Nur 302 Structure and Function of the Hematological System PDF

# Structure and Function of the Hematological System ## Nursing 302 ## Learning Objectives 1. Describe the components of blood. 2. Discuss diagnostic test used to identify red blood cell disorders. 3. Differentiate between the various types of anemia. 4. Discuss the pathophysiology of hematologi...

# Structure and Function of the Hematological System ## Nursing 302 ## Learning Objectives 1. Describe the components of blood. 2. Discuss diagnostic test used to identify red blood cell disorders. 3. Differentiate between the various types of anemia. 4. Discuss the pathophysiology of hematological disorders. 5. Identify common white blood cell and lymphatic disorders. 6. Discuss diagnostic test used to identify white blood cell disorders. 7. Interpret altered hematological lab values. 8. Describe the causative factors, clinical manifestations, and complications of platelet disorders. 9. Discuss the medical treatment of common blood disorders. ## Functions of the Hematological System The constant movement of blood ensures the critical components of blood are available to all parts of the body to carry out their chief functions: * Delivery of substances needed for cellular metabolism (oxygen via RBC) * Removal of wastes of metabolism (CO2) * Defence against microorganisms and injury (WBC) * Maintenance of acid-base balance * Blood clotting (clotting factors & platelets) ## Components of Blood (pg. 478) Blood volume is 5.5L in adults. | Component | Percentage | Description | | --------------------- | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | **Plasma (55%)** | | *Proteins (Albumin, Globulins, Fibrinogen, Prothrombin)*: Albumins maintain oncotic pressure, globulins include antibodies, fibrinogen and prothrombin are involved in clotting. <br> *Water*: Solvents for various components. <br> *Other Solutes (lons, Waste products)*: Various electrolytes to maintain osmotic pressure, waste products are transported to be excreted. | | **Cellular Components (45%)** | | *Erythrocytes ( RBC )*: Red blood cells transport oxygen throughout the body. <br> *Buffy Coat (<2%)*: Composed of platelets and leukocytes. | **Buffy Coat (<2%)** | | *Platelets*: Essential for blood coagulation and control of bleeding. <br> *Leukocytes (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils)*: Fight against microorganisms. Neutrophils are the first responders for early inflammation, Eosinophils are involved in allergic reactions and parasitic infection, Basophils contain histamine and are released during wound healing, lymphocytes mediate the adaptive immune response, monocytes are involved in phagocytosis. | ## Plasma Proteins | Major Type | Description | | ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Albumin | Major component of osmotic pressure of plasma. Functions as a carrier molecule; key role in drawing fluid back into the intravascular space (maintain oncotic pressure). In the case of decreased production (cirrhosis), or excessive loss of albumin (kidney disease), the reduced oncotic pressure leads to fluid movement into the tissue and decreased blood volume (ascites & edema). | | Globulins | Antibodies (immunoglobulin) and transport proteins. Carries our proteins and immunoglobulins (antibodies). | | Fibrinogens | Functions in blood clotting. | | Other | Various roles (α-1-antitrypsin, coagulation factors, etc.). | Plasma proteins can be classified by function. Functions are clotting, defense, transport, and regulation. ## Cellular Components ### Erythrocytes (Red Blood Cells) * Most abundant cells of the blood * Produced in bone marrow (erythropoiesis) * Life cycle of 80-120 days * Responsible for tissue oxygenation * Hemoglobin (Hb) carries the gases * Biconcave shape & ability to be reversible deformed (torpedo-like shape to flow through microcirculation) Development of RBC requires vitamin B12, folic acid, copper, cobalt and especially iron! ### Leukocytes (White Blood Cells) * Immune defense! * **Granulocytes** * Neutrophil: 1st response for early inflammation. * Eosinophil: ingest antibodies. * Basophil: contains histamine. * Mast Cell: released during wound healing. * **Agranulocytes** * Phagocytes: cells which engulf and digest particles as part of the immune response. * Immunocytes: cells which create immunity- Lymphocytes. ### Platelets (thrombocytes) * Essential for blood coagulation and control of bleeding (inducing vasoconstriction) * Will change shape to conform to the injured site (platelet plug) * Activates the coagulation cascade to stabilize the plug * Initiates repair processes including clot retraction and clot dissolution → fibrinolysis * Spleen is a reserve pool for platelets * Life cycle of 8-11 days, then removed by macrophages usually in the spleen * Normal concentration is 150-400 x 10°/L ## Lymphoid Organs The lymphoid system is joined with the circulatory system through lymphoid organs. These organs are the site of residence, proliferation, and differentiation of lymphocytes and phagocytes. ### Primary Lymphoid Organs * the thymus: (where T cells mature) * bone marrow: (where T and B cells are made) ### Secondary Lymphoid Organs: * the spleen: (blood reserve; phagocytosis of old blood cells) * lymph nodes: ("check stops" for immunity, where macrophages reside) ## Development of Blood Cells Hematopoiesis: the process of blood cell production, occurring in the bone marrow Bone marrow is found in the cavities of the bone; not all bones have active marrow Cellular differentiation occurs to then further create erythrocytes, leukocytes, and platelets from stem cells ## Development of Platelets & WBCs ### Platelets * Platelets are fragments of megakaryocytes which are produced in bone marrow * Platelet levels are regulated by thrombopoietin (TPO), which is produced by the liver. * Platelets circulate for 10 days before losing their functional capacity. * The spleen sequesters and destroys aging platelets by phagocytosis. ### WBCs * Leukocytes arise from stem cells in the bone marrow * Stored in the thymus and lymph nodes * Production increases in infection, presence of steroids, and reduced bone marrow reserves ## Development of RBCs Erythropoiesis: development of RBCs Erythrocytes are derived from erythroblasts in the bone marrow and through maturation stimulated by erythropoietin (EPO). * Under the control of a feedback loop. * In conditions of tissue hypoxia, erythropoietin is exceeded by the kidney. * Erythropoietin causes an increase in red blood cell production and release from bone marrow. ## Hemoglobin Synthesis Hemoglobin: oxygen-carrying protein of the erythrocyte * Two pairs (alpha & beta) of polypeptide chains (Globins) * Four colourful iron-protoporphyrin complexes (Heme) * Each heme carries one molecule of oxygen Nutritional Requirements: "building blocks" for RBCs & Hgb * Proteins * Amino acids * Vitamins * Vitamins B12, B6, B2, E, and C; folic acid; pantothenic acid; and niacin * Folate deficiency is more common and occurs rapidly; supplements are prescribed to pregnant women as folate demands increase → prevents anemia & neural tube defects in babe * Minerals * Iron (Hgb) and copper If these components are lacking for a prolonged amount of time, erythrocyte production slows, and anemia may result. ## Iron Cycle Total body iron is bound to heme or muscle cells, or stored bound to ferritin. Less than 1 mg per day (3%) is lost in the urine, sweat, bile, and epithelial cells or from the gut Iron is "recycled" from aged, abnormal or damaged RBCs. ## Mechanisms of Hemostasis Hemostasis: (hemo- blood, stasis- to stop), arrest of bleeding Components of hemostasis include platelets, clotting factors, and the vasculature. ### Sequence of Hemostasis 1. Vascular injury = vasoconstriction to limit blood flow 2. Platelet-to-platelet interactions resulting in formation of a hemostatic plug (platelet plug) 3. Coagulation (or clotting) cascade is activated to form fibrin clots 4. Fibrinolysis is activated to limit the size of the clot (retraction) and begin healing process (dissolution) NURSING ASSESSMENT: petechiae vs. purpura vs. ecchymosis? ## Function of Clotting Factors Blood Clot: a meshwork of protein strands which have stabilized the platelet plug & trap other cells such as erythrocytes (erythema) and phagocytes (remove any unwanted microorganisms that may have entered) Protein strands are made of fibrin which is produced by the clotting (coagulation) system * Initiation of this system results in the clotting cascade * Known as secondary hemostasis ### Intrinsic pathway * Activated when factor XII (Hageman factor) contacts subendothelial substances exposed by vascular injury ### Extrinsic pathway * Activated when tissue factor (TF) (tissue thromboplastin) is released by damaged endothelial cells ## Retraction and Lysis of Blood Clots After a clot is formed, it retracts, or "solidifies". Lysis (breakdown) of blood clots is carried out by the fibrinolytic system. * Tissue plasminogen activator (tPA) triggers fibrin clot degradation * Fibrin degradation products include D-dimer * What does d-dimer diagnose? ## Age and the Hematological System ### Pediatrics * Blood cell counts increase above adult levels at birth (due to trauma of birth and cutting the umbilical cord) * Children tend to have more atypical lymphocytes as a result of frequent viral infections ### Geriatrics * Erythrocyte life span is normal but erythrocytes are replaced more slowly * Iron depletion * Decreased total serum iron, iron-binding capacity, and intestinal iron absorption * Lymphocyte function decreases with age. * Platelet adhesiveness probably increases with age.