Difference Between Compact Bone and Spongy Bone

The key difference between compact bone and spongy bone is that the compact bone is a tough and heavy bone that forms the diaphysis of long bones while the spongy bone is a soft and light bone that forms the epiphysis of long bones.

Bones are hard organs inside our bodies that make up our skeletal system. They serve the purpose of protecting our bodies and also provide a structure and shape to our bodies. Moreover, bones are important as they produce red and white blood cells and also provide a place for storing minerals. Structurally, there are 206 bones in an adult human body, and they come in different shapes and sizes. The longest bone of the human body is femur (one of two bones in the lower leg). Based on the nature of the bone, there are two types of skeletal bones. Namely, they are the compact bones and spongy bones. These two bones differ from each other mainly structurally while they differ functionally too. Compact bone tissues form the outer layer of the bones and they are harder bones. On the other hand, spongy bone tissues form the inner layer of the bones and they are sponge-like soft bones. Likewise, functionally also they share several differences.

CONTENTS

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

What is Compact Bone?

Compact bone lies at the outer layer of the long bones. It is a harder bone. Furthermore, compact bone tissue has very few gaps and spaces (thus has very little porosity). A larger portion of a bone occupies the compact bone. It is also called dense bone or cortical bone because of its low porosity.

The building blocks of the compact bones are osteons. They are concentric structures that are organized in the extracellular matrix or the lamella. Osteons tightly arrange within the compact bone tissue. Hence, it appears as a nonporous harder dense bone. In each osteon, there is a central canal which possesses blood vessels. Furthermore, compact bone contains yellow marrows that aid in fat storage. Structurally, compact bones have a higher calcium composition than the spongy bones. Generally, human skeleton comprises more than 80% of compact bones.

What is Spongy Bone?

Spongy bone is a porous soft bone that makes the interior side of the long bone. It is also called cancellous bone. The building blocks of the spongy bone are trabeculae (spicule-like structures). These trabeculae do not possess a central canal.

Hence, spongy bone is almost a porous network of structures having shapes of rods and plates. Spongy bones make up only 20% of the mass in a bone. However, their surface area is ten times larger than that of compact bones in the human skeleton. Also, compared to the compact bones, spongy bones are less dense and lighter and do not contain osteons. Furthermore, spongy bone has a low level of calcium. However, spongy bones contain red bone marrows that carry out hematopoiesis.

What are the Similarities Between Compact Bone and Spongy Bone?

• Compact bone and spongy bone are components of the osseous.
• Both are skeletal bones.
• Furthermore, both are structural bones.
• Therefore, they provide shape and structure to organisms.
• Also, they support the functions of muscles.

What is the Difference Between Compact Bone and Spongy Bone?

Compact and spongy bones are two types of bones present in a long bone of the human skeleton. 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, spongy bone is the cuboidal, less dense, osseous tissue found in the inner region of the bone. They are soft bones and possess lots of spaces within them. Hence, the key difference between compact bone and spongy bone is their structure.

Furthermore, a notable difference between compact bone and spongy bone is that more than 80% of the skeletal bones are compact bones while only 20% are spongy bones. However, spongy bones have a larger surface area than the compact bones. This is due to the trabeculae of the spongy bones.

The below infographic illustrates the difference between compact bone and spongy bone as a side by side comparison.

Summary – Compact Bone vs Spongy Bone

Compact and spongy bones are not different types of bones but rather different parts of a single bone. Compact bone tissues are the shaft or the outer part of the long bone. It is dense and strong. Spongy bone tissues are found on the inside of a long bone. They are porous and have a sponge-like an appearance having holes in them. It is the part of the bone where blood is made. Here, the yellow bone marrow is found in the cavities of compact bone tissues whereas the red bone marrow is found in spongy bone tissues. Bone tissues are classified as compact or spongy based on proportions of mineralised and soft tissues. Furthermore, Haversian system is present in compact bone tissue, but it is absent in the case of spongy bone tissues. Thus this summarizes the difference between compact bone and spongy bone.

Reference:

1.Editors. “Compact Bone Structure.” Biology Dictionary, Biology Dictionary, 5 Nov. 2017. Available here  
2.Wendy. “Human Anatomy and Physiology Lab (BSB 141).” Lumen Learning, Lumen. Available here 

Image Courtesy:

1.”Structure of a Long Bone”By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work, (CC BY 3.0) via Commons Wikimedia  
2.”Spongy bone – trabecules” (CC BY-SA 3.0) via Commons Wikimedia