Introduction to Hematology

• Hematology is the study of blood.
• The circulatory system consists of the heart, blood vessels, and blood.
• Blood functions in communication, transportation, and immunity.
• Communication: Blood acts as connective tissue, conveying hormones.
• Transportation: Blood moves gases, ions, and waste products.
• Immune Function: Blood carries immune cells and inflammatory proteins, protecting against pathogens and aiding vessel repair.
• Blood is composed of plasma and formed elements.
• Plasma is the aqueous ground substance of blood.
• Hematocrit measures the proportion of red blood cells in blood.
• Human adults have 4-6 liters of blood, varying with height, fitness, weight, and sex.
• The homeostatic set point range for blood pH is 7.35-7.45.
• Erythrocytes are red blood cells, which lack nuclei.
• Hemoglobin, the oxygen transport protein, makes up most of red blood cells.
• Red blood cell lifespan is typically 120 days.
• Hemoglobin transports oxygen (O2) and carbon dioxide (CO2).
• Red blood cells are red due to hemoglobin, which contains iron,.
• Heme, a molecule containing iron, exists within each of the four globulin subunits of hemoglobin. This means each hemoglobin protein has four embedded iron atoms capable of carrying one oxygen apiece.
• Erythropoiesis is the formation of new red blood cells.
• Red blood cell production requires iron, amino acids, heme, folate, vitamin B12, and erythropoietin (EPO).
• Expired red blood cells are trafficked to the spleen or liver, where hemoglobin is recycled.
• Iron recycling involves transferrin transporting iron from heme back to red bone marrow for reuse.
• Heme breaks down into bilirubin, which is excreted in bile and eliminated in feces.
• Plasma is the extracellular matrix of blood, which is connective tissue.
• Plasma contains proteins and ions.
• The buffy coat contains leukocytes and platelets.
• Leukocytes are white blood cells that possess nuclei but not hemoglobin.
• Granulocytes are white blood cells with many granules.
• Agranulocytes are white blood cells lacking granules.

White Blood Cell Types and Functions

• Neutrophil: antibacterial

• Eosinophil: antiparasitic

• Basophil: histamine release

• Lymphocyte: antiviral

• Macrophage: phagocytosis

• Hematopoiesis, the formation of blood cells, occurs in red bone marrow and is controlled by erythropoietin.

• Hematopoietic stem cells form immature precursor cells (-blasts) that mature into blood cells.

• Leukocytes typically live for a few days, but some lymphocytes can survive for months or years.

• White blood cell counts increase during infection.

• WBC differentials can identify which WBC types are elevated, indicating the type of pathogen present.

• White blood cells can exit the bloodstream to act in tissues.

• Platelets are cell fragments released from megakaryocytes in bone marrow.

• Homeostasis is a sequence of responses to stop blood loss from damaged vessels.

• Three hemostasis mechanisms: vascular spasm, platelet plug formation, and blood clotting (coagulation).

• Vascular spasm involves smooth muscle contraction in a damaged vessel wall.

• Platelet plug formation: platelets stick to damaged tissue, release activating chemicals, and aggregate.

• Coagulation: Blood clots are a gel of blood, plasma, platelets, and protein fibers.

Coagulation Process

• Clots are created by a cascade of reactions with platelets and clotting factors, requiring Vitamin K.
• The final clot product includes fibrin.

Intrinsic Pathway Steps

• Exposed collagen fibers activate factor XII (1).
• Factors XI and IX are activated (2).
• Factors IXa, VIIIa, and Ca2+ form an enzyme complex that activates factor X (3).

Extrinsic Pathway Steps

• Subendothelial cells display tissue factor (1).
• Tissue factor activates factor VII (2).
• Factor VIIa, tissue factor, and Ca2+ form an enzyme complex that activates factor X (3).

Common Pathway Steps

• Factors Xa, Va, and Ca2+ form prothrombin activator, converting prothrombin into thrombin (4).
• Thrombin turns fibrinogen into fibrin, which glues the platelet plug together (5).
• The body prevents excess clotting through thrombolysis, the enzymatic breakdown of fibrin.
• Antithrombin secreted by the liver and heparin secreted by basophils are involved in controlling clotting.

Thrombolysis Process

• Endothelial cells release tissue plasminogen activator (tPA) (1).
• tPA activates plasminogen (2).
• Plasmin degrades fibrin, dissolving the clot (3).
• Thrombosis can manifest as pulmonary embolism, stroke, myocardial infarction, or deep vein thrombosis.
• Thrombi can result from atherosclerosis, trauma, or infection.
• An embolus is a thrombus dislodged from a vessel wall.
• Blood typing systems: ABO typing and Rh factor grouping.

ABO Blood Typing

• Identifies the presence or absence of A and B antigens on red blood cells.
• A and B antibodies exist in the plasma.
  • Type A: A antigens, B antibodies
  • Type B: B antigens, A antibodies
  • Type AB: A and B antigens, no antibodies
  • Type O: no antigens, A and B antibodies

Rh Blood Group

• The positive and negative part of blood type.
• Rh factor matters in pregnancy when an Rh- mother carries an Rh+ fetus.
• The mother can develop antibodies against the Rh antigen in the fetal blood.
• During a second Rh+ pregnancy, these antibodies can cause hemolytic disease in the fetus or newborn.

Blood transfusions

• Blood types: A+, A-, B+, B-, AB+, AB- , O+, or O-.
• Blood type incompatibility causes agglutination and hemolysis.
• Type O is the universal donor.
• Universal donor: can give blood to anyone
• A person with blood type A can receive blood from types O and A.
• A person with blood type B can donate to types B and AB.
• Type AB is the universal recipient.
• Universal recipient: a person with blood type AB can receive blood from everyone

Additional Blood Transfusion Notes

• Type O can only receive from type O.
• Type AB can only donate to another AB
• Blood type B can donate to both blood type B and AB.
• A person with blood type A can receive blood from types A and O
• Blood type AB can receive blood from all blood types

Concise summary of hematology, the circulatory system, and blood composition, detailing its roles in communication, transportation, and immune response. It covers blood components like plasma and erythrocytes, hemoglobin function, typical blood volume in adults, and the homeostatic pH range.