Frequently Asked Questions - Blood Basics

The Bombay blood group is a rare exception to the commonly accepted ABO blood types. It is observed to occur in 1 out of every 250,000 people except in parts of India where the incidence has been observed to be as much as 1 in 7600. The rare designation was first identified in Mumbai, also known as Bombay - thus the name of the blood group. The blood type is thought to occur in only those of (Eastern) Indian descent. Blood types are actually ways of differentiating the type of antigens on a person's red blood cells. Being able to match these during donation and transfusions is important because of potential rejection by the immune system. The Bombay blood group is missing an antigen present on cells of the ABO group, the H antigen. The H antigen is a carbohydrate known as fucose.

The ABO blood types, discovered around 1900, consist of A and B antigen which are derived from H antigen, also known as the H substance. Type A has A antigen, type B has B antigen, and type O has neither A nor B antigens. The difference though is that in type O, the H antigen is present, it just is not changed by enzymes and used in blood cell recognition. In Bombay blood type (phenotype hh or Oh) there is no H antigen and those individuals actually have antibodies against the H substance. Bombay blood cells will act like type O when tested for antigens, but the tests currently only look for A and B groupings. Proper blood typing will not identify the Bombay blood group. Specialists point out that reverse grouping, whish are cross comparisons with type O, or serum grouping would have to be done to determine if a person had the rare blood type

Bombay blood groups can donate to any other blood group (with Rhesus compatibility positive or negative) because there is no fear of an immune reaction against antigens, but they must receive only hh blood otherwise face an hemolytic transfusion reaction which is often fatal. The hh phenotype is the inheritance of two recessive alleles (h) of the H gene and is attributed to a deficiency of the enzyme known as fucosyl transferase

Haemoglobin is the iron-containing protein attached to red blood cells that transports oxygen from the lungs to the rest of the body. Haemoglobin bonds with oxygen in the lungs, exchanges it for carbon dioxide at cellular level, and then transports the carbon dioxide back to the lungs to be exhaled.Whether haemoglobin binds with oxygen or carbon dioxide depends on the relative concentration of each around the red blood cell. When it reaches the oxygen-rich lungs, it releases the less-abundant carbon dioxide to bind with oxygen; when it goes back out into the body where cells are producing carbon dioxide, it releases the oxygen and binds with carbon dioxide.Haemoglobin abnormalities result in very serious hereditary diseases, such as sickle-cell anaemia and thalassemia.Haemoglobin is made up of four subunits, with a haem (iron-containing) group in each for oxygen binding. There are slightly different haemoglobins in adults when compared to children and foetuses.The level of haemoglobin is measured to check the oxygen carrying capacity of the blood. The low oxygen carrying capacity of the blood leads to the symptoms of anaemia (low level of haemoglobin).

The human immune system has various ways of responding to an infection caused by bacteria or viruses. Our bodies produce proteins (antibodies) that are highly specific for the infectious agent as a part of our "humoral" immune response. The antibodies help stop the infection from spreading further and help to eliminate the bacteria or virus from the body.Antibodies are also used to help our bodies find and destroy "foreign" cells such as tumors.
Because antibodies bind tightly to only one type of structure on the surface of cells (antigen), they can also be useful for identifying different types of blood cells. It is important to correctly identify blood cells in our bodies if we ever need to receive blood from someone else because we are sick (transfusion). Our blood type is determined based on the presence or absence of two proteins on the surface of our red blood cells (Type A and Type B). There are four possible combinations of blood types namely: Type A, Type B, Type AB, and Type O (contains neither A nor B proteins). This is referred to as the ABO blood type. In addition, red blood cells have a Rhesus factor or Rh, which is either present or absent. If the Rh factor is present, the cells are referred to as Rh positive. Including both the ABO and Rh systems for blood typing, there are a total of 8 possible blood types.

The blood moves through the body through the blood vessels -- essentially, flexible tubes that branch out and subdivide. There are different types of blood vessels: the arteries, capillaries, and veins.

Arteries carry the oxygen-rich blood that the heart pumps to the rest of the body. The heart pumps the blood out through one main artery, the dorsal aorta. This branches out into smaller arteries, which branch out in turn. The smallest arteries are called arterioles, and connect to capillaries. Because the arteries carry large quantities of blood that is under high pressure from the beating of the heart, they are wide and thick. The walls of an artery consist of three layers: a tough outer layer, a middle layer of muscle, and a smooth inner layer through which the blood can flow easily. The muscles in the middle layer help the heart pump the blood, squeezing down to move the blood along. You can feel the pulsing of the arteries as your pulse.

Blood passes from the arterioles into the capillaries. Capillaries are very narrow -- only one cell wide. They have very thin walls made of overlapping flat cells called endothelium; the walls are thin so that oxygen and carbon dioxide can pass through them easily. Inside the capillaries, the red blood cells release their oxygen, which passes through the capillary walls and into the surrounding tissue. The tissue releases its waste products, like carbon dioxide, which passes through the capillary walls and into the red blood cells.

Some organs -- the liver, spleen, and bone marrow -- contain blood vessels called sinusoids instead of capillaries. Like capillaries, sinusoids are composed of endothelium. Sinusoids are a bit larger than capillaries.From the capillaries/sinusoids, the de-oxygenated, waste-laden blood passes into the veins for its return trip to the heart. Veins are like arteries in that they have three layers. But since the blood is not under as much pressure, the walls of veins are thinner. Veins contain one-way valves to keep the blood flowing toward the heart, even against the pull of gravity. Because the blood in veins contains so little oxygen, it appears bluish rather than bright red. That's why the veins you can see through your skin (for example, in the underside of your wrist) are blue.

Plasma is the transporting medium for a myriad of hormones, electrolytes, sugars, waste products, and other substances. It is especially useful in transfusion medicine, as it provides the starting material for the preparation of critical blood-clotting factors, albumin and immune protein preparations. The clotting factor concentrates, prepared from large batches of pooled plasma, provide life-saving treatment for blood clotting disorders such as hemophilia. Plasma is a clear, straw-colored liquid that carries the blood cells and various hormones, nutrients, and so on through the body. It makes up a little more than half of the total blood volume. Plasma is about 90 percent water. Much of the other ten percent comprises various kinds of protein molecules, including enzymes, clotting agents, immunoglobulins (part of the immune system), and proteins that carry hormones, vitamins, cholesterol, and other things the body needs. Plasma also contains sugar (glucose) and electrolytes like sodium, potassium, and calcium, as well as other things like the aforementioned hormones, vitamins, and cholesterol.

The blood cells called platelets (thrombocytes) help blood to clot, in several different ways. When bleeding occurs, platelets clump together to help form a clot. Also, when they are exposed to air (as they would be by a wound), platelets start breaking down and release a substance into the bloodstream. This substance starts a chain of chemical events that eventually causes a protein in the blood, fibrinogen, to turn into a different substance, fibrin, which forms long threads. These threads tangle up red blood cells to help form a clot, or scab, over the wound. In their "resting" state, platelets look like two plates stuck together (hence the name). When "activated" and helping to form a clot, they change shape and look like tiny roundish blobs with tentacles. At only two to three microns, they are the smallest kind of blood cell.

White Blood Cells are responsible for protecting the body from invasion by foreign substances such as bacteria, fungi, and viruses. The majority of white blood cells are produced in the bone marrow, where they outnumber red blood cells by two to one. However, in the blood stream, there are about 600 red blood cells for every white blood cell. There are three types of white blood cell: granulocytes, lymphocytes, and monocytes. There are, in turn, three kinds of granulocyte: neutrophils, eosinophils, and basophils. (Granulocytes are called that because they contain granules that hold digestive enzymes.) Neutrophils kill invading bacteria by ingesting and then digesting them. Eosinophils kill parasites, and are involved in allergic reactions. Basophils also function in allergic reactions, but are not well understood. Lymphocytes are key parts of the body's immune system. There are two kinds of lymphocyte: T cells and B lymphocytes. T cells direct the activity of the immune system. B lymphocytes produce antibodies, which destroy foreign bodies. Monocytes, the largest kind of white blood cells, enter the tissues of the body and turn into even larger cells called macrophages. These eat foreign bacteria and destroy damaged, old, and dead cells of the body itself.

Red Blood Cells are perhaps the most recognizable component of whole blood. Red blood cells contain hemoglobin, a complex iron-containing protein that carries oxygen throughout the body and gives blood its red color. The percentage of blood volume composed of red blood cells is called the “hematocrit.” The average hematocrit in an adult male is 47 percent; the average hematocrit in adult females is 42 percent. There are about one billion red blood cells in two to three drops of blood, and, for every 600 red blood cells, there are about 40 platelets and one white cell. Manufactured in the bone marrow, red blood cells are continuously being produced and broken down. They live for approximately 120 days in the circulatory system and are eventually removed by the spleen. Red blood cells are prepared from whole blood by removing the plasma, or the liquid portion of the blood. They can raise the patient's hematocrit and hemoglobin levels while minimizing an increase in volume. Red blood cells are shaped like tiny doughnuts, with an indentation in the center instead of a hole. They contain a special molecule called hemoglobin, which carries the oxygen. In the lungs, where there is a lot of oxygen, the hemoglobin molecules loosely bind with oxygen. Each molecule of hemoglobin contains four iron atoms, and each iron atom can bind with one molecule of oxygen, allowing each hemoglobin molecule to carry four molecules of oxygen. In the capillaries, where there is little oxygen, the hemoglobin readily sheds the oxygen it is carrying and allows it to be absorbed by the body's cells. The iron in hemoglobin is what makes blood red.
Patients who benefit most from transfusions of red blood cells include those with chronic anemia resulting from disorders such as kidney failure, malignancies, or gastrointestinal bleeding and those with acute blood loss resulting from trauma or surgery. Since red blood cells have reduced amounts of plasma, they are well suited for treating anemia patients who would not tolerate the increased volume provided by whole blood, such as patients with congestive heart failure or those who are elderly or debilitated. Improvements in cell preservative solutions over the last 15 years have increased the shelf life of red blood cells from 21 to 42 days. Red blood cells may be treated and frozen for extended storage (up to 10 years).

Whole Blood is a living tissue that circulates through the heart, arteries, veins, and capillaries carrying nourishment, electrolytes, hormones, vitamins, antibodies, heat, and oxygen to the body's tissues. Whole blood contains red blood cells, white blood cells and platelets suspended in a fluid called plasma.If blood is treated to prevent clotting and permitted to stand in a container, the red blood cells, weighing the most, will settle to the bottom; the plasma will stay on top; and the white blood cells and platelets will remain suspended between the plasma and the red blood cells. A centrifuge may be used to hasten this separation process. The platelet-rich plasma is then removed and placed into a sterile bag, and it can be used to prepare platelets and plasma or cryoprecipitated AHF. To make platelets, the platelet-rich plasma is centrifuged, causing the platelets to settle at the bottom of the bag. Plasma and platelets are then separated and made available for transfusion. The plasma may also be pooled with plasma from other donors and further processed, or fractionated, to provide purified plasma proteins such as albumin, immunoglobulin (IVIG) and clotting factors.

Blood cells are produced in the bone marrow, a jellylike substance inside the bones that is composed of, among other things, fat, blood, and special cells that turn into the various kinds of blood cells. In children, the marrow of most of the bones produces blood. But in adults, only the marrow of certain bones -- the spine, ribs, pelvis, and some others -- continues to make blood. Bone marrow that actively produces blood cells is called red marrow, and bone marrow that no longer produces blood cells is called yellow marrow.

All blood cells come from the same kind of stem cell, which has the potential to turn into any kind of blood cell. These stem cells are called pluripotential hematopoietic stem cells.

As the blood cells develop from the stem cells in the marrow, they seep into the blood that passes through the bones and on into the bloodstream. The different kinds of blood cells have different "life spans" -- red blood cells last about 120 days in the bloodstream; platelets about 10 days; and the various kinds of white blood cells can last anywhere from days to years. The body has a feedback system that tells it when to make new red blood cells. If bodily oxygen levels are low (as they would be if there are too few red blood cells circulating), the kidneys produce a hormone called erythropoietin, which stimulates the stem cells in the marrow to produce more red blood cells.

Whole blood is separated into its component parts for patients needing a particular product. The main blood collection bag has up to three satellite bags attached to it. In a centrifuge process, the red cells, platelets, and plasma are spun, separated and readied for transfusion.
• Red blood cells are made in the bone marrow and carry oxygen to the body and remove carbon dioxide. They are needed for accident victims, certain surgeries, and patients with anemia and blood disorders.
• Platelets are tiny cells, formed in the bone marrow, that control bleeding by helping the blood to clot. The body replaces platelets within 72 hours of donation. Leukemia and cancer patients need platelets because chemotherapy destroys their own supply of platelets.
• Plasma is the liquid part of the blood and makes up 55% of blood volume. It is comprised of 92% water, 7% protein, and 1% minerals, and is essential in the clotting/coagulation process. Plasma is used for patients experiencing heavy bleeding and for burn victims.
• Cryoprecipitate is extracted from plasma in a freezing and thawing process. This component contains a specific clotting agent, Factor VIII, missing in hemophiliacs and essential for controlling bleeding.