Study Notes on Blood - Functions, Composition, Hemostasis, and Blood Types

Chapter 15: Blood

Lesson 15.1: Functions and Composition of Blood

Functions of Blood

  • Transportation: Blood serves as a transport medium for various substances throughout the body.
  • Regulation: Blood helps maintain homeostasis by regulating:
    • Fluid and electrolyte balance
    • Acid-base balance (pH)
    • Body temperature
  • Protection:
    • Blood protects the body against infection.
    • Contains clotting factors that prevent excessive blood loss during injuries.

Composition of Blood

Types of Blood Cells
  • Erythrocytes (Red Blood Cells)
  • Leukocytes (White Blood Cells)
  • Thrombocytes (Platelets)
Formation of Blood Cells
  • Blood cells are formed through a process called hemopoiesis, which occurs in two ways:
    • Myeloid: Involves the formation in the bone marrow
    • Lymphoid: Involves formation in the lymphatic system

Characteristics of Blood

  • Type: Connective tissue consisting of blood cells suspended in a liquid matrix.
  • Color: Ranges from bright red (oxygenated) to darker blue-red (deoxygenated), depending on the oxygen saturation.
  • Volume: Typically ranges from 4 to 6 liters in adults.
  • pH Level: Ranges from 7.35 to 7.45, classified as normal.
  • Viscosity: Blood is three to five times more viscous than water.

Blood Composition Breakdown

  • Plasma: Comprises about 55% of blood.
  • Formed Elements: Comprises about 45% of blood and includes red blood cells, white blood cells, and platelets.

Hemopoiesis and Red Bone Marrow

  • Stem Cells: The precursor cells from which blood cells are derived include:
    • Proerythroblast (RBCs)
    • Myeloblast (Granulocytes)
    • Lymphoblast (Lymphocytes)
    • Monoblast (Monocytes)
    • Megakaryoblast (Platelets)
    • Progranulocyte
    • Reticulocyte
    • Basophil
    • Eosinophil
    • Neutrophil
Bone Marrow Conditions
  • Bone Marrow Depression:
    • Known as myelosuppression, can result in conditions like aplastic anemia, leukopenia, and thrombocytopenia.
  • Bone Marrow Overactivity:
    • Polycythemia vera can lead to overly thick blood, putting pressure on the heart and causing problems such as a ruddy complexion.

Blood Cells

Red Blood Cells (RBCs)

  • Erythropoiesis: The process of producing red blood cells.
  • Shape and Characteristics:
    • Large, round, and doughnut-shaped.
    • Loses organelles as it matures and produces ATP anaerobically.
  • Hemoglobin Composition:
    • Consists of globin (a protein) and heme (an iron-containing molecule).

Color Change of Blood

  • Oxygenated Blood: Appears bright red.
  • Deoxygenated Blood: Appears darker blue-red.

Essential Elements for Hemoglobin

  • Key precursors include:
    • Iron: Critical for hemoglobin production
    • Vitamin B12: Required for RBC health
    • Folic Acid: Important for blood production

Regulation of RBC Production

  • New RBCs are added to circulation constantly while older RBCs are removed.
  • Negative Feedback Loop: Regulated by erythropoietin, a hormone that stimulates RBC production.

Breakdown of Red Blood Cells

  • Macrophage Action: When RBCs are damaged, they are identified and removed by macrophages in the spleen and liver.
  • Recycling: Components of RBCs are recycled or excreted. Excessive breakdown can lead to high bilirubin levels in blood, causing jaundice (yellowing of the skin).

White Blood Cells (WBCs)

  • Characteristics: Large, round cells containing nuclei.
  • Function: Protect against pathogens and clear dead cells via phagocytosis.
  • Concentration: 1 μL of blood contains approximately 5,000 to 10,000 WBCs.
  • Lifespan: WBCs spend less than 12 hours in blood before migrating to tissues.

Types of White Blood Cells

  • Leukopoiesis: The process of producing WBCs.
    • Granulocytes:
    • Neutrophils
    • Eosinophils
    • Basophils
    • Agranulocytes:
    • Lymphocytes
    • Monocytes

Platelets

  • Composition: Tiny cell fragments derived from megakaryocytes.
  • Count: Approximately 150,000 to 450,000 platelets per microliter of blood.
  • Function: Key in preventing blood loss through clot formation.
  • Blood Count Tests:
    • Complete Blood Cell Count (CBC)
    • Differential WBC Count

Lesson 15.2: Hemostasis, Blood Types, and Rh Factor

Hemostasis: Prevention of Blood Loss

  • Definition: Hemostasis is the process of stopping bleeding.
  • Steps of Hemostasis:
    1. Blood Vessel Spasm: Initial contraction to reduce blood flow.
    2. Formation of a Platelet Plug: Platelets adhere to the site of injury to form a temporary seal.
    3. Blood Coagulation: The formation of a stable clot to halt bleeding.

Blood Clot Formation

  • Clotting Cascade:
    • Stage I: Initial injury activates clotting factors.
    • Stage II: In the presence of calcium and other elements, prothrombin is converted to thrombin.
    • Stage III: Thrombin converts fibrinogen to fibrin, forming a mesh that stabilizes the clot.
  • Clot Retraction: The tightening of the clot to reduce the size of the wound.

Clot Busting: Fibrinolysis

  • Prevention of Excessive Clot Formation:
    • Can occur through natural body mechanisms or through medication.

Blood Types

Antigens and Blood Types

  • ABO Grouping: Blood types classified as A, B, AB, and O.
  • Antigen: A molecule located on the RBC membrane that determines blood type.

Antibodies and Blood Type

  • Each blood type contains specific antibodies that react with incompatible antigens.

Antigen-Antibody Interaction

  • Agglutination: Clumping of blood cells caused by the interaction of antibodies with antigens.
  • Hemolysis: Destruction of red blood cells that occurs as a result of agglutination reactions.

Compatibility and Incompatibility of Blood Types

  • To prevent transfusion reactions, the following must be done:
    1. Determine the recipient's blood type (A, B, AB, or O).
    2. Cross-match donor blood with recipient blood.

Rh Classification System

  • Rh Factor: An additional antigen found on the RBC membrane.
    • Rh-positive (+): Presence of the Rh antigen.
    • Rh-negative (−): Absence of the Rh antigen.
  • Plasma Sensitization: Exposure of an Rh-negative individual to Rh-positive blood can lead to sensitization.
  • Erythroblastosis Fetalis: A condition where Rh incompatibility occurs between mother and fetus, leading to hemolytic disease of the newborn.