CANCELLOUS BONE: CHARACTERISTICS, FUNCTIONS AND HISTOLOGY - ANATOMY AND PHYSIOLOGY - 2025

The cancellous bone, also known as trabecular bone, is one of two types of bone tissue that can be found in the human body. It is at the ends of the long bones (the epiphyses), with the harder compact bone surrounding it. It is also inside the vertebrae, in the ribs, in the skull and in the bones of the joints.

The bone matrix is ​​organized in a three-dimensional network of bone processes, called trabeculae, arranged along lines of tension. The spaces between them are generally filled with marrow and blood vessels. It is porous in character and contains red bone marrow, where blood cells are produced.

Cancellous bone is softer and weaker than compact bone, but it is also more flexible. This bone also has a considerably high level of metabolic activity.

General characteristics

Composed of osteocytes

Cancellous bone is made up of osteocytes, which are found in small cavities known as lacunae.

These osteocytes are the mature form of osteoblasts, which are the cells that synthesize and deposit bone matrix and trabeculated bone (the components of cancellous bone), as well as mineralize external compact bone.

When the osteoblast is surrounded by pure bone material created by itself, it is called an osteocyte, and the lagoon that surrounds it is nothing more than the bone created and deposited by it.

20% of the skeleton

Cancellous bone makes up about 20 percent of the human skeleton, provides structural support and flexibility. It is found in most parts of the bone that are not subjected to great mechanical stress.

Trabecula

It is formed by a matrix network called the trabecula; this is responsible for the fluffy appearance. Three types of bone cells are found inside the trabeculae: osteoblasts, osteocytes, and osteoclasts.

Osteoblasts produce new bone. They generate layers of hard tissue composed of calcium and phosphate until they are fully covered, at which point they become osteocytes.

Osteoclasts are larger cells. They act as a kind of white blood cells of the bone, since their function is to incorporate and degrade the old bone, giving rise to the osteoblasts so that they can deposit new bone.

Osteoblasts and osteoclasts act to regulate bone density, and due to an imbalance in this relationship, degenerative bone diseases arise, such as osteopenia, osteoporosis and osteomalacia.

Fabric composition

Regarding tissue, cancellous bone is a polymeric ceramic compound with a composition similar to that of cortical bone. By mass, bone tissue is 65% mineral (calcium and phosphorus), 25% organic, and 10% water.

These proportions vary according to the age of the individual and the length of time the tissue has been present in the body.

The open structure aids in the damping of sudden stresses, such as in the transmission of load through the joints.

There are different proportions of bone space in different bones due to the need for strength or flexibility. In addition, their fenestrations give rise to the growth of the bone marrow, an essential organ for the functioning of the blood.

Features

Bone marrow storage

The bone marrow is formed when the trabecular matrix agglutinates the blood vessels and they condense. Cancellous bone is ideal for the formation and storage of bone marrow within the trabecular network.

The cancellous bone, being highly vascular and having fenestrations, allows the development of the bone marrow, an organ that serves as the perfect niche for the development of stem cells into blood cell precursors, both of the red blood cell and platelet lineage (erythromegakaryocytic) such as the specialized white blood cell lineage (lymphocytic).

Once they have completed their maturation in this tissue, they leave it through the blood vessels, which continue through the trabeculae towards the end of the bone (neck), where they exit towards the systemic circulation and can start their functions as mature cells.

Erythropoiesis site

Inside the cancellous bone, red blood cells are produced in the red bone marrow. This production is generated due to the highly vascularized nature of cancellous bone, which supplies adequate amounts of glucose, lipids, amino acids and trace elements necessary for the production of red blood cells.

Reduces the weight of the skeleton

Cancellous bone has a light weight, low density that balances the heavier and denser compact bone, reducing the overall weight of the human skeleton.

This makes it easier for the muscles to move the limbs, and is ideal for evenly distributing the weight of the body on the bones, so that too much pressure is not placed on the tip and shaft, particularly thin and delicate areas of long bones (such as the femur, tibia and fibula in the lower limbs).

Adds strength and flexibility to bones

The strength and flexibility of the bone is due to the formation of the trabeculae along the stress lines. Similarly, cancellous bone is present in the joints of the body, serving as a shock absorber when walking, running, and jumping.

Mineral storage

99% of the calcium and 85% of the phosphorus in the body are stored in the human skeleton. The mineral content of the blood must be regulated to achieve the ideal function of the muscles and the nervous system.

Histology

Most of the cancellous bone is made up of elastic proteins of the extracellular matrix, such as type I collagen and cell adhesion proteins, which allow the interaction between bone marrow cells for their proper maturation.

However, the extracellular matrix in cancellous bone is deposited in the form of foldable and intercrossed sheets, giving it a trabeculated appearance for which it is also known as trabeculated bone. The importance of the presence of these trabeculae has already been discussed previously.

Towards the periphery, the osteoblasts are located in columns, which synthesize and deposit a protein called osteoid, which is mineralized with calcium and phosphorus to form the external mineral bone.

Also towards the periphery are bone stem cells and osteoclasts, regulating the activity of osteoblasts. Towards the center, the trabeculae, lacunae and in the center are the osteocytes.

References

1. Christopher J. Hernandez, sf, Cancellous Bone: springer.com
2. Cancellous Bone: Definition, Structure & Function, sf: study.com
3. Cancellous bone, nd, Encyclopedia Britannica: britannica.com
4. Dr Arun Pal Singh, sf, Cortical Bone and Cancellous Bone, Bone and Spine: boneandspine.com
5. Spongy Bone, sf, Biology Dictionary: biologydictionary.net