What Is the Volume & Chemical Composition of Blood?

red blood cells
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Blood is slightly more dense and approximately 3-4 times more viscous than water. Blood consists of cells which are suspended in a liquid. As with other suspensions, the components of blood can be separated by filtration, however, the most common method of separating blood is to centrifuge (spin) it. Three layers are visible in centrifuged blood. The straw-colored liquid portion, called plasma, forms at the top (~55%).

A thin cream-colored layer, called the buffy coat, forms below the plasma. The buffy coat consists of white blood cells and platelets. The red blood cells form the heavy bottom portion of the separated mixture (~45%).

What is the Volume of Blood?

Blood volume is variable but tends to be about 8% of body weight. Factors such as body size, the amount of adipose tissue, and electrolyte concentrations all affect volume. The average adult has about 5 liters of blood.

What is the Composition of Blood?

Blood consist of cellular material (99% red blood cells, with white blood cells and platelets making up the remainder), water, amino acids, proteins, carbohydrates, lipids, hormones, vitamins, electrolytes, dissolved gasses, and cellular wastes. Each red blood cell is about 1/3 hemoglobin, by volume. Plasma is about 92% water, with plasma proteins as the most abundant solutes. The main plasma protein groups are albumins, globulins, and fibrinogens.

The primary blood gasses are oxygen, carbon dioxide, and nitrogen.


Hole's Human Anatomy & Physiology, 9th Edition, McGraw Hill, 2002.