The blood is composed of two main parts, the hematocrit and the plasma, which can be assessed clinically (Figure 2.10). Red blood cells (RBCs) are the sole component of the hematocrit and function primarily as a shuttle for oxygen. Hematocrit is the percentage of our blood that is RBCs, which is typically 40 to 45 percent for an adult.
Plasma is about 55 percent of our blood. Of the plasma, about 92 percent is water while the remaining 8 percent includes over 100 different dissolved or suspended substances such as nutrients, gases, electrolytes, hormones, and proteins such as albumin and clotting factors. The remaining components of our blood are the white blood cells (WBCs) and platelets, which collectively make up about 1 percent of blood. WBCs are the principal components of the human immune system and provide a line of defense against bacteria, viruses, and other intruders. Some WBCs attack foreign invaders and useless materials while others manufacture antibodies and other immune factors. Last, but certainly not least, platelets participate in the clotting of blood.
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