- Approximately half of the volume of whole blood consists of cells and cell products. Plasma resembles interstitial fluid but it contains a unique mixture of proteins not found in other extracellular fluids.
- Red blood cells (RBCs) are the most mumerous cells in the body. They remain in circulation for approximately 4 months before being recycled; several million are produced each second. The hemoglobin inside RBCs transports oxygen from the lungs to peripheral tissues; it also carries carbon dioxide from those tissues to the lungs.
- White blood cells (WBCs) are usually outnumbered by RBCs by a ratio of 1000:1.WBCs are responsible for defending the body against infection, foreign cells, or toxins, and for assisting in the cleanup and repair of damaged tissues. The most numerous are neutrophils, which engulf bacteria, and lymphocytes, which are responsible for the specific defenses of the immune response.
- Platelets are involved in the coordination of hemostasis (blood clotting). When platelets are activated by abnormal changes in their local environment, they release clotting factors and other chemicals. Hemostasis is a complex cascade that establishes a fibrous patch that can subsequently be remodeled and then removed as the damaged area is repaired.
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