NOTES FIR RECALL

Chapter 19 - The Blood

I. Functions & Composition

• Functions of Blood:

  1. Transportation of gases (O₂, CO₂); hormones, nutrients, waste, etc.

  2. Regulation of blood pH with blood buffers, body temperature, and fluid balance.

  3. Protection against disease through immune responses.

• Composition of Blood:

  • Blood appears homogeneous but can separate due to density:

    • Plasma (~55%):

      • The fluid part of blood containing water, electrolytes, hormones, and plasma proteins.

      • Plasma Proteins:

        • Albumin: Maintains osmotic pressure.

        • Globulin: Functions in immune response as antibodies.

        • Fibrinogen: Essential for blood clotting.

    • Formed Elements (~45%):

      • Buffy Coat (1%): Contains white blood cells (WBCs) and platelets.

      • Red Blood Cells (RBCs): Erythrocytes responsible for gas transport.

II. Hematocrit

• Definition: The percentage of blood volume occupied by RBCs.

  • Normal hematocrit levels:

    • Males: ~45%

    • Females: ~42%; lower due to menstruation.

  • Anemia: Characterized by decreased RBC levels, which can result from:

    • Iron-deficiency anemia

    • Hemorrhagic anemia

  • Polycythemia: Elevated RBC counts may occur due to high altitude, carbon monoxide inhalation, or certain diseases.

III. Formation of Blood Cells (Hematopoiesis)

• Occurs in red bone marrow.

• Types of Stem Cells:

  • Multipotent Stem Cells: Differentiate into various blood cells.

  • Myeloid Stem Cell: Develops into erythrocytes, eosinophils, basophils, neutrophils, and megakaryocytes (platelets).

  • Lymphoid Stem Cell: Develops into lymphocytes (T-cells, B-cells).

IV. Erythrocytes - Properties

• Characteristics:

  1. Lack a nucleus, maximizing space for hemoglobin (O₂ transport protein).

  2. Biconcave shape: Increases surface area for gas exchange and allows deformability to pass through capillaries.

  3. Lack of mitochondria means they do not use oxygen for ATP production, relying on glycolysis instead.

• Life Cycle of RBCs:

  • Lifespan: Approximately 120 days.

  • RBCs are broken down in the liver and spleen after expiration.

  • Components of hemoglobin are recycled:

    • Globin: Recycled into amino acids.

    • Heme: Processed to bilirubin.

V. Erythropoiesis

• Stimulation of RBC production in response to low O₂ levels (hypoxia).

• Kidneys release erythropoietin (EPO) to stimulate RBC formation.

VI. Leukocytes (WBCs)

• Functions include:

  • Larger than RBCs and can migrate out of blood vessels to target pathogens.

  • Pus Formation: Composed of dead neutrophils that have fought infections.

VII. Hemostasis

• The process of preventing hemorrhage through:

  1. Vascular Spasm: Constriction of blood vessels.

  2. Platelet Plug Formation: Platelets adhere to damaged vessel sites.

  3. Coagulation: Formation of fibrin threads to stabilize the platelet plug.

VIII. Heart Anatomy & Physiology

• Location: Mediastinum, between the lungs.

• Chambers: Comprised of atria and ventricles with distinct functions.

• Heart Valves: Ensure unidirectional blood flow.

  • Atrioventricular (AV) and Semilunar (SL) valves operate based on pressure gradients.

IX. Electrocardiogram (ECG)

• Records the electrical activity of the heart relating to contraction and relaxation cycles.

  • Key components: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

X. Cardiac Cycle

• Consists of Systole (contraction) and Diastole (relaxation) phases.

• Includes events such as atrial systole followed by ventricular systole.

XI. Cardiac Output

• Defined as the volume of blood ejected by the heart per minute.

• Calculated as: Cardiac Output = Stroke Volume x Heart Rate.