Difference Between Compact and Cancellous Bone

The key difference between compact and cancellous bone is their structure. Compact bone is the harder outer shell of the bone while cancellous bone is the inner porous, less dense layers of the bone.

Bones are important components in assisting movement and granting a shape to the body. Bones are components of the skeletal system. The human skeleton is made up of 206 bones. Mainly, the human skeleton has two main divisions upon maturity (reaching maximum density); axial and appendicular skeleton. Apart from supporting the movement and providing a shape to the body, the skeletal system also provides protection, production of blood cells, mineral storage and endocrine regulation. Compact bone and cancellous are two types of bones present within the bone tissue.

CONTENTS

1. Overview and Key Difference
2. What is Compact Bone
3. What is Cancellous Bone
4. Similarities Between Compact and Cancellous Bone
5. Side by Side Comparison – Compact vs Cancellous Bone in Tabular Form
6. Summary

What is Compact Bone?

Compact bone is the cylindrical harder outer layer of the bone. In other terms, they are the cortical bones; the densest and strongest bones in the body. For healthy maintenance of the bone, compact bones possess small passages for nerves and blood vessels. Compact bone consists of yellow bone marrow mainly for the storage of fat.

Moreover, periosteum and endosteum cover the compact bone from outside and inner surface respectively. The endosteum is thin connective tissue. Also, the marrow cavities of long bones are lined by the endosteum.

In the compact bone, the osseous tissue constitutes osteocytes. A solid extracellular matrix surrounds these osteocytes. The matrix consists of hydroxyapatite, which is a compound rich in calcium and phosphorus. Within the hydroxyapatite matrix, collagen fibres are interspersed. This structure provides flexibility to the compact bone.

Figure 01: Compact Bone

The compact bone is made up of osteons, which are the main structural units of the compact bone. Small central canals surround these osteons. In the process of fetal development, osteogenic cells (osteocytes) secrete the bone matrix. Consequently, lacuna is the cavity which contains these osteocytes. Moreover, a network of small canals called canaliculi supplies oxygen and nutrients to the osteocytes.

What is Cancellous Bone?

Cancellous bone, also termed as spongy bone is the cuboidal, inner, porous, less dense, osseous tissue found in the middle region of the bone. Cancellous bones are present in the interior portion of the long bones. In comparison to compact bones, cancellous bones are less dense and lighter. Their matrix consists of trabeculae; mineral bars that arrange a latticework of three dimensional. Moreover, red bone marrow and blood vessels fill the spaces of this 3D lattice. These spaces are interconnected through canaliculi.

Figure 02: Cancellous Bone

Besides, the enlarged ends of the long bones mainly consist of the cancellous bones. These end structures are epiphyses. Protection is the main function of epiphyses. Epiphyses are present in flat bones of the skull, ribs, shoulder blades, etc. A majority of flat bones of the skeleton are composed of cancellous bones.

Moreover, cancellous bones possess a high activity of metabolism. Due to the action of osteoblasts, cancellous bones can be transformed into compact bones. Accordingly, one of the main functions that carry out by the cancellous bone is the red blood cell production (hematopoiesis). It occurs within the red bone marrow of the cancellous bone.

What are the Similarities Between Compact and Cancellous Bone?

  • Compact and cancellous bone are two types of bones.
  • Both are made up of the osseous
  • Also, both contain calcium.
  • Furthermore, the main function of both bone types is the assisting in the movement of the body.

What is the Difference Between Compact and Cancellous Bone?

When considering a long bone, there are two main regions of it. Compact bone is the outer cylindrical harder bone. Cancellous bone is the inner soft cuboidal porous bone. Therefore, this is the key difference between compact and cancellous bone. Furthermore, the skeletal bones have more than 80% of compact bones and only 20% of spongy bones. Hence, this is also a difference between compact and cancellous bone.

Also, a further difference between compact and cancellous bone is that the compact bones contain high amounts of calcium compared to cancellous bones. Hence, compact bones are harder and highly dense compared to cancellous bones. Moreover, compact bones posses yellow bone marrow and involved in fat storage. On the other hand, cancellous bones contain red bone marrow and involve in red blood cell production. Therefore, this is another significant difference between compact and cancellous bone.

The following infographic illustrates more facts on the difference between compact and cancellous bone.

Summary – Compact vs Cancellous Bone

Compact and cancellous bones are two types of bones. In summary of the difference between compact and cancellous bones, the compact bone is the cylindrical harder outer layer of the bone. They are made up of osteons, and they contain high levels of calcium. On the other hand, cancellous bone is the cuboidal inner porous, less dense, osseous tissue found in the middle region of the bone. Also, they are soft bones and possess lots of spaces within them. Moreover, compact bones occur in the outer surface and cancellous bones occur in the middle region of the long bones. Furthermore, compact bones account for the 80% of the bone weight while the rest occupies by the cancellous bone.

Reference:

1.Study.com, Study.com. Available here 
2.Britannica, The Editors of Encyclopaedia. “Compact Bone.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 Mar. 2018. Available here  

Image Courtesy:

1.”Illu compact spongy bone”By SEER – U.S. National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) Program (Public Domain) via Commons Wikimedia  
2.”606 Spongy Bone”By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia