Bone marrow is a semi-solid tissue that can be found in spongy or cancellous bone parts. In birds and mammals, bone marrow is the main site of production of new blood cells or hematopoiesis. It consists of hematopoietic cells, marrow adipose tissue, and supportive stroma cells. In adult humans, the bone marrow is mainly located in the ribs, spine, breastbone, and pelvis. On average, bone marrow constitutes 4% of the total human body mass; in adults who have 65 kilograms of mass (143 lb), bone marrow usually accounts for about 2.6 kilograms (5.7 pounds).
The human marrow produces about 500 billion blood cells per day, which joins the systemic circulation through the permeable vascular sinusoid inside the medullary cavity. All types of hematopoietic cells, including myeloid lineages and lymphoid, are made in bone marrow; However, lymphoid cells should migrate to other lymphoid organs (eg the thymus) to complete maturation.
Bone marrow transplantation can be performed to treat serious diseases of the bone marrow, including certain forms of cancer such as leukemia. In addition, bone marrow stem cells have been successfully converted into functional neuronal cells, and are also potentially used to treat diseases such as inflammatory bowel disease.
Video Bone marrow
Structure
Marrow composition is dynamic, since the mixture of cellular and non-cellular components (connective tissue) shifts with age and in response to systemic factors. In humans, marrow is a colloquial language characterized as "red" or "yellow" marrow (Latin: medulla ossium rubra , Latin: medulla ossium flava , respectively) depends on the prevalence of hematopoetic cells vs fat cells. While the exact mechanisms underlying marrow regulation are not understood, composition changes occur according to stereotypical patterns. For example, newborn bones exclusively contain active "red" hematopoietic marrow, and there is progressive conversion to the "yellow" marrow with age. In adults, red marrow is found primarily in the central skeleton, such as the pelvis, breastbone, cranium, ribs, spine and shoulder blades, and varies found at the epiphyseal end of long bones such as the femur and the proximal humerus. In a state of chronic hypoxia, the body can convert the yellow marrow back into the red marrow to increase blood cell production.
Hematopoietic components
At the cellular level, the major functional components of the bone marrow include progenitor cells that are destined to mature into blood cells and lymphoids. Marrow contains hematopoietic stem cells that give rise to three classes of blood cells found in the circulation: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (platelets).
Stroma
Bone marrow stroma includes all tissues that are not directly involved in the primary function of marrow hematopoiesis. Stromal cells can be indirectly involved in hematopoiesis, providing a microenvironment that affects the function and differentiation of hematopoeietic cells. For example, they produce a colony-stimulating factor, which has a significant effect on hematopoiesis. Types of cells that constitute bone marrow stroma include:
- fibroblasts (reticular connective tissue)
- macrophages, which contribute primarily to the production of red blood cells, because they provide iron for the production of hemoglobin.
- adipocytes (fat cells)
- osteoblasts (synthesize bones)
- osteoclasts (resorbbones)
- endothelial cells, which form sinusoids. It comes from endothelial stem cells, which are also present in the bone marrow.
Maps Bone marrow
Function
Mesenchymal stem
Bone marrow stroma contains mesenchymal stem cells (MSCs), also known as marrow stromal cells. It is a multipotent stem cell that can differentiate into different cell types. MSC has been shown to differentiate, in vitro or in vivo, into osteoblasts, chondrocytes, myocytes, marrow adipocytes and pancreatic beta-pancreatic islet cells.
Bone marrow barrier
Bone marrow vessels are a barrier, inhibiting immature blood cells from leaving the marrow. Only adult blood cells contain membrane proteins, such as aquaporin and glycophorin, which are necessary to attach and pass through the endothelium blood vessels. Hematopoietic stem cells can also cross the bone marrow barrier, and thus can be taken from the blood.
Lymphatic role
The red bone marrow is a key element of the lymphatic system, becoming one of the primary lymphoid organs that produce lymphocytes from immature hematopoietic progenitor cells. The bone marrow and thymus are the primary lymphoid tissues involved in the production and early selection of lymphocytes. Furthermore, the bone marrow performs a valve-like function to prevent backflow of lymphatic fluid in the lymphatic system.
Compartmentalization
Biological compartmentalization is evident in the bone marrow, in certain cell types tending to aggregate in certain areas. For example, their erythrocytes, macrophages, and precursors tend to cluster around the blood vessels, while granulocytes converge on the border of the bone marrow.
Society and culture
The animal bone marrow has been used in cooking around the world for thousands of years, like the famous Milan Ossobuco.
Clinical interests
Disease
Normal bone marrow architecture can be damaged or displaced by aplastic anemia, malignancies such as multiple myeloma, or infections such as tuberculosis, leading to decreased production of blood cells and blood platelets. Bone marrow may also be affected by various forms of leukemia, which attacks the hematologic progenitor cells. In addition, radiation exposure or chemotherapy will kill many cells that divide rapidly from the bone marrow, and therefore will produce a depressed immune system. Many of the symptoms of radiation poisoning are due to damage caused by bone marrow cells.
To diagnose diseases involving bone marrow, bone marrow aspiration is sometimes performed. This usually involves the use of a hollow needle to obtain a red bone marrow sample from the ilium peak under general or local anesthesia.
Stem cell application in therapy
Bone marrow derived stem cells have a variety of applications in regenerative medicine.
Imaging
Medical imaging may provide some limited information about the bone marrow. X-ray films plainly pass through soft tissues such as marrow and do not provide visualization, although changes in the associated bone structure can be detected. CT imaging has a somewhat better capacity for assessing bone marrow cavities, albeit with low sensitivity and specificity. For example, "normal" yellow fat in long adult bones has a low density (-30 to -100 Hounsfield units), between subcutaneous fat and soft tissue. Tissues with an increase in cellular composition, such as a normal "red" marrow cell or cancer cell in the medullary cavity will measure a higher density.
MRI is more sensitive and specific for assessing bone composition. MRI allows the assessment of the average soft tissue molecular composition, and thus provides information on the relative fat content of the marrow. In adult humans, "yellow" marrow fat is the dominant tissue of bone, especially in the apendicular (peripheral) skeleton. Because fatty molecules have high T1-relaxivity, the T1-weighted imaging sequence shows "yellow" marrow fat as bright (hyperintense). Furthermore, normal fatty marrow loses signals in fat-saturated sequences, in the same pattern as subcutaneous fat.
When the "yellow" fatty marrow is replaced by tissue with more cell composition, this change is seen as a decrease in brightness in the T1-weighted sequence. Normal "red" marrow and pathologic marrow lesions (such as cancer) are darker than "yellow" marrow in T1-heavy sequences, although they can often be distinguished by comparisons with MR signal intensity from adjacent soft tissues. Normal "red" marrow is usually equivalent or lighter than skeletal muscle or intervertebral disks in the T1-weighted sequence.
Fatty marrow changes, as opposed to red marrow hyperplasia, can occur with normal aging, although it can also be seen with certain treatments such as radiation therapy. T1 of diffuse marrow monitensity without increased contrast or cortical discontinuity indicates red marrow or mielofibrosis conversion. The normal erroneous tumor in T1 can be seen with diffuse multiple myeloma or leukemia infiltration when the ratio of water to fat is not adequately altered, as seen in lower level tumors or earlier in the disease process.
Histology
Bone marrow examination is a pathological analysis of bone marrow samples obtained through biopsy and bone marrow aspiration. Bone marrow examination is used in the diagnosis of a number of conditions, including leukemia, multiple myeloma, anemia, and pancytopenia. Bone marrow produces blood cell elements, including platelets, red blood cells and white blood cells. While much information can be collected by testing the blood itself (taken from the vein by phlebotomy), it is sometimes necessary to examine the source of blood cells in the bone marrow for more information on hematopoiesis; this is the role of bone marrow aspiration and biopsy.
The ratio between the myeloid series and erythroid cells is relevant to bone marrow function, as well as for peripheral bone marrow and peripheral blood, such as leukemia and anemia. The normal ratio of myeloid-to-erythroid is about 3: 1; this ratio can be increased in myelogenous leukemia, decreased polycythemias, and vice versa in cases of thalassemia.
Donate and transplant
In bone marrow transplantation, hematopoietic stem cells are removed from a person and infused into another person (allogenic) or to another person at a later time (autologous). If the donor and receiver are compatible, the infused cell will then travel to the bone marrow and begin blood cell production. Transplant from one person to another is done for the treatment of severe bone marrow disease, such as congenital defects, autoimmune disease or malignancy. The patient's own marrow was first killed with drugs or radiation, and then new stem cells were introduced. Before radiation therapy or chemotherapy in cases of cancer, some patient's hematopoietic stem cells are sometimes taken and then reinfused when therapy is complete to restore the immune system.
Bone marrow stem cells can be induced into nerve cells to treat neurological diseases, and are also potentially used for the treatment of other diseases, such as inflammatory bowel disease. In 2013, after clinical trials, the scientists proposed that bone marrow transplants could be used to treat HIV in conjunction with antiretroviral drugs; However, it was later found that HIV remained in the body of the test subjects.
Harvest
Stem cells are usually harvested directly from red marrow in iliac crest, often under general anesthesia. The procedure is minimally invasive and requires no stitches afterwards. Depending on the health of the donor and the reaction to the procedure, actual retrieval may be an outpatient procedure, or it may take 1-2 days of recovery at the hospital.
Another option is to provide certain drugs that stimulate the release of stem cells from the bone marrow into circulating blood. Intravenous catheter is inserted into the donor arm, and the stem cells are then filtered out of the blood. This procedure is similar to that used in blood or platelet donors. In adults, bone marrow can also be taken from the sternum, whereas tibia is often used when taking samples from infants. In newborns, stem cells can be removed from the umbilical cord.
Fossil record
Source of the article : Wikipedia
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