Cancellous Bone

Cancellous bones are also called spongy bones or trabecular bones, they are the internal tissue of the skeletal bone and are an open cell porous network. The word cancellous and trabecular refers to the tiny lattice-shaped units or the trabeculae which form the tissue. 

When compared to the cortical bone, the cancellous bone has a higher surface area to volume ratio and it is also less dense. Due to these reasons, it makes it weaker and more flexible. The greater surface area of the cancellous bone also makes it suitable for metabolic activities such as the exchange of calcium ions.  Cancellous bone is found at the end of the long bones which is near the joints and in the interior of the vertebrae. Cancellous bone is very vascular in nature and it often contains the red bone marrow where the production of the blood cells or hematopoiesis usually occurs. 

Trabeculae is the primary anatomical and functional unit of the cancellous bone or the spongy bone. The mechanical load distribution that a bone experiences within a long bone such as the femur is where the trabeculae are aligned. 

In this article, we are going to discuss cancellous bone meaning, cancellous bone function, cancellous bone and its spongy bone structure and along with that, few frequently asked questions about the cancellous bone will be answered. 

Cancellous Bone Meaning

• Cancellous bones are also known as the spongy bone or the trabecular bone. They are very light, porous bones enclosing numerous large spaces that help in giving them a sponge or a honeycomb appearance. Trabeculae is the primary anatomical and functional unit of the cancellous bone or the spongy bone. The framework or the bone matrix is arranged in a three-dimensional latticework of bony process called trabeculae which are arranged along the lines of stress. The blood vessels or the marrow fare basically the things that the spaces are filled with. 

• Twenty percent of the human skeleton is made up of cancellous bone. The spongy bone or the cancellous bone helps in providing structural support and flexibility without the weight of the compact bone. The cancellous bone is found in most areas of bone that are not subjected to any kind of stress. The spongy bone or the cancellous bone makes up much of the enlarged ends of the long bones and is the major component of the shoulder blades, the ribs, the flat bone of the skull, and also the variety of short and flat bones present elsewhere in the skeleton. 

• A shell of compact bones surrounds the cancellous bone that helps in giving them greater strength and rigidity. The open structure of the cancellous bone enables it to moderate the sudden stress as it loads the transmission through the joints. The cancellous bone has a relatively higher level of metabolic rate. 

• Through the action of the bone-forming cells called osteoblasts, the cancellous bone or the spongy bone can develop into the compact bone. It is in such a manner as that of all the long bones that develop in the embryo. A new bone matrix in layers is deposited around the trabeculae by the osteoblasts. The new bone matrix which was deposited then enlarges between the spaces. The spaces which were present get eliminated and the new immature compact bone is produced. 

Cancellous or Spongy Bone Structure

• The spongy bone is lighter and less dense than the compact bone. The spongy bone is composed of cells that are called osteocytes. The osteocytes sit in small cavities known as the lacunae.

• The spongy bone consists of plates or the trabeculae and the bars of the bones which are adjacent to the small, irregular cavities that contain the red bone marrow. The trabeculae are arranged in an orderly manner to provide maximum strength. 

• The accompanying osteocytes and the lacunae are housed in the trabeculae matrix of the bone along with the bone marrow. The blood vessels travel through the harder compact bones to the spongy bone only to supply it with the materials that are required to create the blood cells. 

• Osteocytes that are present close to the blood vessels have the capacity to take the nutrients and expel the waste products out through tiny interconnecting channels on the surface of the trabeculae called canaliculi. 

• Osteoblasts are the bone cells that secrete the material that creates the compact bone matrix and these osteoblasts have the capacity to convert the spongy bone to the compact bone. The long bones in the human embryo develop through the same process. 

Cancellous Bone Function

The Spongy Bone or the Cancellous Bone Is Responsible for the Functions Which are Listed below:

• Storage of the Bone Marrow: Bone marrow which is also called the myeloid tissue is formed when the trabecular matrix crowds the blood vessels together and later when they condense. The cortical bones are denser and have fewer open spaces compared to the cortical bone, the spongy is very much ideal for making and storing bone marrow within the lattice-like trabeculae network. The cortical and cancellous bone has a similar function in one way or another. The cancellous bone contains the red blood cells that are used in erythropoiesis which is the production of the red blood cells. The cortical bone helps in storing the yellow bone marrow which is primarily composed of fat in its medullary cavity. 

• Reduces the Skeletal Weight: The cancellous bone or the spongy bone has a lightweight and low density, due to this reason it is able to balance out the heavier and denser compact bone or the cortical bone to reduce the overall weight of the skeleton. Due to this reason, it makes it easier for the muscles to move limbs. 

• Provides Strength and Flexibility to the Bones: The trabeculae of the cancellous bones tend to form along the line of stress considering the bone strength and flexibility in that area. The joints of the body contain the spongy bone which acts as a shock absorber when we do different exercises such as walking, running, and jumping. 

• The Cancellous Bone Helps in Mineral Storage: 99% of the body’s calcium and 85% of the phosphorus is stored in the human skeleton. To ensure the proper functioning of the muscles and the nervous system, the mineral content of the blood must be tightly regulated. With the help of the hormones in the body, the minerals are released into the bloodstream quickly. 

• Erythropoiesis: The cancellous bone is the main site of Erythropoiesis. The red blood cells are produced in the red bone marrow at a rate of about two million per second and all this process is done inside the spongy bone or the cancellous bone. The high vascularized nature of the spongy bone is the only reason that is allowing for the rapid production of red blood cells. The elements that are required to make the red blood cells such as the amino acids, lipids, and glucose are delivered by the spongy bone. The old and damaged red blood cells return to the bone marrow when they are ready to die. In the bone marrow, the red blood cells are phagocytized by macrophages. The same process also occurs in the spleen and the liver.