Bone marrow

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For bone marrow as eaten by humans, see Bone marrow (food). Bone marrow_sentence_0

Bone marrow_table_infobox_0

Bone marrowBone marrow_header_cell_0_0_0
DetailsBone marrow_header_cell_0_1_0
SystemBone marrow_header_cell_0_2_0 Hematopoietic system Immune system Lymphatic systemBone marrow_cell_0_2_1
IdentifiersBone marrow_header_cell_0_3_0
LatinBone marrow_header_cell_0_4_0 Medulla ossiumBone marrow_cell_0_4_1
MeSHBone marrow_header_cell_0_5_0 Bone marrow_cell_0_5_1
TA98Bone marrow_header_cell_0_6_0 Bone marrow_cell_0_6_1
TA2Bone marrow_header_cell_0_7_0 Bone marrow_cell_0_7_1
FMABone marrow_header_cell_0_8_0 Bone marrow_cell_0_8_1

Bone marrow is a semi-solid tissue found within the spongy or cancellous portions of bones. Bone marrow_sentence_1

In birds and mammals, bone marrow is the primary site of new blood cell production or haematopoiesis. Bone marrow_sentence_2

It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells. Bone marrow_sentence_3

In adult humans, bone marrow is primarily located in the ribs, vertebrae, sternum, and bones of the pelvis. Bone marrow_sentence_4

Bone marrow comprises approximately 5% of total body mass in healthy adult humans, such that a man weighing 73 kg (161 lbs) will have around 3.65 kg (8 lbs) of bone marrow. Bone marrow_sentence_5

Human marrow produces approximately 500 billion blood cells per day, which join the systemic circulation via permeable vasculature sinusoids within the medullary cavity. Bone marrow_sentence_6

All types of hematopoietic cells, including both myeloid and lymphoid lineages, are created in bone marrow; however, lymphoid cells must migrate to other lymphoid organs (e.g. thymus) in order to complete maturation. Bone marrow_sentence_7

Bone marrow transplants can be conducted to treat severe diseases of the bone marrow, including certain forms of cancer such as leukemia. Bone marrow_sentence_8

Additionally, bone marrow stem cells have been successfully transformed into functional neural cells, and can also potentially be used to treat illnesses such as inflammatory bowel disease. Bone marrow_sentence_9

Structure Bone marrow_section_0

The composition of marrow is dynamic, as the mixture of cellular and non-cellular components (connective tissue) shifts with age and in response to systemic factors. Bone marrow_sentence_10

In humans, marrow is colloquially characterized as "red" or "yellow" marrow (Latin: medulla ossium rubra, Latin: medulla ossium flava, respectively) depending on the prevalence of hematopoietic cells vs fat cells. Bone marrow_sentence_11

While the precise mechanisms underlying marrow regulation are not understood, compositional changes occur according to stereotypical patterns. Bone marrow_sentence_12

For example, a newborn baby's bones exclusively contain hematopoietically active "red" marrow, and there is a progressive conversion towards "yellow" marrow with age. Bone marrow_sentence_13

In adults, red marrow is found mainly in the central skeleton, such as the pelvis, sternum, cranium, ribs, vertebrae and scapulae, and variably found in the proximal epiphyseal ends of long bones such as the femur and humerus. Bone marrow_sentence_14

In circumstances of chronic hypoxia, the body can convert yellow marrow back to red marrow to increase blood cell production. Bone marrow_sentence_15

Hematopoietic components Bone marrow_section_1

See also: Hematopoietic system Bone marrow_sentence_16

At the cellular level, the main functional component of bone marrow includes the progenitor cells which are destined to mature into blood and lymphoid cells. Bone marrow_sentence_17

Marrow contains hematopoietic stem cells which give rise to the three classes of blood cells that are found in circulation: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). Bone marrow_sentence_18

Bone marrow_table_general_1

Cellular constitution of the red bone marrow parenchymaBone marrow_table_caption_1
GroupBone marrow_header_cell_1_0_0 Cell typeBone marrow_header_cell_1_0_1 Average
fractionBone marrow_header_cell_1_0_2
Reference rangeBone marrow_header_cell_1_0_3

cellsBone marrow_cell_1_1_0

MyeloblastsBone marrow_cell_1_1_1 0.9%Bone marrow_cell_1_1_2 0.2–1.5Bone marrow_cell_1_1_3
PromyelocytesBone marrow_cell_1_2_0 3.3%Bone marrow_cell_1_2_1 2.1–4.1Bone marrow_cell_1_2_2
Neutrophilic myelocytesBone marrow_cell_1_3_0 12.7%Bone marrow_cell_1_3_1 8.2–15.7Bone marrow_cell_1_3_2
Eosinophilic myelocytesBone marrow_cell_1_4_0 0.8%Bone marrow_cell_1_4_1 0.2–1.3Bone marrow_cell_1_4_2
Neutrophilic metamyelocytesBone marrow_cell_1_5_0 15.9%Bone marrow_cell_1_5_1 9.6–24.6Bone marrow_cell_1_5_2
Eosinophilic metamyelocytesBone marrow_cell_1_6_0 1.2%Bone marrow_cell_1_6_1 0.4–2.2Bone marrow_cell_1_6_2
Neutrophilic band cellsBone marrow_cell_1_7_0 12.4%Bone marrow_cell_1_7_1 9.5–15.3Bone marrow_cell_1_7_2
Eosinophilic band cellsBone marrow_cell_1_8_0 0.9%Bone marrow_cell_1_8_1 0.2–2.4Bone marrow_cell_1_8_2
Segmented neutrophilsBone marrow_cell_1_9_0 7.4%Bone marrow_cell_1_9_1 6.0–12.0Bone marrow_cell_1_9_2
Segmented eosinophilsBone marrow_cell_1_10_0 0.5%Bone marrow_cell_1_10_1 0.0–1.3Bone marrow_cell_1_10_2
Segmented basophils and mast cellsBone marrow_cell_1_11_0 0.1%Bone marrow_cell_1_11_1 0.0–0.2Bone marrow_cell_1_11_2

cellsBone marrow_cell_1_12_0

PronormoblastsBone marrow_cell_1_12_1 0.6%Bone marrow_cell_1_12_2 0.2–1.3Bone marrow_cell_1_12_3
Basophilic normoblastsBone marrow_cell_1_13_0 1.4%Bone marrow_cell_1_13_1 0.5–2.4Bone marrow_cell_1_13_2
Polychromatic normoblastsBone marrow_cell_1_14_0 21.6%Bone marrow_cell_1_14_1 17.9–29.2Bone marrow_cell_1_14_2
Orthochromatic normoblastBone marrow_cell_1_15_0 2.0%Bone marrow_cell_1_15_1 0.4–4.6Bone marrow_cell_1_15_2
Other cell

typesBone marrow_cell_1_16_0

MegakaryocytesBone marrow_cell_1_16_1 < 0.1%Bone marrow_cell_1_16_2 0.0-0.4Bone marrow_cell_1_16_3
Plasma cellsBone marrow_cell_1_17_0 1.3%Bone marrow_cell_1_17_1 0.4-3.9Bone marrow_cell_1_17_2
Reticular cellsBone marrow_cell_1_18_0 0.3%Bone marrow_cell_1_18_1 0.0-0.9Bone marrow_cell_1_18_2
LymphocytesBone marrow_cell_1_19_0 16.2%Bone marrow_cell_1_19_1 11.1-23.2Bone marrow_cell_1_19_2
MonocytesBone marrow_cell_1_20_0 0.3%Bone marrow_cell_1_20_1 0.0-0.8Bone marrow_cell_1_20_2

Stroma Bone marrow_section_2

The stroma of the bone marrow includes all tissue not directly involved in the marrow's primary function of hematopoiesis. Bone marrow_sentence_19

Stromal cells may be indirectly involved in hematopoiesis, providing a microenvironment that influences the function and differentiation of hematopoietic cells. Bone marrow_sentence_20

For instance, they generate colony stimulating factors, which have a significant effect on hematopoiesis. Bone marrow_sentence_21

Cell types that constitute the bone marrow stroma include: Bone marrow_sentence_22

Bone marrow_unordered_list_0

Function Bone marrow_section_3

Mesenchymal stem cells Bone marrow_section_4

Main article: Mesenchymal stem cell Bone marrow_sentence_23

The bone marrow stroma contains mesenchymal stem cells (MSCs), also known as marrow stromal cells. Bone marrow_sentence_24

These are multipotent stem cells that can differentiate into a variety of cell types. Bone marrow_sentence_25

MSCs have been shown to differentiate, in vitro or in vivo, into osteoblasts, chondrocytes, myocytes, marrow adipocytes and beta-pancreatic islets cells. Bone marrow_sentence_26

Bone marrow barrier Bone marrow_section_5

The blood vessels of the bone marrow constitute a barrier, inhibiting immature blood cells from leaving the marrow. Bone marrow_sentence_27

Only mature blood cells contain the membrane proteins, such as aquaporin and glycophorin, that are required to attach to and pass the blood vessel endothelium. Bone marrow_sentence_28

Hematopoietic stem cells may also cross the bone marrow barrier, and may thus be harvested from blood. Bone marrow_sentence_29

Lymphatic role Bone marrow_section_6

The red bone marrow is a key element of the lymphatic system, being one of the primary lymphoid organs that generate lymphocytes from immature hematopoietic progenitor cells. Bone marrow_sentence_30

The bone marrow and thymus constitute the primary lymphoid tissues involved in the production and early selection of lymphocytes. Bone marrow_sentence_31

Furthermore, bone marrow performs a valve-like function to prevent the backflow of lymphatic fluid in the lymphatic system. Bone marrow_sentence_32

Compartmentalization Bone marrow_section_7

Biological compartmentalization is evident within the bone marrow, in that certain cell types tend to aggregate in specific areas. Bone marrow_sentence_33

For instance, erythrocytes, macrophages, and their precursors tend to gather around blood vessels, while granulocytes gather at the borders of the bone marrow. Bone marrow_sentence_34

As food Bone marrow_section_8

See also: Bone marrow (food) Bone marrow_sentence_35

Animal bone marrow has been used in cuisine worldwide for millennia, such as the famed Milanese Ossobuco. Bone marrow_sentence_36

Clinical significance Bone marrow_section_9

Disease Bone marrow_section_10

The normal bone marrow architecture can be damaged or displaced by aplastic anemia, malignancies such as multiple myeloma, or infections such as tuberculosis, leading to a decrease in the production of blood cells and blood platelets. Bone marrow_sentence_37

The bone marrow can also be affected by various forms of leukemia, which attacks its hematologic progenitor cells. Bone marrow_sentence_38

Furthermore, exposure to radiation or chemotherapy will kill many of the rapidly dividing cells of the bone marrow, and will therefore result in a depressed immune system. Bone marrow_sentence_39

Many of the symptoms of radiation poisoning are due to damage sustained by the bone marrow cells. Bone marrow_sentence_40

To diagnose diseases involving the bone marrow, a bone marrow aspiration is sometimes performed. Bone marrow_sentence_41

This typically involves using a hollow needle to acquire a sample of red bone marrow from the crest of the ilium under general or local anesthesia. Bone marrow_sentence_42

Application of stem cells in therapeutics Bone marrow_section_11

Bone marrow derived stem cells have a wide array of application in regenerative medicine. Bone marrow_sentence_43

Imaging Bone marrow_section_12

Medical imaging may provide a limited amount of information regarding bone marrow. Bone marrow_sentence_44

Plain film x-rays pass through soft tissues such as marrow and do not provide visualization, although any changes in the structure of the associated bone may be detected. Bone marrow_sentence_45

CT imaging has somewhat better capacity for assessing the marrow cavity of bones, although with low sensitivity and specificity. Bone marrow_sentence_46

For example, normal fatty "yellow" marrow in adult long bones is of low density (-30 to -100 Hounsfield units), between subcutaneous fat and soft tissue. Bone marrow_sentence_47

Tissue with increased cellular composition, such as normal "red" marrow or cancer cells within the medullary cavity will measure variably higher in density. Bone marrow_sentence_48

MRI is more sensitive and specific for assessing bone composition. Bone marrow_sentence_49

MRI enables assessment of the average molecular composition of soft tissues and thus provides information regarding the relative fat content of marrow. Bone marrow_sentence_50

In adult humans, "yellow" fatty marrow is the dominant tissue in bones, particularly in the (peripheral) appendicular skeleton. Bone marrow_sentence_51

Because fat molecules have a high T1-relaxivity, T1-weighted imaging sequences show "yellow" fatty marrow as bright (hyperintense). Bone marrow_sentence_52

Furthermore, normal fatty marrow loses signal on fat-saturation sequences, in a similar pattern to subcutaneous fat. Bone marrow_sentence_53

When "yellow" fatty marrow becomes replaced by tissue with more cellular composition, this change is apparent as decreased brightness on T1-weighted sequences. Bone marrow_sentence_54

Both normal "red" marrow and pathologic marrow lesions (such as cancer) are darker than "yellow" marrow on T1-weight sequences, although can often be distinguished by comparison with the MR signal intensity of adjacent soft tissues. Bone marrow_sentence_55

Normal "red" marrow is typically equivalent or brighter than skeletal muscle or intervertebral disc on T1-weighted sequences. Bone marrow_sentence_56

Fatty marrow change, the inverse of red marrow hyperplasia, can occur with normal aging, though it can also be seen with certain treatments such as radiation therapy. Bone marrow_sentence_57

Diffuse marrow T1 hypointensity without contrast enhancement or cortical discontinuity suggests red marrow conversion or myelofibrosis. Bone marrow_sentence_58

Falsely normal marrow on T1 can be seen with diffuse multiple myeloma or leukemic infiltration when the water to fat ratio is not sufficiently altered, as may be seen with lower grade tumors or earlier in the disease process. Bone marrow_sentence_59

Histology Bone marrow_section_13

Main article: Bone marrow examination Bone marrow_sentence_60

Bone marrow examination is the pathologic analysis of samples of bone marrow obtained via biopsy and bone marrow aspiration. Bone marrow_sentence_61

Bone marrow examination is used in the diagnosis of a number of conditions, including leukemia, multiple myeloma, anemia, and pancytopenia. Bone marrow_sentence_62

The bone marrow produces the cellular elements of the blood, including platelets, red blood cells and white blood cells. Bone marrow_sentence_63

While much information can be gleaned by testing the blood itself (drawn from a vein by phlebotomy), it is sometimes necessary to examine the source of the blood cells in the bone marrow to obtain more information on hematopoiesis; this is the role of bone marrow aspiration and biopsy. Bone marrow_sentence_64

The ratio between myeloid series and erythroid cells is relevant to bone marrow function, and also to diseases of the bone marrow and peripheral blood, such as leukemia and anemia. Bone marrow_sentence_65

The normal myeloid-to-erythroid ratio is around 3:1; this ratio may increase in myelogenous leukemias, decrease in polycythemias, and reverse in cases of thalassemia. Bone marrow_sentence_66

Donation and transplantation Bone marrow_section_14

Main article: Hematopoietic stem cell transplantation Bone marrow_sentence_67

In a bone marrow transplant, hematopoietic stem cells are removed from a person and infused into another person (allogenic) or into the same person at a later time (autologous). Bone marrow_sentence_68

If the donor and recipient are compatible, these infused cells will then travel to the bone marrow and initiate blood cell production. Bone marrow_sentence_69

Transplantation from one person to another is conducted for the treatment of severe bone marrow diseases, such as congenital defects, autoimmune diseases or malignancies. Bone marrow_sentence_70

The patient's own marrow is first killed off with drugs or radiation, and then the new stem cells are introduced. Bone marrow_sentence_71

Before radiation therapy or chemotherapy in cases of cancer, some of the patient's hematopoietic stem cells are sometimes harvested and later infused back when the therapy is finished to restore the immune system. Bone marrow_sentence_72

Bone marrow stem cells can be induced to become neural cells to treat neurological illnesses, and can also potentially be used for the treatment of other illnesses, such as inflammatory bowel disease. Bone marrow_sentence_73

In 2013, following a clinical trial, scientists proposed that bone marrow transplantation could be used to treat HIV in conjunction with antiretroviral drugs; however, it was later found that HIV remained in the bodies of the test subjects. Bone marrow_sentence_74

Harvesting Bone marrow_section_15

The stem cells are typically harvested directly from the red marrow in the iliac crest, often under general anesthesia. Bone marrow_sentence_75

The procedure is minimally invasive and does not require stitches afterwards. Bone marrow_sentence_76

Depending on the donor's health and reaction to the procedure, the actual harvesting can be an outpatient procedure, or can require 1–2 days of recovery in the hospital. Bone marrow_sentence_77

Another option is to administer certain drugs that stimulate the release of stem cells from the bone marrow into circulating blood. Bone marrow_sentence_78

An intravenous catheter is inserted into the donor's arm, and the stem cells are then filtered out of the blood. Bone marrow_sentence_79

This procedure is similar to that used in blood or platelet donation. Bone marrow_sentence_80

In adults, bone marrow may also be taken from the sternum, while the tibia is often used when taking samples from infants. Bone marrow_sentence_81

In newborns, stem cells may be retrieved from the umbilical cord. Bone marrow_sentence_82

Fossil record Bone marrow_section_16

The earliest fossilised evidence of bone marrow was discovered in 2014 in Eusthenopteron, a lobe-finned fish which lived during the Devonian period approximately 370 million years ago. Bone marrow_sentence_83

Scientists from Uppsala University and the European Synchrotron Radiation Facility used X-ray synchrotron microtomography to study the fossilised interior of the skeleton's humerus, finding organised tubular structures akin to modern vertebrate bone marrow. Bone marrow_sentence_84

Eusthenopteron is closely related to the early tetrapods, which ultimately evolved into the land-dwelling mammals and lizards of the present day. Bone marrow_sentence_85

See also Bone marrow_section_17

Bone marrow_unordered_list_1

  • National Marrow Donor Program, a nonprofit organization that operates a registry of volunteer hematopoietic cell donors and umbilical cord blood units in the United StatesBone marrow_item_1_6
  • Gift of Life Marrow Registry, an American bone marrow transplantation registryBone marrow_item_1_7

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: marrow.