Anemia and Hematopoiesis Overview

Anemia and Blood Parameters

• Anemia is characterized by reduced hematocrit and slower settling of red blood cell aggregates.
• Macrocytic red cells settle quickly; decreased Erythrocyte Sedimentation Rate (ESR) relates to hypofibrinogenemia, hypergammaglobulinemia, and hyperviscosity diseases.
• Various blood diseases lead to irregular RBC shapes, causing slower settling rates.
• Increased albumin concentrations correspond with a decreased ESR.

Hematopoiesis

• Hematopoiesis is the formation of blood cells occurring in the bone marrow.
• Major lineage and production rates include:
  • RBC lifespan: 120 days; daily production: 2.5 × 10⁹/L.
  • Neutrophil lifespan: 7 hours; daily production: 0.85 × 10⁹/L.
  • Platelet lifespan: 10 days; daily production: 2.5 × 10⁹/L.
• Prenatal hematopoiesis starts in the yolk sac, shifts to the liver, and finally settles in the bone marrow by the fourth month.

Factors Affecting Blood Cell Counts

• Newborns typically have higher RBC counts; females have lower counts than males.
• Exercise causes a temporary increase in cell counts; sleep slightly reduces them.
• Higher altitudes stimulate RBC production due to hypoxia.
• Emotional excitement can enhance adrenaline release, elevating erythrocyte counts.

Red Blood Cells (RBCs)

• Normal RBC diameter: 7.2 microns; thickness: 2.2 microns; approximately 65% water and 33% hemoglobin.
• Main functions: oxygen and carbon dioxide transport.
• Polycythemia is the physiological rise in RBC count; pathological condition of elevated RBCs is termed polycythemia vera.
• Anemia is defined as a decreased RBC count or low hemoglobin levels affecting oxygen supply.

Hemoglobin (Hb)

• Hb is a chromoprotein composed of globin and iron-containing heme; iron exists in ferrous form.
• Each Hb molecule contains four iron atoms; essential for transport of oxygen as oxyhemoglobin.
• Hb content ranges from 14 to 18 gm%; oxygen-carrying capacity is 1.34 ml per gm of Hb.
• Types of hemoglobin include fetal hemoglobin, methemoglobin, and carboxyhemoglobin.

Iron Metabolism

• Body iron content is about 4-5 mg/kg; key for hemoglobin synthesis and cellular function.
• Major sources include liver, spleen, kidneys, and dietary sources like leafy vegetables and nuts.
• Dietary iron absorption is low (10%); primarily occurs in the upper duodenum.
• Transported by transferrin; stored in the liver and spleen.
• Daily erythrocyte breakdown releases iron for resynthesis, with minimal iron excretion.

Rh Factor & Blood Transfusion

• Rh factor: presence in over 85% of individuals; Rh-negative individuals can develop antibodies after exposure to Rh-positive blood.
• Rh incompatibility in pregnancy can lead to hemolytic disease of the newborn; prevention requires anti-Rh immunization.
• M and N agglutinogens are non-antigenic but important for paternity determination.
• Blood transfusions require careful matching of donor and recipient blood groups to prevent adverse reactions.

Anticlotting Mechanisms

• Various plasma inhibitors and fibrinolysis prevent abnormal coagulation.
• Clotting cascade includes:
  • Formation of prothrombin activator.
  • Conversion of prothrombin to thrombin.
  • Conversion of fibrinogen to fibrin.
• Antithrombin III inhibits serine proteases, facilitated by heparin; Protein C inactivates factors V and VIII.

Summary of Hematopoiesis and RBC Lifecycle

• RBCs have an average lifespan of 120 days; constant breakdown and renewal regulate cell count.
• Spleen and liver are primary sites for RBC destruction; hemoglobin degradation releases iron for new cell production.