18.3 Erythrocytes - Anatomy and Physiology 2e | OpenStax

Key Points

• Erythrocytes (Red Blood Cells - RBCs):
  • Most common formed element in blood.
  • Males: ~5.4 million/microliter (µL), Females: ~4.8 million/µL.
  • Primary functions: transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs.
  • Small cells with a mean diameter of ~78 micrometers (µm).
  • Estimated to make up ~25% of total cells in the body.

Shape and Structure

• Development:
  • Mature in red bone marrow, extrude nucleus and most organelles as they mature.
  • Immature RBCs (reticulocytes) in circulation still contain remnant organelles.
• Characteristics:
  • Rely on anaerobic respiration; do not utilize transported oxygen.
  • Lack endoplasmic reticula, do not synthesize proteins.
  • Contain structural proteins like spectrin for maintaining structure and flexibility.
  • Biconcave disk shape optimizes surface area for gas exchange.
  • Shape allows flexibility to move through narrow capillaries and stack in wider vessels.

Hemoglobin

• Structure:
  • Composed of four globin proteins, each bound to a heme group containing an iron ion.
  • Can transport four oxygen molecules per hemoglobin molecule.
  • A single erythrocyte can contain 300 million hemoglobin molecules.
• Function:
  • Picks up oxygen in lungs, releases oxygen in tissues.
  • Converts to deoxyhemoglobin after releasing oxygen.
  • Transports carbon dioxide as carbaminohemoglobin.

Lifecycle of Erythrocytes

• Produced in marrow at ~2 million cells per second.
• Require nutrients: glucose, lipids, amino acids, trace elements (iron, copper, zinc, B vitamins).
• Live ~120 days; removed by macrophages in bone marrow, liver, spleen.
• Recycling:
  • Globin broken into amino acids.
  • Iron stored or transported for new RBC production.
  • Non-iron heme converted to biliverdin and bilirubin, excreted as bile.

Disorders of Erythrocytes

• Anemia:
  • Caused by blood loss, faulty/decreased RBC production, or excessive RBC destruction.
  • Types include sickle cell anemia, iron deficiency anemia, vitamin deficiency anemia.
  • Symptoms: fatigue, lethargy, increased infection risk, cognitive impairments.
• Polycythemia:
  • Elevated RBC count, increases blood viscosity, challenging for heart circulation.
  • Can be transient (dehydration), or due to high altitude adaptation or disease (polycythemia vera).