Components of Blood

Hematology is the branch of physiology that addresses the study of blood. Blood is an essential component to human life that serves and carries out many vital bodily functions. Blood facilitates metabolic processes that encompass transportation of oxygen to other systems such as muscles, organs and the brain. Further it transports waste products like carbon dioxide and some toxins to be removed from the body through various mechanisms. Cells suspended in blood act as the first lines of defense against injury or infection by clotting mechanisms, and by transporting disease fighting cells like leukocytes (leuko means white, cyto means cell), and macrophages (macro means large, phage means eater) that clean up and digest debris and or harmful toxins and microorganisms. Lastly, the hematologic system maintains acid-base (pH) balances within the sensitive environment of the body.

Blood primarily consists of a fluid and a solid component that is made of formed elements. The combination of both fluid and formed element is termed blood volume. In an average adult, blood volume is equivalent to 6 quarts or in the metric system 5.5 liters of liquid. The fluid component of blood, called plasma, suspends and shuttles the solid, formed elements throughout the complex cardiovascular system. Plasma is approximately 90% water and the remaining 10% constitutes dissolved substances called solutes, which are made of organic and inorganic elements that contain electrolytes, proteins, gases, nutrients, waste products, and some hormones.

Electrolytes are essential in blood and important because they acts as an electric medium that can influence and regulate acid-base or pH functions. Electrolytes contain ionic compounds like sodium, potassium, calcium, magnesium, chlorine, phosphates, sulfates, and carbonic acids. These compounds ensure the body maintains appropriate balances of pH levels throughout many systems in the body in the form of buffers. The plasma also contains important proteins like albumin, globulins, fibrinogen, transferrin, and ferritin. The names are not as important, but understanding that these proteins main function is to provide osmotic pressure, act as buffers and binding agents, clotting factors and enzyme precursors is key.

Roughly 45-50% of blood volume is composed of formed elements, which are mostly cellular in nature and structure. There are three broad classifications of the types of cells that circulate throughout the vast network of blood vessels, capillaries, and arteries and they are: erythrocytes (red blood cells/RBC’s), leukocytes (white blood cells), and platelets (thrombocytes).

ERYTHROCYTES (red blood cells)
Red blood cells are the most abundant cells in the hematological system and have various important roles in the human body. Their main responsibility is tissue oxygenation as they carry and deliver gases (primarily oxygen) and electrolytes to and from tissue cells and the lungs. They also carry waste in the form of carbon dioxide back to the lungs to be exhaled out of the body through the mouth and nose. Red blood cells are produced in the bone marrow of long bones and live about 120 days.

LEUKOCYTES (white blood cells)
Leukocytes, or white blood cells are another common type of cell that are paramount in the defense of our bodies against harmful organisms and dead or injured host cells. Leukocytes generally do their work in the tissues that are affected, but are transported through the circulatory system. Types of white blood cells are complex and contain several different types. They are classified first by their structure as being either granulocytes or agranulocytes, and then by function as either a phagocyte or immunocyte.

A granulocyte means it has granular membrane bound particles circulating in the cells cytoplasm. The granules are important because they contain enzymes that kill microorganisms and capture and break down debris. Agranulocytes simply do not have this capability of breaking down and digesting foreign bodies. Types of granulocytic leukocytes include neutrophils, eosinophils, and basophils.

The neutrophil is the most common and understood granulocyte. They are the primary cell involved in the early stages of inflammation. When a bacterial invasion or injury to tissues occur, neutrophils leave the capillaries where they are housed and migrate to the site of inflammation, where they destroy and ingest microorganisms and debris; they subsequently die 1 or 2 days after this takes place.

Eosinophils are less common, but have the same function of ingesting antigen-antibody complexes that are the main offenders in parasite attacks and allergic reactions. They also have involvement in controlling the inflammatory process. Lastly, basophils are the least common leukocytes and have a primary role in stimulating the inflammatory process, but the exact function of these cells is not well understood by scientists.

There are three types of agranulocytes circulating the in the body monocytes / macrophages, lymphocytes, and natural killer cells. Monocytes and macrophages work together forming a system that scavenges the body, much like a shark in the ocean, finding and ingesting dead or defective host cells (but cannot digest), particularly red blood cells. They more or less act like janitors that keep our blood clean and free of debris. Monocytes are simply immature macrophages, but have many biological properties that participate in the immune response.

Lymphocytes are the primary movers and play an active role in the immune response. They mostly stay in lymphoid tissue until they are needed, upon which they are circulated throughout the body in the blood. Lymphocytes work when the body was exposed to a pathogen and subsequently builds immunity from it. So for example by receiving a chicken pox vaccine, your body builds an immunity to it by deploying lymphocytes and later exposure will result in these cells attacking and killing the virus. Natural killer cells have a resemblance to lymphocytes, but don’t require prior exposure to virus infected cells or even cancer cells.

THROMBOCYTES (platelets)
The last type of formed element in the body is platelets; which are not cells at all. Platelets are essential for blood coagulation and aid in controlling bleeding by forming clots. Most platelets are stored in the spleen and die after about 10 days if they are not needed and then are removed by macrophages.

The hematologic system that makes up a component and works hand in hand with the cardiovascular system is much more complex and advanced physiologically than one would initially think. Not just made up of red blood cells and plasma, the blood and its components do so much more in keeping our bodies metabolically regulated, oxygenated, and free of disease.