dynamic study module chapter 20 part 1 and part 2

Acquired immunity allows for immunological memory in which lymphocytes respond to specific antigens during a lifetime. Another name for acquired immunity is ____________.

Acquired immunity allows for immunological memory in which lymphocytes respond to specific antigens during a lifetime. Another name for acquired immunity is adaptive immunity. Adaptive immunity responds more slowly than innate immunity because one must be exposed to a specific antigen for the response to be initiated. Adaptive immunity takes 3-5 days to mount a response, but after this point, it is the dominant response. An important difference between the innate and adaptive immunities is that adaptive immunity has the capacity for immunological memory, in which exposure to an antigen is "remembered" by specific lymphocytes and antibodies. This allows a more rapid and efficient response on subsequent exposures. Innate, or nonspecific, immunity responds to all pathogens or classes of pathogen in the same way. The innate immune system consists of antimicrobial proteins and certain cells. Note that innate immunity responds quickly and is the dominant response to pathogens for the first 12 hours after exposure. This occurs because the cells and proteins exist in the bloodstream, even in the absence of a stimulus (hence the term innate). Innate immunity lacks the capacity for immunological memory and will respond in the same way with repeat exposure to a pathogen. Passive immunity is found when preformed antibodies are passed from one organism to another. Passive immunity may be naturally acquired, for example, when the IgG of a pregnant woman crosses from her blood into that of her fetus, or artificially acquired, from an injection with preformed antibodies. This form of immunity lasts only the amount of time that the antibodies stay in the bloodstream, which is about 3 months on average.

Activated B cells differentiate into __________.

Activated B cells differentiate into plasma cells and memory B cells. Among the changes triggered in the B cells when they are activated is rapid cell division, which results in an explosion in the population of these cells. In addition to rapid proliferation, the resulting B cells differentiate into two populations of cells: (1) plasma cells, which secrete antibodies; and (2) memory B cells, which are long-lived cells that do not secrete antibodies but will respond to antigens on a second exposure. Plasma cells secrete antibodies. Activated T cells proliferate and differentiate into effector cells and memory T cells.

All of the following structures are tonsils except:

All are tonsils except hypoglossal tonsils. The pharyngeal tonsil, also known as the adenoid, is located in the posterior nasal cavity (the nasopharynx). The palatine tonsils are found in the posterolateral oral cavity. The lingual tonsil is found at the base of the tongue.

All immune cells of the lymphatic system originate in the _____.

All immune cells of the lymphatic system originate in the bone marrow. Red bone marrow is hematopoietic tissue located within certain bones that produces all of the formed elements of the blood. The bone marrow increases production of leukocytes, leading to leukocytosis. The spleen is a large lymphoid organ in the left upper quadrant of the abdominopelvic cavity that filters blood and processes old erythrocytes. MALT, or mucosa-associated lymphatic tissue, is loosely organized clusters of lymphoid tissue located along mucous membranes. Lymph nodes are clusters of lymphatic tissue located along lymphatic vessels throughout the body.

Which of the following components is not a surface barrier serving as the first line of defense?

An antibody is not a surface barrier serving as the first line of defense. The first line of defense against any potential threat to the body is the coverings that line body surfaces: the skin and the mucous membranes, and certain products they secrete. Both the skin and mucosae are surface barriers, meaning that they provide a continuous physical barrier to block the entry of potential pathogens into the body. Surface barriers protect the underlying tissues from mechanical stress and from pathogen invasion. Besides being continuous and covering nearly every external surface of the body, skin is also relatively resistant to mechanical stresses, thanks to its several layers of epithelial cells filled with the hard protein keratin. In addition, sebaceous glands in the skin secrete sebum or oil, which has a slightly acidic pH that deters the growth of most pathogenic organisms. The components of the immune system offer three lines of defense: The first line of defense involves surface barriers; the second line of defense involves the cells and proteins of innate immunity; and the third line of defense involves the cells and proteins of adaptive immunity. There are two "arms" of the adaptive immune system. The first, cell-mediated immunity, is brought about by two types of T cells. The second, antibody-mediated immunity (also known as humoral immunity), is carried out by B cells and proteins they produce, called antibodies.

Antibodies can bind to viral proteins, animal venoms, and bacterial toxins, rendering them inactive, by a process known as _____.

Antibodies can bind to viral proteins, animal venoms, and bacterial toxins, rendering them inactive, by a process known as neutralization. Bacterial toxins, viral proteins, and animal venoms are molecules with specific components that are harmful. Antibodies bind to these components, as well as certain viruses and bacteria, and prevent them from interacting with our cells. This renders the toxin inactive, which is known as neutralization. Most neutralizing antibodies are of either the IgG or the IgA class. Opsonization involves proteins such as complement coating the pathogen and activating phagocytes. IgG antibodies are also opsonins able to coat pathogens and bind and activate phagocytes, which greatly enhances phagocytosis. Antibodies can bind to antigens on more than one cell. This creates a clump of cells that are cross-linked by their attachment to antibodies. The clumping of cells is known as agglutination. Similar to agglutination is the process called precipitation, which involves soluble antigens (proteins and other biological molecules) instead of whole cells. The antibody IgE directly triggers inflammation by initiating the release of inflammatory mediators from mast cells and basophils. Antibodies also trigger inflammation indirectly through their activation of complement.

What cells display portions of the pathogens (antigens) they ingest on their plasma membranes?

Antigen-presenting cells display portions of the pathogens (antigens) they ingest on their plasma membranes. Macrophages function as antigen-presenting cells, cells that display portions of the pathogens (antigens) they ingest on their plasma membranes. T cells respond to these antigens by becoming activated. Activated T cells in turn secrete substances that increase the activity of the macrophages, in an example of a positive feedback loop. This is one of many instances of innate and adaptive immunity working together. A relatively rare nonphagocytic cell is the basophil. Basophils are granulocytes whose granules contain chemicals that mediate, or convey, inflammation (inflammatory mediators). Basophils are located primarily in the blood, although a related type of cell called the mast cell is located in mucous membranes. Like regular basophils, mast cells contain granules with chemicals that trigger inflammation, particularly that involved in allergic responses. The granulocytes known as eosinophils are phagocytes that can migrate from the blood to the tissues where they are needed. Natural killer (NK) cells have the remarkable ability to recognize cancerous cells and cells infected with certain viruses despite the fact they cannot recognize antigens. They appear to do this by scanning the cells for irregularities and by reacting to cells that have bound to antibodies (another example of innate and adaptive immunity working together). NK cells are also cytotoxic, releasing substances that destroy their target cells. In addition, they secrete an antimicrobial cytokine that activates macrophages and enhances phagocytosis.

Approximately 75-80% of circulating antibodies in serum are ____.

Approximately 75-80% of circulating antibodies in serum are IgG. The most prevalent antibody in the body is IgG, which consists of a single subunit. IgG is the only antibody able to cross from the blood of a pregnant woman to her developing fetus through a structure called the placenta. IgA is usually a dimer, consisting of two Y-shaped subunits, which gives this antibody four antigen-binding sites. IgA is present in secretions from the skin, mucous membranes, and exocrine glands (i.e., tears, saliva, sweat, and breast milk). The largest antibody is the pentamer IgM (think "M" for "massive"), which consists of five subunits in a starlike pentamer, for a total of 10 antigen-binding sites. IgM is generally the first antibody secreted by plasma cells when the body is invaded by a pathogen. The single-subunit antibody IgE is generally present in very low amounts in the body's fluids.

Autoimmune diseases are disorders where the immune system fails to distinguish _______ from foreign ones.

Autoimmune diseases are disorders where the immune system fails to distinguish self antigens from foreign ones. Normally, several processes ensure immune self-tolerance; that the immune system does not react to self-antigens and damage the body's own tissues and cells. However, sometimes these processes fail, and the result is populations of self-reactive T cells or of B cells that secrete antibodies that bind to self-antigens, called autoantibodies. This produces an autoimmune disorder. Autoimmune disorders may be localized and affect only one organ or tissue, or they may be systemic and affect multiple parts of the body. Autoimmunity results in a type II, III, or IV hypersensitivity reaction, which is what produces the organ and tissue damage characteristic of the disease.

B cells develop and mature in the __________.

B cells develop and mature in the bone marrow. B cells develop in the bone marrow from the lymphoid cell line, where billions of B cells are produced each day. They remain in the bone marrow to mature, but only about 10% of these cells finish their maturation process. This is largely because B cell clones that recognize self antigens (self-reactive B cells) are destroyed. This prevents the development of autoimmunity, in which B cells recognize self antigens as foreign and produce autoantibodies that bind self antigens. T cells are formed in the bone marrow, but they leave the bone marrow and migrate to the thymus to mature. The complement system is a group of 20 or more plasma proteins produced primarily by the liver that are involved in cell lysis via a membrane attack complex, enhancing phagocytosis through opsonization, enhancing inflammation, and neutralizing certain viruses. The system may be activated by either the classical or the alternative pathway. Lymph nodes are small, vaguely bean-shaped clusters of lymphatic tissue located along lymphatic vessels throughout the body. Lymph nodes filter lymph.

Blood transfusions between incompatible blood types results in __________.

Blood transfusions between incompatible blood types results in type II, or antibody-mediated, hypersensitivity. In type II hypersensitivity, also known as antibody-mediated hypersensitivity, the antibodies produced by the immune response to foreign antigens also bind to self antigens. This reaction occurs in three situations: (1) Foreign antigens bind to normal self antigens; (2) donor erythrocytes infused into an individual are mismatched in the ABO/Rh antigen groups; and (3) self-reactive B cells are not destroyed in the bone marrow, which leads to autoimmunity. The most common type of hypersensitivity disorder is type I, or immediate, hypersensitivity, which affects a tremendous number of people—about 20% of the U.S. population. This type of hypersensitivity is more commonly known as allergies, and the disorders that accompany it are called allergic disorders. The reactions of type III hypersensitivity are mediated by immune complexes, or clusters of soluble antigens (those not attached to the cell surface) bound to antibodies. Immune complexes are generally cleared by phagocytes, but certain complexes are difficult for macrophages to ingest. The final type of hypersensitivity is type IV, or delayed-type, hypersensitivity (DTH). DTH is unique in that it is mediated by T cells rather than antibodies. In these cases, TH cells recognize antigens bound to major histocompatibility complex (MHC) molecules as foreign and mediate their destruction by activating and recruiting macrophages and in some cases TC cells.

Cell-mediated immunity responds to _______.

Cell-mediated immunity responds to cancer cells. The first arm of the adaptive immune system is cell-mediated immunity. Cell-mediated immunity involves the different classes of T cells, including the helper T (TH) cells, also known as CD4 cells, and the cytotoxic T (TC) cells, also known as CD8 cells. ("CD" stands for "cluster of differentiation," which refers to specific molecules within the plasma membrane that differentiate one cell type from another.) These cells respond primarily to cells infected with intracellular pathogens (viruses and intracellular bacteria), cancer cells, and foreign cells such as those from a transplanted organ. The actions of antibodies are based on their ability to bind antigens, which leads to multiple effects on pathogens. Many of these effects represent an integration of adaptive and innate immunity; the antibodies of adaptive immunity often activate phagocytes and complement proteins of innate immunity. Bacterial toxins, viral proteins, and animal venoms are molecules with specific components that are harmful. Antibodies bind to these components, as well as certain viruses and bacteria, and prevent them from interacting with our cells. This renders the toxin inactive, which is known as neutralization. Most neutralizing antibodies are of either the IgG or the IgA class. The single-subunit antibody IgE is generally present in very low amounts in the body's fluids. IgE binds to two types of antigen: (1) antigens associated with parasitic pathogens such as tapeworms, and (2) environmental antigens known as allergens, which are linked with inflammatory reactions called allergies.

Cells that de-differentiate, lose cell cycle control, and lose their attachment to the surrounding cells, are known as ________.

Cells that de-differentiate, lose cell cycle control, and lose their attachment to the surrounding cells, are known as cancer cells. Cancer cells are formerly normal body cells that have undergone mutations. These mutations result in a mass of unspecialized cells called a malignant tumor, whose cells are capable of indefinite growth and can metastasize, or spread, through the lymphatic system or blood to other parts of the body. Plasma cells are activated B cells that secrete antibodies. The primary function of cytotoxic T cells is evident from their name; they kill other cells, specifically those with foreign antigens bound to class I MHC molecules. The natural killer (NK) cell is a type of lymphocyte that acts primarily in innate immunity. NK cells are generally located in the blood and spleen and are formed in the bone marrow from the same cell line as lymphocytes.

Chemical signals produced by leukocytes that affect other leukocytes are ____.

Chemical signals produced by leukocytes that affect other leukocytes are interleukins. Interleukins, abbreviated as IL followed by a number (e.g., IL-2), constitute a class of 29 cytokines (note that the number in the name of each interleukin indicates the order in which it was discovered, not its order in any process). The name "interleukin" means "between leukocytes," which reflects the fact that they are produced by leukocytes, and many of their actions affect other leukocytes. Examples of these effects include stimulating production of neutrophils by the bone marrow, stimulating NK cells, triggering the production of certain types of interferons from different leukocytes, and activating T cells. The cytokines known as interferons, abbreviated IFN, are produced by a variety of cells, including macrophages, dendritic cells, NK cells, and cells of adaptive immunity. Interferons are generally produced in response to infection with intracellular agents such as viruses or intracellular bacteria and are named for their capacity to "interfere" with the ability of the pathogens to infect other cells. One of their primary actions is to inhibit viral replication inside host cells. In addition, they activate various components of both innate and adaptive immunity, such as stimulating nearby cells to produce antimicrobial proteins. The cytokine, known as tumor necrosis factor, or TNF, is named for the fact that it was originally discovered through its ability to induce necrosis (death) of tumor cells. TNF is secreted primarily by activated macrophages in response to certain bacteria and other pathogens. Effects of TNF include inducing flulike symptoms, attracting phagocytes to the area of infection, increasing the activity of phagocytes, and stimulating phagocytes to release additional cytokines. The group of proteins collectively known as the complement system consists of around 30 plasma proteins that are produced primarily by the liver. Complement proteins circulate primarily in their inactive forms and must be activated by a complex cascade of events mediated by enzymes.

Which of the following cells is not found in most lymphoid tissues?

Chondrocytes are not found in most lymphoid tissues. Chondrocytes are the main cell type in cartilage that maintains the extracellular matrix of the tissue. Lymphoid organs house lymphocytes, including B lymphocytes and T lymphocytes (more commonly referred to as B cells and T cells, respectively). Lymphocytes and T lymphocytes are agranulocytes with diverse immune functions. There are two main types of phagocytic cells in lymphoid tissues and organs: macrophages and dendritic cells. Recall that macrophages are mature monocytes that are active phagocytes. Dendritic cells are leukocytes with spiny processes that resemble the dendrites of neurons. They play an important role in activating lymphocytes. Reticular fibers, composed of a specialized, thin type of collagen protein, are produced by reticular cells. Reticular cells are particularly abundant in organs such as the spleen and lymph nodes.

Which of the following statements are true of class I major histocompatibility complex (MHC) molecules?

Class I MHC molecules present endogenous antigens. Class I MHC molecules are found on the surface of the plasma membrane on nearly all nucleated cells, whereas class II MHC molecules are found only on the surfaces of antigen-presenting cells. Cytotoxic T (TC) cells generally interact only with class I MHC molecules, whereas helper T (TH) cells generally interact with class II MHC molecules. The two classes of molecules also differ in the types of antigens they display. Class I MHC molecules present endogenous antigens, those synthesized inside the cell, whereas class II MHC molecules present exogenous antigens, those the cell takes in by phagocytosis. MHC molecules are found on nearly all nucleated cells. Note, however, that they are not present on the surface of erythrocytes, which is why blood is considerably easier to donate than other organs and tissues. Several antibodies, particularly IgM and IgG, bind and activate the complement proteins of innate immunity.

Clusters of lymph nodes found under the arms are the ____.

Clusters of lymph nodes found under the arms are the axillary lymph nodes. Lymph nodes are small, vaguely bean-shaped clusters of lymphatic tissue located along lymphatic vessels throughout the body. We find clusters of lymph nodes located in specific areas, including the axillary lymph nodes in the axillae (under the arms), the cervical lymph nodes in the neck, the inguinal lymph nodes in the groin, and the mesenteric lymph nodes in the abdominal cavity around the abdominal organs.

Which of the following symptoms is not a cardinal sign of inflammation?

Cold is not a cardinal sign of inflammation. There are two basic stages to the inflammatory response: (1) Damaged cells release inflammatory mediators that cause local changes in the damaged tissue; and (2) phagocytes arrive at the area and clean up the damaged tissue. During the first stage, the injured area becomes red and swollen, feels warm to the touch, and hurts. These four signs—redness, heat, swelling (or edema), and pain—are known as the cardinal signs of inflammation.

Cytotoxic T cells are also known as ____.

Cytotoxic T cells are also known as CD8 cells. Helper t cells are also known as CD4 cells. T cells cannot directly interact with an antigen. Instead, they can interact only with pieces of antigen bound to glycoproteins, called major histocompatibility complex (MHC) molecules. The name comes from the fact that MHC molecules are major determinants of compatibility among tissue and organ donors and recipients.

Fluid found in lymphatic vessels is known as __________.

Fluid found in lymphatic vessels is known as lymph. The amount of fluid that is lost from the plasma is significant, measuring about 2-4 liters per day. This fluid must be returned to the circulation, or both the blood volume and blood pressure will drop too low to maintain homeostasis. The vessels that perform this function are the lymphatic vessels, which pick up excess fluid in the extracellular space, transport it through the body, and deliver it back to the cardiovascular system. When the fluid exits the extracellular space and enters the lymphatic vessels, it is known as lymph. This means that interstitial fluid and lymph are very similar in composition. Recall that the body contains two fluid compartments: (1) the intracellular space, which is the space within our cells that contains the cytosol or intracellular fluid, and (2) the extracellular space, which is the space outside our cells that contains fluid called extracellular fluid (ECF). The plasma membrane forms a barrier between the ECF and the cytosol, and keeps the two fluid compartments separate.

What cells decline in number during the final phase of HIV-1 infection, when an individual is said to have AIDS?

Helper T (TH) cells decline in number during the final phase of HIV-1 infection, when an individual is said to have AIDS. AIDS is caused by human immunodeficiency virus 1 (HIV-1), which is spread through contact with infected blood, semen, vaginal fluid, or breast milk. HIV-1 preferentially binds and interacts with cells displaying CD4 molecules. The affinity of the virus for CD4 molecules results from a glycoprotein on its surface that fits into a CD4 molecule the way a key fits into a lock. This makes cells that display large numbers of CD4 molecules, particularly TH cells, specifically at risk for infection. Keep in mind that certain strains of HIV-1 can also interact with CD4 molecules on other immune cells, such as monocytes, macrophages, and dendritic cells. The signs and symptoms of AIDS are due largely to the destruction of TH cells. As you have read, TH cells are required for almost all parts of the innate and adaptive immune responses to function properly. For this reason, the loss of TH cells causes the entire adaptive immune response to fail (some innate responses remain). B cells develop and mature in the bone marrow. Antibody-mediated immunity is mediated by B cells that secrete antibodies, or immunoglobulins, which bind to specific antigens. Normal antibodies bind only foreign antigens; they do not bind to self antigens. When a naïve B cell encounters its antigen, the antigen binds and triggers the B cell to proliferate and differentiate into antibody-secreting plasma cells and long-lived memory B cells. Memory B cells are responsible for immunological memory. The first exposure to an antigen generates the slower primary immune response. Subsequent exposures to antigens generate the faster, more efficient secondary immune response.

Which cell type is targeted by the human immunodeficiency virus (HIV)?

Helper T cells are targeted by the human immunodeficiency virus (HIV). HIV-1 preferentially binds and interacts with cells displaying CD4 molecules. The affinity of the virus for CD4 molecules is the result of a glycoprotein on its surface that fits into a CD4 molecule the way a key fits into a lock. This makes cells that display large numbers of CD4 molecules, particularly TH cells, specifically at risk for infection. The signs and symptoms of AIDS are due largely to the destruction of TH cells. TH cells are required for almost all parts of the innate and adaptive immune responses to function properly. For this reason, the loss of TH cells causes the entire adaptive immune response to fail (some innate responses remain). This failure leads to recurrent infections, particularly with agents that are opportunistic, or not generally pathogenic in immunocompetent patients.

Which of the following disorders is not a type of hypersensitivity?

Immunodeficiency hypersensitivity is not a type of hypersensitivity disorder. A decrease in the function of one or more components of the immune system results in an immunodeficiency disorder. In the preceding modules, you have seen how the various parts of the immune response are interconnected. For this reason, when one component of the immune response fails, it generally leads to failure of other components, and the results can be catastrophic. There are two basic types of immunodeficiency disorders: primary immunodeficiencies, which are genetic or developmental in nature, and secondary immunodeficiencies, which are acquired through infection, trauma, cancer, or certain medications. The most common type of hypersensitivity disorder is type I, or immediate, hypersensitivity, which affects a tremendous number of people—about 20% of the U.S. population. This type of hypersensitivity is more commonly known as allergies, and the disorders that accompany it are called allergic disorders. In type II hypersensitivity, also known as antibody-mediated hypersensitivity, the antibodies produced by the immune response that bind to foreign antigens also bind to self-antigens. Type IV, or delayed-type, hypersensitivity (DTH) is unique in that it is mediated by T cells rather than antibodies. In these cases, TH cells recognize antigens bound to MHC molecules as foreign and mediate their destruction by activating and recruiting macrophages and in some cases TC cells. This reaction generally takes 2-3 days to manifest, hence its name. As with type I hypersensitivity, TH cells must be sensitized by an initial exposure, and the reaction occurs with subsequent exposures.

_____ will inhibit the ability of pathogens to infect other cells.

Interferons will inhibit the ability of pathogens to infect other cells, are generally produced in response to infection with intracellular agents such as viruses or intracellular bacteria, and are named for their capacity to "interfere" with the ability of the pathogens to infect other cells. One of their primary actions is to inhibit viral replication inside host cells. In addition, they activate various components of both innate and adaptive immunity, such as stimulating nearby cells to produce antimicrobial proteins. Interleukins, abbreviated as IL followed by a number (e.g., IL-2), constitute a class of 29 cytokines (note that the number in the name of each interleukin indicates the order in which it was discovered, not its order in any process). The name interleukin means "between leukocytes," which reflects the fact that they are produced by leukocytes and many of their actions affect other leukocytes. Examples of these effects include stimulating production of neutrophils by the bone marrow, stimulating NK cells, triggering the production of certain types of interferons from different leukocytes, and activating T cells. The cytokine known as tumor necrosis factor (TNF) is named for the fact that it was originally discovered through its ability to induce necrosis (death) of tumor cells. TNF is secreted primarily by activated macrophages in response to certain bacteria and other pathogens. Effects of TNF include inducing flulike symptoms, attracting phagocytes to the area of infection, increasing the activity of phagocytes, and stimulating phagocytes to release additional cytokines. The group of proteins collectively known as the complement system consists of around 30 plasma proteins that are produced primarily by the liver. Complement proteins circulate primarily in their inactive forms and must be activated by a complex cascade of events mediated by enzymes.

Lymph is most closely related to ___________.

Interstitial fluid and lymph are similar in composition. Lymphatic vessels pick up excess interstitial fluid, transport it through the body, and deliver it back to the cardiovascular system. When the interstitial fluid exits the extracellular space and enters the lymphatic vessels, it is known as lymph.

How long after initial tissue damage does leukocytosis occur?

Leukocytosis occurs 3-4 days after initial tissue damage. The final inflammatory response occurs in the bone marrow, where leukocytes are produced. Cytokines produced by the activated phagocytes act on cells in the bone marrow to increase the production of neutrophils and monocytes over the next 3-4 days. This leads to an elevated number of circulating leukocytes, a condition called leukocytosis, commonly referred to as a "high white cell count."

Lymph draining into lymphatic vessels from the right leg to the bloodstream would travel along the following path:

Lymph draining into lymphatic vessels from the right leg to the bloodstream would travel along the following path: right lumbar trunk - cisterna chyli - thoracic duct - left subclavian vein. The intestinal and lumbar trunks all drain into a large, swollen-looking vessel called the cisterna chyli. The cisterna chyli and the other lymphatic trunks drain into one of two lymphatic ducts. The cisterna chyli and the trunks from the left side of the body drain into the thoracic duct, the largest lymphatic duct, which runs along the anterior vertebral column and drains into the junction of the left internal jugular and left subclavian veins. In fact, the thoracic duct drains all of the lower body as well as the left side of the upper body.

Lymph from the thoracic cavity is drained by the _____ trunks.

Lymph from the thoracic cavity is drained by the bronchomediastinal trunk. The lumbar trunks receive lymph from the lower limbs and pelvic area. The jugular trunks receive lymph from the head and neck. The subclavian trunks receive lymph from the upper limbs.

What are the primary cells of adaptive immunity?

Lymphocytes are the primary cells of adaptive immunity. The third line of defense involves the cells and proteins of adaptive immunity. Adaptive immunity requires exposure to a specific antigen to mount a response. The two arms of adaptive immunity are antibody-mediated immunity and cell-mediated immunity. Adaptive immunity is capable of immunological memory. The cells of adaptive immunity include B and T lymphocytes. Proteins of innate immunity include the group of proteins known as complement and many types of cytokines. Proteins of adaptive immunity include many types of cytokines and antibodies. The cytokines involved in innate immunity include tumor necrosis factor (TNF), interferons, and interleukins. The cells of innate immunity include phagocytes and natural killer (NK) cells, as well as dendritic cells.

MALT is an acronym for _________ in the lymphatic system.

MALT is an acronym for mucosa-associated lymphatic tissue in the lymphatic system. The mucous membranes, such as those of the oral and nasal cavities, are all vulnerable parts of the body because they are exposed to large numbers of pathogens. These areas are protected by loosely organized clusters of lymphoid tissue collectively called mucosa-associated lymphatic tissue (MALT). MALT is found scattered throughout the gastrointestinal tract, the respiratory passages, and to a limited extent, the genitourinary tract.

What is a determinant for organ compatibility and rejection of transplants?

Major histocompatibility complex (MHC) molecules are a determinant for organ compatibility and rejection of transplants. T cells cannot directly interact with an antigen. Instead, they can interact only with pieces of antigen bound to glycoproteins, called major histocompatibility complex (MHC) molecules. The name comes from the fact that MHC molecules are major determinants of compatibility among tissue and organ donors and recipients (remember that histo- means "tissue"). MHC molecules are found on nearly all nucleated cells. An activated TC cell binds its target cell, after which it releases a protein called perforin. Perforin forms pores in, or perforates, the target cell's plasma membrane. The TC cell then releases enzymes that can now enter the target cell's cytosol. These enzymes catalyze reactions that degrade target cell proteins and eventually lead to fragmentation of the target cell's DNA and its death. Interleukins constitute a class of 29 cytokines produced mainly by different types of leukocytes. Examples of the effects of interleukins include stimulating production of neutrophils by the bone marrow, stimulating NK cells, triggering the production of certain types of interferons, and activating T cells. Fever is an innate response to cellular injury. Fever is initiated when chemicals called pyrogens are released from damaged cells or certain bacteria. Pyrogens act on the hypothalamus, the small component of the diencephalon (the central core of the brain) that regulates many aspects of homeostasis.

Mucosa-associated lymphatic tissues (MALT) include the __________.

Mucosa-associated lymphatic tissues (MALT) include the tonsils. The mucous membranes, such as those of the oral and nasal cavities, are all vulnerable parts of the body because they are exposed to large numbers of pathogens. These areas are protected by loosely organized clusters of lymphoid tissue collectively called MALT. MALT is found scattered throughout the gastrointestinal tract, the respiratory passages, and to a limited extent, the genitourinary tract. In the gastrointestinal tract, we find these specialized clusters of MALT in three locations: the tonsils, located around the oral and nasal cavities; Peyer's patches, or aggregated lymphoid nodules, located in the last portion of the small intestine (called the ileum); and the appendix, located off the large intestine. The liver, kidneys, and spleen are not part of MALT.

Mucous membranes and tears contain antimicrobial substances such as _____.

Mucous membranes and tears contain antimicrobial substances such as IgA. IgA is present in secretions from the skin, mucous membranes, and exocrine glands (i.e., tears, saliva, sweat, and breast milk). IgG is the only antibody able to cross from the blood of a pregnant woman to her developing fetus through a structure called the placenta. Passive immunity may be naturally acquired, for example, when the IgG of a pregnant woman crosses from her blood into that of her fetus, or artificially acquired, from an injection with preformed antibodies. IgM is generally the first antibody secreted by plasma cells when the body is invaded by a pathogen. Note that IgM also exists as a single subunit embedded in the B cell plasma membrane, where it functions as a B cell receptor. IgE binds to two types of antigen: (1) antigens associated with parasitic pathogens such as tapeworms, and (2) environmental antigens known as allergens, which are linked with inflammatory reactions called allergies. IgE molecules bind to mast cells in mucous membranes, and when they come into contact with their specific antigens, they trigger mast cells to release the contents of their granules, a process called degranulation. Mast cell granules contain inflammatory mediators such as histamine that initiate a localized inflammatory response. The ensuing inflammation is responsible for common allergy symptoms such as a runny nose and watery eyes.

_____, cells that have not yet encountered their specific antigens, reside in the blood, lymphoid organs, or other lymphatic tissue.

Naïve T cells, cells that have not yet encountered their specific antigens, reside in the blood, lymphoid organs, or other lymphatic tissue. Naïve T cells must bind their specific antigens before they become activated. Some T cell clones are capable of recognizing and responding to pathogens, whereas others are not. The thymus "screens" these cells and mediates the destruction of those clones that cannot recognize antigens. Other T cell clones, known as self-reactive T cells, recognize self antigens as foreign and would attack your cells if released into the circulation. These self-reactive T cells are also destroyed, ensuring self-tolerance and preventing our T cells from attacking our own cells. More than 95% of all T cells die in the thymus in this manner. T cells that do survive this screening are released into the circulation when they mature. Among the changes triggered in the B cells when they are activated is rapid cell division, which results in an explosion in the population of these cells. In addition to rapid proliferation, the resulting B cells differentiate into two populations of cells: (1) plasma cells, which secrete antibodies; and (2) memory B cells, which are long-lived cells that do not secrete antibodies but will respond to antigens upon a second exposure. Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells (APCs). Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response.

Which of the following immune responses is not associated with the common cold?

Neutrophils enter the area in large numbers and phagocytize bacteria is the immune response not associated with the common cold. The common cold is due to a variety of viruses, not bacteria, that typically have a high mutation rate, which is why researchers have yet to develop a vaccine for the pathogens. Although it might seem that you frequently get sick with a cold, in truth most pathogens, viruses included, are deterred by the body's surface barriers and so never even gain entry into the body.

_____ will increase their oxygen consumption when activated, known as respiratory burst, allowing them to create chemicals such as hydrogen peroxide.

Neutrophils will increase their oxygen consumption when activated, known as respiratory burst, allowing them to create chemicals such as hydrogen peroxide. The most predominant granulocyte is the neutrophil. Like macrophages, neutrophils are highly effective phagocytes. When they are activated, their oxygen consumption increases, a phenomenon called the respiratory burst. This allows them to create chemicals such as hydrogen peroxide, hypochlorous acid, and hydroxide anions, which kill ingested pathogens. Natural killer cells are lymphocytes with the remarkable ability to recognize cancerous cells and cells infected with certain viruses despite the fact they cannot recognize antigens. They appear to do this by scanning the cells for irregularities and by reacting to cells that have bound to antibodies (another example of innate and adaptive immunity working together). NK cells are also cytotoxic, releasing substances that destroy their target cells. In addition, they secrete an antimicrobial cytokine that activates macrophages and enhances phagocytosis. The primary function of cytotoxic T cells is evident from their name; they kill other cells, specifically those with foreign antigens bound to class I MHC molecules. Their ability to interact with class I MHC molecules means they can detect abnormalities in any cell type with a nucleus, which is critical for the detection of cancer cells, foreign cells, and cells infected with intracellular pathogens such as viruses and bacteria. A relatively rare cell that is generally nonphagocytic is the basophil. Basophils are granulocytes whose granules contain chemicals that mediate inflammation (inflammatory mediators). Basophils are located primarily in the blood, although a related type of cell called the mast cell is located in mucous membranes.

Which of the following molecules is not a cytokine involved in innate immunity?

Opsonins are not a cytokine involved in innate immunity. The complement protein C3b acts as an opsonin, binding both pathogens and phagocytes. This action, known as opsonization, makes phagocytes bind more strongly to the pathogen and enhances phagocytosis. This function is evident from the name because opsonin means "prepare for eating." Immunity is classified according to the way it responds to different pathogens or forms of cellular injury. As implied by its name, innate, or nonspecific, immunity responds to all pathogens or classes of pathogen in the same way. The innate immune system consists of antimicrobial proteins and certain cells. Note that innate immunity responds quickly and is the dominant response to pathogens for the first 12 hours after exposure. This occurs because the cells and proteins exist in the bloodstream, even in the absence of a stimulus (hence the term innate). Cytokines are proteins produced by several types of immune cells that enhance the immune response in some way. Interestingly, many cytokines induce "flulike" symptoms, including fever, chills, and aches (the aches are a result of the stimulation of inflammation). The cytokines involved in innate immunity include tumor necrosis factor (TNF), interferons, and interleukins.

Passive immunity provided to newborns through the placenta belong to the _____ class of immunoglobulins.

Passive immunity provided to newborns through the placenta belong to the IgG class of immunoglobulins. Passive immunity is found when preformed antibodies are passed from one organism to another. IgG is the only antibody able to cross from the blood of a pregnant woman to her developing fetus through a structure called the placenta. Passive immunity may be naturally acquired, for example, when the IgG of a pregnant woman crosses from her blood into that of her fetus, or artificially acquired, from an injection with preformed antibodies. IgM is generally the first antibody secreted by plasma cells when the body is invaded by a pathogen. Note that IgM also exists as a single subunit embedded in the B cell plasma membrane, where it functions as a B cell receptor. IgE binds to two types of antigen: (1) antigens associated with parasitic pathogens such as tapeworms, and (2) environmental antigens known as allergens, which are linked with inflammatory reactions called allergies. IgE molecules bind to mast cells in mucous membranes, and when they come into contact with their specific antigens, they trigger mast cells to release the contents of their granules, a process called degranulation. Mast cell granules contain inflammatory mediators such as histamine that initiate a localized inflammatory response. The ensuing inflammation is responsible for common allergy symptoms such as a runny nose and watery eyes. The antibody IgD is unique because it is the only antibody not secreted by B cells in significant amounts. Rather, its single subunit is located on the surface of B cells, where it acts as an antigen receptor that helps activate B cells in a similar manner to IgM.

Where are pathogens filtered from lymph?

Pathogens are filtered from lymph in lymph nodes. Lymph flows into the node through multiple small lymphatic vessels called afferent lymphatic vessels. Lymph percolates through the reticular network, where many pathogens in the lymph become trapped in the reticular "net." Trapped pathogens then encounter leukocytes and dendritic cells, which eliminate these threats. Lymph that has been "cleaned" of pathogens drains out through efferent lymphatic vessels on the other side of the node at an area called the hilum. Lymph nodes are remarkably effective at their job and trap approximately 90% of the pathogens in lymph. This prevents these pathogens from being delivered to the blood, where they could easily spread to other tissues and organs. The tonsils are located around the oral and nasal cavities and trap bacteria and debris. The tonsils' location puts them into contact with a large number of potential pathogens. The spleen protects us from pathogens in the blood. Specialized lymphatic capillaries known as lacteals collect fat in the small intestine.

What protein, released by cytotoxic T (TC) cells, perforates a target cell's plasma membrane so that enzymes can enter and fragment the target cell's DNA?

Perforins, released by cytotoxic T (TC) cells, perforate a target cell's plasma membrane so that enzymes can enter and fragment the target cell's DNA. An activated TC cell binds its target cell, after which it releases a protein called perforin. Perforin forms pores in, or perforates, the target cell's plasma membrane. The TC cell then releases enzymes that can now enter the target cell's cytosol. These enzymes catalyze reactions that degrade target cell proteins and eventually lead to fragmentation of the target cell's DNA and its death. TC cells also bind to proteins on the plasma membrane of target cells that induce the process of apoptosis, or programmed cell death (see chapter 3). When the target cell begins to degrade, the TC cell detaches and searches for a new target cell. The cytokines involved in innate immunity include tumor necrosis factor (TNF), interferons, and interleukins.

Which of the following processes is not a function of antibodies?

Phagocytosis is not a function of antibodies. Antibody-mediated immunity is mediated by B cells that secrete antibodies, or immunoglobulins, which bind to specific antigens. Normal antibodies bind only foreign antigens; they do not bind to self antigens. The actions of antibodies are based on their ability to bind antigens, which leads to multiple effects on pathogens. Many of these effects represent an integration of adaptive and innate immunity; the antibodies of adaptive immunity often activate phagocytes and complement proteins of innate immunity. The basic effects of secreted antibodies are agglutination and precipitation, opsonization, neutralization, complement activation, and stimulation of inflammation. We can divide the cells of innate immunity into two types, phagocytic cells and nonphagocytic cells. The phagocytic cells include macrophages, neutrophils, and eosinophils. The process by which cells ingest particles and other cells is called phagocytosis. The nonphagocytic cells include NK cells, basophils, and dendritic cells.

Pyrogens act on the ______ and disrupts the body's thermostat.

Pyrogens act on the hypothalamus and disrupts the body's thermostat. The hypothalamus is the small component of the diencephalon (the central core of the brain) that regulates the homeostasis of many regulated physiological variables. The hypothalamus normally functions as the body's thermostat and maintains body temperature within the normal range through a series of negative feedback loops. Pyrogens cause the hypothalamic thermostat to reset to a higher range. At this higher range, the hypothalamus interprets normal body temperature as being too low, which triggers the negative feedback loop. This is why you feel cold, or have "chills," when you have a fever; the hypothalamus is triggering responses to elevate body temperature to the new, higher range.

Removal of which of the following lymphoid organs would be most detrimental to immune function in an infant?

Removal of the thymus, a lymphoid organ, would be most detrimental to immune function in an infant. The thymus is large and very active in infants and children, as you can see in Figure 20.9a, and it reaches its maximum size in individuals about 12-14 years old. After this point, it begins to atrophy, and the thymic tissue is gradually replaced with fat. As the thymus atrophies, its production of T cells decreases as well. Indeed, by age 65, the rate of T cell production falls to about 2% of the rate at which an infant produces T cells. This drop in production does not normally lead to a decline in immune function, however, because of the enormous number of T cells produced during infancy and childhood.

Specialized clusters of MALT known as Peyer's patches are found in the ____________.

Specialized clusters of MALT known as Peyer's patches are found in the small intestine. In the gastrointestinal tract, we find these specialized clusters of MALT in three locations: the tonsils, located around the oral and nasal cavities; Peyer's patches, or aggregated lymphoid nodules, located in the last portion of the small intestine (called the ileum); and the appendix, located off the large intestine.

Specialized lymphatic capillaries known as _____ absorb dietary fats in the small intestine.

Specialized lymphatic capillaries known as lacteals absorb dietary fats in the small intestine. The breakdown products of fats in the diet are too large to pass through the tiny spaces between the endothelial cells of blood capillaries. However, they are able to enter small lymphatic vessels in the small intestine. The dietary fats travel through the lymphatic vessels and are delivered to the blood with lymph. We see features in lymphatic vessels that we also see in the low-pressure venous circuit of the cardiovascular system. For example, lymphatic vessels have lymphatic valves that prevent lymph from flowing backward. Lymph nodes limit the spread of pathogens through the body by acting as filters, trapping pathogens and preventing them from traveling elsewhere. Lymphatic capillaries are blind-ended, which makes the lymphatic vasculature a one-way system that only moves lymph away from the tissues. Blood capillaries, of course, form a two-way system that moves blood both toward and away from the tissues.

Surface barriers, such as cutaneous and mucous membranes, serve the immune system as the __________.

Surface barriers, such as cutaneous and mucous membranes, serve the immune system as the first line of defense. The first line of defense against any potential threat to the body is the coverings that line body surfaces: the skin and the mucous membranes, and certain products they secrete. Both the skin and mucosae are surface barriers, meaning that they provide a continuous physical barrier to block the entry of potential pathogens into the body. The second line of defense consists of the responses of the cells and proteins that make up innate immunity. The third line of defense consists of the responses of the cells and proteins of adaptive immunity. There is no fourth line of defense.

T cells and natural killer (NK) cells are largely involved in scanning the cells in the body for tumor antigens, a function known as __________.

T cells and natural killer (NK) cells are largely involved in scanning the cells in the body for tumor antigens, a function known as immune surveillance. Immune surveillance is absolutely critical to the prevention of tumor development. When tumor cells are discovered via immune surveillance, they are eliminated. Cancer cells damage surrounding cells and induce an inflammatory response. NK cells migrate to the area and begin to destroy the cancer cells and secrete interferons. Dendritic cells ingest cellular debris and migrate to lymph nodes, where they activate TH cells. Activated TH cells secrete cytokines that stimulate TC cells to kill cancer cells. The complement system is a group of 20 or more plasma proteins produced primarily by the liver that are involved in cell lysis via a membrane attack complex, enhancing phagocytosis through opsonization, enhancing inflammation, and neutralizing certain viruses. Antibodies can bind to antigens on more than one cell. This creates a clump of cells that are cross-linked by their attachment to antibodies. The clumping of cells is known as agglutination. A vaccination, also known as an immunization, involves exposing an individual to an antigen to elicit a primary immune response and generate memory cells. Then if the individual is exposed to the antigen a second time, a secondary immune response will occur and symptoms will be minimal.

Where do T cells become immunocompetent?

T cells become immunocompetent in the thymus. T cells are formed in the bone marrow, but they leave the bone marrow and migrate to the thymus to mature. As T cells mature, they undergo gene rearrangements that lead to a huge variety of genetically distinct T cells. Each population of T cells that can respond to a specific antigen is known as a clone. There are millions of different clones in the immune system, but only a few cells of each clone exist in the body at any given time. Some T cell clones are capable of recognizing and responding to pathogens, whereas others are not. The thymus "screens" these cells and mediates the destruction of those clones that cannot recognize antigens. This ensures that an individual is immunocompetent, or able to mount a normal response to foreign antigens. B cells develop and mature in the bone marrow. Mucosa-associated lymphatic tissue (MALT) consists of clusters of unencapsulated lymphoid tissue located along the mucous membranes. Specialized MALT, which may be partially encapsulated, includes the tonsils, Peyer's patches, and appendix. Recall that the thyroid gland is located in the anterior neck, just superficial to the larynx. The thyroid gland secretes two types of hormones: thyroid hormones, which regulate growth and metabolism, and calcitonin, which helps to regulate calcium ion homeostasis.

____ cells are required for almost all parts of the innate and adaptive immune responses to function properly.

TH cells are required for almost all parts of the innate and adaptive immune responses to function properly. For this reason, the loss of TH cells causes the entire adaptive immune response to fail (some innate responses remain). This failure leads to recurrent infections, particularly with agents that are opportunistic, or not generally pathogenic in immunocompetent patients.

Dead leukocytes, dead tissue cells, and fluid can all accumulate to form ____.

The accumulation of dead leukocytes, dead tissue cells, and fluid leads to a whitish mixture known as pus (a wound filled with pus is said to be purulent). The neutrophils and macrophages in the damaged tissue go to work digesting pathogens and damaged cells. Eventually, all of the neutrophils and many of the macrophages die themselves. Fever is defined simply as a body temperature above the normal range, which is generally between 36° and 38° C (or 97 and 99° F); an individual with a fever is referred to as febrile. Many conditions can cause fever, but in this section we primarily focus on those related to the immune system. Fever is initiated when chemicals called pyrogens are released from damaged cells or certain bacteria. Cytokines produced by the activated phagocytes act on cells in the bone marrow to increase the production of neutrophils and monocytes over the next 3-4 days. This leads to an elevated number of circulating leukocytes, a condition called leukocytosis, commonly referred to as a "high white cell count." The elevated numbers of leukocytes allow the damaged area to be cleared and any pathogens removed so that cells such as fibroblasts can begin the process of healing. previous

The antibody IgE directly triggers _______.

The antibody IgE directly triggers inflammation by initiating the release of inflammatory mediators from mast cells and basophils. Antibodies also trigger inflammation indirectly through their activation of complement. Several antibodies, particularly IgM and IgG, bind and activate the complement proteins of innate immunity. When several antibodies bind a single cell, their complement-binding sites are exposed. This allows complement to activate and lyse the foreign cell with its membrane attack complex. This effect is particularly important in defense against cellular pathogens such as bacteria and is partly responsible for our reaction to foreign cells such as donated erythrocytes. Antibodies can bind to antigens on more than one cell. This creates a clump of cells that are cross-linked by their attachment to antibodies. The clumping of cells is known as agglutination. IgM is the most potent agglutinating and precipitating antibody as a result of its 10 antigen-binding sites. Opsonization involves proteins such as complement coating the pathogen and activating phagocytes. IgG antibodies are also opsonins able to coat pathogens and bind and activate phagocytes, which greatly enhances phagocytosis.

The deep indents that trap bacteria in the epithelium lining the tonsils are known as _____.

The deep indents that trap bacteria in the epithelium lining the tonsils are known as crypts. The epithelium lining the tonsils indents deeply in several locations, forming tonsillar crypts that trap bacteria and debris. The tonsils' location puts them into contact with a large number of potential pathogens. As a result, they commonly become inflamed, a condition known as tonsillitis.

Which of the following lists the body's first, second, and third line of defense in order?

The following lists the body's first, second, and third line of defense in order surface barriers, innate immunity, and adaptive immunity. The first line of defense against any potential threat to the body is the coverings that line body surfaces: the skin and the mucous membranes and certain products they secrete. Both the skin and mucosae are surface barriers, meaning that they provide a continuous physical barrier to block the entry of potential pathogens into the body. The second line of defense consists of the responses of the cells and proteins that make up innate immunity. Immunity is classified according to the way it responds to different pathogens or forms of cellular injury. As implied by its name, innate, or nonspecific, immunity responds to all pathogens or classes of pathogen in the same way. The innate immune system consists of antimicrobial proteins and certain cells. Note that innate immunity responds quickly and is the dominant response to pathogens for the first 12 hours after exposure. This occurs because the cells and proteins exist in the bloodstream, even in the absence of a stimulus (hence the term innate). The third line of defense consists of the responses of the cells and proteins of adaptive immunity. In adaptive immunity, the components respond to unique markers called antigens. Antigens are present on all cells, including our own cells, and most biological molecules, and they identify a cell or molecule as belonging to a specific group. Adaptive immunity is also known as specific immunity because its cells and proteins respond individually to only a specific, individual antigen. This is in contrast to innate immunity, which reacts in the same manner to every potential pathogen.

The cisterna chyli receive lymph drained from the ______________________.

The intestinal and lumbar trunks all drain into a large, swollen-looking vessel called the cisterna chyli. The cisterna chyli and the other lymphatic trunks drain into one of two lymphatic ducts. The cisterna chyli and the trunks from the left side of the body drain into the thoracic duct, the largest lymphatic duct, which runs along the anterior vertebral column and drains into the junction of the left internal jugular and left subclavian veins.

The largest lymphatic duct, which runs along the anterior vertebral column, is the ______.

The largest lymphatic duct, which runs along the anterior vertebral column, is the thoracic duct. The cisterna chyli and the trunks from the left side of the body drain into the thoracic duct, which drains into the junction of the left internal jugular and left subclavian veins. In fact, the thoracic duct drains all of the lower body as well as the left side of the upper body.

The lymph from the right lymphatic duct and thoracic duct empty into the _______________.

The lymph from the right lymphatic duct and thoracic duct empty into the subclavian veins. The thoracic duct, the largest lymphatic duct, runs along the anterior vertebral column and drains into the junction of the left internal jugular and left subclavian veins. The tiny right lymphatic duct drains into the junction of the right internal jugular and right subclavian veins. At these venous junctions, the lymph drains into the blood of the low-pressure venous circuit at the subclavian veins.

The lymphatic organ that atrophies as we age is the ____.

The lymphatic organ that atrophies as we age is the thymus. The thymus is large and very active in infants and children, as you can see in Figure 20.9a, and it reaches its maximum size in individuals about 12-14 years old. After this point, it begins to atrophy, and the thymic tissue is gradually replaced with fat. As the thymus atrophies, its production of T cells decreases as well. Indeed, by age 65, the rate of T cell production falls to about 2% of the rate at which an infant produces T cells. This drop in production does not normally lead to a decline in immune function, however, because of the enormous number of T cells produced during infancy and childhood. The spleen, which is the largest lymphoid organ in the body, is located on the lateral side of the left upper quadrant of the abdominopelvic cavity. Here pathogens encounter macrophages and dendritic cells, which process portions of the pathogens. The appendix—a blind-ended, worm-shaped tube that juts from the large intestine. Like the Peyer's patches, the appendix defends against bacteria in the large intestine, specifically those that could be pathogenic. Unfortunately, it is easy for bacteria and fecal matter to become trapped in the appendix. The result is a condition known as appendicitis, in which the appendix swells much like lymph nodes do (as you have likely noticed) when you are sick and they are filled with bacteria or other pathogens. The blind-ended structure of the appendix gives it little room to expand, which creates the potential for rupture. Such a rupture spills bacteria into the abdominopelvic cavity and leads to internal bleeding, which may be fatal if not treated promptly. Lymph nodes are small, vaguely bean-shaped clusters of lymphatic tissue located along lymphatic vessels throughout the body

The lymphatic organ that protects us from pathogens in our blood is the _____.

The lymphatic organ that protects us from pathogens in our blood is the spleen. The spleen, which is the largest lymphoid organ in the body, is located on the lateral side of the left upper quadrant of the abdominopelvic cavity. It is a purplish-brown organ about the size of a large bar of soap. The lymph nodes, Peyer's patch, and tonsils protect us from pathogens on our mucous membranes and in the lymph.

Which lymphoid organ is required for the selection of a functional population of T lymphocytes (T cells) for the immune system?

The lymphoid organ required for the selection of a functional population of T lymphocytes (T cells) for the immune system is the thymus. The thymus secretes hormones that enable it to carry out its primary function: generating a population of functional T cells capable of protecting the body from pathogens. Unlike the spleen and lymph nodes, the thymus doesn't trap pathogens. The epithelium lining the tonsils indents deeply in several locations, forming tonsillar crypts that trap bacteria and debris. The tonsils' location puts them into contact with a large number of potential pathogens. The complement system is a group of 20 or more plasma proteins produced primarily by the liver that are involved in cell lysis via a membrane attack complex, enhancing phagocytosis through opsonization, enhancing inflammation, and neutralizing certain viruses. Recall that the thyroid gland is located in the anterior neck. It consists of hollow, spherical thyroid follicles that are filled with colloid and lined by cuboidal follicle cells. Follicle cells produce and secrete thyroid hormones. Between follicles are parafollicular cells that secrete calcitonin.

The lymphoid organ that is the site of maturation of T-lymphocytes is the ____.

The lymphoid organ that is the site of maturation of T-lymphocytes is the thymus. The thymus secretes hormones that enable it to carry out its primary function: generating a population of functional T cells capable of protecting the body from pathogens. The spleen is a large lymphoid organ in the left upper quadrant of the abdominopelvic cavity that filters blood and processes old erythrocytes. Lymph nodes limit the spread of pathogens through the body by acting as filters, trapping pathogens and preventing them from traveling elsewhere. When lymphoid follicles have been exposed to pathogens, they develop light-staining regions, the germinal centers, where the B cells are actively dividing. In the gastrointestinal tract, we find these specialized clusters of MALT in three locations: the tonsils, located around the oral and nasal cavities; Peyer's patches, or aggregated lymphoid nodules, located in the last portion of the small intestine (called the ileum); and the appendix, located off the large intestine.

A systemic release of histamine and other inflammatory mediators leads to the most dramatic immediate hypersensitivity reaction known as ______.

The most dramatic immediate hypersensitivity reaction, anaphylactic shock, involves a systemic release of histamine and other inflammatory mediators. Anaphylactic shock consists of several life-threatening events, including (1) severe spasm of the smooth muscle of the respiratory tract, particularly the smooth muscle in the larynx (the "voice box"); (2) systemic vasodilation, which causes blood pressure to drop and decreases blood flow to all organs, including the brain; and (3) increased capillary permeability in all of the body's capillaries, which further lowers blood pressure and causes body-wide swelling because there is a massive loss of fluid to the tissue spaces and lungs. More potent reactions occur in patients with the allergic respiratory disease asthma, in which allergen exposure severely limits the ability to breathe by triggering inflammation, smooth muscle spasm, and excess mucus secretion in the respiratory passages. One of the most common types of delayed type hypersensitivity reactions is contact dermatitis, in which skin comes into contact with an allergen such as the oils in poison ivy or poison oak, certain metals, or other chemicals that can form complexes with skin proteins. The allergens are taken in and displayed by dendritic cells in the skin, which activate TH cells. The TH cells then secrete cytokines that recruit macrophages. The macrophages arrive in large numbers and destroy the self-cells with the foreign antigens through phagocytosis and the release of enzymes and other chemicals that also damage surrounding cells. This results in a rash that is itchy and occasionally painful. In type II hypersensitivity, also known as antibody-mediated hypersensitivity, the antibodies produced by the immune response that bind to foreign antigens also bind to self-antigens. This reaction occurs in three situations: (1) Foreign antigens bind to normal self-antigens; (2) donor erythrocytes infused into an individual are mismatched in the ABO/Rh antigen groups; and (3) self-reactive B cells are not destroyed in the bone marrow, which leads to autoimmunity.

The only lymphatic organ with afferent lymphatic vessels is the _____.

The only lymphatic organ with afferent lymphatic vessels is the lymph node. Lymph flows into the node through multiple small lymphatic vessels called afferent lymphatic vessels. In the node, it first enters a hollow area called the subcapsular sinus, after which it flows through cortical sinuses that run next to the trabeculae. As lymph passes through these sinuses, pathogens and immune cells such as dendritic cells migrate into the lymphoid nodule to initiate an immune response. Lymph continues to flow through the node from the cortical sinuses to the medullary sinuses, after which it drains out through efferent lymphatic vessels on the other side of the node at an area called the hilum.

The primary immune response can take up to ____ for the antibody to peak, whereas the secondary immune response can take up to _____ for the antibody to peak.

The primary immune response can take up to 7-14 days for the antibody to peak, whereas the secondary immune response can take up to 3-5 days for the antibody to peak. The primary immune response is effective, but it is slow; there is an initial 4- to 5-day lag phase as the B cells proliferate, differentiate into plasma cells and memory cells, and begin to secrete antibodies. Antibody levels peak about 7-14 days after the antigen is encountered. It is during the lag phase that you generally feel "sick." When these memory B cells encounter the antigen for which they are specific, the secondary immune response begins. There are several key differences between the two responses. First, the secondary immune response has a shorter lag phase (about 1-3 days), and its antibody levels peak more rapidly (3-5 days) and reach a peak 100-1000 times larger.

The reason why some vaccines require booster shots is because they are ______.

The reason why some vaccines require booster shots is because they are inactivated vaccines. Vaccines may be prepared with inactivated, or "killed," pathogens. Inactivated pathogens are not capable of dividing in the body, so they generate a weaker primary immune response and generally require several repeat vaccinations, known as "boosters." A vaccination, also known as an immunization, involves exposing an individual to an antigen to elicit a primary immune response and generate memory cells. Then if the individual is exposed to the antigen a second time, a secondary immune response will occur and symptoms will be minimal. Certain pathogens can be attenuated, meaning that their ability to cause disease has been greatly reduced. When these pathogens are administered as a vaccine, they can still divide to a limited extent in the body and so induce a primary immune response. The ability of the pathogens to divide generates a strong primary immune response because of their extended presence in the body. Live, attenuated vaccines are completely safe for most individuals, although there is an extremely small risk that the organisms could revert to a pathogenic form.

Which region is not drained by the right lymphatic duct?

The right side of the abdomen is not drained by the right lymphatic duct. The thoracic duct drains all of the lower body as well as the left side of the upper body. The remaining trunks from the right upper side of the body drain into the tiny right lymphatic duct, which drains into the junction of the right internal jugular and right subclavian veins.

The second line of defense consists of responses of the cells and proteins that make up ____________.

The second line of defense consists of the responses of the cells and proteins that make up innate immunity. Immunity is classified according to the way it responds to different pathogens or forms of cellular injury. As implied by its name, innate, or nonspecific, immunity responds to all pathogens or classes of pathogen in the same way. The innate immune system consists of antimicrobial proteins and certain cells. Note that innate immunity responds quickly and is the dominant response to pathogens for the first 12 hours after exposure. This occurs because the cells and proteins exist in the bloodstream, even in the absence of a stimulus (hence the term innate). The other type of immunity is adaptive immunity, the components of which respond to unique markers called antigens. Antigens are present on all cells, including our own cells, and most biological molecules, and they identify a cell or molecule as belonging to a specific group. Adaptive immunity is also known as specific immunity because its cells and proteins respond individually to only a specific, individual antigen. This is in contrast to innate immunity, which reacts in the same manner to every potential pathogen. The second, antibody-mediated immunity (also known as humoral immunity), is carried out by B cells and proteins they produce, called antibodies. Adaptive immunity responds more slowly than innate immunity because one must be exposed to a specific antigen for the response to be initiated.

Which lymphatic organ contains both red pulp and white pulp?

The spleen is the lymphatic organ that contains both red pulp and white pulp. Like all lymphoid organs, the spleen's internal structure consists of a network of reticular fibers made by reticular cells. Within the reticular tissue framework of the spleen we find two distinct histological regions: red pulp, which contains macrophages that destroy old erythrocytes, and white pulp, which filters pathogens from the blood and contains leukocytes.

Which lymph trunks receive lymph from the upper limbs?

The subclavian trunks receive lymph from the upper limbs. Lymph is collected in vessels appropriately called lymph-collecting vessels, which merge to form larger vessels, the lymph trunks. There are nine lymph trunks that drain the lymph from body regions. The intestinal trunk receives fat-containing lymph from the small lymphatic vessels in the small intestine. The jugular trunks receive lymph from the head and neck. The bronchomediastinal trunks receive lymph from the thoracic cavity.

The system that contains no organs or tissue of its own but instead consists of proteins and cells located in the blood is known as the __________ system.

The system that contains no organs or tissue of its own but instead consists of proteins and cells located in the blood is known as the immune system. The immune system is not technically a system according to the definition you have learned. This system contains no organs or tissues of its own and instead consists of cells and proteins located in the blood and the tissues of other systems, including the lymphatic system. The immune system works to defend the body against internal and external threats. The lymphatic system is a group of organs and tissues that not only works with the immune system but also participates in a number of functions such as fluid homeostasis.

What mucosa-associated lymphatic tissue (MALT) traps pathogens entering the nasal and oral cavities?

The tonsils are mucosa-associated lymphatic tissue (MALT) that trap pathogens entering the nasal and oral cavities. The epithelium lining the tonsils indents deeply in several locations, forming tonsillar crypts that trap bacteria and debris. The tonsils' location puts them into contact with a large number of potential pathogens. As a result, they commonly become inflamed, a condition known as tonsillitis. In the gastrointestinal tract, we find specialized clusters of MALT in three locations: tonsils, Peyer's patches, and the appendix. Peyer's patches, or aggregated lymphoid nodules, are located in the last portion of the small intestine (called the ileum). The appendix is located off the large intestine. Lymph nodes are small, vaguely bean-shaped clusters of lymphatic tissue located along lymphatic vessels throughout the body. Lymph nodes filter lymph.

Which of the following basic functions is not associated with the lymphatic system?

Transport of blood is not a basic function of the lymphatic system. The lymphatic system has three basic functions that are carried out by its vessels and organs. These functions include the following: Regulation of interstitial fluid volume. The net filtration pressure in blood capillaries favors filtration, meaning that water is lost from the plasma in the blood to the interstitial fluid (see chapter 18). The amount of fluid that is lost from the plasma is significant, measuring about 2-4 liters per day. This fluid must be returned to the circulation, or both the blood volume and blood pressure will drop too low to maintain homeostasis. The vessels that perform this function are the lymphatic vessels, which pick up excess interstitial fluid, transport it through the body, and deliver it back to the cardiovascular system. When the interstitial fluid exits the extracellular space and enters the lymphatic vessels, it is known as lymph (LIMF). This means that interstitial fluid and lymph are very similar in composition. Absorption of dietary fats. The breakdown products of fats in the diet are too large to pass through the tiny spaces between the endothelial cells of blood capillaries. However, they are able to enter small lymphatic vessels in the small intestine. The dietary fats travel through the lymphatic vessels and are delivered to the blood with lymph. Immune functions. The lymphatic system has an important role in the immune system. Lymphoid organs filter pathogens from the lymph and blood. They also house several types of leukocytes and play a part in their maturation.

Vaccinations involve exposure to an antigen to elicit __________.

Vaccinations involve exposure to an antigen to elicit a primary immune response. A vaccination, also known as an immunization, involves exposing an individual to an antigen to elicit a primary immune response and generate memory cells. Then if the individual is exposed to the antigen a second time, a secondary immune response will occur and symptoms will be minimal. Passive immunity is found when preformed antibodies are passed from one organism to another. The most common type of hypersensitivity disorder is type I, or immediate, hypersensitivity, which affects a tremendous number of people—about 20% of the U.S. population. This type of hypersensitivity is more commonly known as allergies, and the disorders that accompany it are called allergic disorders.

Which type of cell is most effective in attacking parasitic pathogens such as tapeworms?

When a person is infected with a parasite, eosinophils cover it and release the contents of their granules. The chemicals from the granules damage the parasite and either destroy it or make it easier for other immune cells to destroy. Eosinophils are phagocytes that can migrate from the blood to the tissues where they are needed. However, their phagocytic functions appear to be less critical than those of neutrophils, and they are primarily involved in responses to parasitic pathogens. Macrophages are activated by a variety of stimuli, including certain substances present on pathogens, chemicals secreted by damaged cells, and signals from the cells of adaptive immunity. Activated local macrophages are generally the first cells to respond to a cellular injury. The most predominant granulocyte is the neutrophil. Like macrophages, neutrophils are highly effective phagocytes. Neutrophils can ingest many types of cells but are particularly effective at destroying bacterial pathogens. Neutrophils generally reside in the blood and must be recruited to damaged tissues by chemical signals. A relatively rare cell that is generally nonphagocytic is the basophil. Basophils are granulocytes whose granules contain chemicals that mediate inflammation (inflammatory mediators). Basophils are located primarily in the blood, although a related type of cell called the mast cell is located in mucous membranes.