CH 17

Learning Objectives

  • Describe the functions and composition of the blood.

  • Describe the formed elements of blood and their functions.

  • List major plasma components and their roles (albumin, globulin, fibrinogen).

  • Explain hematopoiesis, stem cell differentiation, and development of mature blood cells.

  • Identify characteristics and functions of red blood cells (RBCs), hemoglobin structure, recycling of components, and erythropoiesis with erythropoietin's role.

  • Discuss abnormal lab values of RBCs, types, and causes of anemia.

  • Categorize types of white blood cells (WBCs), their structure, count, and functionality.

  • Explain normal percentages of leukocytes and significance of abnormal counts (leukopenia, leukocytosis, leukemia).

  • Describe structure, function, and production of platelets.

  • Explain the phases of hemostasis: vascular spasm, platelet plug formation, and coagulation.

  • Differentiate between intrinsic and extrinsic pathways of the clotting cascade and the joint pathway of coagulation.

  • Explain fibrinolysis and disorders like thrombosis, thrombus, embolus, and thrombocytosis/thrombocytopenia.

  • Distinguish antigens and antibodies in ABO and Rh blood types, compatibility in blood transfusion, and conditions like erythroblastosis fetalis.

Functions and Composition of Blood

  • Definition: Blood is a liquid connective tissue made of cells suspended in a liquid matrix (plasma).

  • Composition Breakdown:

    • Erythrocytes (Red Blood Cells): (approx. 45% of blood volume)

    • Hematocrit:

      • Normal values: Males: 47% ± 5%; Females: 42% ± 5%.

    • White Blood Cells and Platelets: (< 1%, located in Buffy coat)

    • Plasma: (approx. 55%)

Major Plasma Components

  • Water: ~91.5% of plasma.

  • Proteins:

    • Albumins (54%): Regulate osmotic pressure and transport substances.

    • Globulins (38%): Involved in immune response.

    • Fibrinogen (7%): Essential for blood clotting.

    • Other solutes (1.5%): Nutrients, electrolytes, gases, hormones, wastes.

Hematopoiesis

  • Definition: Process of blood cell production.

  • Stem Cells: Pluripotent stem cells differentiate into:

    • Erythrocytes

    • Leukocytes (lymphocytes, monocytes, granulocytes)

    • Platelets (from megakaryocytes)

Red Blood Cells

  • Function: Carry oxygen to tissues and some carbon dioxide back to lungs.

  • Structure:

    • No nucleus, biconcave shape: enhances flexibility and gas exchange.

    • Hemoglobin (Hb):

    • Contains iron; can bind up to four oxygen molecules.

    • Involved in blood flow regulation via nitric oxide (NO) release.

  • Lifespan: About 120 days, removed by spleen and liver.

Erythropoiesis

  • Stimulated by: Erythropoietin (hormone released in response to low oxygen).

  • Reticulocytes: Immature RBCs released into circulation, mature in 1-2 days.

White Blood Cells

  • Types: Granular (neutrophils, eosinophils, basophils) and agranular (lymphocytes, monocytes).

  • Functions: Combat infections, involved in immune response.

  • Emigration: Process where WBCs leave bloodstream to attack pathogens.

  • Counts: Normal range is 5000-10,000 cells per microliter of blood.

Disorders associated with WBCs

  • Leukopenia: Low WBC count; can be drug-induced or due to various diseases.

  • Leukemia: Cancer characterized by overproduction of abnormal WBCs.

Platelets

  • Formation: Derived from megakaryocytes in the bone marrow.

  • Function: Essential for blood clotting; survive 5-9 days.

Hemostasis

  • Definition: The physiological process that prevents and stops bleeding.

  • Stages:

    1. Vascular spasm (contraction of blood vessels).

    2. Platelet plug formation (activation and aggregation of platelets).

    3. Coagulation (clotting).

Coagulation Pathways

  • Intrinsic Pathway: Triggered by blood in contact with vessel walls; factors present in blood.

  • Extrinsic Pathway: Triggered by external factors (tissue damage).

  • Both pathways converge to form prothrombinase, leading to thrombin production and fibrin formation.

Fibrinolysis

  • The breakdown of clots post-repair; plasminogen is converted to plasmin, digesting fibrin.

  • Vitamin K is vital for clotting factor synthesis.

Blood Typing and Transfusion

  • ABO Blood Group:

    • A, B antigens present; O type has neither.

    • Agglutinins (antibodies) present to combat foreign antigens.

  • Rh Factor: Rh+ (presence of D antigen) and Rh- (absence).

  • Universal Donor: Type O; Universal Recipient: Type AB.

Hemolytic Disease of the Newborn (Erythroblastosis Fetalis)

  • Occurs when Rh- mother carries Rh+ fetus; maternal antibodies destroy fetal RBCs.

  • Prevention: RhoGam injection to inhibit antibody formation.