Chapter 7

Question 1

The lymphatic system consists of what two portions?

Answer 1

The lymphatic system consists of lymphatic vessels and the lymphatic organs.

Question 2

What are the four main functions of the lymphatic system?

Answer 2

It has four main functions:
* lymphatic capillaries absorb excess interstitial fluid and return it to the bloodstream;
* lacteals absorb fats in the form of lipoproteins from the small intestine and transport them to the bloodstream;
* the lymphatic system produces, maintains, and distributes lymphocytes;
* the lymphatic system defends the body against pathogens.

Question 3

Lymphatic vessels form a one-way system. What does this mean?

Answer 3

Lymphatic vessels form a one-way system of capillaries, vessels, and ducts. These vessels take lymph to cardiovascular veins in the shoulders. Lymphatic capillaries take up excess interstitial fluid, which is called lymph once inside the lymphatic vessels.

Question 4

Name the primary organs of the lymphatic system. What are their functions?

Answer 4

Red bone marrow is the site of stem cells that divide and produce blood cells. B cells mature in the bone marrow, but T cells mature in the thymus, located in the thoracic cavity. The thymus also produces thymic hormones and is absolutely critical to immunity.

Question 5

Name the secondary organs of the lymphatic system. What are their functions?

Answer 5

The spleen contains white pulp and red pulp. The white pulp contains a concentration of lymphocytes, while the red pulp is involved in filtering the blood. In the case of an infection or a blow, the spleen can burst. Lymph nodes occur along lymphatic vessels. Each node is packed with lymphocytes. Lymph is filtered through the lymph nodes. Lymphocytes react with pathogens present in the filtered blood and lymph. They fight infections and attack cancer cells. The tonsils are patches of lymphatic tissue located around the pharynx.

Question 6

What is the difference between innate immune defenses and adaptive defenses?

Answer 6

Immunity involves innate and adaptive defenses. Innate defenses protect against any pathogen, while adaptive defenses are effective against a particular infectious agent.

Question 7

Describe and give examples of the following innate immune defenses.
a) physical barriers
b) chemical barriers

Answer 7

Intact skin and mucous membranes are very effective physical barriers that prevent infection.

Example: Ciliated cells that line the upper respiratory tract sweep mucus and trapped particles up into the throat, where they can be swallowed or coughed out.

Chemical barriers include:

• secretions of the sebaceous glands of the skin;
• the antibacterial enzyme lysozyme in perspiration, saliva, and tears;
• the acid pH of the stomach and vagina.
  All of these can inhibit the growth of, or kill, bacteria.

Question 8

What is the function of normal flora in the body? What problems arise from chronic use of antibiotics?

Answer 8

A significant chemical barrier is created by the normal flora, microbes that normally reside in certain areas of the body. These normal flora prevent potential pathogens from taking up residence. Chronic antibiotic use can harm the body by killing normal flora.

Question 9

Regarding the inflammatory response, what are the functions or significance of the following?
a) histamine
b) rise in temperature
c) swelling
d) cytokines

Answer 9

Redness, heat, swelling, and pain characterize the inflammatory reaction.
* The release of histamine from damaged tissue cells and mast cells brings about redness and swelling.
* A rise in temperature increases phagocytosis by neutrophils and macrophages.
* The swollen area stimulates free nerve endings, causing the sensation of pain.
* Chemical mediators called cytokines attract white blood cells to the area. Among them, monocytes become macrophages, which attract lymphocytes, part of the specific arm of the immune system.

Question 10

Regarding protective proteins, briefly describe the complement system and its functions.

Answer 10

The complement system, which includes various plasma proteins, assists innate immunity. It amplifies the inflammatory reaction by attracting phagocytes and promoting phagocytosis.

Some complement proteins form pores in the surface of bacteria and thereby cause them to burst.

Question 11

What are interferons? What is their function?

Answer 11

Interferons are proteins produced by virus-infected cells that help noninfected cells prepare for possible viral attack. Interferons are used to treat certain viral infections.

Question 12

How do adaptive defenses work?

Answer 12

Adaptive defenses respond to antigens, which are molecules the immune system recognizes as foreign to the body. Adaptive defenses primarily depend on the action of lymphocytes, which differentiate as either B cells or T cells.

Question 13

What is the clonal selection model?

Answer 13

The receptor on a B cell is called a B-cell receptor. The clonal selection model states that an antigen selects, then binds to, the B-cell receptor of only one type of B cell. Then this B cell produces multiple copies (clones) of itself.

Question 14

What are plasma cells? From where do they come? What is their function? What is apoptosis?

Answer 14

Plasma cells secrete antibodies and eventually undergo apoptosis.

Question 15

What are memory B cells? From where do they come? What is their function?

Answer 15

Memory B cells remain in the body and produce antibodies if the same antigen enters the body at a later date.

Question 16

Briefly describe the structure of an antibody. How do they interact with antigens?

Answer 16

The basic unit that composes antibody molecules is a Y-shaped protein molecule with two arms. Each arm has a “heavy” (long) and a “light” (short) polypeptide chain. These chains contain variable and constant regions. In the variable regions, the antigen combines with the antibody in a lock-and-key manner.

Question 17

What are the five classes of antibodies? Which one is found in secretions such as saliva and tears? Which one is associated with allergies?

Answer 17

There are five different classes of circulating antibodies: IgG, IgM, IgA, IgD, and IgE. They differ from each other as outlined in Table 7.1 on page 138 of the text.

Question 18

What are monoclonal antibodies?

Answer 18

Every plasma cell derived from the same B cell secretes antibodies against a specific antigen. These are monoclonal antibodies. Monoclonal antibodies can be made outside the body, and they are being used to diagnose certain conditions or infections, deliver drugs, and treat cancers.

Question 19

What are T cells? How do they recognize a foreign antigen? What are the functions of APC and MHC?

Answer 19

T cells directly attack diseased cells and cancer cells. Other T cells release cytokines that stimulate both innate and adaptive defenses.

How T Cells Recognize an Antigen
Like B cells, each T cell bears a specific receptor. However, for a T cell to recognize an antigen, the antigen must be presented by an antigen-presenting cell (APC), such as a macrophage. A piece of a phagocytized pathogen is displayed in the groove of a major histocompatibility complex (MHC) protein on the APC’s surface. The two classes of MHC proteins are called MHC I and MHC II. Human MHC II proteins are called human leukocyte antigens (HLAs). MHC antigens are self proteins that mark the cell as belonging to a particular individual. The T cell can compare the antigen and self protein side by side in the plasma membrane of the antigen-presenting cell and destroy cells carrying foreign antigens.

Question 20

Define clonal expansion. What are the functions of cytotoxic T cells and helper T cells?

Answer 20

T cells have specific TCRs (T-cell receptors). An activated T cell undergoes clonal expansion producing many copies of itself. The two main types of T cells are cytotoxic and helper T cells. Cytotoxic T cells are responsible for cell-mediated immunity, causing virus-infected cells or tumor cells to undergo apoptosis and die. Helper T cells secrete cytokines, which enhance immune cell responses.

Question 21

What type of T cells does HIV attack? What are opportunistic infections?

Answer 21

HIV, the virus that causes AIDS, infects helper T cells, making HIV-infected individuals susceptible to opportunistic infections.

Question 22

What is the function of memory T cells?

Answer 22

Memory T cells remain in the body to initiate an immune reaction to a previous antigen in the case of another exposure.

Question 23

What is acquired immunity? Compare active immunity with passive immunity. How might a person achieve active immunity? How might a person achieve passive immunity?

Answer 23

Active Immunity
Active immunity sometimes develops naturally after a person is infected with a pathogen. Active immunity can also be induced. Vaccines are available to induce long-lived active immunity. After exposure to a vaccine, antibodies are present in the body. Measuring the antibody titer, or the amount of antibody present in a sample of plasma, will show that the secondary response (booster) is higher than the primary response. Active immunity is long-lived because there are memory B cells and memory T cells in the body.

Passive Immunity
Passive immunity occurs when an individual is given antibodies from an outside source to fight a disease (e.g., nursing passes antibodies from mother to child). Passive immunity is temporary.

Question 24

What do cytokines have to do with immunity?

Answer 24

Cytokines, including interferons, are signaling molecules produced by T lymphocytes, macrophages, and other cells that are used in an attempt to promote the body’s ability to recover from cancer. Interferons and interleukins have been used as immunotherapeutic drugs.
Interleukin antagonists are used to prevent transplant rejection.

Question 25

What are allergies? What is anaphylactic shock?

Answer 25

Allergic responses occur when the immune system reacts vigorously to substances not normally recognized as foreign. Immediate allergic responses are due to the activity of antibodies. Symptoms can vary from mild, coldlike symptoms to anaphylactic shock, which is an immediate allergic response that occurs because an allergen has entered the bloodstream. IgE appears to be responsible. Delayed allergic responses, such as contact dermatitis, are due to the activity of T cells. The skin test for TB is a classic example of a delayed allergic response.

Question 26

What occurs during transplant rejection? What is xenotransplantation?

Answer 26

Transplant rejection occurs when cytotoxic T cells bring about the destruction of foreign tissue in the body. Immunosuppressive drugs act by inhibiting the response of T cells to cytokines. Xenotransplantation is the use of animal organs instead of human organs in human transplant patients. Genetic engineering can make these organs less antigenic to humans. Laboratory-grown urinary bladders have been successfully used in human transplantations.

Question 27

What do SCID and AIDS have to do with immunity problems?

Answer 27

In individuals with severe combined immunodeficiency disease (SCID), both antibody- and cell-mediated immunity are lacking or severely reduced. AIDS is an example of an acquired immune deficiency.

Question 28

What are some examples of autoimmune diseases?

Answer 28

In individuals with severe combined immunodeficiency disease (SCID), both antibody- and cell-mediated immunity are lacking or severely reduced. AIDS is an example of an acquired immune deficiency. An autoimmune disease occurs when T cells or antibodies mistakenly attack the body’s own cells. In rheumatoid arthritis, the joints are affected. A person with systemic lupus erythematosus has various symptoms eventually leading to death from kidney damage. In myasthenia gravis, neuromuscular junctions do not work properly. In multiple sclerosis, the myelin sheath of the nerve fibers is broken down.