Module 1 : Blood (created b knowt)

These notes provide a comprehensive yet concise overview of formed elements (leukocytes and platelets), hemostasis, blood replacement, and laboratory blood tests, highlighting key processes, cell types, functions, and associated disorders.

1.4 Formed Elements Part II

Leukocytes (White Blood Cells - WBC)

• Main Defense: Inside the body against invading microorganisms and defective body cells (old, defective DNA, virus-infected).

• Clean Up: Remove cellular debris.

• Characteristics:

• Less abundant and much larger than RBCs.

• Only formed elements that are complete cells (possess nuclei and organelles).

• Many different types.

• Much shorter lifespan than RBCs (minutes to hours for some).

• Diapedesis: WBCs can leave capillaries to perform defense functions in tissues.

• Chemotaxis: Attracted to infection sites by chemical signals.

• Some WBCs become fixed in tissues (e.g., lymphatic tissue, bone marrow, spleen) instead of reentering the bloodstream.

• Classification: Granular leukocytes and Agranular leukocytes.

Platelets (Thrombocytes)

• Nature: Not true cells; cytoplasm fragments branching off megakaryocytes.

• Megakaryocytes: Large cells with lobed nuclei, remain in bone marrow.

• Release 2000-3000 platelets per lifetime into bloodstream, each enclosed by a plasma membrane.

• Phagocytized by macrophages after cytoplasm release.

• Thrombopoietin: Hormone from kidneys and liver, stimulates megakaryoblasts to mature into megakaryocytes.

• Function:

• Hemostasis: Stoppage of blood flow from a damaged vessel.

• Blood clotting.

• Secrete growth factors for tissue growth and repair.

Disorders of Leukocytes

• Leukopenia: Too few WBCs.

• Causes: Chemotherapy.

• Effect: Vulnerability to infection, increased susceptibility to life-threatening complications (e.g., sepsis).

• Leukocytosis: Too many leukocytes.

• Effect: Often means cells are improperly formed/non-functional, leading to vulnerability to infection and life-threatening complications.

• Leukemia: Cancer caused by an abundance of improperly developed leukocytes.

• Lymphoma: Cancer caused by malignant B and T cells collecting in spleen, lymph nodes, and liver, impairing their function.

Disorders of Platelets

• Thrombocytosis: Too many platelets in circulation.

• Effect: Increased blood clotting frequency, unnecessary clot formation.

• Thrombocytopenia: Too few platelets in circulation.

• Effect: Lack of blood clotting, excessive bleeding.

1.5 Hemostasis

• Definition: Closure of a broken blood vessel, preventing excessive blood loss. Effective for small wounds.

• Steps:

1. Vascular Spasm:

• Smooth muscle in vessel wall constricts to close the vessel and reduce blood flow.

• Triggered by vessel damage; endothelins released by vessel wall cells induce constriction.

• Lasts 30 minutes to several hours.

2. Formation of Platelet Plug:

• Temporary seal formed by platelets.

• Activation: Platelets become spiked and sticky, clumping at the injury site.

• Von Willebrand factor: Bridges platelets and exposed collagen in the vessel wall.

• Platelet Chemicals Released:

• ADP: Attracts more platelets.

• Serotonin: Maintains vasoconstriction, enhances platelet aggregation.

• PDGF (Platelet Derived Growth Factors): Attracts fibroblasts.

3. Coagulation Cascade:

• Chain of events creating a fibrin mesh to reinforce the platelet plug.

• Clotting Factors: 12 known factors, primarily secreted by the liver, circulate in inactive (pre-enzyme) form. Activation is exponential.

• Requirements: $Ca^{2+}$ and Vitamin K are essential for synthesis of many factors.

• Ultimate Goal: Convert fibrinogen (soluble plasma protein) to fibrin (insoluble fibrous protein).

• Pathways:

• Extrinsic Pathway (Tissue Factor Pathway):

• Faster (seconds), initiated by damage to tissues surrounding the blood vessel.

• Damaged tissues release Factor III (tissue factor) $\rightarrow$ activates Factor VII $\rightarrow$ Tissue Factor Complex $\rightarrow$ activates Factor X.

• Intrinsic Pathway (Contact Activation Pathway):

• More steps, more complex (minutes), initiated by factors intrinsic to blood (e.g., exposed collagen).

• Activates Factor XII $\rightarrow$ activates Factor X (activator complex).

• Common Pathway:

• Both extrinsic and intrinsic pathways merge here to activate Factor X.

• Factor X $\rightarrow$ prothrombin activator (inactive prothrombin).

• Prothrombin activator $\rightarrow$ thrombin (active).

• Thrombin transforms inactive fibrinogen (soluble) $\rightarrow$ active fibrin (insoluble).

4. Clot Retraction:

• Proteins within platelets contract, pulling fibrin threads tighter.

5. Clot Repair:

• Follows coagulation and retraction, restoring vessel lining.

• PDGF: Stimulates proliferation of smooth muscle cells and fibroblasts.

• Fibroblasts: Reconstruct vessel wall by secreting collagen and elastin.

• VEGF (Vascular Endothelial Growth Factor): Activates endothelial cell multiplication, regenerating the blood vessel lining.

• Fibrinolysis:

• Gradual degradation of the clot once the vessel lining is healed, restoring normal blood flow.

• Begins within 2 days after injury.

• Goal: Convert plasminogen (inactive enzyme) $\rightarrow$ plasmin (active enzyme that breaks down fibrin network).

• Requires plasminogen activator (tPA) and thrombin.

• Bradykinin: Released by basophils, acts as a vasodilator to counteract vasoconstriction and restore normal circulation.

• Factors Limiting Clot Growth and Formation:

• Anticoagulants: Substances that oppose blood clotting, preventing unnecessary clot formation.

• Remove/deactivate clotting factors.

• Protein C system: Inactivates clotting factors in the intrinsic pathway.

• TFPI (Tissue Factor Pathway Inhibitor): Inhibits Factor VII activation in the extrinsic pathway.

• Antithrombin: Inactivates Factor X, preventing prothrombin to thrombin conversion.

• Heparin: Released by basophils, opposes prothrombin.

Disorders of Hemostasis

• Delicate balance; imbalances can be fatal.

• Hemophilia: Inherited (X-linked recessive, mostly males) deficiency or inadequacy of clotting factors, leading to excessive bleeding. Treatment: Replacement of missing factors.

• Thrombocytopenia: Low platelet count, causes excessive bleeding due to ineffective platelet plug formation.

• Thrombocytosis: Excessive platelets, increases risk of clot formation.

• Thrombus: Blood clot formed inside a blood vessel.

• Embolus: Portion of a thrombus that breaks free and enters circulation.

• Embolism: An embolus that clogs a smaller vessel.

• PE: Pulmonary embolism (lungs).

• MI: Myocardial infarction (heart).

• CVA: Cerebrovascular accident (brain).

• Thrombosis: Formation of a thrombus within a blood vessel.

• Liver Dysfunction: Liver produces many clotting factors; scarring or damage can reduce or impair their synthesis.

• Causes: Vitamin K deficiency (needed for clotting factor synthesis), Hepatitis (liver inflammation), Cirrhosis (scarring).

1.6 Transfusion and Blood Replacement

Blood Replacement (Hematopoiesis)

• Definition: Continuous process of blood cell replacement.

• Lifespan: Most cells live hours to weeks (except memory cells, which can last years/lifetime).

• Donation (0.5 L):

• Plasma replacement: 24 hours.

• Formed element replacement: 4-6 weeks.

• Location: Most hematopoiesis occurs in red bone marrow.

• Children: Medullary cavity of long bones.

• Adults: Cranial, pelvis, sternum, proximal epiphysis of femur and humerus.

• Stem Cells:

• Hematopoietic stem cell: Undifferentiated stem cell in red bone marrow.

• Hemocytoblast: Mitotically active cell that forms all formed elements.

• Hematopoietic growth factors: Stimulate hemocytoblasts to divide and differentiate.

• Differentiation:

• Lymphoid stem cells: Give rise to lymphocytes (T cells mature in thymus, B cells mature in bone marrow).

• Myeloid stem cells: Become all other formed elements (erythrocytes, megakaryocytes $\rightarrow$ platelets, myeloblasts $\rightarrow$ neutrophils, eosinophils, basophils).

Erythropoiesis (RBC Production)

• Stages:

1. Proerythroblast: Early cell, synthesizing proteins and hemoglobin precursors.

2. Erythroblast: Filling with hemoglobin.

3. Normoblast: Ejects nucleus, forming a reticulocyte.

4. Reticulocyte: Enters circulation, maintains organelles for a few days.

5. Mature Erythrocyte: Remaining organelles ejected, circulates for 120 days.

• Homeostasis:

• Kidneys monitor blood oxygen saturation (filter 180 L/day).

• Hypoxia: Too low oxygen reaching tissues.

• Hypoxemia: Too low oxygen in blood.

• Low blood oxygen in kidneys $\rightarrow$ EPO (Erythropoietin) released.

• Testosterone increases EPO production (males have higher RBC count).

• EPO stimulates red bone marrow $\rightarrow$ increased RBC production $\rightarrow$ increased oxygen carrying capacity.

• Increased oxygen saturation $\rightarrow$ EPO secretion falls $\rightarrow$ homeostasis restored.

• Too many RBCs $\rightarrow$ increased blood viscosity, decreased cardiac output (CO) and tissue perfusion.

Laboratory 1: Blood Components, Typing and Tests

Standard Precautions for Handling Blood Samples

• Universal Precautions: Treat all samples as infectious.

• Autoclaving: Industrial sterilization using pressurized steam.

• PPE (Personal Protective Equipment): Gloves, face mask, protective eyewear, disposable protective clothing.

• Hand Hygiene: Wash hands before and after handling blood, even with gloves.

• Face Mask/Shield: Protect eyes, nose, mouth from airborne particles.

• Disinfection and Disposal:

• Use proper chemicals/autoclaving for tools, surfaces.

• Dispose of contaminated materials in designated hazardous bags/containers.

• Avoid Direct Skin Contact: Cover cuts/wounds with waterproof dressing, even under gloves.

• Spill Management: Clean spills immediately with disinfectant; follow protocols.

• Exposure Incidents: Report and seek immediate medical attention.

Hematocrit

• Definition: Percentage of red blood cells in total blood volume.

• Indication: Anemia, dehydration, other conditions.

• Normal Range:

• Men: 38-50% (Testosterone stimulates RBC production).

• Women: 35-47% (Menstruation causes monthly blood loss).

• Procedure: Blood centrifuged; RBCs settle at bottom, buffy coat (WBCs and platelets) in middle, plasma on top.

• Factors that Increase Hematocrit: Dehydration (less plasma), change in elevation (increased $O_2$ demand), increased exercise, Polycythemia Vera (too many blood cells).

• Factors that Decrease Hematocrit: Anemia, recent bleeding (including menstruation), vitamin/mineral deficiencies affecting RBC production, cirrhosis of the liver (affects iron).

Blood Smear

• Purpose: Examines visual characteristics (number, size, shape, abnormalities) of blood cells under a microscope.

• Indicates: Anemia, Leukemia, Malaria, blood-borne infections.

• Procedure: Drop of blood smeared on slide, often stained (e.g., for WBCs).

• Terms:

• Hypochromic: Decreased color in RBCs (less red), often due to iron deficiency.

• Hyperchromic: Increased color in RBCs (more red), RBCs look like whole red dots instead of typical donut shape.

Complete Blood Cell Count (CBC)

• Purpose: Counts number and types of cells, analyzes cell structure, size, and volume.

• Indicates: Various problems or disorders.

• Differential WBC Count (Diff): Measures percentage of each leukocyte type.

• WBC Abundance (Never Let Monkeys Eat Bananas):

1. Neutrophils (50-70%):

• Rapid responders to bacterial infections (first responders).

• Secretory granules stain light purple, nuclei 2-5 lobes.

• Phagocytosis: Ingest materials (cells, bacteria, debris).

• Granule Contents: Lysozyme (lyse bacterial cell walls), Defensins (puncture bacterial/fungal cell walls).

2. Lymphocytes (25-45%):

• Second most abundant WBC type, arise from lymphoid stem cells.

• Round nucleus, little cytoplasm. Initially form in bone marrow, travel to lymphatic tissues.

• Natural Killer (NK) cells: Recognize non-self/abnormal cells (cancerous, virus-infected) and kill locally. Non-specific immunity.

• B lymphocytes (B cells): Form plasma cells that produce Y-shaped antibodies to mark pathogens for destruction.

• T lymphocytes (T cells): Kill virus-infected or tumor cells by secreting local toxins.

3. Monocytes (3-8%):

• Originate from myeloid stem cells, large U-shaped nucleus.

• Leave circulation to become macrophages (phagocytic) in tissues.

• Help activate lymphocytes, engulf pathogens and cellular debris.

4. Eosinophils (2-4%):

• Phagocytic, nuclei 2 lobes, large red-orange granules.

• Granule Contents: Antihistamine molecules (counteract histamine, balance inflammatory response), molecules toxic to parasitic worms.

5. Basophils (0.5-1%):

• Intensify immune response, large dark blue granules, nuclei 2 lobes.

• Release histamine (inflammatory, vasodilator, attracts other WBCs) and heparin (opposes blood clotting).

Blood Typing and Rh Factor: Importance in Transfusion

• Blood Type (ABO Group): Determined by antigens (glycoproteins) on the surface of RBCs (agglutinogens).

• A type: A antigen.

• B type: B antigen.

• AB type: A and B antigens.

• O type: No antigens.

• Rh Factor: Another blood group antigen (D antigen).

• Rh+: D antigen present.

• Rh-: D antigen absent.

• Rh- individuals exposed to Rh+ blood (e.g., transfusion, pregnancy) can produce anti-D antibodies (agglutinins).

• Hemolytic disease of the newborn: Occurs if an Rh- mother carries an Rh+ fetus and her antibodies cross the placenta in a subsequent pregnancy. Prevented by RhoGAM injection.

• Compatibility: Crucial for safe transfusions. Antibodies in recipient's plasma will detect foreign antigens on donor RBCs.

• Transfusion Reaction: If antibodies recognize foreign antigens, they bind and cause agglutination (clumping), leading to hemolysis (RBCs burst).

• Universal Donor: Type O (no antigens), but typically only packed RBCs are given to limit plasma antibodies.

Serum Reactions (Blood Typing Test)

• Procedure: Patient's blood sample is mixed with bottles containing specific antibodies (e.g., anti-A, anti-B).

• Result: Clumping indicates the presence of the antigen that reacts with the added antibody (e.g., clumping with anti-A means A antigen is present).