What are the components of blood?
Your blood makes up about 7% of your
body weight, and in an adult amounts to around 5 liters (= 1.3
gallons)1. If you lose too much blood, for instance
during a trauma or an accident, it can be life-threatening,
and you may need a blood transfusion. We are able to donate up
to half a liter, which is about 10% of our total blood volume,
however such blood donation requires overall good health, and
time to rest and recover afterwards. Roughly half of the blood
volume consists of various blood cells, while the other half
is blood plasma, the liquid which enables your blood to flow
throughout your body. Every component in the blood has their
own critical function, which will be introduced in this
The blood plasma consists of approximately 90 % water1
Water is critical for life. A human can survive for days and even weeks without food, but only a few days without water. The reason is that water is a resource that constantly recycles. We lose water from our body both through urine and as evaporation from our skin through sweat. Neither of these processes are something we can consciously control, but they are important processes for temperature control as well as getting rid of waste products. On the other hand, our water intake is under our control. We get water from what we drink, but also through food. Mild dehydration may lead to headache, overheating, or dizziness, but is not life-threatening under normal circumstances. In cases of extreme dehydration, you can get liquid through intravenous transfusions directly into your blood.
The blood plasma contains various soluble components
In addition to giving blood its fluidity, so that blood cells can be transported throughout the body, water is also important as a solvent for transport of nutrients and waste products. Minerals, vitamins, glucose, and various types of proteins, along with the water, make up the blood plasma. Although the color of the blood is red, the color of the blood plasma is actually yellow. The red color comes from the large amount of red bloods cells, as will be described below. The yellow color of the blood plasma comes from the various water-soluble components, such as nutrients and various signaling molecules. Furthermore, your blood is the carrier of various waste products, that are filtered out from the blood to the urine through the kidneys. In addition, the blood contains various proteins that have both structural as well as regulating or signaling roles. One type of important structural proteins are the coagulation factors that are required for proper blood clotting. Insulin is an example of signaling molecule. People suffering from diabetes must closely monitor and adjust the glucose and insulin levels in their blood, to ensure a proper balance.
The cells in our blood
The cells in our blood are divided into two main types: The red blood cells, and the white blood cells. In addition, there are specialized cell fragments, called platelets, that are derived from a specific type of white blood cells, the megakaryocytes. The red blood cells (RBC, also called erythrocytes) take up about 45% of the total blood volume1. The red color is due to abundant amounts of the protein hemoglobin, which binds and transports oxygen from the lungs throughout our body. The white blood cells are critical for our immune system, which can broadly be divided into the innate and the adaptive immune system. The innate immune system recognizes patterns that are associated with pathogens, and mounts a fast reaction towards infections. The adaptive immune cells recognize specific eptiopes, and can be educated to recognize epitopes associated with disease. The response of adaptive immune cells are initially slower, but the education leads to a "memory" so that upon later encounters, we can quickly recognize and eliminate the threat. Immunization is based on the ability of the adaptive immune system to recognize the pathogen and develop a protective "memory" or immunization. Lastly, the platelets, also called thrombocytes, are not cells, but rather cell fragments. They are critical for blood coagulation, to ensure that upon a cut or damage to a blood vessel, the bleeding will stop.
Human blood has many well defined components, and is the major transport system of both nutrients, signaling molecules, waste products and immune cells. Therefore, a simple blood sample can reveal many types of disease or unbalance in the body, and thereby help with initial diagnosis.
Molecular Biology of the Cell, Fourth Edition, 2002, Editiors: Alberts et al., Publisher: Garland Science
Adaptive Immune System: Is the
part of the immune system that can adapt to and "remember" the
pathogen based on "memory". This feature is unique to higher
vertebrates, and is based on a clonal expansion of cells that
are able to react to a pathogen. Immunizations take advantage
of the adaptive immune system, by introducing the body to
potential pathogens (for instance the inactivated flu virus)
to elicit a memory response to protect you from future
Epitope: A surface that can be recognized by the immune system. It is also called an antigenic determinant, as it is a part of an antigen, the unit that an antibody or immune receptor recognize. The epitope can be a linear sequence of for instance amino acids (a small part of a protein, called a peptide), or it can be a 3-dimensional surface composed of different parts.
Innate Immune System: Is the part
of the immune system that is innate, that we are born with. It
generally recognizes so-called Pathogen-Associated Molecular
Patterns (PAMPs), for instance common repetitive structures on
the surface of bacteria and viruses.
Pathogen: A foreign organism that leads to damage or disease (pathology). Bacteria, virus, parasites are all examples of potential pathogens. However, the commensal bacteria in your gut, or the cultures in yoghurt, are not pathogens.
Acknowledgement: Thanks to
Sharp for critical review of and valuable feedback for
10/13-2012: Educational article: The Components of the
Blood and the immune System.