Blood, Lymphatic, and Immune Systems

Blood, Lymphatic, and Immune Systems

Chapter at a Glance

Use these key word parts and terms to assess your knowledge. Check off the ones you have mastered.

Functions of the Blood, Lymphatic, and Immune Systems

Homeostasis (hoh mee oh STAY sis), 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 (limf), have separate but interrelated functions in maintaining this balance. They work with the immune (ih MYOON) system to protect the body against pathogens (PATH oh jenz) that could threaten the organism’s viability. The blood is responsible for the following:

The lymphatic system is responsible for the following:

The immune system is responsible for the following:

Fig. 9-1 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 (hem AT ick) and lymphatic (lim FAT ick) 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.

Fig. 9-2 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 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 process of blood formation is called hematopoiesis (hee mah toh poy EE sis). All blood cells originate from a single type of cell called a stem cell. Because blood can be an extremely important part of the diagnostic process, students need to understand its normal composition. Blood is composed of a solid portion that consists of formed elements, or cells, and a liquid portion called plasma (PLAZ muh). Blood cells make up 45% of the total blood volume, and plasma makes up the other 55% (Fig. 9-3).

(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 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 pt (5 L) 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. 9-4). The vehicle for this transportation is a protein-iron pigment called hemoglobin (HEE moh gloh bin).

The formation of RBCs in the red bone marrow, the blood-producing cavities found in many bones, is stimulated by a hormone produced in the kidneys called erythropoietin (eh rith roh POY uh tin). RBCs have a life span of approximately 120 days, after which they decompose into hemosiderin (hee moh SID uh rin), an iron pigment resulting from hemolysis (heh MALL uh sis), 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 (more FALL uh jee), the study of shape or form. RBCs normally have a biconcave, disklike shape. (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.

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. There are two main types of WBCs: granulocytes and agranulocytes.

Granulocytes (Polymorphonucleocytes)

Named for their appearance, granulocytes (GRAN yoo loh sites), also called polymorphonucleocytes (pah lee morf oh NOO klee oh sites) (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.

Agranulocytes (Mononuclear Leukocytes)

Agranulocytes (a GRAN yoo loh sites) 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 [plats])

Platelets (also known as thrombocytes) have a round or oval shape and are so named because they look like small plates. Platelets aid in coagulation (koh agg yoo LAY shun), the process of changing a liquid to a solid. When blood cells escape their normal vessels, they agglutinate (ah GLOO tih nate), or clump together, by the following process: First, they activate clotting factors (such as Factor X) that produce prothrombin activator (PTA). Next, in the presence of calcium, the PTA reacts with the blood protein, prothrombin (proh THROM bin), to form thrombin. Thrombin then converts another blood protein, fibrinogen (fye BRIN ah jen), to fibrin (FYE brin), which eventually forms a meshlike fibrin clot (blood clot), achieving hemostasis (hee moh STAY sis) (control of blood flow; that is, stopping the bleeding). See Fig. 9-5 for a visual explanation of the clotting process.

image Exercise 1: The Hematic System

Match the following combining forms with their meanings.

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 Fig. 9-6 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 (ANN tih jens) 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 (ah gloo TIN oh jens) because their presence can cause the blood to clump. The antibody is termed an agglutinin (ah GLOO tin nin). 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 (hee moh LIT ick) disease of the newborn (HDN). 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.

Lymphatic System

The lymphatic system is responsible for the following:

The lymphatic system (Fig. 9-7) is composed of lymph (or interstitial fluid), lymph vessels, lymph nodes or lymph glands, lymph organs (e.g., tonsils, adenoids, appendix, spleen, thymus gland, patches of tissue in the intestines called Peyer’s patches), and lymphoid tissue. Monocytes and lymphocytes pass from the bloodstream through the blood capillary walls into the spaces between the cells in body tissue. When they pass into this lymph or interstitial fluid that surrounds cells, they perform their protective functions. Monocytes change into macrophages (MACK roh fay jehs), destroy pathogens, and collect debris from damaged cells. Lymphocytes are much more complicated and are essential to the immune response, so they are discussed in the next section. Once monocytes and lymphocytes pass into the lymphatic capillaries, the fluid is termed lymph or lymphatic fluid.

Lymph moves in one direction to prevent pathogens from flowing through the entire body. The system filters out the microorganisms as the lymph passes through its various capillaries, vessels, and nodes. Lymph travels in the following sequence:

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 of the abdomen and serves to filter, store, and produce blood cells; remove 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.

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 (SYE toh kynez), 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 (LIM foh kynez). Monocytes and macrophages secrete monokines (MAH noh kynez). Interleukins (in tur LOO kinz) 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.

Fig. 9-8 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 under “Specific Immunity.”

Oct 6, 2017 | Posted by in GENERAL SURGERY | Comments Off on Blood, Lymphatic, and Immune Systems
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