What Is the Difference between the Epiphysis and Diaphysis?

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  • Written By: Rebecca Harkin
  • Edited By: Melissa Wiley
  • Last Modified Date: 23 March 2017
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The epiphysis and diaphysis are different parts of a long bone, or a bone found in a limb. Knobby ends of a long bone are referred to as the epiphyses, and the diaphysis is the shaft or middle section of the long bone. The epiphysis and diaphysis are different in their size, structure, and function. Separating them is a part of the bone known as the metaphysis.

One of the main differences between the epiphysis and diaphysis is their shape. The swollen rounded ends of the long bone are the epiphyses. These structures look somewhat similar to a clenched fist. Tubular and centrally positioned, the diaphysis makes up the main shaft of the long bone. On a long bone, the diaphysis is much larger than the epiphysis.

Structurally, the epiphysis and diaphysis are also distinct. The epiphysis is composed of compact or cortical bone on the outside and spongy, or trabecular, bone on the inside. Compact bone is fairly dense, providing strength. In the epiphysis, the spongy bone is slightly porous, leaving some space for red bone marrow and blood vessels. The porous nature of spongy bone also lightens the weight of the bone.

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The diaphysis is composed of compact bone surrounding a marrow cavity filled with a fairly porous yellow marrow. Both red and yellow marrow are packed with blood vessels and capillaries to feed the bone. Red marrow contains white and red blood cells and platelets. Yellow marrow contains primarily fat cells, with some white blood cells.

Functionally, the epiphysis and diaphysis are very different. The epiphysis is the site of bone growth and is also often the place where a tendon anchors onto the long bone. In children, an epiphyseal plate is located between the epiphysis and the metaphysis. Long bones elongate when new cartilage, produced in the epiphyseal plate, is pushed to the edge of the epiphysis while older cartilage, located at the diaphysis side of the epiphysis plate, gets converted into bone.

When the body has finished growing, the epiphyseal plate ceases to manufacture new cartilage. Gradually, the cartilage in the plate area is transformed into bone. Once this occurs, the epiphyseal plate disappears and all that is left behind is a small line in the epiphysis area that is henceforth referred to as the epiphyseal line.

In contrast, the function of the diaphysis is to structurally support the body. With a thick outer shell of compact bone encompassing a porous inner cavity, this bone is perfectly constructed for this task. The outer margin of the diaphysis can bear the weight, while the inner core can house the marrow and minimize the weight of the bone.

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Discuss this Article

Certlerant
Post 2

Bones are a good way to see the physical changes man has gone through but looking at residences of ancient man can yield big dividends as well.

Some of the earliest digs show how man lived, how they hunted and showed the diet of our ancestors.

Tool fragments are the real finds in these digs. Some of these tools showed man's early ingenuity as well as his ability to adapt.

Telsyst
Post 1

Studying bones is one of the only ways to see where mankind has come.

Charles Darwin's theory of evolution has scientists digging up older versions of humanity to see how mankind became what we are today.

A scientist is lucky if they can get a specimen of a large intact bone to study. Often they have bits of bone pieces. There are many gaps in the actual progression of our evolution because there are just not enough clues, in the form of bones, to piece together.

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