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What is Bone Marrow?

S. Mithra
S. Mithra

Bone marrow is a distinctive class of tissue that fills the cores of larger bones in humans and other animals. Unlike the hard, or compact, tissue that forms the outer shells of bones, the marrow has a malleable, sponge-like texture. It serves an active function in the body by producing all three types of blood cells, as well as lymphocytes, which support the immune system. Transplants are frequently performed in patients whose own marrow has become diseased. Additionally, marrow is a major source of stem cells, which can be harvested for certain medical treatments. Rich in nutrients, bone marrow even makes a highly desirable food source for animals as well as for humans in numerous cultures.

Bones that Contain Marrow

Three pieces of bone with the marrow in the middle.
Three pieces of bone with the marrow in the middle.

In humans, marrow is found in the interior of most major bones of the body. These include flat bones such as the sternum, skull, and pelvis, as well as most long bones, such as the humerus and the femur. Other smaller bones, by contrast, like those in the spine and lower jaw, contain little or no marrow. Marrow is referred to as a spongy bone. It's infused with blood vessels that supply oxygen and carry away newly created cells.

Types of Marrow

A diagram of the anatomy of a bone, including the marrow.
A diagram of the anatomy of a bone, including the marrow.

There are two categories of bone marrow: yellow and red. The yellow type mostly contains fat, and serves to provide sustenance and maintain the correct environment for the bone to function. It tends to be located in the center-most cavities of long bones, and is generally surrounded by a layer of red marrow. Red marrow is directly involved in cell production. As a body ages, the quantity of red marrow tends to shrink while the amount of yellow marrow increases, but it tends to have the strongest concentrations in flat bones such as the sternum or ilium.

Function

Red blood marrow is one of the two categories of bone marrow, along with yellow.
Red blood marrow is one of the two categories of bone marrow, along with yellow.

Immature stem cells, along with extra iron, can be found inside bone marrow. These stem cells wait until weak, unhealthy, or damaged cells need to be replaced, and then differentiate, or become specialized. An undifferentiated stem cell can, for example, turn into a red or white blood cell or a platelet. Likewise, lymphocytes, part of the lymphatic system, are formed in this way. This is how such cells get replaced to keep the body healthy, making healthy bone marrow tissue crucial in fighting pathogens like fungi, bacteria, and viruses.

Long bones, like the tibia and fibula, are those bones whose length exceeds their width.
Long bones, like the tibia and fibula, are those bones whose length exceeds their width.

A number of diseases, often incurable, pose a threat to bone marrow. Put simply, they prevent it from turning stem cells into essential cells. Leukemia, Hodgkin's Disease, and other lymphoma cancers are known to damage the marrow's productive ability and destroy stem cells.

Bone Marrow Transplants and Stem Cell Harvesting

The leading treatment for conditions that threaten the marrow's ability to function is a bone marrow transplant. This procedure typically begins with chemotherapy to eliminate the compromised marrow. A matching donor must then be found; in most cases, this is a close family member. A needle is usually used to extract the donor's red marrow, often from one of the pelvic bones. The red marrow is then injected into the patient's bloodstream. With luck, the donation will "take," and make its way into the central shaft of larger bones to restore stem cell function.

Bone marrow is found in many of the body's long bones, such as the femur.
Bone marrow is found in many of the body's long bones, such as the femur.

Through a similar procedure, stem cells themselves can be harvested for certain cancer treatments, as well as for ongoing medical research into other potential medical uses. Stem cells may either be directly extracted, in the same way as they are for bone marrow transplants, or medication can be given that stimulates the marrow to release the cells into the bloodstream. In the latter case, after blood is drawn from the donor, the stem cells are then filtered out.

As a Food Source

The high concentration of fat, as well as minerals including iron, make bone marrow an eagerly sought food source. Many species of animals chew on large bones of their prey, even after the meat is gone, in order to crack them open and gain access to the treat held within. Likewise, it is considered a delicacy in a variety of human cultures around the world, ranging from parts of Europe to Asia and the Americas.

Discussion Comments

anon975048

@anon942777: People who have a bone marrow transplant and the donors for the one who is getting the BMT are not paralyzed. The donor is sore for a few days to a week, but that is it. The only reason why I know this is because I had a bone marrow transplant for ALL. This is a type of leukemia called Acute Lymphocytic Leukemia.

anon942777

After a bone marrow transplant, is the donor paralyzed?

anon158373

bone marrow cancer is not something any one should joke about. i take it very personally! my mother got sick with it at the age of 32 and died at the age of 37 with it. people should have a little more respect for things!

anon68412

That's so wrong even to joke about. What if someone was dumb enough to actually try that? Does this relate to bone marrow?

anon63894

Bone marrow is harmful more than cancer and its treatment is as expensive as transplant. the other treatment is given through injections but that is not reliable.

anon62791

"4: Try it from a high building, Einstein - anon22431"

That's so wrong even to joke about. What if someone was dumb enough to actually try that?

anon62251

now it is true that you can levitate or fly by magnetizing the iron in you nervous system. i've tried it.

anon38923

Well anon1741 if you could levitate or fly by magnetizing the iron in your nervous system without destoying the nervous system itself you could, quite possibly, and with a powerful enough magnitized force, be able to fly. But those are all pretty big if's.

anon27670

The bone marrow is the red blood cells, the fatty part, and stem cells, right? But what part of a bone marrow transplant is used from the marrow? The fat, the blood and/or only the stem cells?

anon22431

Try it from a high building, Einstein

anon1741

I was wondering how much iron can be stored in bones. i'm a physicist and a runner. i discovered some equations that say you can condense all the laws of physics into 8 words. If copper is high, molybdenum is low, iron. i was wondering if i had a strong enough electrical current because of my nervous system if i could magnetize all the stores of iron in my bones. if i can control the nervous current with my brain could one produce enough force to levitate or fly?

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    • Three pieces of bone with the marrow in the middle.
      By: Maurice Metzger
      Three pieces of bone with the marrow in the middle.
    • A diagram of the anatomy of a bone, including the marrow.
      By: Alila
      A diagram of the anatomy of a bone, including the marrow.
    • Red blood marrow is one of the two categories of bone marrow, along with yellow.
      By: Alila Medical Media
      Red blood marrow is one of the two categories of bone marrow, along with yellow.
    • Long bones, like the tibia and fibula, are those bones whose length exceeds their width.
      By: andreaxt
      Long bones, like the tibia and fibula, are those bones whose length exceeds their width.
    • Bone marrow is found in many of the body's long bones, such as the femur.
      By: maya2008
      Bone marrow is found in many of the body's long bones, such as the femur.