Blood Composition and Function

Plasma and Its Components

The plasma is the liquid portion of blood, serving as a transport medium for nutrients, hormones, and waste products.

• Plasma Composition: Plasma is approximately 55% of total blood volume and consists of water, proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, and waste products.

• Plasma Proteins: Albumin maintains osmotic pressure and fluid balance; globulins are involved in immune responses; fibrinogen is essential for blood clotting.

• Water Homeostasis: Changes in plasma protein concentration, especially albumin, affect water movement between blood and tissues.

Example: Low albumin levels can lead to edema due to decreased osmotic pressure.

Formed Elements of Blood

Blood contains three main types of formed elements: erythrocytes, leukocytes, and platelets.

• Erythrocytes (RBCs): Specialized for oxygen transport; contain hemoglobin.

• Leukocytes (WBCs): Involved in immune defense; include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

• Platelets: Cell fragments essential for blood clotting.

Example: The life cycle of an erythrocyte involves production in bone marrow, circulation, and removal by the spleen.

Hematopoiesis and Erythropoiesis

Hematopoiesis is the process of blood cell formation, occurring primarily in the bone marrow.

• Major Cells: Hematopoietic stem cells (HSCs) give rise to all blood cells. Erythropoiesis produces RBCs via stages: proerythroblast, erythroblast, reticulocyte, and mature RBC.

• Feedback Regulation: Erythropoietin (EPO), produced by the kidneys, stimulates RBC production in response to hypoxia.

Example: Anemia from blood loss increases EPO secretion, enhancing erythropoiesis.

Leukocyte Types and Functions

Leukocytes are classified by structure and function.

• Granulocytes: Neutrophils, eosinophils, basophils (contain granules).

• Agranulocytes: Lymphocytes and monocytes (lack granules).

• Leukopenia: Low WBC count; Leukemia: Cancer of WBCs.

Hemostasis and Coagulation

Platelet Activation and Aggregation

Platelets play a central role in stopping bleeding by forming plugs at injury sites.

• Activation: Platelets change shape and release granules upon vessel injury.

• Aggregation: Platelets stick together to form a temporary plug.

• Degranulation: Release of substances that promote clotting.

Coagulation Pathways

Blood clotting involves a cascade of reactions leading to fibrin formation.

• Intrinsic Pathway: Initiated by damage inside the vessel; involves contact activation.

• Extrinsic Pathway: Triggered by tissue factor from outside the vessel.

• Common Pathway: Both pathways converge to activate factor X, leading to fibrin formation.

Equation:

Regulation of Coagulation

• Vitamin K: Essential for synthesis of clotting factors.

• Calcium: Required for several steps in the cascade.

• Positive Feedback: Thrombin accelerates its own production.

Fibrinolysis and Thrombosis

• Fibrinolysis: Breakdown of clots by plasmin.

• Thrombosis: Formation of abnormal clots within vessels.

• Thromboembolism: Clot travels and blocks another vessel.

Blood Typing and Transfusion

ABO and Rh Blood Groups

Blood types are determined by antigens on RBC surfaces.

• ABO System: Type A, B, AB, O based on presence of A and/or B antigens.

• Rh System: Rh+ (antigen present), Rh- (antigen absent).

• Universal Donor: Type O-; Universal Recipient: Type AB+

Transfusion Reactions

• Transfusion Reaction: Occurs when incompatible blood is transfused, leading to agglutination and hemolysis.

• Crossmatching: Laboratory tests ensure compatibility.

Laboratory Calculations

• Hematocrit (Ht): Percentage of RBCs in blood.

• WBC Percentage: Normal ranges must be memorized.

Equation:

Lymphatic System and Immunity

Functions and Organization

The lymphatic system returns excess tissue fluid to the bloodstream and is vital for immune defense.

• Major Functions: Fluid balance, absorption of fats, immune responses.

• Organization: Lymphatic vessels, lymph nodes, spleen, thymus, tonsils.

Lymph Formation and Circulation

• Lymph Formation: Fluid enters lymphatic capillaries from tissues.

• Circulation: Lymph flows through vessels and nodes, returning to venous blood.

Immune System Overview

• Innate Immunity: Non-specific, immediate defense (e.g., skin, phagocytes).

• Adaptive Immunity: Specific, slower response (e.g., lymphocytes, antibodies).

• Cell-Mediated Immunity: T cells attack infected cells.

• Antibody-Mediated Immunity: B cells produce antibodies.

Inflammation and Fever

• Inflammatory Response: Stages include vasodilation, increased permeability, phagocyte migration, and tissue repair.

• Fever: Elevated body temperature enhances immune function.

Lymphocyte Activation and Differentiation

• T Lymphocytes: Mature in thymus; involved in cell-mediated immunity.

• B Lymphocytes: Mature in bone marrow; produce antibodies.

• NK Cells: Destroy cancer and virus-infected cells.

Antibodies and Immunological Memory

• Antibody Structure: Y-shaped proteins that bind antigens.

• Immunological Memory: Memory cells enable faster secondary response.

• Primary vs. Secondary Response: Secondary is faster and stronger due to memory cells.

Vaccination and Immunity Types

• Active Immunity: Body produces its own antibodies (e.g., vaccination).

• Passive Immunity: Antibodies are transferred from another source (e.g., maternal antibodies).

Transplantation and Hypersensitivity

• Transplant Rejection: Immune system attacks transplanted tissue.

• Hypersensitivity Disorders: Excessive immune responses (e.g., allergies, autoimmune diseases).

Key Calculations and Reference Values

Cell Volume Calculations

• % Cell Volume: Used to determine proportions of WBCs and RBCs in blood.

Normal Reference Ranges

• Hematocrit (Ht): Normal range for males: ~40-54%; females: ~36-48%.

• WBC Percentage: Normal value: ~1% of total blood volume.

Additional info: Reference ranges may vary slightly by source; always use values provided by your instructor or textbook for exams.