Bone Marrow: Anatomy & Types

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  • 0:00 Bone and Bone Marrow
  • 0:40 Definition and Location
  • 2:12 Types of Bone Marrow
  • 2:51 Function
  • 3:55 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Bone marrow is the soft, spongy material that fills the inner core of our bones. In this this lesson, learn more about where it is found, the different types, and how it serves the body.

Bone and Bone Marrow

What do you think of when you hear the word 'bones?' You may recall gnawing on one last night at dinner. Or, you may picture the skeleton that gets put up on your neighbor's lawn every Halloween. You might even wince at the memory of a broken bone.

But what do you think of when you try to picture bone marrow? The image of a round soup bone with mushy stuff in the middle may have just popped into your head. Or, maybe you are familiar with a life-saving procedure called a bone marrow transplant. At any rate, bone marrow may not be as recognizable as a bone itself, but it plays a very important role in our body.

Definition and Location

The framework of our body is a skeleton made up of many different bones. You may have a general idea of which bones are located in various parts of your body. For instance, the bones in our head make up our skull and jaw. We have many small bones connected by cartilage that make up our backbone. And, our arms and legs each have one large bone on top and then two smaller bones below connected to it by a joint.

So, where does bone marrow enter the picture, and where is it located within a bone? Let's think back to the soup bone with the mushy stuff in the middle. That is exactly where the marrow is located. Bone marrow is the light, spongy tissue found in the inner core of many different bones in our body. Different from the cooked soup bone, in a living organism it is a light and spongy tissue surrounded by the dense shell of the bone.

Bone marrow is a type of connective tissue. It is made of a variety of cells within a soft and fibrous framework. There are many blood vessels throughout the marrow, which deliver oxygen and carry away newly formed cells. Bone marrow is found in bones such as the sternum (breastbone), ribs, pelvis, and skull. It is also found in the large bones of the arms (the humerus) and the legs (the femur).

Some marrow is found in what is called spongy bone. If you can imagine a sponge, the structure of spongy bone is similar. There is a light bone framework with lots of holes and spaces filled with marrow. Marrow also fills the open core of some long bones. The hard outer shell of a bone is called compact bone.

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