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Ch.18 Notes

Chapter 18: The Unity of Form and Function: The Circulatory System: Blood

Introduction

  • Blood has been historically cloaked in myths, being seen as a mysterious "vital force."

  • Early therapies included the draining of "bad blood."

  • Blood cells were first observed with early microscope technology.

  • Hematology: the scientific study of blood, which has seen recent advancements that improve medical outcomes.

Functions of the Circulatory System

  • The circulatory system consists of the heart, blood vessels, and blood.

  • The cardiovascular system specifically refers to the heart and blood vessels.

  • Functions of the circulatory system include:

    • Transport:

      • Oxygen (O2), carbon dioxide (CO2), nutrients, wastes, hormones, and stem cells.

    • Protection:

      • Inflammation, limiting infection spread, destroying microorganisms and cancer cells, neutralizing toxins, and initiating clotting.

    • Regulation:

      • Maintaining fluid balance, stabilizing pH of extracellular fluid (ECF), and regulating temperature.

Components and General Properties of Blood

  • Adults typically have 4 to 6 liters of blood.

  • Blood is a liquid connective tissue made up of cells and an extracellular matrix:

    • Plasma: the liquid matrix, clear and light yellow.

    • Formed Elements: Red blood cells, white blood cells, and platelets.

Types of Blood Cells

  • Formed Elements Breakdown:

      1. Erythrocytes (RBCs): Red blood cells.

      1. Platelets: Cell fragments from specialized bone marrow cells.

      1. Leukocytes (WBCs): White blood cells categorized into:

      • Granulocytes:

          1. Neutrophils.

          1. Eosinophils.

          1. Basophils.

      • Agranulocytes:

          1. Lymphocytes.

          1. Monocytes.

Blood Composition and Properties

  • Hematocrit: centrifugation separates blood components.

    • Erythrocytes settle first (37% to 52% of total volume).

    • White blood cells and platelets make up about 1%.

    • Plasma consists of 55% of total blood volume, containing water, proteins, nutrients, and other substances.

Blood Plasma Composition

  • Plasma is the liquid component of blood, while serum is what remains after blood clots and solids are separated.

  • Three major plasma protein categories:

    • Albumins: the smallest and most abundant, involved in viscosity and osmolarity regulation.

    • Globulins: transport proteins binding ions and hormones; includes antibodies for defense.

    • Fibrinogen: precursor for fibrin threads in clot formation.

Nutrients in Plasma

  • Nutrients include:

    • Lipids (fatty acids, cholesterol).

    • Carbohydrates (glucose).

    • Free amino acids from protein metabolism.

  • Electrolytes: majorly sodium ions (Na+).

  • Waste Products: nitrogenous wastes (urea).

Blood Viscosity and Osmolarity

  • Viscosity: blood is 4.5 to 5.5 times more viscous than water, affecting circulatory function.

  • Osmolarity: regulates total molarity of dissolved particles, crucial for maintaining blood pressure and preventing edema.

Blood Production and Erythropoiesis

  • Hematopoiesis: production of blood cells primarily in the red bone marrow sparsely.

  • Erythropoiesis: process of producing red blood cells (RBCs).

    • Involves multipotent stem cells (hemocytoblasts), erythrocyte colony-forming units, erythroblasts, and reticulocytes.

  • Lifespan of RBCs is approximately 120 days.

Iron Metabolism

  • Iron is critical for hemoglobin production; dietary iron is absorbed in the small intestine.

  • Ferritin: stored form of iron, created when transferrin carries it to the liver.

Erythrocyte Function

  • Main functions of erythrocytes:

    • Carry oxygen from lungs to tissues and transport CO2 back to lungs.

    • Structure: biconcave disc, lack organelles to increase hemoglobin content for effective gas transport.

Erythrocyte Disorders

  • Polycythemia: excessive RBCs potentially from various causes.

  • Anemia: categorized by inadequate RBC production, hemorrhage, or destruction. Includes several types such as:

    • Iron-deficiency anemia, aplastic anemia, and hemolytic anemias.

  • Sickle-Cell Disease: hereditary condition leading to misshaped RBCs causing various complications.

Blood Typing and The ABO Group

  • Blood type determined by surface antigens (agglutinogens) on RBCs; four main groups (A, B, AB, O).

  • Antibodies: produced in response to foreign blood cells; crucial for transfusion compatibility.

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

The Rh Blood Group

  • Rh factor indicates presence of specific antigens; complications arise in pregnancy if an Rh- mother is carrying an Rh+ child.

  • Hemolytic disease of the newborn (HDN) can occur if mother produces antibodies against Rh antigens.

Leukocytes: Functions and Types

  • White blood cells (WBCs) protect against pathogens, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).

  • Leukopoiesis: production of WBCs with distinct functions in immune defense.

Platelets and Hemostasis

  • Hemostasis: process to stop bleeding involving three mechanisms: vascular spasm, platelet plug formation, and coagulation.

  • Platelets (small cell fragments) play a pivotal role in all hemostatic processes.

Clotting Mechanisms

  • Coagulation involves transformation of fibrinogen into fibrin creating the clot framework; cascades activated by intrinsic and extrinsic pathways.

  • Clot retraction: helps in healing by repairing vessel walls, while fibrinolysis clears the clot post-repair.

Clotting Disorders

  • Hemophilia: hereditary conditions leading to bleeding due to factor deficiencies.

  • Thrombosis: abnormal clot formation can lead to severe health risks including embolism.