Anatomy and Physiology I Unit 18 ReviewThe Cardiovascular System – Blood

Key Components of Blood

• Plasma constitutes ~55% of blood volume and consists primarily of water, proteins, and dissolved substances
  • Proteins in plasma include albumins, globulins, and fibrinogen
  • Dissolved substances encompass nutrients, electrolytes, hormones, and waste products
• Formed elements comprise ~45% of blood volume and include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes)
  • Red blood cells are the most abundant formed elements (~5 million/μL) and contain hemoglobin for oxygen transport
  • White blood cells are less numerous (~5,000-10,000/μL) and play crucial roles in immune defense
  • Platelets are small, anucleate cell fragments (~150,000-400,000/μL) that participate in blood clotting
• Hematocrit represents the percentage of blood volume occupied by red blood cells, typically ranging from 38-48% in adults
• Blood pH is tightly regulated between 7.35-7.45 to ensure proper functioning of cells and enzymes
• Blood viscosity, influenced by hematocrit and plasma proteins, affects blood flow resistance and pressure

Blood Composition and Functions

• Blood is a connective tissue consisting of plasma and formed elements that serves vital functions in the body
• Transports oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs for exhalation
• Delivers nutrients (glucose, amino acids, lipids) absorbed from the digestive tract to cells throughout the body
• Removes metabolic waste products (urea, creatinine, uric acid) from cells and transports them to excretory organs
• Distributes hormones from endocrine glands to target tissues, enabling communication and regulation of body functions
• Helps regulate body temperature by absorbing and redistributing heat through circulation
• Maintains osmotic balance and pH homeostasis in tissues by adjusting plasma composition and buffering capacity
  • Plasma proteins contribute to colloid osmotic pressure, which helps retain fluid within blood vessels
• Provides immune defense through white blood cells and circulating antibodies that combat pathogens and foreign substances

Red Blood Cells and Hemoglobin

• Red blood cells (erythrocytes) are biconcave, anucleate cells that primarily function in oxygen transport
  • Lack of nucleus and organelles allows for maximum space for hemoglobin and enhances flexibility for capillary passage
• Hemoglobin, the oxygen-binding protein in red blood cells, consists of four globin subunits, each with an iron-containing heme group
  • Iron in heme reversibly binds to oxygen, allowing for efficient oxygen loading in the lungs and unloading in tissues
• Red blood cell production (erythropoiesis) occurs in the bone marrow and is regulated by the hormone erythropoietin (EPO)
  • EPO is produced by the kidneys in response to low blood oxygen levels (hypoxia)
• Red blood cells have a lifespan of ~120 days and are removed from circulation by the liver and spleen when they become senescent or damaged
• Anemia, a decrease in red blood cell count or hemoglobin concentration, can result from blood loss, decreased production, or increased destruction
  • Symptoms of anemia include fatigue, pallor, shortness of breath, and dizziness
• Polycythemia, an increase in red blood cell count, can occur due to chronic hypoxia (high altitude) or bone marrow disorders

White Blood Cells and Immunity

• White blood cells (leukocytes) are nucleated cells that defend the body against infections and foreign substances
• Granulocytes, which contain cytoplasmic granules, include neutrophils, eosinophils, and basophils
  • Neutrophils (~60% of leukocytes) are phagocytic cells that engulf and destroy bacteria and fungi
  • Eosinophils (~2-4%) target parasitic infections and participate in allergic reactions
  • Basophils (<1%) release histamine and other mediators involved in inflammation and allergic responses
• Agranulocytes, which lack cytoplasmic granules, include lymphocytes and monocytes
  • Lymphocytes (~30%) include T cells (cell-mediated immunity) and B cells (humoral immunity)
    • T cells directly attack infected or cancerous cells and regulate immune responses
    • B cells produce antibodies that neutralize pathogens and mark them for destruction
  • Monocytes (~5%) migrate into tissues and differentiate into macrophages, which phagocytose pathogens and cellular debris
• Leukocytosis, an increase in white blood cell count, often indicates an ongoing infection or inflammatory process
• Leukopenia, a decrease in white blood cell count, can result from bone marrow disorders or immunosuppressive conditions

Platelets and Coagulation

• Platelets (thrombocytes) are small, anucleate cell fragments derived from megakaryocytes in the bone marrow
• Play a critical role in hemostasis, the process of stopping blood loss from damaged blood vessels
  • Adhere to exposed collagen in damaged vessel walls and release chemicals that promote platelet aggregation and activation
  • Activated platelets change shape, express surface receptors, and release factors that amplify the coagulation cascade
• Coagulation (blood clotting) involves a series of enzymatic reactions that convert fibrinogen into insoluble fibrin strands
  • Intrinsic pathway is initiated by contact with negatively charged surfaces and involves factors XII, XI, IX, and VIII
  • Extrinsic pathway is triggered by tissue factor released from damaged cells and involves factor VII
  • Both pathways converge on the common pathway, which includes factors X, V, and II (prothrombin), leading to fibrin formation
• Anticoagulants, such as heparin and warfarin, are used to prevent excessive clotting in conditions like deep vein thrombosis and pulmonary embolism
• Disorders of platelet function or coagulation factors can lead to bleeding disorders, such as hemophilia and von Willebrand disease
  • Hemophilia is caused by deficiencies in factors VIII (hemophilia A) or IX (hemophilia B), leading to prolonged bleeding
  • Von Willebrand disease results from a deficiency in von Willebrand factor, which helps platelets adhere to damaged vessel walls

Blood Types and Transfusions

• Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells
• ABO blood group system is based on the expression of A and B antigens
  • Type A individuals have A antigens and produce anti-B antibodies
  • Type B individuals have B antigens and produce anti-A antibodies
  • Type AB individuals have both A and B antigens and do not produce antibodies against either
  • Type O individuals lack A and B antigens and produce both anti-A and anti-B antibodies
• Rh blood group system is based on the presence (+) or absence (-) of the Rh factor (D antigen)
  • Rh incompatibility between an Rh-negative mother and Rh-positive fetus can lead to hemolytic disease of the newborn
• Compatibility testing (cross-matching) is performed before transfusions to ensure donor and recipient compatibility
  • ABO incompatibility can cause immediate and severe transfusion reactions due to preformed antibodies
  • Rh incompatibility can lead to sensitization and future transfusion reactions or complications in pregnancy
• Universal donors (Type O-) can donate to all blood types, while universal recipients (Type AB+) can receive from all types

Blood Disorders and Diseases

• Anemias are characterized by decreased red blood cell count or hemoglobin concentration, leading to reduced oxygen-carrying capacity
  • Iron-deficiency anemia results from inadequate dietary iron intake or chronic blood loss
  • Pernicious anemia is caused by vitamin B12 deficiency due to lack of intrinsic factor production in the stomach
  • Sickle cell anemia is an inherited disorder caused by a mutation in the hemoglobin gene, leading to abnormally shaped red blood cells
• Leukemias are cancers of the blood-forming tissues that result in the uncontrolled production of immature or abnormal white blood cells
  • Acute leukemias (lymphoblastic or myeloid) progress rapidly and require immediate treatment
  • Chronic leukemias (lymphocytic or myeloid) develop more slowly and may not require treatment in early stages
• Lymphomas are cancers of the lymphatic system that arise from lymphocytes in lymph nodes, spleen, or other tissues
  • Hodgkin lymphoma is characterized by the presence of Reed-Sternberg cells and often presents with enlarged lymph nodes
  • Non-Hodgkin lymphomas encompass a diverse group of cancers with varying cell types and clinical presentations
• Myeloproliferative disorders, such as polycythemia vera and essential thrombocythemia, involve the overproduction of red blood cells or platelets
• Bleeding disorders, like hemophilia and von Willebrand disease, result from deficiencies in coagulation factors or platelet function
  • Treatment involves replacing the missing factors or using medications to promote clotting
• Disseminated intravascular coagulation (DIC) is a life-threatening condition characterized by widespread, uncontrolled activation of the coagulation cascade
  • Can be triggered by severe infections, trauma, or certain cancers and leads to simultaneous clotting and bleeding

Clinical Applications and Lab Tests

• Complete blood count (CBC) is a routine lab test that measures red blood cell count, white blood cell count, platelet count, and hemoglobin concentration
  • Used to diagnose anemia, infections, leukemia, and other blood disorders
  • Differential white blood cell count provides information on the relative proportions of different types of leukocytes
• Coagulation tests, such as prothrombin time (PT) and activated partial thromboplastin time (aPTT), assess the function of the extrinsic and intrinsic pathways, respectively
  • Prolonged PT or aPTT may indicate deficiencies in coagulation factors or the presence of anticoagulants
• Blood typing and antibody screening are performed before transfusions or during pregnancy to ensure compatibility and prevent complications
• Hemoglobin electrophoresis is used to diagnose hemoglobinopathies, such as sickle cell anemia and thalassemia
  • Separates different types of hemoglobin based on their electrical charge and migration pattern
• Flow cytometry is a technique that analyzes the expression of cell surface markers on blood cells
  • Used to diagnose and classify leukemias and lymphomas based on the immunophenotype of the abnormal cells
• Bone marrow aspiration and biopsy are invasive procedures that involve collecting samples of bone marrow for microscopic examination
  • Performed to diagnose blood cancers, assess response to treatment, or evaluate unexplained anemia or thrombocytopenia
• Therapeutic apheresis is a procedure that selectively removes specific components of blood, such as platelets or plasma, for treatment purposes
  • Plasmapheresis is used to remove antibodies in autoimmune disorders like Guillain-Barré syndrome and myasthenia gravis
  • Plateletpheresis is used to collect donor platelets for transfusion or to treat conditions like thrombotic thrombocytopenic purpura (TTP)