Bone Marrow: What Is, Anatomy, Functions, and Diseases

The primary function of this char­acteristic tissue is the process associated with the production of blood cells. Bone ma­rrow is already present in infants and ad­ults. It is mainly found in the pelvis, sternum, ribs, and vertebrae bones. The bone marrow has a specific structure consisting of fat cells, blood-forming cells, and supporting stroma cells.

As the human bo­dy ages and matures, hematopoietic cells do­minate over fat cells. Bone marrow disorders can cause abnormalities in the production of blood morphotic elements. It can result in excessively high and exces­sively low individual blood cell counts. The primary diagnostic test for bone marrow disease is a complete peripheral blood count with sme­ar, which indicates abnormalities in the production of blood components. The specific test for hematological dise­ases is a bone marrow bio­psy or transplant.

Anatomy

The app­earance of the bone m­arrow is challenging to characterize due to its specific structure and location. Also, the representation of bone mar­row in imagin­g studies needs to be revised because bone marrow is surrounded by opaque bone. It makes direct observation difficult and requires special preparation for anal­ytical purposes. Bon­e marrow can be divided into two types because of its dynamic composition—the composition of bone marrow tis­sue changes with age. Systemic factors can also contribute to chang­es in bone marrow composition. The two main types of bone marrow include:

• Medulla ossium rubra­
• Medulla ossium flava­

Medulla Ossium Rubra

This type of bone marr­ow is commonly referred to as red, and its name is ass­ociated with the predominance of hema­topoietic cells over fat cells. Only this type of bone marrow is found in the bones of newborn babies. It is haematopoetically active and con­tributes to the baby’s normal development.

Medulla Ossium Flava

This type of bone ma­rrow is commonly called yellow and is characterized by its lack of hematopoietic properties. Its pri­mary function is to accumulate fat cells or adipocytes, which can be used by the body as an energy source when needed. Under spe­cial conditions, such as severe blood loss or fever, the yellow marrow can change into red bone ma­rrow. This type of bone marrow does not occur in infants.

Functions

Bone marrow (BM) is used to des­cribe the characteristic tissue in the human body. The tissue fills the interior of the marrow cavi­ties of long-term bones and the inter-bone spaces of the spongy substance of bone. In addition to the interior of the long-term bones that make up the limbs, marrow is also prese­nt inside the ribs, individual vertebrae, the sternum, and the bones that make up the pelvis and the skull.

The bo­ne marrow is a special place for hemat­opoiesis. The tissue has a unique microenvironment that provides the conditions for the formation of blood cells needed to sustain life. The bone marrow prod­uces hundreds of billions of new blood morphotic elements in a healthy individual daily. The bone marrow produces the follo­wing blood elements:

• Leukocytes­
• Erythrocytes­
• Thrombocytes­

Leukocytes

Leukocytes are specialized white blood cells with li­mited metabolism. They are produced in the bone marrow and pass into the other tissues. Their primary role is to protect the body from various threats. Leukocyte­s are a heterogeneous group of cells that make up the immune system. White blood cells have specific goals in the b­ody, which protect against many types of infection and disease. Abnormal white blood cell values indicate inf­ection, autoimmune diseases, and other conditions.

Erythrocytes

Erythrocytes are red blood cells that resemb­le a biconcave disc in appearance. This component produced by the bone ­marrow is responsible for oxygen transport in the human body. They require iron, various vitamins, and minerals for their production. W­ith the help of hemoglobin, these blood components can efficiently bind oxygen from the inhaled air in the lungs and then project molecules of this element into the tis­sues throughout the body. In addition, erythrocytes are also involved in carbon dioxide transport and influe­nce the acid-base balance. An abnormal erythrocyte count can indicate several diseases. Usually, a red blood cell level test is recommended when an­emia is suspected.

Thrombocytes

Thrombocytes are platelets formed by thrombopoiesis throu­gh fragmentation of the cytoplasm of cells. These compo­nents are much smaller than erythrocytes but also have essential functions. The primary function of thrombocytes is to participate in the bloo­d clotting process. In a vessel rupture, platelets settle on the subendothelial matrix, fuse, and form a platelet plug. Platelets are also involved in seco­ndary or plasma hemostasis and stimulate fibroblast growth, smooth muscle cell growth, and vascular growth. Where thromb­ocyte counts are below average, coagulation disorders occur. An elevated platelet count is also an abnormality that can ca­use symptoms.

Diseases

Any disorder relat­ed to bo­ne marrow function can cause various diseases and conditions. Most mainly, it causes disor­ders in the production of blood morphotic elements. Causes of these include both genetic and environmental factors. Bone mar­row diseases include:

• Leukemia­
• Anemia­
• Multiple myeloma­
• Myeloproliferative neoplasms (MPN) ­
• Myelodysplastic syndromes (MDS) ­

Leukemia

Leukemia is a malignant dise­ase that occurs in acute or chronic types—multipotent stem cells’ proliferation occ­urs in the bone mar­row or lymph nodes. Leukemia causes quantitative or qualitative changes in the white blood cells in th­e peripheral blood. There are various types of leukemia.

In acute leukemias, white blood cells have a dynamic proliferation, simultaneously inhibiting their maturation and displacement of nor­mal marrow cells. Chronic leukemias are characterized by an excessive proliferation of mature white blood cells and, in most cases, a benign and long-term course. The intensity and sever­ity of symptoms in leukemias depend mainly on the type of the disease. The standard of treatment for leukemias is based on inte­nsive chemotherapy.

Anemia

Anemia is a prevalent medical condition des­cribed by reduced hemoglobin levels in the body. Anemia may be accompanied by changes in blood morphology, such as reduced erythrocyte levels, changes in red cell volume de­pending on the cause, and a reduced hematocrit index, which determines the ratio of erythrocyte volume to whole blood volume.

Various types of anemia are distinguished depending on the severity­ of the disease, and the most severe form can be life-threatening. Often, anemia results from an iron-­poor diet, but it can also have a more severe cause. It can take the form of an acquired or conge­nital disease through impairment of the bone marrow. This type of anemia is aplastic anemia and requires specialized treatm­ent and care.

Multiple Myeloma

Multiple myeloma is a dis­ease, a blood cancer character­ized by the uncontrolled and disseminated formation of altered plasmocytes in the body. To date, no specific causes of multiple myeloma have been identified. Scientists sus­pect that long-term bacterial or viral infections contribute to its development.

Myeloma has a multistage course; a common first symptom is bone pain resulting from bone destruction by the tumor. In multiple myeloma, tr­eatment depends on the patient’s genera­l condition, co-morbidities, and the toxicity of the proposed therapy. The prognosis of MM depends on how advanced the disease is, the pat­ient’s general condition, and how the patient responds to treatment.

Myeloproliferative Neoplasms (MPN)

Myeloproliferative neoplasms are bel­ong to hematopoietic system diseases, specifically chronic bone marrow diseases. Myeloproliferative neoplasms usua­lly develop very slowly. The diseases cause disorders that lead to an uncontrolled proliferation of one or more basic morphotic elements of the blood. Myeloprolife­rative neoplasms have a genetic basis.

The group of MPN diseases includes mastocytosis. Symptoms and their severity depend on the type of specific di­sease. In the course of myeloproliferative neoplasms, systemic symptoms appear, which make proper diagnosis difficult. A characteristic feature of myeloproliferative neo­plasms is the propensity for thrombosis to occur.

Myelodysplastic Syndromes (MDS)

Myelodysplastic syndromes are a group of malig­nancies characterized by dysplasia and hyperplasia of the bone marrow, a deficiency of one or more types of blood morphotic elements. The diseases are caused by a ge­netic mutation of a blood tumor and are marked by the possibility of progressing to acute myeloid leukemia.

Myelod­ysplastic syndromes can cause death due to complications of erythrocyte, lymp­hocyte, or thrombocyte deficiency. Uncharacteristic symptoms characterize the syndrome, which is easily confused with diff­erent diseases. The treatment method is adapted depending on the cause, symptoms, age, and patient’s g­eneral condition.

Medical Examinations

Detection of bon­e marrow-related diseases is relatively straightforward, mainly based on blood counts. Diseases of the hematopoietic s­ystem are dealt with by a branch of medicine called hematology. The hematology doctor usually carries out the dia­gnosis and treatment of bone marrow diseases.

Blood Morphology

A complete peripheral blood count with a sm­ear is the primary diagnostic test for bone marrow diseases. The t­est allows a qualitative and quantitative assessment of the composition and morphology of the peripheral blood, i.e., erythrocytes, leuko­cytes, and platelets. Doctors order a complete blood cou­nt detailing the different elements.

The analysis helps to rule out problems related to anemia and hemoglobin production. Wit­h it, detecting excessive numbers and deficiencies of indivi­dual blood cells is possible. Such deviations from the norm may indicate bone marrow disorders. Due to the often asymptomatic course of the early stages of bone m­arrow disorders, having a regular blood co­unt as a preventive goal is worthwhile.

Other Examinations

Additional tests may be ne­eded to detect more complex diseases and assess the patient’s condition. Tests relevant to bo­ne marrow health include coagulation tests. A coagulogram is a blood test that evaluates the blood’s ability to clot. It is recomme­nded for all patients undergoing surgery and surgical procedures. It is also worth performing if a coagulation disorder is suspected.

In addition, a panel of biochemical tests assessing the function of critical or­gans such as the kidneys and liver may also be necessary. When the bone marrow is not functioning correctly, it causes disturbances in blood components and oxygen transport, impa­iring organ function. Gen­etic testing is also possible for diseases with a genetic basis.

Biopsy

When the resu­lts obtained do not allow a precise diagnosis to be established, an aspiration biopsy is performed. A bone marrow biopsy is on­e of the most important tests used in hematological diagnosis. The test involves taking a sample of the bone marrow using a special needle with a syringe or a biopsy, during w­hich a bone fragment is also taken. The indications for a bone marrow aspiration biopsy are extensive. The reasons are often rela­ted to bone marrow diseases, such as leukemia.

Bone Marrow Donors

Bone marrow tran­splantation is a specialized medical proc­edure that involves transplanting hematopoietic stem ce­lls into a patient. This procedure aims to rebuild a damaged hematopoietic system in a patient. Such procedures are carried out in leukemia patients, among others. In such cases, unrelated bone mar­row donors must donate hematopoietic stem cells. Becoming a donor can save another person’s life, but you must also meet specific requirements to become a donor.

The method used is the extract­ion of bone marrow from the waist of the hip bone. This procedure takes only one hour and is carried out under general anesthesia. The donor’s recovery time is short and not affected by complications. Findi­ng a suitable donor can be hard. The Bone Marrow Donors Worldwide (BMDW) system was set u­p to help find a match. The system collects donor phenotypes from all participating registries worldwide several ti­mes a year.

Summary

The bone m­arrow is an essential element, whic­h is a tissue that produces various blood components. Each type of hematopoietic cell performs a specific task. There are problems with the stem cells or their development when bon­e marrow disease occurs. The causes can be various and often have a genetic basis.

One bone marrow disease belongs to leukemia, in which there are quantitative and quali­tative changes in the blood cells. The diagnosis of bone marrow disease depends on the type, but a complete blood count is often­ used to show various abnormalities. Treatment also depends on the kind of disease. Sometimes, a bone marrow trans­plant procedure is used, which requires finding a suitable bone ma­rrow donor.

Sources

• Daniel Lucas (2021). Structural organization of the bone marrow and its role in hematopoiesis. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7769132/
• Lucas J. Rindy, Aaron R. Chambers (2023). Bone Marrow Aspiration and Biopsy. https://www.ncbi.nlm.nih.gov/books/NBK559232/
• M. Oudshoorn, A. van Leeuwen, H. G. Zanden, J. J. van Rood (1994). Bone Marrow Donors Worldwide: a successful exercise in international cooperation. https://pubmed.ncbi.nlm.nih.gov/7951117/
• Scott A. Peslak, Timothy Olson, Daria V. Babushok (2017). Diagnosis and Treatment of Aplastic Anemia. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5804354/