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General Composition of Blood
If a tube of whole blood is left standing or spun briefly in a centrifuge, the components will separate into layers, based on their density.
The bottom, red-colored layer is made up of red blood cells (RBCs or erythrocytes). Red blood cells normally occupy about 45% of the total blood volume (females = 37-48%; males = 45-52%).
Above the RBCs is the "buffy coat". This narrow, white band is composed of white blood cells (WBCs or leukocytes) and cell fragments called platelets (thrombocytes). Approximately 1% of the blood volume is occupied by these components.
Together, the RBCs, WBCs, and platelets are referred to as the blood's formed elements.
On top of the formed elements is the blood plasma. This straw-colored fluid makes up approximately 55% of the total blood volume.
By weight, the composition of plasma is about 91.5 % water and 8.5% dissolved solutes. Most of the dissolved solutes are proteins. The remaining solutes are a mixture of nutrients, electrolytes, nitrogenous wastes, respiratory gases, and regulatory compounds.
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