Blood, Blood-Forming Organs, and the Immune Mechanism

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Blood, Blood-Forming Organs, and the Immune Mechanism

ICD-10-CM Examples from Tabular

D72.82 Elevated white blood cell count

Excludes1 eosinophilia (D72.1)

D72.820. Lymphocytosis (symptomatic)

D72.821. Monocytosis (symptomatic)

    Excludes1 infectious mononucleosis (B27.-)

D72.822. Plasmacytosis

D72.823. Leukemoid reaction

D72.824. Basophilia

D72.825. Bandemia

Excludes1 confirmed infection—code to infection leukemia (C91.-, C92.-, C93.-, C94.-, C95.-)

D72.828. Other elevated white blood cell count

D72.829. Elevated white blood cell count, unspecified

D72.89. Other specified disorders of white blood cells

Functions of the Blood and Immune Systems

Homeostasis, or a “steady state,” is a continual balancing act of the body systems to provide an internal environment that is compatible with life. The two liquid tissues of the body, the blood and lymph, have separate but interrelated functions in maintaining this balance. They combine with a third system, the immune system, to protect the body against pathogens that could threaten the organism’s viability.

The blood is responsible for the following:

The lymph system is responsible for the following:

The immune system is responsible for the following:

Figure 8-1 is a Venn diagram of the interrelationship among the three systems, with the shared goals of homeostasis and protection at the intersection of the three circles.

Anatomy and Physiology

The hematic and lymphatic systems flow through separate yet interconnected and interdependent channels. Both are systems composed of vessels and the liquids that flow through them. The immune system, a very complex set of levels of protection for the body, includes blood and lymph cells.

Figure 8-2 shows the relationship of the lymphatic vessels to the circulatory system. Note the close relationship between the distribution of the lymphatic vessels and the venous blood vessels. Tissue fluid is drained by the lymphatic capillaries and is transported by a series of larger lymphatic vessels toward the heart.

The organs in the lymphatic system are the spleen, the thymus gland, the tonsils, the appendix, and Peyer’s patches. The spleen is located in the upper left quadrant and serves to filter, store, and produce blood cells; remove red blood cells (RBCs); and activate B lymphocytes. The thymus gland is located in the mediastinum and is instrumental in the development of T lymphocytes (T cells). The tonsils are lymphatic tissue (lingual, pharyngeal, and palatine) that helps protect the entrance to the respiratory and digestive systems. The vermiform appendix and Peyer’s patches are lymphoid tissue in the intestines.

The clearest path to understanding the interconnected roles of these three systems is to look at the hematic system first.

Hematic System

The hematic system is composed of blood and the vessels that carry the blood throughout the body. The formation of blood, hematopoiesis, begins in the bone marrow with a single type of cell, a multipotential (pluripotent) hematopoietic stem cell (HSC), or hemocytoblast. This cell divides into cells that mature in lymphatic tissue (band T lymphocytes) and cells that mature in the bone marrow. Refer to Figure 8-3 to follow the development from the stem cell to specialized mature blood cells.

Whole blood is composed of a solid portion that consists of formed elements, or cells, and a liquid portion called plasma. Blood cells make up 45% of the total blood volume, and plasma makes up the other 55% (Fig. 8-4).

< ?xml:namespace prefix = "mml" />(whole) blood=blood cells (45%)+plasma (55%)


The solid portion of blood is composed of three different types of cells:

In a milliliter of blood, there are 4.2 million to 5.8 million RBCs, 250,000 to 400,000 platelets, and 5000 to 9000 WBCs. These cells together account for approximately 8% of body volume. Converted to more familiar liquid measure, there are about 10.5 pints (5 liters) of blood in a 150-lb (68-kg) person.

Components of Blood

Erythrocytes (Red Blood Cells)

The erythrocytes (which are normally present in the millions) have the important function of transporting O2 and CO2 throughout the body (Fig. 8-5). The vehicle for this transportation is a protein-iron pigment called hemoglobin. When combined with oxygen, it is termed oxyhemoglobin.

The formation of RBCs in the red bone marrow, the blood-producing cavities found in many bones, is stimulated by a hormone from the kidneys called erythropoietin. RBCs have a life span of approximately 120 days, after which they decompose into hemosiderin, an iron pigment resulting from hemolysis, and bilirubin. The iron is stored in the liver to be recycled into new RBCs, and the bile pigments are excreted via the liver.

Abnormal RBCs can be named by their morphology, the study of shape or form. RBCs normally have a biconcave, disclike shape and are anuclear (without a nucleus). (Although the center is depressed, there is not an actual hole.) Those that are shaped differently often have difficulty in carrying out their function.

For example, sickle cell anemia is a hereditary condition characterized by erythrocytes (RBCs) that are abnormally shaped. They resemble a crescent or sickle. An abnormal hemoglobin found inside these erythrocytes causes sickle-cell anemia in a number of Africans and African Americans.

Leukocytes (White Blood Cells)

Although there are fewer leukocytes (thousands, not millions), there are different types with different functions. In general, WBCs protect the body from invasion by pathogens. The different types of cells provide this defense in a number of different ways. There are two main types of WBCs: granulocytes and agranulocytes.

Granulocytes (Polymorphonucleocytes)

Named for their appearance, granulocytes, also called polymorphonucleocytes (PMNs, or polys) are white blood cells that have small grains within the cytoplasm and multilobed nuclei. These names are used interchangeably.

There are three types of granulocytes, each with its own function. Each of them is named for the type of dye that it attracts.

1. Eosinophils (eosins) are cells that absorb an acidic dye, which causes them to appear reddish. An increase in eosinophils is a response to a need for their function in defending the body against allergens and parasites.

2. Neutrophils (neuts), the most numerous WBCs, are cells that do not absorb either an acidic or a basic dye and consequently are a purplish color. They are also called phagocytes because they specialize in phagocytosis and generally combat bacteria in pyogenic infections. This means that these cells are drawn to the site of a pathogenic “invasion,” where they consume the enemy and remove the debris resulting from the battle. Because the nucleus in immature neutrophils has a long “bandlike” shape, these cells are often referred to as band cells. They are also called stabs; the name is from the German word for rods because of their rodlike appearance. As the cells continue to mature, the bands divide, and the adult cells are renamed segs because now the nuclei are divided into clumps (segmented).

3. Basophils (basos) are cells that absorb a basic (or alkaline) dye and stain a bluish color. Especially effective in combating parasites, they release histamine (a substance that initiates an inflammatory response) and heparin (an anticoagulant), both of which are instrumental in healing damaged tissue.

Agranulocytes (Mononuclear Leukocytes)

Agranulocytes are white blood cells named for their lack of granules. The alternative name mononuclear leukocytes is so given because they have one nucleus. The two names are used interchangeably. Although these cells originate in the bone marrow, they mature after entering the lymphatic system. There are two types of these WBCs:

Thrombocytes (Platelets)

Platelets (also known as thrombocytes or plats) have a round or oval shape and are so named because they look like small plates. Platelets aid in coagulation, the process of changing a liquid to a solid. When blood cells escape their normal vessels, they agglutinate, or clump together, by the following process: First, they release factor X (formerly called thrombokinase), which, in the presence of calcium, reacts with the blood protein prothrombin to form thrombin. Thrombin then converts another blood protein, fibrinogen, to fibrin, which eventually forms a meshlike fibrin clot (blood clot), achieving hemostasis (control of blood flow; that is, stopping the bleeding). See Figure 8-6 for a visual explanation of the clotting process.


Plasma, the liquid portion of blood, is composed of the following:

Serum (pl. sera) is plasma minus the clotting proteins. Serology is the branch of laboratory medicine that studies blood serum for evidence of infection by evaluating antigen-antibody reactions in vitro.

Serum=Plasma (Prothrombin+Fibrinogen)



B. Match the following suffixes with their meanings.

Decode the terms.

Blood Groups

Human blood is divided into four major different types: A, B, AB, and O. See Figure 8-7 for a table of blood types, agglutinogens, and agglutinins. The differences are due to antigens present on the surface of the red blood cells. Antigens are substances that produce an immune reaction by their nature of being perceived as foreign to the body. In response, the body produces substances called antibodies that nullify or neutralize the antigens. In blood, these antigens are called agglutinogens because their presence can cause the blood to clump. The antibody is termed an agglutinin. For example, type A blood has A antigen, type B has B antigen, type AB has both A and B antigens, and type O has neither A nor B antigens. If an individual with type A blood is transfused with type B blood, the A antigens will form anti-B antibodies because they perceive B blood as being foreign. Following the logic of each of these antigen-antibody reactions, an individual with type AB blood is a universal recipient, and an individual with type O blood is a universal donor.

Another antigen, the Rh factor, is important in pregnancy because a mismatch between the fetus and the mother can cause erythroblastosis fetalis, or hemolytic disease of the newborn (HDN) (see Fig. 7-10). In this disorder, a mother with a negative Rh factor will develop antibodies to an Rh+ fetus during the first pregnancy. If another pregnancy occurs with an Rh+ fetus, the antibodies will destroy the fetal blood cells.

Immune System

The immune system is composed of organs, tissues, cells, and chemical messengers that interact to protect the body from external invaders and its own internally altered cells. The chemical messengers are cytokines, which are secreted by cells of the immune system that direct immune cellular interactions. Lymphocytes (leukocytes that are categorized as either B cells or T cells) secrete lymphokines. Monocytes and macrophages secrete monokines. Interleukins are a type of cytokine that sends messages among leukocytes to direct protective action.

The best way to understand this system is through the body’s various levels of defense. The goal of pathogens is to breach these levels to enter the body, reproduce, and, subsequently, exploit healthy tissue, causing harm. The immune system’s task is to stop them.

Figure 8-8 illustrates the levels of defense. The two outside circles represent nonspecific immunity and its two levels of defense. The inner circle represents the various mechanisms of specific immunity, which can be natural (genetic) or acquired in four different ways. Most pathogens can be contained by the first two lines of nonspecific defense. However, some pathogens deserve a “special” means of protection, which is discussed in the section titled “Specific Immunity.”

Nonspecific Immunity

This term refers to the various ways that the body protects itself from many types of pathogens, without having to “recognize” them. The first line of defense in nonspecific immunity (the outermost layer) consists of the following methods of protection:

The second line of defense in nonspecific immunity comes into play if the pathogens make it past the first line. Defensive measures include certain processes, proteins, and specialized cells.

Defensive processes include the following:

• Phagocytosis: Phagocytosis is the process of cells “eating” and destroying microorganisms. Pathogens that make it past the first line of defense and enter into the bloodstream may be consumed by neutrophils and monocytes.

• Inflammation: Acquiring its name from its properties, inflammation is a protective response to irritation or injury. The characteristics (heat, swelling, redness, and pain) arise in response to an immediate vasoconstriction, followed by an increase in vascular permeability. These provide a good environment for healing. If caused by a pathogen, the inflammation is called an infection.

• Pyrexia: Pyrexia is the medical term for fever. When infection is present, fever may serve a protective function by increasing the action of phagocytes and decreasing the viability of certain pathogens.

The protective proteins are part of the second line of defense. These include interferons, which get their name from their ability to “interfere” with viral replication and limit a virus’s ability to damage the body. The complement proteins, a second protein type, exist as inactive forms in blood circulation that become activated in the presence of bacteria, enabling them to lyse (destroy) the organisms.

Finally the last of the “team” in the second line of defense are the natural killer (NK) cells. This special kind of lymphocyte acts nonspecifically to kill cells that have been infected by certain viruses and cancer cells.

Specific Immunity

Specific immunity may be either genetic—an inherited ability to resist certain diseases because of one’s species, race, sex, or individual genetics—or acquired. Specific immunity depends on the body’s ability to identify a pathogen and prepare a specific response (antibody) to only that invader (antigen). Antibodies are also referred to as immunoglobulins (Ig). The acquired form can be further divided into natural and artificial forms, which in turn can each be either active or passive. After the specific immune process is described, each of the four types is discussed.

Specific immunity depends on the agranulocytes (lymphocytes and monocytes) for its function. The monocytes metamorphose into macrophages, which dispose of foreign substances. The lymphocytes differentiate into either T lymphocytes (they mature in the thymus) or B lymphocytes (they mature in the bone marrow or fetal liver). Although both types of lymphocytes take part in specific immunity, they do so in different ways.

The T cells neutralize their enemies through a process of cell-mediated immunity. This means that they attack antigens directly. They are effective against fungi, cancer cells, protozoa, and, unfortunately, organ transplants. B cells use a process of humoral immunity (also called antibody-mediated immunity). This means that they secrete antibodies to “poison” their enemies, either during the attack (plasma B cells) or in subsequent attacks (memory B cells).

Types of Acquired Immunity

Acquired immunity is categorized as active or passive and then is further subcategorized as natural or artificial. All describe ways that the body has acquired antibodies to specific diseases.

Active acquired immunity can take either of the following two forms:

Passive acquired immunity can take either of the following two forms:


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