Introduction

Changes in different types of blood cells occur in many diseases (Chapters 24: Blood: I. Structure & Function; Anemias Due to Decreased Erythropoiesis, 26: Blood: III. The White Blood Cells). For instance, changes in leukocyte count provide useful information in infectious diseases (Chapter 13: Infectious Diseases: I. Mechanisms of Tissue Changes in Infection). Anemia is an extremely common clinical problem that has many causes (Chapters 24: Blood: I. Structure & Function; Anemias Due to Decreased Erythropoiesis, 25: Blood: II. Hemolytic Anemias; Polycythemia). Neoplasms of the hematopoietic system include myeloproliferative disorders (Chapters 25: Blood: II. Hemolytic Anemias; Polycythemia, 26: Blood: III. The White Blood Cells), leukemias (Chapter 26: Blood: III. The White Blood Cells), malignant lymphomas (Chapter 29: The Lymphoid System: II. Malignant Lymphomas), and plasma cell myeloma (Chapter 30: The Lymphoid System: III. Plasma Cell Neoplasms; Spleen & Thymus). Leukemias and lymphomas represent the most common malignant neoplasms in persons under age 30 years. Successful treatment of these hematopoietic neoplasms has made their early and accurate diagnosis very important. Students may find it worthwhile to review the discussion of normal hemostasis in Chapter 9: Abnormalities of Blood Supply before undertaking a study of bleeding disorders (Chapter 27: Blood: IV. Bleeding Disorders).

Chapters 28: The Lymphoid System: I. Structure & Function; Infections & Reactive Proliferations, 29: The Lymphoid System: II. Malignant Lymphomas, and 30: The Lymphoid System: III. Plasma Cell Neoplasms; Spleen & Thymus deal with diseases of the lymph nodes, spleen, and thymus. These include infections, reactive proliferations, and malignant lymphomas. The student may find it helpful to review earlier chapters relating to the immune system (Chapter 4: The Immune Response) and immunodeficiency states (Chapter 7: Deficiencies of the Host Response) before embarking on these chapters.