Many people with blood cancers, such as leukaemia and lymphoma, sickle cell anaemia, and other life-threatening conditions rely on bone marrow or cord blood transplants to survive.

In the below article, Pritish Kumar Halder described bone marrow, that is is soft, gelatinous tissue.

People need healthy bone marrow and blood cells to live. When a condition or disease affects bone marrow so that it can no longer function effectively, a marrow or cord blood transplant could be the best treatment option. For some people, it may be the only option.

What is bone marrow?

Bone marrow is soft, gelatinous tissue that fills the medullary cavities, or the centers of bones. The two types of bone marrow are red bone marrow, known as myeloid tissue, and yellow bone marrow, known as fatty tissue.

Both types of bone marrow are enriched with blood vessels and capillaries.

Bone marrow makes more than 220 billion new blood cells every day. Most blood cells in the body develop from cells in the bone marrow.

Bone marrow

Bone marrow stem cells

Bone marrow contains two types of stem cells: mesenchymal and hematopoietic.

Red bone marrow consists of a delicate, highly vascular fibrous tissue containing hematopoietic stem cells. These are blood-forming stem cells.

Yellow bone marrow contains mesenchymal stem cells, or marrow stromal cells. These produce fat, cartilage, and bone.

Stem cells are immature cells that can turn into a number of different types of cells.

Hematopoietic stem cells in the bone marrow give rise to two main types of cells: myeloid and lymphoid lineages. These include monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, dendritic cells, and megakaryocytes, or platelets, as well as T cells, B cells, and natural killer (NK) cells.

The different types of hematopoietic stem cells vary in their regenerative capacity and potency. They can be multipotent, oligopotent, or unipotent, depending on how many types of cells they can create.

Pluripotent hematopoietic stem cells have renewal and differentiation properties. They can reproduce another cell identical to themselves, and they can generate one or more subsets of more mature cells.

The process of developing different blood cells from these pluripotent stem cells is known as hematopoiesis. It is these stem cells that are needed in bone marrow transplants.

Stem cells constantly divide and produce new cells. Some new cells remain as stem cells, while others go through a series of maturing stages, as precursor or blast cells, before becoming formed, or mature, blood cells. Stem cells rapidly multiply to make millions of blood cells each day.

Blood cells have a limited life span. This is around 120 days for red blood cells. The body is constantly replacing them. This production of healthy stem cells is vital.

The blood vessels act as a barrier to prevent immature blood cells from leaving bone marrow.

Red bone marrow

Red bone marrow produces all red blood cells and platelets and around 60–70% of lymphocytes in human adults. Other lymphocytes begin life in red bone marrow and become fully formed in the lymphatic tissues, including the thymus, spleen, and lymph nodes.

Together with the liver and spleen, red bone marrow also plays a role in getting rid of old red blood cells.

Yellow bone marrow

Yellow bone marrow mainly acts as a store for fats. It helps provide sustenance and maintain the correct environment for the bone to function. However, under particular conditions — such as with severe blood loss or during a fever — yellow bone marrow may revert to red bone marrow.

Yellow bone marrow tends to be located in the central cavities of long bones and is generally surrounded by a layer of red bone marrow with long trabeculae (beam-like structures) within a sponge-like reticular framework.

Bone marrow timeline

Before birth but toward the end of fetal development, bone marrow first develops in the clavicle. It becomes active about 3 weeks later. Bone marrow takes over from the liver as the major hematopoietic organ at 32–36 weeks’ gestation.

Bone marrow remains red until around the age of 7 years, as the need for new continuous blood formation is high. As the body ages, it gradually replaces the red bone marrow with yellow fat tissue. Adults have an average of about 2.6 kilograms (kg) (5.7 pounds) of bone marrow, about half of which is red.

In adults, the highest concentration of red bone marrow is in the bones of the vertebrae, hips (ilium), breastbone (sternum), ribs, and skull, as well as at the metaphyseal and epiphyseal ends of the long bones of the arm (humerus) and leg (femur and tibia).

All other cancellous, or spongy, bones and central cavities of the long bones are filled with yellow bone marrow.

What’s the function of red bone marrow?

Red bone marrow is involved in hematopoiesis. This is another name for blood cell production. Hematopoietic stem cells that are found in red bone marrow can develop into a variety of different blood cells, including:

Red blood cells. These are the cells that work to carry oxygen-rich blood to the cells of the body. Old red blood cells can also be broken down in red bone marrow, but this task is mostly performed in the liver and spleen.

Platelets. Platelets help your blood clot. This prevents uncontrolled bleeding.

White blood cells. There are several types of white blood cells. They all work to help your body fight off infections.

Newly produced blood cells enter your bloodstream through vessels called sinusoids.

As you age, your red bone marrow is gradually replaced with yellow bone marrow. By adulthood, red bone marrow can be found only in a handful of bones, including the:

  • skull
  • vertebrae
  • sternum
  • ribs
  • the ends of the humerus (upper arm bone)
  • pelvis
  • the ends of the femur (thigh bone)
  • the ends of the tibia (shin bone)

What’s the function of yellow bone marrow?

Yellow bone marrow is involved in the storage of fats. The fats in yellow bone marrow are stored in cells called adipocytes. This fat can be used as an energy source when needed.

Yellow bone marrow also contains mesenchymal stem cells. These are cells that can develop into bone, fat, cartilage, or muscle cells. Because yellow bone marrow starts to replace red bone marrow over time, most bones in an adult body contain yellow bone marrow.

Which conditions involve bone marrow?

Bone marrow is crucial for producing blood cells. Therefore, a range of blood-related conditions involve issues with bone marrow. Many of these conditions affect the numbers of blood cells produced in bone marrow. This causes the conditions to share many common symptoms, including:

Fever. This can be a result of not having enough healthy white blood cells.

Fatigue or weakness. This is caused by a lack of hemoglobin, the protein in red blood cells that carries oxygen.

Increased infections. This is due to having fewer healthy white blood cells, which help fight infections.

Shortness of breath. A lower red blood cell count can result in less oxygen being delivered to tissues in your body.

Easy bleeding and bruising. This is due to having fewer healthy platelets, which are important for helping your blood to clot.


Leukemia is a type of cancer that can affect both your bone marrow and lymphatic system.

It happens when blood cells get mutations in their DNA. This causes them to grow and divide more rapidly than healthy blood cells. Over time, these cells start to crowd out the healthy cells in your bone marrow.

Some of the major types of leukemia include:

acute myeloid leukemia (AML)

chronic myeloid leukemia (CML)

acute lymphocytic leukemia (ALL)

chronic lymphocytic leukemia (CLL)

Aplastic anemia

Aplastic anemia occurs when bone marrow doesn’t produce enough new blood cells. It occurs due to damage to the stem cells of bone marrow, which makes it harder for them to grow and develop into new blood cells.

Myeloproliferative disorders

Myeloproliferative disorders happen when the stem cells in bone marrow grow abnormally. This can lead to increased numbers of a specific type of blood cell. There are several types of myeloproliferative disorders, including:

  • Primary myelofibrosis. With this condition, red blood cells don’t develop normally and have an unusual shape. It can also cause a decrease in red blood cell production.
  • Polycythemia vera. Bone marrow produces too many red blood cells. These extra cells may collect in the spleen, causing swelling and pain. Itching is also a common symptom of polycythemia vera, possibly because of an abnormal histamine release.
  • Essential thrombocythemia. Bone marrow produces too many platelets, making blood sticky or thick. This slows down the flow of blood through the body.
  • Hypereosinophilic syndrome. Bone marrow produces too many eosinophils. This is a type of white blood cell involved in allergic reactions and destroying parasites. This may lead to itching or swelling around the eyes and lips.
  • Systemic mastocytosis. This condition involves having too many mast cells. These are white blood cells that alert infection-fighting blood cells to target specific areas of the body. Having too many mast cells can affect the function of your skin, spleen, bone marrow, or liver.