The Composition and Functions of Blood

The Composition and Functions of Blood

The Composition and Functions of Blood      When a blood sample is prevented from clotting and spun in a centrifuge tube, it separates into two layers (Fig. 11.1). The lower layer consists of white blood cells (note the buffy layer), blood platelets, and red blood cells. Collectively, these are the formed elements, which make up about 45% of the total volume of whole blood; the percentage of blood attributed to red blood cells is called the hematocrit. The upper layer is plasma, which contains a variety of inorganic and organic molecules dissolved or suspended in water. Plasma accounts for about 55% of the total volume of whole blood. Functions of Blood      The functions of blood fall into three categories: transport, defense, and regulation.Transport     Blood moves from the heart to all the various organs, where exchange with tissues takes place across thin capillary walls. Blood picks up oxygen from the lungs and nutrients from the digestive tract and transports these to the...
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