There is more to blood than the red substance that comes out of our bodies when we’re injured. In fact, blood is a highly complex part of existence. Within that simple red liquid lies several very important substances. Blood consists of both plasma and the formed elements found within the plasma. This latter is made up of three different elements, red blood cells, white blood cells, and platelets. Each of these substances provide our bodies with the support we need to survive both internally and externally.
Plasma, which makes up around 55 percent of human blood, is the liquid portion of our blood. 90 percent of blood plasma is water. The red blood cells within the plasma make up around 45 percent of the blood, while white blood cells make up a meager 1 percent. Amazingly enough, blood volume (i.e. the amount of red blood cells, white blood cells, and platelets) vary according to place of residence. David Chiras, author of Human Biology’s 5th Edition textbook notes that the blood volume (also known as hematocrit) of “people living in Denver, a mile above sea level…are typically about 5% higher than in people living at sea level” (2005). The change in hematocrit is a result of our body’s homeostatic abilities. Because those living above sea level require more oxygen, the blood composition varies, by increasing oxygen transporting red blood cells, in order to compensate for this need.
Blood plasma itself also plays a critical role in homeostasis. While platelets, red and white blood cells are often praised for being the most critical parts of the human blood, plasma too plays an important role that should not be passed over. Indeed plasma too plays a role in maintaining homeostasis. For one, plasma is responsible for transporting gases like oxygen, carbon dioxide, and nitrogen; nutrients like glucose and amino acids, hormones; proteins; lipids; ions such as sodium, chloride, and calcium; and various waste products (Chiras, 2005). As if such an important role as transportation weren’t enough, blood plasma also contains proteins that serve very specific and important roles as “carriers” for hormones, ions, and fatty acids. These carrier proteins protect smaller molecules from destruction by the liver as well as facilitate transport for other molecules through the bloodstream. Fibrinogen, another type of blood protein aids in blood clotting, another critical homeostasis function (Chiras, 2005).
Another important function of plasma protein is the regulation of osmotic pressure. This regulation allows for the distribution of materials, including waste and nutrients, throughout the body. Additionally, these same blood proteins aid in the regulation of blood pH, a critical function in maintaining blood homeostasis.
Clearly blood plasma, which not only carries the platelets, red blood cells, and white blood cells, but also aids in maintaining homeostasis, plays a critical role in the human body. Although red blood cells, white blood cells, and platelets get a lot of attention for their critical roles in the body and the way we think of blood, plasma is a part of the blood that acts as the transportation, pH and osmosis regulator, and “carrier.
References:
Chiras, D., D. (2005). Human Biology, 5th Ed. Sudbury, Ma. Jones and Bartlett Publishers.
Puget Sound Blood Center. (2006). Introduction to Hematology. Retreived February 15, 2008, from http://www.psbc.org/hematology/index.htm
The Franklin Institute. (2008). The Human Heart: Blood. Retrieved February 15, 2008, from http://www.fi.edu/learn/heart/blood/red.html
