Bone Marrow and Spleen

• The bone marrow is the main site of haematopoiesis, producing red cells, leukocytes, and platelets
• The bone marrow is also a lymphoid organ involved in the immune system
• Sites of haematopoiesis change from the embryo to adulthood, with the bone marrow being a key site from the third trimester onwards
• In adults, all blood cells are produced in the red marrow found in bones of the axial skeleton
• The bone marrow environment includes a mix of blood cells, adipocytes, osteoblasts, endothelial cells, stromal cells, cytokines, adhesion molecules, and macrophages
• Haematopoietic stem cells differentiate into erythrocytes, leukocytes, and megakaryocytes (which form platelets)
• Cellular differentiation is the process where undifferentiated cells become specialized with specific functions
• Proliferation is driven by growth factors and anti-apoptotic signals, leading to mature cells being released into circulation
• Cytopenias refer to decreased blood cell counts, while cytosis indicates increased blood cell counts
• Cytopenias can be due to bone marrow pathology or peripheral destruction/consumption
• Bone marrow pathology can result from infiltration, failure, or suppression, with various causes and consequences
• Apoptosis is programmed cell death, a normal process removing old or damaged cells from the system
• Apoptosis is programmed cell death, a normal physiological process where old, damaged, or unneeded cells are removed from the system
• Red blood cells have a lifespan of approximately +/-120 days
• Neutrophils have a lifespan of approximately +/-5 days
• Platelets have a lifespan of approximately +/-10 days
• Lymphocytes and macrophages have a lifespan of months to years
• Macrophages act as the 'garbage collectors' of the body and clean up apoptotic bodies
• Bone marrow procedure involves obtaining material for examination and testing by inserting a wide-bore needle through the bone into the bone marrow
• Entry sites for bone marrow procedure:

  • Infants: anterior tibia
  • Older children and adults: posterior superior iliac crests of the pelvic bones
• Samples obtained during bone marrow procedure:

  • Bone marrow aspirate: aspirated with a 2 mL syringe for morphological assessment and a 10 mL syringe for other testing
  • Bone marrow trephine: core biopsy for histological assessment
• Indications for bone marrow examination include suspected bone marrow pathology, staging of disease, disease monitoring, and instances where peripheral testing is inconclusive
• The spleen is a wedge-shaped, encapsulated organ located in the left upper quadrant of the abdomen, behind the 9th - 11th ribs
• The spleen's blood supply comes from the splenic artery and drainage via the splenic vein
• The spleen has two distinct areas:

  1. The White Pulp:

  • Involves immunity and antibody production

  2. The Red Pulp:

  • Has a phagocytic function and contains macrophages that remove abnormal red blood cells
• Splenomegaly is the abnormal enlargement of the spleen and can be caused by various factors such as haematopoiesis, congestion, infection, immune disorders, malignancies, and storage diseases
• Hypersplenism is characterized by an enlarged spleen leading to rapid and premature destruction of blood cells, resulting in cytopenias of one or more cell lines