Study Notes on Blood Characteristics, Functions, and Hemostasis

CHAPTER 19 - BLOOD

19-1 Physical Characteristics of Blood

  • Important Functions of Blood
    • Transportation of dissolved substances

    • Oxygen

    • Carbon dioxide

    • Nutrients

    • Hormones

    • Immune system components

    • Waste products
      • Regulation of pH and ions
      • Restriction of fluid losses at injury sites
      • Defense against toxins and pathogens
      • Stabilization of body temperature

  • Three General Characteristics of Blood
    • Normal temperature: 38°C (100.4°F)
    • High viscosity: 4 times that of water
    • Slightly alkaline pH: 7.35–7.45
    • Red color due to hemoglobin
    • Blood volume: 7% of body weight (in kilograms)

    • Adult male: 5 to 6 liters

    • Adult female: 4 to 5 liters

  • Whole Blood
    • Plasma

    • Fluid consisting of:

      • Water

      • Dissolved plasma proteins

      • Other solutes
        • Formed Elements

    • All cells and solids

19-2 Plasma

  • The Composition of Plasma
    • Plasma makes up 50–60% of blood volume
    • More than 90% of plasma is water
    • Plasma Proteins
    • Solutes
    • Extracellular Fluids

    • Interstitial fluid (IF) and plasma
      • Serum

    • Liquid part of blood after fibrinogen has converted to solid fibrin

  • Major Proteins of the Blood Plasma

    Protein

    Percentage

    Functions

    Albumin

    60%

    Responsible for colloid osmotic pressure; major contributor to blood viscosity; transports lipids, hormones, calcium, and other solutes; buffers blood pH

    Globulins

    36%


     Alpha (α) globulins


    Transports hemoglobin released by dead erythrocytes; transports copper (Haptoglobulin, Ceruloplasmin, Prothrombin); promotes blood clotting

     Beta (β) globulins


    Transferrin; complement proteins; transport lipids, fat-soluble vitamins, and hormones; transports iron; aids in destruction of toxins and microorganisms

     Gamma (γ) globulins


    Antibodies; combat pathogens

    Fibrinogen

    4%

    Becomes fibrin, the major component of blood clots

  • Other Solutes
    • Organic Nutrients

    • Lipids (fatty acids, cholesterol, glycerides)

    • Carbohydrates (primarily glucose)

    • Amino acids
      • Electrolytes

    • Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO₃⁻, HPO₄²⁻, SO₄²⁻
      • Organic Wastes

    • Urea

    • Uric acid

    • Creatinine

    • Bilirubin

    • Ammonium ions

19-3 Red Blood Cells (RBCs)

  • Formed Elements
    • Red blood cells (RBCs) make up 99.9% of blood’s formed elements.
    • Hemoglobin

    • The red pigment that gives whole blood its color

    • Binds and transports oxygen and carbon dioxide

  • Abundance of RBCs
    • Red Blood Cell Count

    • Male: 4.5–6.3 million cells per microliter of whole blood

    • Female: 4.2–5.5 million cells per microliter of whole blood
      • Hematocrit

    • Percentage volume of RBCs in centrifuged whole blood

    • Male: 40–54%

    • Female: 37–47%

  • Structure of RBCs
    • Small and highly specialized discs
    • Thin in the middle and thicker at the edge

  • Three Important Effects of RBC Shape on Function
    • High surface-to-volume ratio allows for quick absorption and release of O₂
    • RBCs form stacks called rouleaux, smoothing flow through narrow blood vessels
    • Discs bend and flex to pass through small capillaries (e.g., a 7.8-µm RBC can pass through a 4-µm capillary)

  • Hemoglobin (Hb)
    • Protein molecule that transports respiratory gases
    • Normal hemoglobin levels:

    • Adult male: 14–18 g/dL of whole blood

    • Adult female: 12–16 g/dL of whole blood

  • Hemoglobin Structure
    • Complex quaternary structure with four globular protein subunits
    • Each subunit has one molecule of heme
    • Each heme contains one iron ion that binds to one O₂

  • Hemoglobin Function
    • Transports oxygen; at peripheral capillaries where oxygen is low, hemoglobin releases oxygen
    • Binds carbon dioxide and transports it to the lungs; forms carbaminohemoglobin

  • RBC Formation and Turnover
    • 1% of circulating RBCs wear out per day, about 3 million RBCs are produced per second
    • Hemoglobin Conversion and Recycling

    • Monitored by macrophages in the liver, spleen, and bone marrow; they engulf aged RBCs before they hemolyze

  • Breakdown of Biliverdin
    • Biliverdin (green) converted to bilirubin (yellow); normal level 1-1.5 mg/dL
    • Excreted by liver (as bile); jaundice results from bilirubin buildup (>2-3 mg/dL)
    • Converted by intestinal bacteria into urobilins and stercobilins

19-4 Blood Typing

  • RBC Surface Antigens (Agglutinogens)
    • Cell surface proteins identifying cells to the immune system; normal cells are ignored while foreign cells are attacked
    • Blood types are genetically determined by the presence or absence of surface antigens A, B, Rh (or D)

  • Blood Plasma Antibodies
    • Type A (with surface antigen A) has Type B antibodies
    • Type B (with surface antigen B) has Type A antibodies
    • Type O (neither A nor B) has both A and B antibodies
    • Type AB (with both A and B) has neither A nor B antibodies

  • The Rh Factor (D antigen)
    • Either Rh positive (Rh+) or Rh negative (Rh-)
    • Only sensitized Rh- blood has anti-Rh antibodies; this may cause Hemolytic Disorder of Newborn (HDN)

19-5 White Blood Cells (WBCs)

  • White Blood Cells
    • Also called leukocytes; count: 5,000 to 10,000 per microliter
    • Do not contain hemoglobin; possess nuclei and other organelles
    • Main functions:

    • Defend against pathogens

    • Remove toxins and wastes

    • Attack abnormal cells

  • WBC Circulation and Movement
    • Four Characteristics of Circulating WBCs

    • Can migrate out of the bloodstream (emigration via diapedesis)

    • Exhibits amoeboid movement

    • Attracted to chemical stimuli (positive chemotaxis)

    • Some are phagocytic (e.g., neutrophils, eosinophils, monocytes)

  • Types of WBCs
    • Neutrophils
    • Eosinophils
    • Basophils
    • Monocytes
    • Lymphocytes

  • The Differential Count
    • Detects changes in WBC populations which may signal infections, inflammation, or allergic reactions
    • Mnemonic: "Never let monkeys eat bananas"

  • WBC Production
    • All blood cells originate from hemocytoblasts, producing myeloid and lymphoid stem cells
    • WBC Disorders

    • Leukopenia: Abnormally low WBC count

    • Leukocytosis: Abnormally high WBC count

    • Leukemia: Extremely high WBC count

19-6 Platelets (Thrombocytes)

  • Platelet Production (Thrombocytopoiesis)
    • Megakaryocytes (up to 160 microns) in the bone marrow release cytoplasmic fragments - platelets involved in clotting.
    • Platelets circulate for 9 to 12 days; removed by the spleen

  • Platelet Counts
    • Normal count: 150,000 to 500,000 per microliter
    • Thrombocytopenia vs. Thrombocytosis

    • Abnormally low platelet count vs. abnormally high platelet count

  • Three Functions of Platelets
    • Release important factors (ADP, Thromboxane, serotonin, PDGF, Ca²⁺)
    • Temporarily patch damaged vessel walls
    • Reduce size of a break in the vessel wall

19-7 Hemostasis

  • Hemostasis
    • Cessation of bleeding with three phases:

    • Vascular phase

    • Platelet phase

    • Coagulation phase

  • Healthy Endothelial Cells of Blood Vessels
    • Secrete antiplatelet substances:

    • Nitric Oxide (vasodilator)

    • Prostacyclin/PGI₂ (vasodilator)

    • ADP phosphatase

    • Heparin (activates Antithrombin III, breaking down thrombin, Xa, and IXa)

    • Thrombomodulin (modulates thrombin, activating Protein C which breaks down VIIIa and Va)

    • Tissue plasminogen activator (t-PA) (breaks down fibrin)

  • The Platelet Phase
    • Begins within 15 seconds after injury
    • Platelet Adhesion and Aggregation

    • Damaged endothelial cells produce Von Willebrand factor (VW)

    • VW factor causes platelets to adhere to surfaces, basement membranes, and exposed collagen fibers

    • Platelet aggregation leads to the formation of a platelet plug

    • GPIb receptors bind to VW factor, leading to the:

      • Formation of Thromboxane A₂ (promoting platelet adhesion)

      • Release of serotonin (vasoconstriction), Ca²⁺ (clotting), and ADP (platelet adhesion) from platelet granules

    • Inhibitors: Aspirin inhibits cyclooxygenase; Ticlopidine inhibits ADP platelet receptors

  • Factors that Limit Platelet Plug Growth
    • Prostacyclin inhibits platelet aggregation
    • Inhibitory compounds by WBCs
    • Circulating enzymes (e.g., ADPase) break down ADP
    • Negative feedback of high serotonin concentrations on ADP
    • Development of fibrin isolates the area

  • The Coagulation Phase
    • Begins 30 seconds or more after an injury
    • Blood clotting involves cascade reactions forming three pathways:

    • Extrinsic

    • Intrinsic

    • Common
      • Converts circulating fibrinogen into insoluble fibrin

  • Clotting Factors
    • Also referred to as procoagulants; proteins or ions in plasma essential for normal clotting

  • The Extrinsic Pathway
    • Initiated by damaged cells releasing tissue factor (TF) that activates factor VII, which, in tandem with Ca²⁺, activates Factor X

  • The Intrinsic Pathway
    • Initiated by activated platelets releasing factors (like PF3) due to exposure to collagen or damaged endothelium.
    • Cascade: XII → XI → IX → VIII activates Factor X

  • The Common Pathway
    • Where intrinsic and extrinsic pathways converge; Activated Factor X leads to:

    • Xa + Va + Ca²⁺ + platelets = prothrombinase complex

    • Converts prothrombin to thrombin

    • Thrombin converts fibrinogen to fibrin

  • Clot Retraction
    • Platelet contraction pulls torn edges of the vessel together, stabilizing the injury site and reducing bleeding

  • Fibrinolysis
    • Slow process dissolving the clot
    • Involves thrombin and tissue plasminogen activator activating plasminogen to produce plasmin, which digests fibrin strands

  • Clot Limitation Factors
    • Fibrin absorbs thrombin
    • Factors released by the endothelium (prostaglandins, antithrombin III) inhibit further clotting
    • Disseminated intravascular coagulation (DIC) can occur due to conditions like sepsis or abruptio placentae

  • Thrombus vs. Embolus
    • Thrombus: a clot
    • Embolus: a dislodged clot
    • Antithrombotics (e.g., warfarin, heparin) and thrombolytics (e.g., streptokinase, urokinase) are used to manage clotting