Blood, Lymphatic, and Immune Systems

Chapters 5 and 6

Objectives

  • Recognize and use terms related to the anatomy and physiology of blood, lymphatic, and immune systems.
  • Recognize and use terms related to the pathology of the blood, lymphatic, and immune systems.
  • Recognize and use terms related to the diagnostic procedures for the blood, lymphatic, and immune systems.
  • Recognize and use terms related to the therapeutic interventions for the blood, lymphatic, and immune systems.

Functions of the Blood, Lymphatic, and Immune Systems

Homeostasis, or a “steady state,” is a continual balancing act of the body systems to provide an internal environment that is comparable 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, to protect the body against pathogens that could threaten the organism’s viability. The blood is responsible for the following:

  • Transportation of gases (oxygen O2) and carbon dioxide (CO2), chemical substances (hormones, nutrients, salts), and cells that defend the body.
  • Regulation of the body’s fluid and electrolyte balance, acid-base balance, and body temperature.
  • Protection of the body from infection.
  • Protection of the body from loss of blood by the action of clotting.

The lymph system is responsible for the following:

  • Cleansing the cellular environment
  • Returning proteins and tissue fluids to the blood (drainage)
  • Providing a pathway for the absorption of fats and fat-soluble vitamins into the bloodstream.
  • Defending the body against disease.

The immune system is responsible for the following:

  • Defending the body against disease via the immune response

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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.

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

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 Hematic System

The hematic system is composed of blood and the vessels that carry the blood throughout the body. 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 called plasma. Blood cells make up 45% of the total blood volume, and plasma makes up the other 55%.

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

  • Erythrocytes – also called red blood cells (RBCs).
  • Leukocytes – also called white blood cells (ABCs).
  • Thrombocytes – also called clotting cells, cell fragments, or platelets. Be Careful!

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 Components of Blood

Erythrocytes (Red Blood Cells)

The erythrocytes (which are normally present in the millions) have the important function of transport O2 and CO2throughout the body. The vehicle for this transportation is a protein-iron pigment called hemoglobin.

The formation of RBCs in the bone marrow 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, dislike 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 in a number of Africans and African-Americans. Did You Know?

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

Named for their appearance, granulocytes also called polymorphonucleocytes have small grains within the cytoplasm and multilobed nuclei. Both names are used interchangeably.

These 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 – are cells that absorb an acidic dye, causing 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 are cells that do not absorb either an acidic or 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.
  3. Basophils 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.

Be Careful!

Be Careful!

Agranulocytes

Agranulocytes are cells named for their lack of granules. The alternative names, mononuclear leucocytes, is so given because they have one nucleus. Both 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:

  1. Monocytes: These cells, named for their single, large nucleus, transform into macrophages, which eat pathogens and are effective against severe infections.
  2. Lymphocytes: these cells are key in what is called the immune response, which involves the “recognition” of dangerous, foreign (viral) substances, and the manufacture of their neutralizers. The foreign substances are called antigens, and the neutralizers are called antibodies

Thrombocytes (Platelets)

Platelets (also known as thrombocytes) have a round or oval shape and are so named because they look like small plates. Platelets aid in the process of 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 mesh like fibrin clot (blood clot), achieving hemostasis (control of blood flow; that is, stopping the bleeding).

Plasma

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

  1. Water, or H2O (90%)
  2. Inorganic substances (calcium, potassium, sodium)
  3. Organic substances (glucose, amino acids, fats, cholesterol, hormones)
  4. Waste products (urea, uric acid, ammonia, creatinine)
  5. Plasma proteins (serum albumin, serum globulin, and two clotting proteins: fibrinogen and prothrombin)

Serum 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.

Did You Know

The clotting process

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Blood Groups

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Human blood is divided into four major different types: A, B, Ab, and O. The differences are due to antigens present on the surface of the 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 antibodiesthat nullify or neutralize the antigens. In blood, these antigens are called agglutinogens because their presence can cause the blood to clot.

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. 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.

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Lymphatic System

The lymphatic system is responsible for the following:

  • Cleansing the cellular environment
  • Returning proteins and tissue fluids to the blood
  • Providing a pathway for the absorption of fats into the bloodstream
  • Defending the body against disease

The lymphatic system is composed of lymph (or interstitial fluid), lymph vessels, lymph nodes, lymph organs (e.g. tonsils, adenoids, appendix, spleen,, thymus gland, and patches of tissue in the intestines called Peyer patches), and lymphoid tissue. Monocytes and lymphocytes pass from the bloodstream through the blood capillary walls into the spaces between the cells in the body. When they pass into this lymph or interstitial fluid that surrounds cells, they perform their protective functions. Monocytes change into macrophages, 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 orlymphatic fluid.

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Lymph moves in one directo 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:

  1. From the interstitial spaces between the cells, then
  2. Toward the heart through lymphatic capillaries.
  3. To lymphatic vessels that carry lymph using a valvular system.
  4. To the lymphatic nodes, which are also called lymph glands, that filter the debris that has been collected through the use of macrophages. These nodes can become enlarged when pathogens are present. Note the major lymph nodes in the figure, including the cervical, axillary, inguinal , and mediastinal nodes.
  5. Then to either the right lymphatic duct or the thoracic duct, both of which empty into the large subclavian veins in the neck.
  6. Once in the venous blood, the lymph is then recycled through the body through the circulatory system.

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 RBCs; and activate B lymphocytes. The thymus gland is located 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 patches are lymphoid tissue in the intestines.

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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 send 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.

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The above graphic 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.”

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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 methods of protection:

  • Mechanical – examples include the skin, which acts as a barrier, and the sticky mucus on mucous membranes, which serves to trap pathogens.
  • Physical – examples include coughing, sneezing, vomiting, and diarrhea. Although not pleasant, these serve to expel pathogens that have gotten past the initial barriers.
  • Chemical – examples include tears, saliva, and perspiration. These have a slightly acidic nature that deters pathogens from entering the body while also washing them away. In addition, stomach acids and enzymes serve to kill germs.

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 – 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, this 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 health. If caused by a pathogen, the inflammation is called an infection.
  • Pyrexia – 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. A second protein type, the complement proteins, 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 is dependent 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 (lg). The acquired form can be further divided into natural and artificial forms, which in turn can each be either active or passive. After a description of the specific immune process, each of the four types is discussed. Did You Know?

Specific immunity is dependent on the agraulocytes (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 lympocytes take part in specific immunity, they do it 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.

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:

  1. Natural: Development of memory cells to protect the individual from a second exposure.
  2. Artificial: Vaccination (immunization) that uses a greatly weakened form of the antigen, thus enabling the body to develop antibodies in response to this intentional exposure. Examples are the DTP and MMR vaccines.

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

  1. Natural: Passage of antibodies through the placenta or breast milk.
  2. Artificial: Use of immunoglobulins harvested from a donor who developed resistance against specific antigens

6 Ways to Boost Circulation for Detoxing and Immunity

The link between cleansing and circulation

You probably give a lot more thought to maintaining your weight than your circulation. But if you’re interested in preventing disease and cleansing your body of  toxins, pollutants, additives and chemicals, your circulatory system is your friend — and it needs your help to stay strong.

Imagine your circulatory system as a network of tubular highways reaching every part of your body. Now imagine a traffic jam on one of those highways, with massive delays, excess pollution and a high risk of accidents.

To keep your circulation moving right along, you need to know these basics about circulation and the most effective ways to keep yours pumping.

The two types of circulation

The circulatory system actually consists of two distinct systems that work in tandem: the cardiovascular circulatory system and the lymphatic circulatory system. Mia Harper, a licensed massage therapist at MediSpa at Mercy Hospital in Baltimore, explains how the two systems work together to detox the body.

“As nutrient-rich blood travels away from your heart, it progresses through smaller and smaller tubes, called capillaries,” she says. “In nearby tissue cells, nutrients and waste are exchanged. Fluid squeezed from the blood, called interstitial fluid or “lymph,” transports waste to your lymph nodes (via a series of vessels similar to veins) where the fluid is neutralized, filtered and eventually returned to the bloodstream.”

1. Cardiovascular circulation

Your heart is the power behind your cardiovascular circulatory system, pumping blood through your blood vessels, supplying every part of your body with the oxygen and nutrients it needs for proper functioning. With poor circulation, not only is your blood flow impaired, compromising that blood supply, but your heart is unduly taxed. Both have negative consequences and can lead to a variety of health problems.

“Poor circulation can lead directly to heart attack, stroke, eye disease, kidney disease, and claudication (leg muscle pain or weakness that comes and goes after an activity like walking),” says Dr. David Katz, Associate Professor in Public Health Practice at the Yale University School of Public Health and director of the Integrative Medicine Center in Derby, Conn. “But poor circulation also plays a role in almost every disease, from dementia to diabetes, influenza to cirrhosis.”

2. Lymphatic flow

Your lymphatic circulatory system works directly with your cardiovascular circulatory system to keep blood and lymphatic fluid levels in balance and flush toxins out of the body. It also carries immune cells throughout the body to help defend against infections.

But your lymphatic system isn’t lucky enough to have a powerful organ like the heart to keep fluid flowing. “The lymph system is stimulated by gravity, muscle contraction (exercise), hydrotherapy (alternating hot and cold water on the skin), breathing, lymph drainage therapy and massage,” says MediSpa’s Harper.

If your lymphatic circulation slows or stagnates, toxins will accumulate and immune cells won’t be delivered to the areas of the body where they’re needed, causing a variety of ailments, the very least of which are aches, pains and swelling (lymph edema). This can also cause deterioration of your thymus gland, tonsils and spleen – key components of your immune system — and weaken your body’s ability to fight infection and disease.

6 activities that boost both kinds of circulation

There are a number of easy and effective ways to improve the health of both your cardiovascular and lymphatic circulatory systems:

1. Drink plenty of water

“Circulation is vital to all of the body’s functions, and water makes up a large part of blood volume,” explains Katz. So make sure you drink enough water every day and don’t allow yourself to get dehydrated, causing undue taxation on your circulatory system.

But does water help flush toxins from your system? Katz explains that adequate hydration is required for adequate perfusion, which in turn is required for adequate function, detox included. “And water-soluble toxins go out with water, so adequate hydration is certainly directly relevant for kidney function.”

2. Exercise regularly (both cardio and strength training)

Any activity that contributes to overall fitness will also contribute to a strong circulatory system.

  • Regular aerobic activity is good for the health of your heart and blood vessels.
  • Resistance training adds to muscle mass, which increases the efficiency of both cardiovascular and lymph circulation, explains Katz.

3. Eat healthy

Circulation is yet another aspect of your health that benefits when you eat healthfully. “Lymph is made up of immune cells,” says Katz, “so the quality of lymph is enhanced by practices that boost immunity, including a healthy, balanced diet and weight control.“

4. Get a massage

By applying pressure to the body, massage stimulates the blood and lymph vessels, helping move the fluid along.

“Studies suggest that massage may enhance circulation in a localized manner to alleviate pain, reduce inflammation, and perhaps accelerate healing,” says Katz, “similar to the way that applying pressure to a tube squeezes out the toothpaste.”

5. Try manual lymph drainage therapy

By applying pressure in specific ways that target lymph nodes and vessels, a therapist trained in the lymphatic drainage therapy technique can directly target the lymph system to activate lymphatic fluid circulation and stimulate the functioning of the immune and parasympathetic nervous systems.

The technique includes holding the hands flat and moving them over the body to detect and assess current lymph flow patterns, and moving them in wave-like movements to release blockages in the network of lymph nodes and vessels.

“The benefits of lymph drainage therapy include a reduction of inflammatory responses (both acute and chronic), detoxification, regeneration of tissue, and deep relaxation, to name just a few,” says Harper.

The American Massage Therapist Association’s locator page can help you find a massage therapist trained in lymph drainage therapy techniques.

6. Shake it up with vibration and rebounding therapies

It seems obvious that shaking and bouncing your body around will get your blood pumping. But is there any evidence that they actually work to increase cardiovascular circulation and lymph flow? Turns out there is: A recent study published in Medical Science Monitor found that “Five minutes of 30 Hz or 50 Hz vibration produced significant increases in skin blood flow.”

Rebounding (jumping on a trampoline) appears to be especially effective at improving lymph system circulation. Lymphatic fluid is completely dependent on physical exercise to move, and the up-and-down rhythmic gravitational force caused by jumping on a trampoline causes the lymph system’s one-way valves to open and close, increasing lymph flow.

“The repetitive rhythmic motion of bouncing on a mini trampoline provides a simple, zero-impact exercise method with long-term mental and physical health benefits,” writes Dr. Tina Wellman, a psychoneuroendocrinologist and author of books on blending exercise, nutrition and detoxification to achieve wellness, in an article for Total Health. ”These benefits include increasing oxygen uptake and promoting detoxification via the lungs, skin, and lymph.”

Lymph System

Lymph

Lymph is a fluid derived from blood plasma. It is pushed out through the capillary wall by pressure exerted by the heart or by osmotic pressure at the cellular level. Lymph contains nutrients, oxygen, and hormones, as well as toxins and cellular waste products generated by the cells. As the interstitial fluid accumulates, it is picked up and removed by lymphatic vessels that pass through lymph nodes, which return the fluid to the venous system. As the lymph passes through the lymph nodes, lymphocytes and monocytes enter it.

At the level of the gastrointestinal (GI) tract, lymph has a milky consistency that is attributable to fatty acids, glycerol, and rich fat content. Lacteals are lymph vessels that transport intestinal fat and are localized to the GI tract.[1, 5, 3]

Lymphatic vessels

Lymphatic capillaries are blind-ended tubes with thin endothelial walls (only a single cell in thickness). They are arranged in an overlapping pattern, so that pressure from the surrounding capillary forces at these cells allows fluid to enter the capillary (see the image below). The lymphatic capillaries coalesce to form larger meshlike networks of tubes that are located deeper in the body; these are known as lymphatic vessels.

Lymph capillaries in spaces. Blind-ended lymphaticLymph capillaries in spaces. Blind-ended lymphatic capillaries arise within interstitial spaces of cells near arterioles and venules.

The lymphatic vessels grow progressively larger and form 2 lymphatic ducts: the right lymphatic duct, which drains the upper right quadrant, and the thoracic duct, which drains the remaining lymphatic tributaries. Like veins, lymphatic vessels have 1-way valves to prevent any backflow (see the image below). The pressure gradients that move lymph through the vessels come from skeletal muscle action, smooth muscle contraction within the smooth muscle wall, and respiratory movement.[1, 6, 2, 5, 4, 7]

Lymphatic 1-way valves. Lymphatic 1-way valves.

Lymph nodes

Lymph nodes are bean-shaped structures that are widely distributed throughout the lymphatic pathway, providing a filtration mechanism for the lymph before it rejoins the blood stream. The average human body contains approximately 600-700 of them, predominantly concentrated in the neck, axillae, groin, thoracic mediastinum, and mesenteries of the GI tract. Lymph nodes constitute a main line of defense by hosting 2 types of immunoprotective cell lines, T lymphocytes and B lymphocytes.

Lymph nodes have 2 distinct regions, the cortex and the medulla. The cortex contains follicles, which are collections of lymphocytes. At the center of the follicles is an area called germinal centers that predominantly host B-lymphocytes while the remaining cells of the cortex are T-lymphocytes. Vessels entering the lymph nodes are called afferent lymphatic vessels and, likewise, those exiting are called efferent lymphatic vessels (see the image below).

Lymph node structure. Lymph node structure.

Extending from the collagenous capsule inward throughout the lymph node are connective tissue trabeculae that incompletely divide the space into compartments. Deep in the node, in the medullary portion, the trabeculae divide repeatedly and blend into the connective tissue of the hilum of the node. Thus the capsule, the trabeculae, and the hilum make up the framework of the node. Within this framework, a delicate arrangement of connective tissue forms the lymph sinuses, within which lymph and free lymphoid elements circulate.

A subcapsular or marginal sinus exists between the capsule and the cortex of the lymph node. Lymph passes from the subcapsular sinus into the cortical sinus toward the medulla of the lymph node. Medullary sinuses represent a broad network of lymph channels that drain toward the hilum of the node; from there, lymph is collected into several efferent vessels that run to other lymph nodes and eventually drain into their respective lymphatic ducts (see the image below).[1, 6]

Lymph drainage flow; lymphatic duct anatomy. Lymph drainage flow; lymphatic duct anatomy.

Thymus

The thymus is a bilobed lymphoid organ located in the superior mediastinum of the thorax, posterior to the sternum. After puberty, it begins to decrease in size; it is small and fatty in adults after degeneration.

The primary function of the thymus is the processing and maturation of T lymphocytes. While in the thymus, T lymphocytes do not respond to pathogens and foreign organisms. After maturation, they enter the blood and go to other lymphatic organs, where they help provide defense. Structurally, the thymus is similar to the spleen and lymph nodes, with numerous lobules and cortical and medullary elements. It also produces thymosin, a hormone that helps stimulate maturation of T lymphocytes in other lymphatic organs.[2, 5, 3, 4]

Spleen

The spleen, the largest lymphatic organ, is a convex lymphoid structure located below the diaphragm and behind the stomach. It is surrounded by a connective tissue capsule that extends inward to divide the organ into lobules consisting of cells, small blood vessels, and 2 types of tissue known as red and white pulp. Red pulp consists of venous sinuses filled with blood and cords of lymphocytes and macrophages; white pulp is lymphatic tissue consisting of lymphocytes around the arteries. Lymphocytes are densely packed within the cortex of the spleen.

The spleen filters blood in much the same way that lymph nodes filter lymph. Lymphocytes in the spleen react to pathogens in the blood and attempt to destroy them. Macrophages then engulf and phagocytose damaged cells and cellular debris. The spleen, along with the liver, eradicates damaged and old erythrocytes from the blood circulation. Like other lymphatic tissue, it produces lymphocytes in an immunologic response to offending pathogens.[5, 3, 4]

Therefore, the spleen conducts several important functions, as follows:

  • It serves as a reservoir of lymphocytes for the body
  • It filters blood
  • It plays an important role in red blood cell and iron metabolism through macrophage phagocytosis of old and damaged red blood cells
  • It recycles iron by sending it to the liver
  • It serves as a storage reservoir for blood
  • It contains T lymphocytes and B lymphocytes for immunologic response

Tonsils

Tonsils are aggregates of lymph node tissue located under the epithelial lining of the oral and pharyngeal areas. The main areas are the palatine tonsils (on the sides of the oropharynx), the pharyngeal tonsils (on the roof of the nasopharynx; also known as adenoids), and the lingual tonsils (on the base of the posterior surface of the tongue).

Because these tonsils are so closely related to the oral and pharyngeal airways, they may interfere with breathing when they become enlarged. The predominance of lymphocytes and macrophages in these tonsillar tissues offers protection against harmful pathogens and substances that may enter through the oral cavity or airway.

http://emedicine.medscape.com/article/1899053-overview#aw2aab6b3