Lymphatic and Immune Systems

Question 1

Describe the general structure of the lymphatic system.

Answer 1

The lymphatic system is a network of vessels that transport a fluid called lymph. Lymph nodes, or small clusters of lymphatic tissue, are positioned along these vessels.

Other organs, such as the thymus and the spleen, also contain lymphoid tissue.

Question 2

What are the characteristics of a lymph vessel?

Answer 2

Like veins, lymph vessels contain valves and have thin walls composed of smooth muscle and connective tissue. However, lymph vessels are more flexible to accommodate excess fluid.

Lymph vessels vary in size, like those of the circulatory system. Smaller lymph capillaries give rise to larger vessels.

Question 3

What are the characteristics of a lymph node?

Answer 3

Lymph nodes are small structures, oval in shape, and positioned along lymph vessels. They contain immune cells, namely lymphocytes and macrophages.

Lymph nodes function to filter the fluid that is being transported through the lymphatic system.

Question 4

Where does lymph originate from, and what are its main components?

Answer 4

Lymph is composed of excess fluid that has diffused into the tissues from capillaries. As a result, its composition is similar to plasma.

More specifically, lymph mainly contains water, lymphocytes, and proteins. It also transports fats that have been absorbed in the form of chylomicrons.

Question 5

The lymphatic system serves what main function apart from its immune role?

Answer 5

The lymphatic system drains excess interstitial fluid from the tissues. After filtration through lymph nodes, this fluid is eventually returned to the bloodstream.

This activity minimizes edema, or swelling due to fluid accumulation.

Question 6

Define:

lacteal

Answer 6

A lacteal is a small lymphatic vessel found in a villus of the small intestinal epithelium.

Lacteals play a major role in the absorption of fats, which are first taken up by the lymphatic system in the form of chylomicrons.

Question 7

Through which vessel does lymph return to venous circulation?

Answer 7

Lymph enters venous circulation through the thoracic duct.

The thoracic duct, a large lymphatic vessel, is found in the upper region of the chest. It drains into the left subclavian vein.

Question 8

What is the difference between a closed and open circulatory system, and which type does the lymphatic system exemplify?

Answer 8

A closed circulatory system is comprised of a complete loop of vessels, while an open system is open-ended and drains fluid from one location into another.

The human lymphatic system is open, while the main circulatory system is closed.

Question 9

What is the difference between innate and specific immunity?

Answer 9

Innate immunity provides a broad line of defense against foreign material. Its response to pathogens is general, not specific to the identity of the pathogen.

Specific immunity is highly specialized, using immunological memory of previous infections to respond to certain pathogens.

Macrophages, neutrophils, mast cells, natural killer cells, and dendritic cells are involved in innate immunity. T and B lymphocytes are involved in specific immunity.

Question 10

Give another name for innate immunity.

Answer 10

Innate immunity is also known as nonspecific immunity.

Question 11

Which of the following is not directly involved in the innate immune response?

• Macrophages
• Skin
• B lymphocytes
• Mucus in the respiratory tract

Answer 11

B lymphocytes do not play a major role in innate immunity. The other choices all provide a first line of defense against a wide variety of pathogens.

B lymphocytes, on the other hand, produce antibodies. These products are highly specialized to recognize certain antigens, and form a large part of specific immunity.

Question 12

What is phagocytosis?

Answer 12

Phagocytosis is the engulfment of a foreign particle by an immune cell, or phagocyte. The particle is taken up in a vesicle and can then be degraded.

This process can often involve chemotaxis, a form of movement in which a cell is drawn toward or away from specific chemical substances.

Question 13

Which of the following cells can not perform phagocytosis?

• Monocytes
• Erythrocytes
• Macrophages
• Neutrophils

Answer 13

Erythrocytes cannot perform phagocytosis. Erythrocytes are red blood cells, which do not serve a major function in the immune system.

Neutrophils, monocytes, and macrophages all perform phagocytosis as an important part of innate immunity.

Question 14

Diphenhydramine, an allergy medication, functions as an antihistamine. Which immune response is likely to be inhibited by the administration of diphenhydramine?

Answer 14

Diphenhydramine will inhibit the inflammatory response.

Histamine is a chemical that functions as part of the inflammatory response. Specifically, it increases capillary permeability and can lead to many common allergy symptoms.

Question 15

Describe three main effects of the inflammatory response.

Answer 15

• Capillary permeability increases, allowing immune cells to access the infected site. This results in redness and swelling.
• The infected area becomes warm.
• The infected area is often painful due to swelling and the presence of certain chemicals.

Question 16

What name is given to an adverse inflammatory response to non-pathogenic material such as animal hair or pollen?

Answer 16

Allergies, or immune responses to typically harmless compounds, commonly occur when the inflammatory response is overactive.

Allergies are often treated with antihistamines, which counteract a main inflammatory chemical agent.

Question 17

What enzyme is found in tears and catalyzes the breakdown of bacterial cell walls?

Answer 17

Lysozyme

Specifically, lysozyme catalyzes the breaking of glycosidic linkages within peptidoglycan molecules. This role is part of the innate immune system.

Question 18

Give another name for specific immunity.

Answer 18

Specific immunity is also known as adaptive or acquired immunity.

Question 19

Which of the following is not directly involved in the specific immune response?

• T lymphocytes
• Macrophages
• B lymphocytes
• Antibodies

Answer 19

Macrophages do not play a direct role in specific, or acquired, immunity.

Specific immunity involves cells that specialize to recognize and attack a limited class of antigens. In contrast, macrophages phagocytose a wide variety of pathogens and foreign particles.

Question 20

Define:

leukocyte

Answer 20

A leukocyte, also known as a white blood cell, is a cell involved in immune function.

Leukocytes are a broad category of cells, including neutrophils, monocytes, and lymphocytes, among others.

Question 21

A deficiency in monocytes will likely lead to a lower-than-average number of what other type of cell?

Answer 21

Macrophages

Monocytes differentiate into macrophages, which are phagocytic cells that act as a part of the innate immune response.

Question 22

Name the most abundant leukocyte found in the blood.

Answer 22

The most abundant leukocytes are neutrophils, which constitute 50-70% of all white blood cells by number.

As one of the first cell types to reach the site of an infection, neutrophils are the main component of pus. Like macrophages, they can perform phagocytosis.

Question 23

What is the difference between granulocytes and agranulocytes?

Answer 23

Granulocytes contain cytoplasmic granules, while agranulocytes do not. Granules are small vesicles that contain enzymes and other cytotoxic substances.

Granulocytes include neutrophils, eosinophils, and basophils, while agranulocytes include monocytes, macrophages, and B and T lymphocytes.

Question 24

In what part of the body are lymphocytes synthesized?

Answer 24

Lymphocytes (B and T cells) are synthesized in the bone marrow.

B lymphocytes also remain in the bone marrow to mature, while T lymphocytes move to the thymus for maturation.

Question 25

Name the two types of specific immunity.

Answer 25

The two types of specific immunity are cell-mediated and humoral immunity.

Question 26

Which type of specific immunity involves B lymphocytes?

Answer 26

Humoral immunity

Humoral immunity involves antibodies, which are produced by B lymphocytes to recognize specific bloodborne antigens. It also involves the differentiation of plasma and memory B cells upon exposure to a pathogen.

Question 27

A certain virus inhibits the functioning of cytotoxic T cells. Which type of specific immunity would be limited in this case?

Answer 27

Cell-mediated immunity would be inhibited.

Cell-mediated immunity involves cytotoxic T lymphocytes, as well as other immune cells. Specifically, it allows the destruction of body cells that have been marked for destruction after viral infection or other damage.

Question 28

Name the two main types of T lymphocytes and describe their functions.

Answer 28

T lymphocytes are broadly classified into cytotoxic (killer) T cells and helper T cells.

Cytotoxic T cells directly bind damaged or infected cells that express certain antigens. They then kill the cell through the release of apoptosis-inducing factors. Helper T cells secrete cytokines that chemically facilitate B cell and cytotoxic T cell activity.

Question 29

A lesser-known subtype of T lymphocyte plays a major role in counteracting autoimmune disease. What term describes this cell type?

Answer 29

These lymphocytes are called suppressor or regulatory T cells.

Suppressor T cells limit the activation and continuation of immune responses. This reduces the likelihood that the host’s immune system will react against “self” tissues, or those of its own body.

Question 30

Define:

antigen

Answer 30

An antigen is a substance that causes an immune response. Specifically, antigens are markers that can be recognized by antibodies.

The surface proteins that determine blood type (A and B) are examples of antigens.

Question 31

What broad name is given to cell surface proteins that aid in T cell recognition?

Answer 31

The major histocompatibility complex (MHC)

MHC genes code for glycoproteins located on cell surfaces. In a process termed antigen presentation, they bind to antigens and display them for T cells to recognize. MHC proteins are divided into two main classes, MHC I and MHC II.

Question 32

Describe the role of MHC I receptor proteins.

Answer 32

MHC I receptors bind to normal proteins that are produced within the cells of the body. When a cell becomes infected or cancerous, it triggers recognition as “non-self” and can be marked for destruction by a T cell.

Antigens presented by MHC I are recognized only by cytotoxic T cells that contain the CD8 surface protein.

Question 33

Describe the role of MHC II receptor proteins.

Answer 33

MHC II receptors bind to foreign antigens that have been broken down by phagocytosis. When fragments of these antigens are presented on immune cells, helper T cells recognize a threat and can activate other immune responses.

Antigens presented by MHC II are recognized only by helper T cells that contain the CD4 surface protein.

Question 34

A sample of normal human cells are found to be lacking MHC I receptors. What cell type(s) might this sample contain?

Answer 34

The sample must contain cells that lack nuclei, likely erythrocytes (red blood cells).

MHC I glycoproteins are present on every body cell, except for those that do not contain nuclei. These receptors allow T cells to recognize cells that are malfunctioning.

Question 35

A sample of human cells is found to contain a significant number of MHC II receptors. What cell type(s) might this sample contain?

Answer 35

The sample must contain immune cells, specifically those that present antigens to CD4+ helper T cells.

Antigen-presenting immune cells include dendritic cells, B lymphocytes, and macrophages.

Question 36

Define:

antibody

Answer 36

An antibody is an immune protein that recognizes a specific, potentially harmful antigen or class of antigens. Antibodies are produced by B lymphocytes.

For the MCAT, be sure to avoid confusion between antibodies and antigens. Antigens are attacked, while antibodies do the attacking.

Question 37

What immune product is shown here, and what is its function?

Answer 37

This molecule is an antibody.

Antibodies are produced by B lymphocytes. They play a major role in specific, or acquired, immunity by recognizing and binding specific antigens.

Question 38

Label the following parts of the antibody shown below: heavy chain, light chain, constant region, variable region, antibody binding sites.

Answer 38

Question 39

What word is synonymous with the term “antibody?”

Answer 39

Antibodies are also known as immunoglobulins.

Immunoglobulins are abbreviated “Ig.” Though you do not need to know the function of each type, IgM, IgE, and IgG most commonly appear in MCAT passages. Other antibody types are IgD and IgA.

Question 40

A defect in a certain immune cell type results in a dramatic decrease in the production of antibodies. Which cell type is likely affected?

Answer 40

This defect likely affects B lymphocytes.

B lymphocytes act as a vital part of acquired immunity by producing protein products called antibodies.

Question 41

Which two types of B lymphocytes arise from naive B cells?

Answer 41

Naive, or undifferentiated, B cells can differentiate into plasma and memory B cells.

Upon exposure to a pathogen, the majority of cells produced are plasma B lymphocytes; these cells produce antibodies to target the invader. In contrast, memory B cells remain in the blood and activate a faster response in the case of a second exposure to the same antigen. Note that memory T cells also exist.

Question 42

Name three ways that antibodies hinder and facilitate the destruction of pathogens.

Answer 42

1. Antibodies activate the complement system, a protein cascade that promotes immune function.
2. In a process called agglutination, antibodies bind to antigens on an invading cell’s surface. This limits the pathogen’s movement and keeps it from entering body cells.
3. Antibodies perform opsonization, which alerts phagocytes to engulf the pathogen.

Question 43

In class, a student mentions that antibodies function by directly lysing foreign cells. What is wrong with this explanation?

Answer 43

Antibodies do not directly kill pathogens; they simply bind to and mark the invading cell for destruction.

In contrast, phagocytes and killer T cells are capable of destroying pathogens.

Question 44

Which theory explains how specific antibody-producing cells proliferate despite the enormous variety of these cells in the body?

Answer 44

Clonal selection

An extremely diverse range of B cells are present in the body; as a result, a wide variety of antibodies can be produced. According to clonal selection, B cells specific for an antigen will be “cloned,” or copied, after exposure. B lymphocytes that are specific for “self” tissues will be destroyed.

Question 45

How does the speed of the primary immune response differ from that of the second, and subsequent, responses?

Answer 45

The primary immune response takes much longer, as B cells specific for the antigen in question have not differentiated.

A primary response can take 14 days or longer, while a secondary response can eliminate a pathogen in less than a day.

Question 46

Define:

pathogen

Answer 46

A pathogen is a disease-causing organism. The purpose of the immune system is to protect against pathogens, foreign particles, and the body’s own damaged cells.

Pathogens can include bacteria, viruses, and fungi.

Question 47

Which immune cells are targeted by the human immunodeficiency virus (HIV)?

Answer 47

HIV infects and incapacitates helper T cells, possible through interactions with the CD4 glycoprotein receptor.

As a result, HIV⁺ individuals have severely limited immune systems and are prone to a variety of infections.

Question 48

What is the function of the spleen?

Answer 48

With regard to the immune system, the spleen produces and stores immune cells such as lymphocytes and monocytes. It also filters the blood, removing old or nonfunctioning red blood cells.

Question 49

A main function of the spleen involves the engulfment and breakdown of red blood cells. With this in mind, which type of immune cell is likely highly active in this organ?

Answer 49

The spleen contains an especially high number of macrophages.

Since macrophages are phagocytic cells, they are generally active in organs where debris or damaged cells must be engulfed and destroyed.

Question 50

What is the function of the thymus, and which hormone does it mainly secrete?

Answer 50

During infancy and childhood, the thymus serves as the site of T cell maturation. Specifically, it promotes the inactivation of T cells that would otherwise attack “self” tissues.

As part of this function, the thymus produces the peptide hormone thymosin.

Question 51

Though every cell contains antigens on its surface, the body tissues of a healthy individual are protected from attack by his or her own immune system. What name is given to these cells?

Answer 51

These cells are part of the self. Except in cases of autoimmune disorders, only nonself cells should provoke an immune response.

The process of distinguishing self from nonself occurs in the thymus during development. Immune cells that are specific to normal body tissues are isolated and destroyed before they can harm the individual.

Question 52

Which type of pathogen do interferons combat?

Answer 52

Interferons, a subtype of cytokines, are generally associated with viral infection. However, they can also be activated by bacterial infection or cancerous growth.

As signaling molecules, interferons do not directly kill infected cells; instead, they activate surrounding immune cells.

Question 53

What happens to an individual who suffers from an autoimmune disease?

Answer 53

The individual’s immune cells attack his or her healthy tissue, causing a variety of damaging effects.

Though the exact causes of most autoimmune responses are unclear, a genetic component is often involved, and environmental factors may play a role.

Question 54

Lupus, psoriasis, and rheumatoid arthritis are examples of what class of disease?

Answer 54

These disorders are autoimmune diseases.

In all of these conditions, the immune system attacks normal body tissues - the skin in psoriasis, joints in rheumatoid arthritis, and a variety of tissues types in lupus.

Question 55

If a man has type A⁺ blood, against which antigens will his immune system produce antibodies?

Answer 55

His immune system will produce antibodies against B antigens only.

Antibodies are produced against foreign antigens. Since the man’s own blood cells contain A and Rh antigens on their surfaces, antibodies will not be produced to attack those markers.

Question 56

If a man has type O^- blood, which antigens are present on the surface of his own red blood cells?

Answer 56

No antigens are present.

An individual’s blood type describes the antigens displayed on his or her red blood cells. Type A refers to A antigens, type B refers to B antigens, and type AB refers to both. Type O signifies the lack of either A or B antigens. Similarly, the “+” designation refers to the presence of the Rh antigen, and the “-“ designation refers to its absence.

Question 57

What occurs when a person is given a blood transfusion that contains foreign antigens?

Answer 57

In a process called hemagglutination, the recipient’s antibodies cause the transfused blood to bind and clump together.