Ch14

Characteristics of Blood

  • Blood as Connective Tissue:

    • Only type with a liquid matrix (plasma).

    • Transports vital substances, regulates homeostasis, maintains interstitial fluid stability, distributes heat.

    • Blood volume varies with body size, fluid concentration, electrolyte concentration, and amount of adipose tissue.

    • Comprises about 8% of body weight; consumption: 4-5 liters (females), 5-6 liters (males).

  • Blood Cells (Formed Elements):

    • Formed in red bone marrow, includes:

      • Red Blood Cells (RBCs): Erythrocytes, biconcave shape, transport oxygen via hemoglobin.

      • White Blood Cells (WBCs): Immune function, includes neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

      • Platelets: Cell fragments involved in clotting.

Components of Centrifuged Blood Samples

  • Blood Sample Analysis

    • Centrifuged components:

      • Plasma: Clear fluid (55% of blood), occupies top of tube.

      • Red Blood Cells: Occupy bottom (hematocrit ranges: females 35%-46%, males 40%-54%).

      • Buffy Coat: Contains WBCs and platelets, less than 1% of blood volume.

Clinical Application: Universal Precautions

  • Safety Measures:

    • Used in healthcare to prevent bloodborne pathogen transmission, essential for HIV, hepatitis B and C.

    • Assumed all patients could be carriers.

    • Preventive measures include gloves, masks, sharps containers, and hand-washing.

Hematopoiesis: Blood Cell Formation

  • Origin of Blood Cells

    • Blood cells formed from hematopoietic stem cells (hemocytoblasts) in red marrow under growth factors:

      • Lymphoid stem cells → Lymphocytes.

      • Myeloid stem cells → RBCs, WBCs, platelets.

Red Blood Cells (RBCs)

  • Structure & Function:

    • Biconcave discs, no nuclei or mitochondria.

    • Contain hemoglobin (one-third), transports oxygen as oxyhemoglobin; without oxygen as deoxyhemoglobin.

  • Production:

    • Erythropoiesis occurs in red marrow. Low O2 stimulates EPO release from kidneys and liver, enhancing RBC production.

    • Nutritional needs: Vitamin B12, folic acid (DNA synthesis), and iron.

  • Anemia:

    • Condition reducing oxygen capacity due to low RBC or hemoglobin levels.

Mechanism and Events of RBC Breakdown

  • RBC Breakdown:

    • RBCs phagocytized in spleen/liver after losing elasticity; hemoglobin splits into heme and globin.

    • Heme degraded into iron and biliverdin, further converted to bilirubin, designated as bile pigments.

    • Globin chains break down into amino acids.

White Blood Cells (Leukocytes)

  • Roles and Life Cycle:

    • Protect against disease; produced in red bone marrow.

    • Recognized by type and function: Granulocytes (neutrophils, eosinophils, basophils) and Agranulocytes (lymphocytes, monocytes).

  • Functions:

    • Diapedesis (migration toward infection), phagocytosis (engulf pathogens), inflammatory response, and positive chemotaxis.

Platelets (Thrombocytes)

  • Function:

    • Cytoplasmic fragments help in hemostasis (stopping bleeding).

    • Count of 150,000 to 400,000/µL, where thrombocytosis indicates a high count, and thrombocytopenia indicates a low count.

Blood Plasma

  • Composition and Roles:

    • Clear, straw-colored liquid (55% of blood volume), 92% water.

    • Contains nutrients, hormones, and wastes, while also regulating fluid balance and pH.

  • Plasma Proteins:

    • Albumins (60%), Globulins (36%), Fibrinogen (4%); aid in osmotic pressure maintenance and coagulation.

Hemostasis (Stopping of Bleeding)

  • Mechanisms:

    • Vascular spasms, platelet plug formation, and blood coagulation.

    • Activated by tissue damage and foreign surface exposure; involves clotting factors.

  • Extrinsic vs. Intrinsic Clotting Mechanisms:

    • Extrinsic initiated by tissue damage; intrinsic by blood contact with non-endothelial surfaces.

Blood Groups and Transfusions

  • ABO Blood Group:

    • Defined by antigens A and B. Type O lacks both; Type AB has both.

    • Universal donors are type O; universal recipients are type AB.

  • Rh Factor:

    • Positive (presence of antigen D) vs. negative (absence). Important in pregnancy and transfusion contexts.