Blood Composition and Red Blood Cells

Blood Composition

• Whole blood consists of:
  • Plasma (55%): liquid portion, 92% water, proteins, nutrients, hormones, gases, waste products
  • Formed elements (45%): red blood cells, white blood cells, platelets

Red Blood Cells (RBCs or Erythrocytes)

• Function: carry oxygen from lungs to tissues, carbon dioxide from tissues to lungs
• Characteristics:
  • Biconcave disk shape, flexible, no nucleus
  • Contain hemoglobin (Hb), a protein that binds to oxygen
  • Average lifespan: 120 days
  • Produced in bone marrow, regulated by erythropoietin (EPO)

White Blood Cells (WBCs or Leukocytes)

• Function: defend the body against infection and disease
• Characteristics:
  • Produced in bone marrow, lymphoid organs
  • Types:
    • Neutrophils (50-70%): phagocytosis, antimicrobial
    • Lymphocytes (20-40%): specific immune response, B cells and T cells
    • Monocytes (5-10%): mature into macrophages, phagocytosis
    • Eosinophils (1-3%): parasitic infections, allergic reactions
    • Basophils (0.5-1%): allergic reactions, inflammation

Platelets (Thrombocytes)

• Function: blood clotting, hemostasis
• Characteristics:
  • Produced in bone marrow, derived from megakaryocytes
  • Average lifespan: 7-10 days
  • Contain granules with clotting factors, adhere to damaged endothelium

Blood Clotting

• Process:
  1. Injury to blood vessel, exposure of collagen
  2. Platelet activation, adhesion, and aggregation
  3. Release of chemical signals, clotting factors
  4. Formation of fibrin clot, stabilization by platelets and clotting factors
• Coagulation pathways:
  • Intrinsic pathway: activated by contact with damaged endothelium
  • Extrinsic pathway: activated by tissue factor release

Blood Types

• ABO blood group system:
  • A and B antigens on RBC surface
  • A and B antibodies in plasma
  • Four main blood types: A, B, AB, O
• Rh blood group system:
  • Rh antigen on RBC surface
  • Rh positive (Rh+) or negative (Rh-)

Hematopoiesis

• Process of blood cell production, occurs in bone marrow
• Stages:
  1. Hemocytoblast: stem cell, differentiates into myeloid or lymphoid lineage
  2. Myeloid lineage: develops into RBCs, platelets, granulocytes, monocytes
  3. Lymphoid lineage: develops into lymphocytes

Blood Composition

• Plasma makes up 55% of whole blood, comprising 92% water, proteins, nutrients, hormones, gases, and waste products.
• Formed elements consist of 45% of whole blood, including red blood cells, white blood cells, and platelets.

Red Blood Cells (RBCs or Erythrocytes)

• RBCs carry oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs.
• They have a biconcave disk shape, are flexible, and lack a nucleus.
• RBCs contain hemoglobin, a protein that binds to oxygen.
• They have an average lifespan of 120 days and are produced in the bone marrow, regulated by erythropoietin (EPO).

White Blood Cells (WBCs or Leukocytes)

• WBCs defend the body against infection and disease.
• They are produced in the bone marrow and lymphoid organs.
• There are five types of WBCs: neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• Neutrophils comprise 50-70% of WBCs and are involved in phagocytosis and antimicrobial activities.
• Lymphocytes comprise 20-40% of WBCs and are responsible for specific immune responses, including B cells and T cells.
• Monocytes comprise 5-10% of WBCs and mature into macrophages, participating in phagocytosis.
• Eosinophils comprise 1-3% of WBCs and are involved in parasitic infections and allergic reactions.
• Basophils comprise 0.5-1% of WBCs and are involved in allergic reactions and inflammation.

Platelets (Thrombocytes)

• Platelets are responsible for blood clotting and hemostasis.
• They are produced in the bone marrow, derived from megakaryocytes.
• Platelets have an average lifespan of 7-10 days.
• They contain granules with clotting factors and adhere to damaged endothelium.

Blood Clotting

• Blood clotting involves a process of injury, platelet activation, adhesion, and aggregation, followed by the release of chemical signals and clotting factors.
• The process ultimately leads to the formation of a fibrin clot, stabilized by platelets and clotting factors.
• There are two coagulation pathways: intrinsic and extrinsic.
• The intrinsic pathway is activated by contact with damaged endothelium, while the extrinsic pathway is activated by tissue factor release.

Blood Types

• The ABO blood group system is classified into four main blood types: A, B, AB, and O.
• A and B antigens are present on the surface of RBCs, while A and B antibodies are present in plasma.
• The Rh blood group system is classified into Rh positive (Rh+) or negative (Rh-), depending on the presence of the Rh antigen on RBCs.

Hematopoiesis

• Hematopoiesis is the process of blood cell production, which occurs in the bone marrow.
• The process involves three stages: hemocytoblast, myeloid lineage, and lymphoid lineage.
• Hemocytoblasts are stem cells that differentiate into myeloid or lymphoid lineages.
• Myeloid lineage develops into RBCs, platelets, granulocytes, and monocytes.
• Lymphoid lineage develops into lymphocytes.