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REGULATION AND DISORDERS OF BLOOD

BLOOD DOPING

  • Blood Doping: Refers to methods athletes use to enhance performance by increasing the number of red blood cells (RBCs).
  • Methods:
    • Transfusions: Blood is removed from an athlete and preserved (usually frozen) and then reinfused, leading to increased hematocrit levels. This can increase RBC counts by over 50%.
    • Erythropoietin (EPO) Injections: EPO is a peptide hormone that stimulates the bone marrow to produce more RBCs, potentially increasing hematocrit levels to 50% or higher.
    • Synthetic Oxygen Carriers: Include purified proteins or chemicals that can elevate tissue oxygen levels.

Erythropoietin (EPO)

  • Definition: A peptide hormone secreted primarily by the kidneys when they sense low oxygen levels (hypoxia) in renal tissue.
  • Functions of EPO:
    • Stimulates erythropoiesis, the formation of red blood cells in the red bone marrow, increasing the supply of oxygen-carrying cells.
    • Testosterone enhances EPO production, contributing to higher RBC counts observed in males (≈47%) compared to females (≈42%).

HEMATOCRIT (PACKED CELL VOLUME)

  • Definition: The percentage of blood volume that consists of red blood cells.
  • Normal Values:
    • Average: 45%
    • Males: 47% ± 5%
    • Females: 42% ± 5%
  • Calculation of Hematocrit:
    • Hematocrit=Volume of RBCTotal Blood Volume×100\text{Hematocrit} = \frac{\text{Volume of RBC}}{\text{Total Blood Volume}} \times 100
  • Reasons for Measurement: Hematocrit levels can provide information on athlete performance, hydration status, and potential disorders (e.g., anemia, polycythemia).

HYPOXIA

  • Definition: A state of low oxygen availability in tissues.
  • Causes of Hypoxia:
    • Decreased red blood cell numbers (e.g., hemorrhage, increased destruction of RBC, reduced hemoglobin levels).
    • Insufficient environmental oxygen levels (e.g., high altitude).

ANEMIA

Causes of Anemia:
  • Four Major Causes:
    1. Blood loss (hemorrhage)
    2. Low RBC production
    3. High RBC destruction
    4. Abnormalities in hemoglobin
Types Based on High RBC Destruction:
  • Hemolytic Anemias: Premature lysis of RBCs due to:
    • Hemoglobin abnormalities (e.g., sickle-cell anemia, thalassemia)
    • Incompatible blood transfusions
    • Infections leading to blood cell destruction.
Types Based on Low RBC Production:
  • Iron-Deficiency Anemia: Caused by insufficient iron for hemoglobin synthesis.
  • Renal Anemia: Caused by a lack of erythropoietin production, often seen in renal diseases. Can be treated with synthetic EPO.
  • Pernicious Anemia: Caused by the destruction of cells that produce intrinsic factor in the stomach, leading to Vitamin B12 deficiency.
  • Aplastic Anemia: Inhibition or destruction of red bone marrow from drugs, chemicals, or radiation, leading to decreased production of RBCs.

HEMATOCRIT INTERPRETATION

Low Hematocrit:
  • Associated with conditions like anemia or long-term illness, insufficient RBC production.
High Hematocrit:
  • Indicators can include dehydration or overproduction of RBCs as in diseases like polycythemia vera and secondary polycythemia (often due to low oxygen levels from high altitude).

HORMONAL CONTROL OF ERYTHROPOIESIS

  • Hormone: Erythropoietin (EPO) is the primary regulator of erythropoiesis.
  • Mechanism:
    • Hypoxia stimulates kidneys to release EPO, increasing RBC production.
    • Testosterone further enhances EPO production.
  • Feedback Loop: Negative feedback mechanism maintains homeostasis, as sufficient O2 delivery returns erythropoietin production to baseline.

FATE AND DESTRUCTION OF ERYTHROCYTES

  • RBC lifespan is approximately 120 days. Old/damaged RBCs are removed from circulation, primarily in the spleen, where macrophages engulf them.
  • Destruction Process:
    • Hemoglobin is broken down into heme and globin. Heme is then converted to bilirubin in the liver, which aids in bile production.
    • Iron is recycled and stored as ferritin or hemosiderin in the liver.

IMPLICATIONS OF BLOOD DISORDERS

  • Blood Doping Risks: Increased hematocrit can lead to thicker blood, higher viscosity, and an increased risk of clots, strokes, and other cardiovascular issues.
  • Ethical Considerations: Blood doping methods raise significant ethical issues regarding fairness and health risks in competitive sports.

CONCEPT REVIEW

  • Erythropoiesis: Dependent on EPO; imbalances can lead to anemia (low RBC production) or polycythemia (high RBC production).
  • Consequences of Hematocrit Imbalance: Low hematocrit indicates potential anemia; high hematocrit can be a sign of polycythemia vera or secondary responses to low oxygen availability.
  • Responses to Hypoxia: Include stimulation of EPO, leading to increased RBC production and adjustments in blood viscosity.