounded by alternating layers of lamellae, lacunae, and canaliculi

 

Spongy Bone

Trabecular, cancellous, or spongy bone, is made up of an open structure that looks much like a lattice. Spongy bone can be found at the end of a bone and in joints.


Structure of Spongy Bone

Unlike compact bone, spongy bone is not made up of osteons. Its structure looks like a sponge. These bone structures are made of thin columns called trabeculae that contain canaliculi, lacunae, osteocytes, and lamellae. Red bone marrow fills the spaces between the trabeculae which transports blood that nourishes the bones.

Spongy bone is softer, lighter, and weaker than compact bone but it contains more blood vessels.

 

Spongy Bone Function

The central structural element of spongy bone is trabeculae. This rod-shaped microscopic structure uses collagen for support. It is ideal as a vehicle for metabolic functions and the exchange of nutrients.

At birth all of our bone marrow is red and as we age it slowly changes to yellow because it is mostly made up of fat cells. These do not synthesize blood cells. A typical adult will have an equal mix of the two. When there is a severe loss of blood, yellow bone marrow can be changed to red.

 

Abnormal Bones

When abnormal bone tissue development occurs, it is called heterotopic ossification. When this happens, the extra tissue that is formed will be removed. If this condition is allowed to go untreated, the bone will build up and form a woven bone. The spongy bone becomes bone marrow. Some areas of the body that are affected by this condition are the lower and upper jawbone, temporal and occipital skull bones, the parietal, the kneecap and the collarbone.

 

Conclusion

The mechanical framework of the body is made up of bone. It is formed from connective tissues that include endosteum, yellow bone marrow, red bone marrow, periosteum, and osseous (bone tissue). It is made up of either spongy or compact bone tissue, depending on the bone matrix and the organization of cells.

Bone tissue is complex because it is neither as static nor as solid as it appears. It is a living tissue that uses minerals and has regenerative properties. There is a great deal of activity going on inside bone tissue. The two types of bone tissue are complex and trabecular, or spongy. They are made of a collagen fiber network. Within this network is phosphate and calcium that mix with water to form the hard bone we are familiar with.

As bone is living tissue, it serves as a reservoir of minerals that the body uses as it sees fit. These minerals are continually being used and replaced, in a constant state of movement. It's an amazing arrangement how the skeletal system ebbs and flows, using the correct type of bone for the use that bone will get. And when a bone breaks, it can heal itself as it is a living organism capable of regeneration.