Red Blood Cell Physiology Quiz

Erythrocytes and Red Blood Cell Destruction

• Erythrocytes (red blood cells) undergo senescence, characterized by decreased enzyme function, ATP depletion, reduced size, and increased density.
• Mature erythrocytes lack nuclei and cannot regenerate proteins, leading to functional decline and eventual death; lifespan averages 120 days.
• RBCs rely exclusively on glycolysis for ATP production due to the absence of mitochondria.
• Aging RBCs undergo phagocytosis, with approximately 1% leaving circulation daily, predominantly handled by the mononuclear phagocytic system.
• The spleen performs culling, filtering out aged RBCs through macrophage phagocytosis.

Types of RBC Destruction

• Extravascular Hemolysis:

  • Primary method of normal RBC death, responsible for a significant portion of destruction.
  • Requires flexibility for RBCs to pass through splenic sieve; rigid cells become trapped and phagocytized by macrophages.

• Intravascular Hemolysis:

  • Accounts for a smaller percentage (10-20%) of RBC destruction, occurring in peripheral circulation due to mechanical factors.
  • Results in hemoglobin release into the bloodstream, dissociated into dimers which bind plasma globulin.

Hemolysis Mechanisms

• Haptoglobin binds hemoglobin for hepatic removal; depletion leads to filtered and reabsorbed hemoglobin in kidneys.
• Excess hemoglobin not bound to haptoglobin is converted to methemoglobin and heme groups associate with transport proteins like hemopexin.

Pathways Related to Erythrocyte Metabolism

• Glycolysis: Primary energy production pathway in RBCs.
• Pentose Phosphate Pathway: Generates NADPH for glutathione reduction, protecting erythrocytes from oxidative damage; G6PD deficiency is common and associated with Heinz bodies.
• Methemoglobin Reductase Pathway: Converts ferric hemoglobin back to its ferrous state, crucial for oxygen transport.
• Rapaport Luebering Pathway: Produces 2,3-DPG which decreases hemoglobin's oxygen affinity, aiding gas exchange.

Heme Synthesis

• Heme synthesis depends on biochemicals like glycine and vitamin B6, occurring in mitochondria.
• Globin synthesis relies on genetic coding from chromosomes 16 and 11.

Oxygen Dissociation Curve (ODC)

• Illustrates the relationship between oxygen saturation of hemoglobin and the partial pressure of oxygen; typically sigmoidal in shape.
• P50 indicates oxygen tension required for 50% saturation of hemoglobin.
• The Bohr effect describes how lower pH enhances oxygen release in tissues via rightward shift of the curve.
• Carbon monoxide binding to hemoglobin reduces its oxygen-carrying capacity, causing leftward shift on the ODC and increased blood color.

Iron Metabolism

• Iron is vital, mainly existing in hemoglobin and must be in ferrous (Fe2+) state for effective transport; ferric (Fe3+) cannot bind hemoglobin.
• Daily intake of iron is about 15mg, with 1-2mg absorbed primarily in the duodenum; iron transport is mediated by DMT (Divalent Metal Transporter).
• Iron can be stored as ferritin in enterocytes or exported via Fpn1 (Ferroportin).
• Transferrin, produced in the liver, regulates systemic iron metabolism, facilitating delivery to cells through transferrin receptors.

Test your knowledge on the physiology of red blood cells! This quiz covers the causes of aging in red blood cells, processes involved in their hemolysis, and changes in enzyme activity. Understanding these concepts is crucial for comprehending how red blood cells function and ultimately perish within the body.