What is the Difference Between Epiphysis and Diaphysis

The main difference between epiphysis and diaphysis is that epiphysis is the rounded end of a long bone, at its joint with adjacent bone(s), whereas diaphysis is the main or midsection (shaft) of a long bone. Furthermore, epiphysis is made up of spongy bone while diaphysis is made up of cortical bone.

Epiphysis, metaphysis, and diaphysis are three different parts of a long bone. Each part of the long bone has a unique function.

Key Areas Covered

1. What is Epiphysis
     – Definition, Structure, Function
2. What is Diaphysis
     – Definition, Structure, Function
3. What are the Similarities Between Epiphysis and Diaphysis
     – Outline of Common Features
4. What is the Difference Between Epiphysis and Diaphysis
     – Comparison of Key Differences

Key Terms

Cortical Bone, Diaphysis, Epiphysis, Long Bone, Red Bone Marrow, Spongy Bone

What is Epiphysis

Epiphysis is the rounded end of a long bone. Its main function is to form joints with adjacent bones. The other prominent region of the long bone is diaphysis, which is its shaft. In between epiphysis and diaphysis, there is another part of the long bone; we call this metaphysis. Metaphysis contains the growth plate of the epiphysis known as the epiphyseal plate. Furthermore, the epiphysis is covered by articulate cartilage at the joint. Meanwhile, subchondral bone is the bone below the articulate cartilage and its growth plate.

Figure 1: Inferior Epiphysis of Humerus

Furthermore, epiphysis is made up of spongy bone also known as trabecular bone. The main functional unit of this type of bone tissue is the trabecula, which forms a structural framework of the bone. The space between the trabeculae contains red bone marrow, which undergoes hematopoiesis. Moreover, osteoblasts that surround the epiphysis are responsible for the conversion of spongy bone to compact bone.

What is Diaphysis

The diaphysis is the long, narrow shaft of the long bone. Many muscles are attached to the shaft of a long bone. Therefore, long bone can involve in the movement of the limbs of the body. Generally, diaphysis is attached to the epiphyses from both ends through the metaphysis. In addition, the outer layer of the diaphysis is made up of cortical bone, which is a type of dense and hard bone tissue. In contrast, the medullary cavity of the diaphysis contains yellow bone marrow.

Figure 2: Structure of a Long Bone

Moreover, the main functional unit of the compact bone of diaphysis is the osteon. An osteon contains a central canal – Haversian canal. Lamellae make up of bone matrix surrounding the central canal. Inside small cavities known as lacunae, osteocytes occur and lacuna is connected with each other by canaliculi. Blood vessels, lymphatic vessels, and nerves pass through the central canal.

Similarities Between Epiphysis and Diaphysis

• Epiphysis and diaphysis are two parts of a long bone.
• Bone tissues make up both these parts.
• Their main function is to make up the skeletal system, providing shape and support to the animal.
• Also, they contain osteoblasts and osteoclasts responsible for creating bones.
• Furthermore, collagen and other proteins and inorganic mineral salts make up their matrix.
• Both also contain nerves, blood vessels, and bone marrow.
• Moreover, cartilage and membranes including endosteum and periosteum cover them. 

Difference Between Epiphysis and Diaphysis

Definition

Epiphysis refers to the end part of a long bone, initially growing separately from the shaft, while diaphysis refers to the shaft or central part of a long bone. Thus, this is the main difference between epiphysis and diaphysis.

Shape

While epiphysis makes up the swollen rounded ends of the long bone, diaphysis makes up the long and narrow region of the long bone.

Occurrence

Two epiphyses occur at the proximal and distal end of a long bone while single diaphysis occurs per long bone.

Made up of

Another difference between epiphysis and diaphysis is their composition. Epiphysis is made up of spongy bone while diaphysis is made up of cortical bone.

Functional Unit

The functional unit of the epiphysis is the trabecula while the functional unit of the diaphysis is the osteon.

Marrow Cavity

Furthermore, epiphysis contains a marrow cavity while diaphysis lacks a marrow cavity.

Type of Bone Marrow

Also, one other difference between epiphysis and diaphysis is that epiphysis contains red bone marrow while diaphysis contains yellow bone marrow.

Amount of Calcium

Amount of calcium is another difference between epiphysis and diaphysis. Epiphysis contains a less amount of calcium while diaphysis contains a higher amount of calcium.

Porosity

Furthermore, epiphysis is more porous while diaphysis is less porous.

Strength

Strength is another difference between epiphysis and diaphysis. Diaphysis is stronger than epiphysis.

Function

Moreover, epiphysis articulates with other bones, forming joints, while diaphysis provides sites for the attachment of bones.

Conclusion

The epiphysis is the swollen, and rounded region of a long bone. Two epiphyses occur per long bone. Generally, the epiphysis is made up of spongy bone. It contains a marrow cavity filled with red bone marrow. The main function of the epiphysis is to make an attachment with other bones, forming joints. In contrast, diaphysis is the long, narrow shaft of a long bone. It is made up of cortical bone. It does not contain a marrow cavity and it contains yellow bone marrow. The main function of the diaphysis is to provide sites for the attachment of muscles. However, the main difference between epiphysis and diaphysis is their shape and composition.

References:

1. Biga, Lindsay M., et al. “Anatomy & Physiology.” 6.3 Bone Structure | Anatomy & Physiology, Open Oregon State, Oregon State University, Available Here.

Image Courtesy:

1. “Inferior epiphysis of humerus” By Anatomist90 – Own work (CC BY-SA 3.0) via Commons Wikimedia   
2. “603 Anatomy of Long Bone” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia