Why Is Cancellous Bone Vital in the Human Body?
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.
FAQs on Cancellous Bone: Structure, Functions, and Key Roles
1. What exactly is cancellous bone and where is it located in the human body?
Cancellous bone, also known as spongy or trabecular bone, is one of the two main types of bone tissue. It has a porous, honeycomb-like structure composed of a network of rods and plates called trabeculae. This design makes it lighter and more flexible than dense cortical bone. It is typically found at the ends of long bones (epiphyses), inside the vertebrae, in the ribs, the skull, and the pelvis.
2. What are the primary functions of cancellous bone in the skeletal system?
The primary functions of cancellous bone are multifaceted and crucial for the body. These include:
- Structural Support: It provides support and strength to the skeletal frame, particularly in areas that experience multidirectional stress, like joints.
- Hematopoiesis: The porous spaces within cancellous bone are filled with red bone marrow, which is the primary site for the production of red blood cells, white blood cells, and platelets.
- Metabolic Activity: It has a high surface area and is highly vascular, making it metabolically active. It acts as a reservoir for minerals like calcium, which can be exchanged with the bloodstream.
- Shock Absorption: Its spongy nature allows it to absorb shock and distribute mechanical loads, protecting joints from impact.
3. How does cancellous bone differ from cortical bone in structure and function?
Cancellous and cortical bones are structurally and functionally distinct. Cortical bone is the dense, hard outer layer of bone, providing protection and rigidity; it makes up about 80% of the skeleton. In contrast, cancellous bone is the inner, spongy layer. Cortical bone is organized into dense units called osteons, while cancellous bone is a lattice-like network of trabeculae. Functionally, cortical bone primarily provides mechanical strength and protection, whereas cancellous bone's main roles are metabolic regulation and housing the bone marrow for blood cell production.
4. What are some clear examples of bones with a high proportion of cancellous tissue?
Bones that are not subjected to the highest mechanical stresses but require flexibility or house bone marrow have a high proportion of cancellous tissue. Prime examples include the vertebrae of the spinal column, the ribs, the flat bones of the skull, and the pelvis. Additionally, the ends of long bones, such as the femur and humerus, known as the epiphyses, are rich in cancellous bone.
5. What is the importance of the trabeculae in cancellous bone's structure?
The trabeculae are the defining structural elements of cancellous bone. Their importance lies in their arrangement, which forms a strong, lightweight lattice. This network is not random; it aligns along lines of mechanical stress, providing maximum strength with minimum mass. This intricate structure creates ample space for housing red bone marrow and allows for a large surface area, which is vital for the metabolic exchange of calcium and other minerals with the blood.
6. Why is cancellous bone often called 'spongy bone,' and does this imply it is weak?
Cancellous bone is called 'spongy bone' due to its porous, sponge-like appearance under a microscope. However, this name is misleading if it suggests weakness. Far from being weak, its structure is an engineering marvel. The interconnected trabeculae form a resilient framework that can withstand and distribute compressive forces from multiple directions. While it is less dense than cortical bone, its design provides flexibility and shock absorption, which is essential in areas like the vertebrae and near joints.
7. How does the unique structure of cancellous bone facilitate the production of blood cells?
The structure of cancellous bone is perfectly adapted for hematopoiesis (blood cell production). The network of trabeculae creates numerous interconnected cavities, or interstitial spaces. These spaces are not empty; they are filled with red bone marrow, a highly vascular tissue containing hematopoietic stem cells. This arrangement provides a protected, nutrient-rich environment where these stem cells can proliferate and differentiate into red blood cells, white blood cells, and platelets, which then enter the bloodstream.
8. How does the metabolic rate of cancellous bone contribute to bone healing and remodelling?
Cancellous bone has a significantly higher metabolic rate than cortical bone. This is because its vast surface area (due to the trabeculae) and rich blood supply allow for a more rapid exchange of minerals and nutrients. This high metabolic turnover means that bone remodelling—the process of breaking down old bone (resorption) and forming new bone (ossification)—occurs much faster. Consequently, fractures in areas with a high proportion of cancellous bone, like the wrist or hip, often heal more quickly than fractures in the dense shaft of a long bone.
