Diaphysis of Bone: Definition & Function

Diaphysis of Bone: Definition & Function
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  • 0:02 What Is Diaphysis?
  • 0:25 Parts of the Diaphysis
  • 1:22 Bone Remodeling
  • 3:00 Functions
  • 4:50 Lesson Summary
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Lesson Transcript
Instructor: Jay Mallonee

Jay is a wildlife biologist, college professor and writer. His master's degree is in neurobiology and he has studied animal behavior since 1976.

Did you know your bones are used for more than just standing upright? This lesson looks at the fascinating contributions made by the diaphysis in long bones towards your body's overall health. At the end of the lesson, you'll find a short quiz.

What Is a Diaphysis?

Did you ever watch the beginning of the movie, 2001: A Space Odyssey? In one scene, a pre-human ape picks up a long bone and uses it to violently break apart the skeleton from which it originated. Structurally, long bones are very strong, as seen in the movie. They're long because of the shaft in the middle called the diaphysis.

Parts of the Diaphysis

Compared to the other parts that make up a long bone, the diaphysis is quite different. It has a hollow inside with an open space called the medullary cavity. The cavity is filled with yellow bone marrow, along with blood vessels that supply the living bone tissue. The light color of the marrow is due to the high concentration of fat cells, as opposed to the red marrow where blood cells are made.

As a child, all of your bone marrow was red, but as you age into adulthood, much of it becomes yellow. Red marrow is found at the ends of long bones called epiphyses, which are covered with articular cartilage used to connect, or articulate, with other bones. Epiphyses are composed of spongy bone, which look like a sponge you use in the kitchen. Its tiny chambers are filled with red marrow, a very different setup from the diaphysis. The shaft is made of compact bone, a matrix of minerals, which makes it strong and useful for supporting a good deal of weight.

Bone Remodeling

The surface of the diaphysis is often slightly irregular, rather than completely smooth, and is covered in a thin layer of connective tissue called the periosteum, which provide areas where tendons and ligaments can attach, along with adhering nerves and blood vessels to the bone surface so they can enter the diaphysis. The periosteum also houses the live cells that create and remove bone material, a process called remodeling, which constantly reshapes bones. Osteoblasts create bone material, while osteoclasts break down bone material (the prefix 'osteo' means 'bone'). If a long bone becomes broken, these cells are used in the healing process to help mend the fracture site.

Although bones constantly reshape themselves, they can only grow in length during childhood and adolescence. There is also an inherent problem with bones that grow: you still need to use them. It would be easy to just add bone material to either end, but the epiphyses are being used to connect with other bones. So how does the diaphysis become longer?

There is an area between the diaphysis and the epiphysis called the metaphysis; the prefix 'meta-' refers to being 'in the middle.' In this area, we find the epiphyseal or growth plate. Other types of bone cells, called chondrocytes, produce cartilage on the joint side of the plate, while the other side becomes calcified. In other words, minerals are added which lengthens the diaphysis. By the time bones reach their full length in adulthood, the epiphyseal plate has become completely calcified. This creates a thin, detectable area called the epiphyseal line.

Functions

The diaphysis of long bones serves several purposes, including ones you may not expect.

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