Formed Elements of Blood

Overview of Blood Cell Types

The blood contains several types of cells, each with distinct functions essential for immunity, oxygen transport, and hemostasis.

• Red blood cells (erythrocytes): Specialized for oxygen transport via hemoglobin.

• Platelets (thrombocytes): Derived from megakaryocytes; crucial for blood clotting.

• Granulocytes: Includes neutrophils, eosinophils, and basophils; involved in innate immune responses.

• Monocyte and macrophage lineage: Engulf and destroy pathogens and debris; derived from myeloid stem cells.

• Lymphocytes: T lymphocytes (T cells) and B lymphocytes (B cells) originate in bone marrow and migrate between blood and lymphatic tissues.

Key Point: All blood cells are derived from hematopoietic stem cells in the bone marrow.

Hematopoietic Tissue

Sites of Blood Cell Formation

Hematopoietic tissues are responsible for the formation of blood cells throughout life.

• Myeloid tissue: Bone marrow found in flat bones and ends of long bones; also present in liver and spleen before birth.

• Lymphoid tissue: Includes lymph nodes, thymus, and spleen.

Hematopoiesis is the process of forming new blood cells from stem cells, which differentiate into committed progenitor cells and then into mature blood cells.

• WBCs are formed partially in bone marrow and partially in lymphatic system.

• RBCs and platelets are formed in the marrow and released into circulation.

Growth and Reproduction of White Blood Cells

Regulation and Renewal

White blood cell (WBC) production is tightly regulated by hematopoietic growth factors.

• Different stem cells are controlled by multiple growth factors or inducers.

• WBCs have a relatively short lifespan, requiring constant renewal to maintain normal levels.

• Decreased availability of stem cells or growth factors leads to reduced WBC counts.

Diseases of Deficient Blood Cell Production

Types and Causes

Deficiencies in blood cell production can lead to various clinical conditions.

• Leukopenia: Deficiency of leukocytes (WBCs).

• Neutropenia: Low number of neutrophils; increases risk of bacterial/fungal infections. Causes include autoimmune disorders, medications, leukemia, and genetic disorders.

• Granulocytopenia: Low granulocytes (neutrophils, eosinophils, basophils, eosinophils); associated with leukemia, aplastic anemia, infections, autoimmune diseases, and medications.

• Aplastic anemia: Failure to produce enough blood cells, leading to anemia (low RBCs), thrombocytopenia (low platelets), and agranulocytosis (low granulocytes).

Neutropenia: Causes and Symptoms

Etiology and Clinical Manifestations

Neutropenia can result from various mechanisms and presents with characteristic symptoms.

• Causes:

  • Accelerated removal or destruction of WBCs (e.g., infection, drugs).

  • Drug-induced granulocytopenia.

  • Periodic or cyclic neutropenia.

  • Neoplasms involving bone marrow.

  • Idiopathic neutropenia (unknown cause).

  • Autoimmune conditions (e.g., Felty syndrome in rheumatoid arthritis).

• Symptoms:

  • Malaise

  • Chills

  • Fever

  • Extreme weakness and fatigue

  • Reduced white blood cell count

High-risk patients: Cancer patients undergoing chemotherapy. Neutropenic precautions include strict hygiene, avoiding sick contacts, raw foods, and invasive procedures.

Infectious Mononucleosis

Definition and Etiology

Infectious mononucleosis is a self-limited lymphoproliferative disorder, commonly known as "mono" or the "kissing disease."

• Caused by the Epstein-Barr virus (EBV), a member of the herpesvirus family, transmitted via saliva.

• Characterized by fever, generalized lymphadenopathy, sore throat, and atypical lymphocytes in blood.

• Most common in adolescents and young adults.

• Treatment is symptomatic and supportive.

Neoplastic Disorders of Hematopoietic and Lymphoid Origin

Major Categories

Neoplastic disorders involve abnormal growth of blood or lymphoid cells, often resulting in tumors or masses.

• Lymphomas: Includes Hodgkin disease and non-Hodgkin lymphoma.

• Leukemia: Malignant transformation of blood cell lines.

• Plasma cell dyscrasias: Disorders affecting plasma cells, such as multiple myeloma.

Clinical Features of Neoplasms

Determinants and Chromosomal Aberrations

The clinical presentation of hematopoietic neoplasms is influenced by their origin and genetic changes.

• Site of origin and progenitor cell type (mature vs. immature).

• Molecular events leading to malignant transformation.

• Chromosomal aberrations:

  • Deletions

  • Polyploidy

  • Translocations

  • Hyperploidy

  • Inversions

Hodgkin Disease and Non-Hodgkin Disease

Comparison and Diagnosis

Both are lymphomas but differ in clinical features, prognosis, and diagnostic markers.

Symptoms and Categories of Lymphomas

Clinical Manifestations

• Hodgkin Disease:

  • Stage A: Lack of constitutional symptoms

  • Stage B: Enlarged lymph node, weight loss, fever, pruritus, night sweats

  • Advanced: Fatigue, anemia, organ involvement

• Non-Hodgkin Lymphomas:

  • Low-grade: Predominantly B-cell tumors

  • Intermediate-grade: B-cell and some T-cell lymphomas

  • High-grade: Immunoblastic (B-cell), lymphoblastic (T-cell), Burkitt, and non-Burkitt lymphomas

Treatment for Hodgkin and Non-Hodgkin Lymphomas

Therapeutic Approaches

• Depends on histologic type, stage, and clinical status.

• Radiation and combination chemotherapy are standard.

• For NHL: Adjuvant radiation therapy and monoclonal antibodies may be used.

Leukemias

Definition and Classification

Leukemias are malignant neoplasms of hematopoietic stem cells, classified by cell lineage.

• Lymphocytic: Involves lymphocytes.

• Myelocytic: Involves granulocytes and monocytes.

Chronic Leukemias

Types and Features

• Chronic lymphocytic leukemia (CLL): Proliferation of well-differentiated lymphoid cells.

• Chronic myelogenous leukemia (CML): Proliferation of well-differentiated myeloid cells.

Classification of Leukemia Types

Major Forms and Characteristics

Additional info: The Philadelphia chromosome is a translocation between chromosomes 9 and 22, resulting in the BCR-ABL fusion gene, which drives CML.

Criteria for Remission and Treatment Goals

ALL, AML, and CML

• Remission (ALL/AML):

  • Age, type, and stage of leukemia at presentation

  • Less than 5% blasts in bone marrow

  • Normal peripheral blood counts

  • Absence of cytogenetic abnormalities

  • Return to pre-illness performance status

• Goals for CML:

  • Normalized blood counts

  • Reduction/elimination of Philadelphia chromosome (Ph gene)

  • Elimination of BCR-ABL fusion protein

Leukemic Cells: Pathophysiology and Complications

Cellular Features and Clinical Signs

• Leukemic cells are immature, poorly differentiated, proliferate rapidly, and have a long lifespan.

• They do not function normally and interfere with normal blood cell maturation.

• Can circulate in blood, cross the blood-brain barrier, and infiltrate organs.

Key Terms and Definitions

• Erythrocytes: Red blood cells responsible for oxygen transport.

• Thrombocytes: Platelets involved in blood clotting.

• Granulocytes: Neutrophils, eosinophils, basophils; part of innate immunity.

• Monocytes/Macrophages: Phagocytic cells that engulf pathogens.

• Lymphocytes: T cells and B cells; central to adaptive immunity.

• Leukopenia: Low WBC count.

• Neutropenia: Low neutrophil count.

• Aplastic anemia: Failure of bone marrow to produce blood cells.

• Leukemia: Malignant proliferation of blood cell precursors.

• Lymphoma: Malignant proliferation of lymphoid tissue.

• Multiple myeloma: Malignant proliferation of plasma cells.

Relevant Equations

• White Blood Cell Count:

• Blast Percentage in Remission: