Hematology and Related Disorders

Introduction

Hematology is the study of blood, its components, and related disorders. Understanding the composition, function, and pathology of blood is essential for students of Anatomy & Physiology, as blood plays a critical role in homeostasis, transport, and immune defense.

Composition of Blood

Main Components

• Plasma: Makes up about 55% of blood volume; consists of 90% water, 8% proteins (mainly albumin, globulins, and fibrinogen), and 2% hormones, electrolytes, and enzymes.

• Cellular Elements: Includes erythrocytes (red blood cells, RBCs), leukocytes (white blood cells, WBCs), and thrombocytes (platelets).

Functions of Blood Elements

• Transport: Delivers nutrients, hormones, oxygen, and other substances to tissues; removes cellular waste (e.g., CO2).

• Regulation: Maintains temperature and distributes heat.

• Protection: Immune defense via WBCs and antibodies; clotting via platelets and fibrinogen.

Plasma Proteins

• Albumin: Maintains blood volume and oncotic pressure.

• Globulins: Transport substances (e.g., bilirubin, steroids, iron); include antibodies.

• Fibrinogen: Essential for blood coagulation.

Blood Cells

Erythrocytes (Red Blood Cells)

• Structure: Flexible, biconcave cells containing hemoglobin (~270 million molecules per cell).

• Function: Transport oxygen via hemoglobin; facilitate CO2 removal with carbonic anhydrase.

• Lifespan: Approximately 120 days in circulation.

Hemoglobin and Oxygen Saturation

• Hemoglobin (Hb): Protein with 2 alpha and 2 beta chains, each containing iron (Fe) for oxygen binding.

• Oxygen Saturation Curve: Shows the relationship between partial pressure of oxygen (PO2) and hemoglobin saturation.

Leukocytes (White Blood Cells)

• Types: Neutrophils (polymorphonucleocytes), lymphocytes, monocytes, eosinophils, basophils.

• Function: Immune defense; neutrophils are first responders to infection.

• Development: Immature forms (bands) indicate increased production during infection.

Thrombocytes (Platelets)

• Function: Initiate clotting, aggregate at injury sites, and promote vasoconstriction.

• Normal Count: Present in circulation of healthy individuals.

Formation and Lifecycle of Blood Cells

Hematopoiesis

• Process: Formation of blood cells from stem cells in bone marrow.

• Regulation: Controlled by cytokines and interleukins.

Erythrocyte Lifecycle

• Production: Stimulated by erythropoietin.

• Destruction: Old RBCs are removed by the spleen and liver.

Laboratory Values in Hematology

Common Laboratory Values

Interpreting Abnormal Values

• Low Hb/HCT: Indicates anemia.

• High WBC: Suggests infection or inflammation.

• Low PLT: May indicate bleeding risk.

Hematology Disorders

Anemia

Anemia is defined as a decrease in the number or function of RBCs, resulting in reduced oxygen delivery to tissues. It can be classified by cause and cell morphology.

• Iron Deficiency Anemia

• Megaloblastic Anemias (Vitamin B12 and Folate deficiency)

• Anemia of Chronic Disease

• Hemolytic Anemias

Iron Deficiency Anemia

• Cause: Insufficient iron for hemoglobin synthesis.

• Symptoms: Fatigue, pallor, glossitis, koilonychia (spoon nails), pica (craving non-food substances).

• Lab Findings: Low Hb, low ferritin, microcytic hypochromic RBCs.

Iron Physiology

• Functions: Hemoglobin synthesis, mitochondrial function, neurotransmitter production.

• Storage: In hemoglobin (RBCs), myoglobin, enzymes, liver (ferritin), and plasma (transferrin-bound).

Iron Absorption and Regulation

• Absorption: Occurs in duodenum via enterocytes; regulated by hepcidin and ferroportin.

• Transport: Iron is carried in blood by transferrin.

• Storage: Stored in liver as ferritin.

Types of Iron Deficiency

• Absolute Iron Deficiency: Total body iron is low due to blood loss, poor intake, or absorption issues.

• Functional Iron Deficiency: Iron stores are adequate but unavailable due to increased hepcidin (often in chronic disease).

Common Causes of Iron Deficiency

• Blood loss (menstruation, GI bleeding)

• Poor dietary intake

• Malabsorption (celiac disease, gastritis)

• Increased requirements (pregnancy)

Megaloblastic Anemias

• Vitamin B12 Deficiency: Impaired DNA synthesis; requires intrinsic factor for absorption in ileum. Causes include pernicious anemia (autoimmune destruction of gastric mucosa), malabsorption, and dietary deficiency.

• Folate Deficiency: Also impairs DNA synthesis; often due to poor intake, malabsorption, or increased demand.

• Symptoms: Macrocytic anemia, neurologic changes (in B12 deficiency), glossitis, and pancytopenia.

Hemolytic Anemias

• Definition: Increased destruction of RBCs, either intravascularly or extravascularly.

• Causes: Sickle cell disease, thalassemias, G6PD deficiency, autoimmune reactions, toxins.

Sickle Cell Disease

• Genetics: Mutation in beta chain of hemoglobin (valine replaces glutamic acid).

• Pathophysiology: RBCs become sickle-shaped, aggregate, and occlude vessels, causing hypoxia and organ damage.

• Clinical Presentation: Pain crises, anemia, asplenia.

Thalassemias

• Definition: Defective synthesis of alpha or beta globin chains.

• Symptoms: Microcytic, hypochromic anemia; bone deformities; iron overload.

G6PD Deficiency

• Definition: Enzyme deficiency leading to oxidative damage and hemolysis.

• Triggers: Certain drugs, infections, fava beans.

Polycythemia

• Definition: Increased RBC mass.

• Types: Primary (polycythemia vera), secondary (due to hypoxia or increased erythropoietin), and relative (due to plasma loss).

Summary Table: Anemia Types and Lab Findings

Treatment Approaches

• Iron Deficiency: Oral iron supplementation (ferrous sulfate); absorption enhanced with vitamin C; IV iron for intolerance or severe deficiency.

• Vitamin B12 Deficiency: Parenteral or oral supplementation.

• Folate Deficiency: Oral supplementation.

Key Terms and Definitions

• Hemoglobin (Hb): Oxygen-carrying protein in RBCs.

• Hematocrit (HCT): Percentage of blood volume occupied by RBCs.

• MCV: Mean corpuscular volume; average size of RBCs.

• Reticulocyte: Immature RBC; indicates bone marrow activity.

• Ferritin: Protein for iron storage.

• Transferrin: Iron transport protein in plasma.

• Hepcidin: Hormone regulating iron absorption and release.

Important Equations

• Oxygen Content of Blood:

• Transferrin Saturation (TSAT):

Additional info: Some content was inferred and expanded for clarity and completeness, including definitions, normal ranges, and clinical context.