Hematology is the study of the blood. Blood is an essential, specialized body fluid that delivers necessary substances to the body's cells and carries waste products away from those same cells. Blood serves many other different functions within our bodies as well. It performs various actions in the circulatory, respiratory, urinary, digestive, endocrine, and integumentary systems to maintain homeostasis. Blood is comprised of formed elements and plasma which provide oxygen transport, immune defense, and blood clotting.


Major Components and Functions of the Circulatory System

The circulatory system has three major functions:
1. With an estimated 60,000 miles of vessels throughout the average adult body, a major function of these vessels is the transport of nutrients, oxygen, and hormones to cells throughout the body and removal of metabolic wastes (carbon dioxide, nitrogenous wastes, and heat). The blood also transports viruses, bacteria and other toxins.
2. To provide protection against these foreign microbes and toxins, the circulatory system has protective mechanicapillary_beds.jpgsms that provide protection of the body by white blood cells, antibodies, and other proteins that circulate in the blood. Clotting mechanisms are also present to help protect the body from blood loss after injuries.
3. The circulatory system works together with the respiratory, urinary, digestive, endocrine, and integumentary systems to maintain homeostasis. Regulation of body temperature, fluid pH, water content of cells, and hormones are all part of the regulatory function.

Blood is confined to a closed system of blood vessels and to the four chambers of the heart. It travels away from the heart through the arteries, which then branch into smaller vessels called arterioles. Arterioles branch further into the smallest of vessels, the capillaries. Gas, nutrient, and waste exchange occurs across the capillary walls. The blood returns to the heart as capillaries merge to form venules, which in turn merge to form large veins, which connect to the heart.

Composition of the Blood

Blood volume varies, but tends to be around 8% of our body weight. Factors such as body size, amount of adipose tissue, and electrolyte concentrations all affect blood volume. The average adult has about 5 liters of blood.
Blood consists of cells which are suspended in a liquid. These components can be separated by centrifuging (or spinning) it. Three layers become visible after this process has occurred.

At the top is the straw-colored liquid that consists of water and dissolved solutes. This is the plasma, and it accounts for approximat150px-Blood-centrifugation-scheme.pngely 55% of the total blood volume. Plasma is about 92% water, with plasma proteins being the most abundant solutes. The main plasma protein groups are albumins, globulins, and fibrinogens.

The next layer in the centrifuged sample is a thin, cream-colored layer called the “buffy coat.” This layer consists of white blood cells (leukocytes) and cell fragments called platelets (thrombocytes). This layer is part of what are known as the formed elements. Approximately 1% of the blood volume is occupied by the “buffy coat“. A cubic millimeter of blood normally contains only 5,000 to 9,000 leukocytes. Leukocytes can be categorized into two groups…the granular leukocytes (those that have granules in their cytoplasm) and agranular leukocytes (those without clearly visible granules). These two categories can further be broken down into eosinophil, basophils, and neutrophils (granular), and lymphocytes and monocytes (agranular). Neutrophils are the most abundant type of leukocyte, accounting for 50% to 70% of the leukocytes in the blood. Lymphocytes are usually the second most numerous types of leukocytes. Thrombocytes (platelets) are the smallest of all the formed elements, and are actually fragments of large cells called megakaryocytes, which are found in bone marrow. Platelet counts range from 130,000 to 140,000 per cubic millimeter of blood, but this count can vary depending on physiological conditions. Platelets play an important role in blood clotting.

The bottom layer of the centrifuged blood sample is made up of red blood cells (erythrocytes). Erythrocytes are the most abundant of the blood cells, and they (along with leukocytes and thrombocytes) are what are referred to as the formed elements. Red blood cells compose most of the formed elements (36% to 46% in women and 41% to 53% in men); the percentage of red blood cell volume to total blood volume in a centrifuged blood sample is a measurement called the hematocrit. A cubic millimeter of blood normally contains 5.1 million to 5.8 million erythrocytes in males and 4.3 million to 5.2 million erythrocytes in females. These cells contain hemoglobin. Hemoglobin is what gives blood its red color. The red blood cells are marked by glycoprotiens that define the different blood types.

The following video gives a great explaination of the composition of the blood!

ABO Blood Typing System

There are many different ways to classify blood types, but the most common blood type classification system is the ABO system. There are four blood types in the ABO system: Type A, Type B, Type AB, and Type O. These blood types refer to the different versions of carbohydrate molecules (antigens) which are present on the surface of red blood cells. People with type A blood have type A antigens on their red blood cells. People with type B blood have type B antigens on their red blood cells. People with type AB blood have both type A and type B antigens on their red blood cells. People with type O blood have neither type A nor type B antigens on their red blood cells. Type A and type B carbohydrate molecules are called antigens because they can stimulate the body to produce an immune response, including the making of antibodies.
Antibodies are special proteins that travel in the blood and help us destroy viruses or bacteria that may have infected our bodies. Normally, our bodies do not make antibodies against any molecules that are part of our own bodies. They help to defend against invading viruses and bacteria, but normally do not attack our own body cells. People with type A blood do not make antibodies against the type A antigen which is present on their red blood cells, but they do make antibodies against the Type B antigen. People who are type AB develop tolerance to both of the antigens, and therefore do not produce either anti-A or anti-B antibodies. Those who are type O do not develop tolerance to either antigen, therefore, they have both anti-A and anti-B antibodies. So, if someone with type A blood was given type B blood during a blood transfusion, the antibodies would attack against the type B antigen on the received blood cells. This would cause the blood to clump (agglutinate), which could be fatal to the patient.To determine blood type, the test blood is dropped on a slide and antibodies are added to determine if the antibodies will attack the red blood cells. This attack is identified by agglutination (clumping) of the red blood cells. If anti-A antibodies attack the blood, it must be blood type A. This is because type A blood naturally has anti-B antibodies in the plasma, but not anti-A. It is the opposite for blood type B. If the test blood is type AB, agglutination will show in each sample (one with anti-A and one with anti-B antibodies added). If the test blood is type O, agglutination will not be present in either sample.

The following chart shows which blood types can give/receive each type of blood. Because type O red blood cells lack A and B antigens, it is considered a universal donor, but only as long as the volume of plasma donated is small. Type AB people are considered to be universal recipients because they lack anti-A and anti-B antibodies, and therefore cannot agglutinate donor red blood cells. Because of the dangers involved, use of the universal donor and recipient concept is to be avoided if possible.


American Red Cross Games
The above website has some fun games and even a downloadable official American Red Cross coloring book!


Hematology plays a big role in the career of a nurse. The CBC (Complete Blood Count) is a very common test that most of us have undergonblood_draw.jpge several times upon visiting our doctors. Many patients have baseline CBC tests done at the request of their doctor to determine their general health status. If they are healthy and they have cell populations that are within normal limits, then they will probably not require another CBC until their health status changes or the doctor feels it is necessary. If a patient is having symptoms of fatigue or has an infection, inflammation, bruising, or bleeding (just to name a few), then the doctor may order a CBC to help diagnose the cause. A nurse is often responsible for informing the patient about the test. The nurse will have to obtain a history of the patient’s complaints, allergies, medical history, and current medications before the sample is drawn. Depending on the results of the CBC, in some cases, the nurse is also responsible for patient education.

CBCs are also done before a patient is given chemotherapy. My mother in law is receiving chemo for ovarian cancer. If her blood count is too low she will not get a treatment. About a month ago she wasn't doing very well, fatigued, no appetite, didn't recover from her last chemo treatment like she had before. She really looked tough. They did a CBC and she was really low, I want to say 6 or 7. She received 2 pints of blood and has felt much better ever since. Her last round of treatment she didn't get real ill and was very excited about life again.
Dr. Dan has a CBC drawn on everyone when they have their physicial, just to make sure the levels are all normal. If things are low, then he needs to start to look for other reasons. He might have them recheck it in a week. Colonoscopy comes up alot when patients have a low Hgb because it is a sign that they might be losing blood from somewhere and it is a good way to look to see if there is anything going on with the colon. Anemia is another thing that is very common with patients because they do not always get enough iron in their diet. Young women have anemia with their menstrual cycles and may need to take an extra vitamin. With breaking down the WBC, which are also part of the CBC, physicians can tell if the illness the patient has is viral or bacterial. In a clinic setting, nursing would probably draw blood in the oncology department. Otherwise, blood is drawn in the lab. We do have nurses that help out in lab.


Case Study Questions

1. Describe the structure of a molecule of hemoglobin and explain the role played by iron in the transport of oxygen.
Hemoglobin contains both a protein portion (globin) and nonprotein heme groups. Globin consists of four polypeptide chains, each of which contains a heme group. The heme group is a red pigment that contains a single iron atom surrounded by a ring of nitrogen-containing carbon rings. One oxygen atom attaches to the iron of each heme group, allowing a single hemoglobin molecule to carry four oxygen atoms. Each erythrocyte contains about 250 million hemoglobin molecules.
Iron is necessary for oxygen transport in the blood. Iron is the central atom of the heme group, which binds oxygen in the lungs and carries it to all the other cells in the body that need oxygen to perform their activities. Without iron in the heme group, there would be no site for oxygen to bind, andhemoglobin_molecule.png therefore no oxygen would be delivered to the cells causing them to die. It is necessary for allowing the cells that need oxygen to obtain O2 for supplying the body with a reliable source of energy, and for maintaining several other important structures and systems in the body. Iron is also used to help produce the connective tissues in the body, some of the neurotransmitters in our brain, and to maintain the immune system.

2. How is iron stored and transported in the body?
Iron is mostly stored in the body in the hemoglobin. About 30% of iron is also stored in the bone marrow, liver, and spleen.
Iron is present in two oxidation states: ferrous (Fe2+) or ferric (Fe3+). Iron from our diet is either free iron or heme iron. Free iron is reduced from the ferric to the ferrous in the intestines, on the luminal surface of intestinal enterocytes and them moves into the cells. When heme iron is consumed, the iron is freed within the enterocytes. It can be stored within intestinal enterocytes bound to ferritin and transported along the basolateralmembrane of intestinal enterocytes. The liver is the main storage site for iron and the main site of iron consumption is the bone marrow for heme synthesis.

3. What is Iron Deficiency Anemia (IDA) and how frequently does it occur?
Iron deficiency anemia is a condition where a person has inadequate amounts of iron to meet the body’s demands. It is a decrease in the amount of red blood cells caused by having too little iron.
IDA is the most widespread type of anemia. Approximately 20% of women, 50% of pregnant women, and 3% of men are iron deficient.

4. What are the most common causes of IDA?
The main causes of iron deficiency are poor absorption of iron by the body, inadequate intake of iron, pregnancy, growth spurts or blood loss due to heavy menses or internal bleeding. Anemia develops slowly after the normal stores of iron have been depleted in the body in the bone marrow.

5. Why are women more prone to IDA than men?
Women are more prone to IDA than men is because on average, women have a lower supply of iron than men and lose iron more often than men due to blood loss during menstruation.

6. What are the red blood cells indices, and what tests are diagnostic for IDA?
There are three red blood cell indices: mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). The MCV demonstrates the size of the red blood cells. The MCH value represents hemoglobin quantity in an average red blood cell. The MCHC determines the concentration of hemoglobin in an average red blood cell.
Diagnostic tests for IDA are red blood cell measures of hemocrit and hemoglobin, size of red blood cells, serum iron level and iron binding capacity in the blood. IDA patients will have low MCV and MCHC results.

7. How is IDA treated and prevented?
IDA can be treated and prevented by eating a diet that is high in iron such as in red meat, liver, raisins, spinach, broccoli, and egg yolks. Taking iron supplements can also help.


All information was obtained from Human Physiology; Stuart Ira Fox; 12th Edition, Burton’s Microbiology For The Health Sciences; Paul G. Engelkirk and Janet Duben-Engelkirk; 9th Edition, http://www.wikipedia.org/_, and http://www.howstuffworks.com/_.
All sources for photos can be accessed directly by clicking on the photos.