Haematology and Bone Marrow Physiology

Amity Institute of Virology & Immunology - Medical Haematology

Introduction to Haematology

  • Definition: Haematology is the study of blood and blood disorders.
  • Key Areas:
    • Physiology of blood
    • Pathology related to blood disorders
    • Etiology: causes of blood disorders
    • Diagnosis of blood-related disorders
    • Treatment options
    • Prognosis and prevention strategies

Organs of the Immune System

  • Overview: The immune system comprises various organs that are responsible for defending the body against pathogens.
    • Physical Barriers: Skin & mucous membranes serve as the first line of defense against external pathogens.
    • Lymphoid System: Includes primary and secondary lymphoid organs.
Skin and Mucous Membrane
  • Functions as Physical Barriers:
    • Antibacterial Substances: Enzymes in saliva, airways, and tears destroy bacterial cell walls.
    • Mucus: Traps germs in the bronchi, allowing them to be cleared via cilia.
    • Stomach Acid: Destroys most ingested pathogens.
    • Normal Flora: Harmless bacteria on skin and mucous membranes contribute to immune defense.
    • Reflex Actions: Coughing and sneezing help expel germs from the airways.
Lymphoid Organs
  • Types:
    • Primary Lymphoid Organs: Bone marrow and thymus produce lymphocytes.
    • Secondary Lymphoid Organs: Lymph nodes, spleen, and tonsils are locations where immune responses take place.

Bone Marrow

  • Types:
    • Red Bone Marrow: Contains stem cells that can differentiate into red blood cells, white blood cells, and platelets.
    • Yellow Bone Marrow: Consists mostly of fat and can convert to red bone marrow in emergencies.
Anatomy of Bone Marrow
  • Sections:
    • Vascular Section: Contains blood vessels for nutrient supply and transport of blood cells.
    • Non-vascular Section: Site of haematopoiesis (blood cell formation), contains immature blood cells, fat cells, and reticular connective tissue.
Functions of Bone Marrow

  • Red Bone Marrow:

    • Produces red blood cells that transport oxygen.
    • Generates platelets essential for blood clotting.
    • Produces white blood cells to strengthen the immune system.

  • Yellow Bone Marrow:

    • Stores fats and assists in blood production during severe conditions.
    • Converts to red marrow during life-threatening events to support blood cell production.
Development and Changes in Bone Marrow
  • Bone marrow remains red until approximately age seven; afterward, a transition to yellow marrow occurs.
  • Adults possess an average of 5.7 pounds of red bone marrow.
  • Location of Bone Marrow: Found in the cavities of long bones, along with the shoulder blades, hips, skull, and flat bones.

Haematopoiesis

  • Definition: The formation of blood cellular components, ongoing from embryonic development into adulthood.
  • Location: Takes place in the cervical blood system, primarily within the bone marrow, liver, and spleen during early development.
  • Types of Blood Cells Produced:
    • Red Blood Cells (Erythrocytes): Carry oxygen throughout the body.
    • White Blood Cells (Leukocytes): Comprise several subtypes including lymphocytes, neutrophils, basophils, eosinophils, and macrophages.
    • Platelets (Thrombocytes): Aid in clotting.
Primitive Haematopoiesis
  • Occurs during embryonic development to provide oxygen to developing organs via erythrocytes produced in the yolk sac.
  • Haematopoiesis later shifts to the liver and spleen before finally establishing in the bone marrow.
Self-Renewal of Hematopoietic Stem Cells (HSCs)
  • Importance of Self-Renewal: Critical for maintaining the HSC population Necessary for lifelong blood cell production.
  • Mechanisms: Includes asymmetric cell division and stochastic differentiation.

Types of Stem Cells

  • Definitions:
    • Totipotent Stem Cells: Can differentiate into any cell type including embryonic and extra-embryonic tissues (e.g., complete organism).
    • Pluripotent Stem Cells: Ability to become any cell type within the body, derived from early embryos or reprogrammed adult cells (iPSCs).
    • Multipotent Stem Cells: Limited to differentiate into a specific lineage (e.g., hematopoietic stem cells).

Importance of HSCs

  • Essential in various stem cell transplantation therapies, including providing a functional immune response for immunodeficient individuals, replacing defective hematopoietic systems, and restoring function post-chemotherapy.

Challenges in iPSC Generation

  • iPSCs are derived from adult somatic cells, with inherent challenges in reprogramming while avoiding oncogenic transformations.

Haematopoietic Differentiation Pathways

  • Differentiation leads to red blood cells, lymphocytes, and myeloid-origin cells, crucial in innate immunity and clotting processes.
  • Regulation is heavily influenced by cytokines and growth factors which determine the specific lineage and functionality of blood cells produced.