BIOL 320 Chapter 22 Textbook

Describe the three functions of the lymphatic system.

1. Fluid balance — lymphatic capillaries collect lymph, which passes through lymphatic vessels and back to the blood

2. Lipid absorption — lacteals absorb lipids and other substances from the digestive tract; lymph passing through these vessels, called chyle, appears white because of its lipid content

3. Defense — microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by the spleen; the lymphatic system fights infections, and filters blood and lymph to remove microorganisms

Name the parts of the lymphatic system.

The lymphatic system includes lymph, lymphatic vessels, as well as lymphatic organs and lymphatic tissues.

How is lymph formed?

Fluid from blood capillaries moves into tissues and from tissues into lymphatic capillaries to form lymph.

Describe the structure of a lymphatic capillary. Why is it easy for fluid and other substances to enter a lymphatic capillary?

Lymphatic capillaries lack a basement membrane. Also, the cells of the simple squamous endothelium slightly overlap and are loosely attached to one another. The overlapping cells of the lymphatic capillary endothelium function as a series of one-way valves that allow fluid to enter the capillary but prevent it from passing back into the interstitial spaces.

They are far more permeable than blood capillaries, so nothing in the interstitial fluid is excluded from entering the lymphatic capillaries.

What is the function of valves in lymphatic vessels? Name three mechanisms responsible for moving lymph through the lymphatic vessels.

The one-way valves allow fluid to enter the capillary but prevent it from passing back into the interstitial spaces.

1. Contraction of lymphatic vessels — lymph moves into a chamber, smooth muscle in the chamber wall contracts, and lymph moves into the next chamber

2. Contraction of skeletal muscles — when surrounding skeletal muscles contract, lymphatic vessels are compressed, causing lymph to move

3. Thoracic pressure changes — during inspiration, pressure in the thoracic cavity decreases, lymphatic vessels expand, and lymph flows into them; during expiration, pressure in the thoracic cavity increases, and lymphatic vessels are compressed, causing lymph to move

What are lymphatic trunks and ducts? Name the largest lymphatic vessel. What is the cisterna chyli?

Lymphatic vessels converge to form larger vessels called lymphatic trunks, each of which drains lymph from a major portion of the body. The lymphatic trunks either connect to large veins in the thorax or join to yet larger vessels called lymphatic ducts, which then connect to the large veins.

The largest lymphatic vessel is the thoracic duct.

In a small proportion of cases, the lymphatic trunks form a sac called the cisterna chyli.

What areas of the body are drained by the right lymphatic trunks, left lymphatic trunks, and thoracic duct?

Right lymphatic trunks — drains lymph from the right side of the head, upper-right limb, and right thorax

Thoracic duct — drains lymph from the right side of the body inferior to the thorax and the entire left side of the body

What are the primary lymphatic organs? What are the secondary lymphatic organs and tissues?

The primary lymphatic organs are the red bone marrow and the thymus.

The secondary lymphatic organs and tissues include lymphatic nodules, including the tonsils, and diffuse lymphatic tissue, as well as lymph nodes and spleen.

What is mucosa-associated lymphoid tissue (MALT)? In what way is the location of MALT beneficial?

Nonencapsulated lymphatic tissues that are associated with mucous membranes that line the digestive, respiratory, urinary, and reproductive tracts.

MALT is well-positioned to intercept microorganisms and other foreign materials as they enter the body.

Distinguish among lymphatic tissue, lymphatic nodules, lymphatic follicles, and Peyer patches.

Tissue — contains dispersed lymphocytes, macrophages, and other cells; has no clear boundary and blends with surrounding tissues, and located deep to mucous membranes, around lymphatic nodules, and within the lymph nodes and spleen.

Nodules — denser arrangements of lymphatic tissue organized into compact, somewhat spherical structures ranging in size; they are numerous in the loose connective tissue of the digestive, respiratory, urinary, and reproductive systems

Follicles — lymphatic nodules that are found within lymph nodes and the spleen

Peyer patches — large collections of lymphatic nodules; aggregations of lymphatic nodules in the distal half of the small intestine

Describe the structure, function, and location of the tonsils.

Large groups of lymphatic nodules and diffuse lymphatic tissue located deep to the mucous membranes within the pharynx; they protect against bacteria and other potentially harmful material entering the pharynx from the nasal or oral cavity

• Palatine — on each side of the junction between the oral cavity and the pharynx

• Pharyngeal — near the junction between the nasal cavity and the pharynx

• Lingual — posterior surface of the tongue

Where are lymph nodes found? Describe the parts of a lymph node, and explain how lymph flows through a lymph node.

They are distributed along the course of the lymphatic vessels.

A dense connective capsule surrounds each lymph node. Extensions of the capsule, called trabeculae, form a skeleton in the lymph node. Reticular fibers extend from the capsule and trabeculae to form a fibrous network. The reticular fibers can also extend across open spaces to form lymphatic sinuses.

Lymphatic tissue and sinuses within the lymph node are arranged into two somewhat distinct layers, an outer cortex and inner medulla. The cortex consists of a subscapular sinus, beneath the capsule, and cortical sinuses, which are separated by diffuse lymphatic tissue, trabeculae, and lymphatic nodules. The inner medulla is organized into branching, irregular strands of diffuse lymphatic tissue, called the medullary cords, separated by medullary sinuses.

Describe the function of lymph nodes. What is a germinal center?

Lymph nodes are the only structures that filter lymph.

Areas of rapid lymphocyte division are called germinal centers. Proliferation is stimulated when microorganisms and other foreign substances are found in the lymph.

Where is the spleen located? Describe the structure of the spleen.

It is located on the left, superior part of the abdominal cavity.

The spleen has an outer capsule of dense irregular connective tissue and a small amount of smooth muscle. Bundles of connective tissue fibers from the capsule form trabeculae, which extend into the organ, subdividing it into compartments. Arteries, veins, and lymphatic vessels extend through the trabeculae to supply the compartments, which are filled with white pulp and red pulp.

Explain how the spleen performs its three main functions.

1. Destroying defective red blood cells — the cells can rupture as they pass slowly through the meshwork of the splenic cords or the intercellular slits of the venous sinus walls

2. Detecting and responding to foreign substances in the blood — foreign substances in the blood passing through the spleen can stimulate an immune response because of the presence of specialized lymphocytes in the white pulp

3. Acting as a blood reservoir — the splenic cords of the spleen are a limited reservoir for blood

Where is the thymus located? Describe its structure and function

Located in the superior mediastinum, the partition dividing the thoracic cavity into the left and right parts.

Each lobe of the thymus is surrounded by a thin connective tissue capsule. Trabeculae extend from the capsule into the substance of the gland, dividing it into lobules. The framework of the thymic tissue consists of epithelial cells. Their processes are joined by desmosomes, and the cells form small compartments filled with lymphocytes. It has a cortex and medulla. The medulla contains rounded epithelial structures called thymic corpuscles.

The thymus is the site for maturation of T cells. Thymosin, a hormone secreted by the thymus, is important in the T-cell maturation process.

What is immunity?

Immunity is the ability to resist damage from foreign substances, such as microorganisms; harmful chemicals, such as toxins released by microorganisms; and internal threats, such as cancer cells

Why do specificity and memory relate to adaptive immunity but not to innate immunity?

Specificity is the ability of adaptive immunity to recognize a particular substance. Innate immunity can act against bacteria in general, whereas adaptive immunity can distinguish among various kinds of bacteria.

Memory is the ability of adaptive immunity to “remember” previous encounters with a particular substance. As a result, the response is faster, stronger, and longer lasting.

What are the differences between innate immunity and adaptive immunity?

In innate immunity, the body recognizes and destroys certain foreign substances, but the response to them is the same each time the body is exposed.

In adaptive immunity, the body recognizes and destroys foreign substances, but the response to them is faster and stronger than the first time they were encountered since the body remembers how to best handle them.

List the three components of innate immunity.

(1) Physical barriers that prevent microbes from entering the body or physically remove them from body surfaces; (2) chemical mediators that act directly against microorganisms or activate other mechanisms, leading to the destruction of the microorganisms; and (3) cells involved in phagocytosis and the production of chemicals that participate in the immune response

Name two physical barriers that prevent microorganisms from entering the body. In what ways are microorganisms removed from body surfaces?

The skin and mucous membranes.

Substances can be washed from the eyes by tears, from the mouth by saliva, and from the urinary tract by urine. In the respiratory tract, ciliated mucous membranes sweep microbes trapped in the mucous to the back of the throat, where they are swallowed. Coughing and sneezing also remove microorganisms from the respiratory tract.

What roles do cytokines play as chemical mediators?

Cytokines are proteins or peptides secreted by cells that bind to receptors on cell surfaces, stimulating a response. They regulate the intensity and duration of immune responses and stimulate the proliferation and differentiation of cells.

What is complement? In what two ways is it activated? How does complement provide protection?

Complement is a group of plasma proteins that increase vascular permeability, stimulate the release of histamine, activate kinins, lyse cells, promote phagocytosis, and attract neutrophils, monocytes, macrophages, and eosinophils.

They can form a membrane attack complex (MAC) that produces a channel through a cell’s plasma membrane.

They can also enhance other aspects of immunity. They act as the chemical signals attracting different immune system cells to the sites of injury or infection. They can also attach to the surface of bacterial cells and stimulate macrophages to phagocytize the bacteria.

What are interferons? How do they protect against viral infection?

Interferons are proteins that protect the body against viral infection and perhaps some forms of cancer.

Viruses and other substances can stimulate infected cells to produce interferons, which neither protect the cell that produces them nor act directly against viruses. Instead, interferons bind to the surface of neighboring cells and stimulate them to produce antiviral proteins.

Define chemotactic factor, chemotaxis, and phagocytosis.

Chemotactic factors are signals that attract white blood cells. They can include parts of microbes as well as chemicals released by cells of the body, including complement, leukotrienes, kinins, and histamine.

Chemotaxis is when white blood cells move from areas of lower chemotactic factor concentration to areas of higher concentration by detecting small differences in chemotactic factor concentration.

Phagocytosis is the endocytosis and destruction of particles by cells called phagocytes.

What are functions of neutrophils and macrophages? What is pus?

Neutrophils — phagocytosis and inflammation; usually the first cell to leave the blood and enter infected tissues

Macrophages — most effective phagocyte; important in later stages of infection and in tissue repair; involved in the activation of B cells and T cells

Pus — an accumulation of dead neutrophils, dead microorganisms, debris from dead tissue, and fluid.

What effects are produced by the chemicals released from basophils, mast cells, and eosinophils?

Their chemicals produce an inflammatory response or activate other mechanisms, such as smooth muscle contraction in the lungs

How do NK cells function?

Natural Killer cells recognize classes of cells rather than specific tumor cells or cells infected by a specific virus; they use a variety of methods to kill their target cells, including releasing chemicals that damage plasma membranes and cause the cells to lyse.

What kinds of tissue damage can result in inflammation?

Trauma, burns, chemicals, and infections can damage tissues and lead to inflammation.

Describe the events that take place during an inflammatory response.

1. Damage stimulates the release of activation of chemical mediators, such as histamine, complement, kinins, and eicosanoids

2. Chemical mediators cause vasodilation to increase blood flow and bring phagocytes and other white blood cells to the area

3. Increased vascular permeability allows fibrinogen and complement to enter the tissue from the blood → redness and swelling

4. WBCs increase in number at the injury site as they move from the blood into the tissue by diapedesis

5. Chemical mediators increase at the injury site as well; fibrinogen is converted to fibrin, which walls off the infected area, preventing the spread of infection

6. The process of releasing chemical mediators and attracting phagocytes and other WBCs continues until bacteria are destroyed

7. Phagocytes remove microorganisms and dead tissue, and the damaged tissues are repaired

What are symptoms of local inflammation and of systemic inflammation?

Local inflammation — confined to a specific area of the body; redness, heat, swelling due to increased blood flow and increased vascular permeability, and pain caused by swelling and chemical mediators acting on pain receptors → loss of function

Systemic inflammation — red bone marrow produces and releases large numbers of neutrophils to promote phagocytosis, fever is induced by the release of pyrogens, and large amounts of fluid can be lost from the blood into tissues in severe cases

Define antigen. Distinguish between a foreign antigen and a self-antigen.

Antigens are substances that stimulate adaptive immunity.

Foreign antigens are not produced from the body but are introduced from outside it.

Self-antigens are molecules the body produces to stimulate an adaptive immune system response.

What are allergic reactions and autoimmune diseases?

An allergic reaction is an overreaction of the immune system in some people.

An autoimmune disease can develop when self-antigens stimulate unwanted tissue destruction.

What are the two types of adaptive immunity?

Antibody-mediated immunity and cell-mediated immunity.

Define antigenic determinant and antigen receptor. How are they related to each other?

Antigenic determinants, or epitopes, are specific regions of the antigen.

Antigen receptors are identical proteins on the surfaces of the lymphocytes of a given clone.

The antigen receptors combine with a specific antigenic determinant of a given antigen. Any given antigenic determinant can combine only with a specific antigen receptor.

What types of cells display MHC class I and class II antigen complexes, and what happens as a result?

MHC class I molecules are found on nucleated cells and display endogenous antigens on the cell’s plasma membrane. This complex functions as a signal, or “red flag”, that prompts the immune system to destroy the displaying cell.

MHC class II molecules display exogenous antigens and are found on phagocytic cells called antigen-presenting cells. Antigen-presenting cells engulf substances encountered in the extracellular environment and process them within the cytoplasm.

What types of antigens are displayed by MHC class I molecules? By MHC class II molecules?

MHC class I molecules display endogenous antigens.

MHC class II molecules display exogenous antigens.

What does MHC-restricted mean?

MHC-restricted is when both the antigen and the individual organism’s own MHC molecule are required. MHC class I/antigen complex falls under this category.

What are lymphocyte clones? What is the difference between positive and negative lymphocyte selection?

Lymphocyte clones are identical lymphocytes that result from clonal selection.

A positive selection process results in the survival of pre-B and pre-T cells capable of an immune response. Cells that are incapable of an immune response die.

A negative selection process eliminates or suppresses clones acting against self-antigens, thereby preventing the destruction of a person’s own cells. This occurs mostly during prenatal development.

What is costimulation? State two ways it can happen.

Costimulation is the use of additional signals to produce a response from a B cell or a T cell.

It can be accomplished by cytokines released from cells, as well as molecules attached to the surface of cells.

Why are helper T cells sometimes called CD4 or T4 cells? Why are cytotoxic T cells sometimes called CD8 or T8 cells?

Helper T cells have a glycoprotein called CD4, which helps connect helper T cells to the macrophage by binding to MHC class II molecules.

Cytotoxic T cells are sometimes called CD8 cells or T8 cells because they have a glycoprotein called CD8, which helps connect cytotoxic T cells to cells displaying MHC class I molecules.

Describe how antigen-presenting cells stimulate an increase in the number of helper T cells. Why is this important?

Before exposure to an antigen, the number of lymphocytes in a clone is too small to produce an effective response against the antigen. Exposure to an antigen results in an increase in lymphocyte number.

This is important because the increased number of helper T cells responding to the antigen can find and stimulate B cells or cytotoxic T cells.

Describe how helper T cells stimulate an increase in the number of B cells or T cells. Why is this important?

Helper T cells responding to the antigen can find and stimulate B cells or cytotoxic T cells. Subsequently, the number of B cells or cytotoxic T cells increases.

This is important because the B cells and cytotoxic T cells are responsible for the immune response that destroys the antigen.

What is tolerance? Explain three ways it is accomplished.

Tolerance is a state of unresponsiveness of lymphocytes to a specific antigen.

1. Deletion of self-reactive lymphocytes — because immature lymphocytes are exposed to self-antigens, this process eliminates self-reactive lymphocytes

2. Prevention of the activation of lymphocytes — preventing either the MHC/antigen complex binding with an antigen receptor or costimulation

3. Activation of regulatory T cells — regulatory T cells control the activities of both antibody-mediated immunity and cell-mediated immunity

What type of lymphocyte is responsible for antibody-mediated immunity? What are the functions of antibody-mediated immunity?

Exposure of the body to an antigen can lead to the activation of B cells and to the production of antibodies

Destroying the antigen and causing immediate hypersensitivity reactions.

What are the functions of the variable and constant regions of an antibody?

The variable region is formed by the ends of the combined heavy and light chains. This is the part of the antibody that combines with the antigenic determinant of the antigen.

The constant region is responsible for the activities of antibodies, such as the ability to activate complement or to attach the antibody to cells such as macrophages, basophils, mast cells, and eosinophils.

List the five classes of antibodies, and state their functions.

IgG — activates complement and promotes phagocytosis; can cross placenta and provide immune protection to the fetus and newborn; responsible for Rh reactions

IgM — activates complement and acts as an antigen-binding receptor on the surface of B cells; often the first antibody produced in response to an antigen; responsible for transfusion reactions in the ABO blood system

IgA — secreted into saliva, tears, and onto mucous membranes to provide protection on body surfaces; found in colostrum and milk to provide immune protection to newborns

IgE — binds to mast cells and basophils and stimulates the inflammatory response

IgD — functions as antigen-binding receptors on B cells

Describe the 5 different ways that antibodies participate in destroying antigens.

1. The antibody can bind to the antigenic determinant and interfere with the antigen’s ability to function

2. The antibody can combine with an antigenic determinant on two different antigens, rendering the antigens ineffective

3. It can combine with an antigen through the variable region, and the constant region can activate the complement cascade through the classical pathway

4. Antibodies can initiate an inflammatory response

5. Opsonins are substances that make an antigen more susceptible to phagocytosis

What are plasma cells and memory B cells, and how to they function?

Plasma cells are derived from B cells and produce antibodies.

Memory B cells are daughter cells that do not differentiate to become plasma cells and instead reduce in size. They may become active in future encounters with the same antigen.

What are primary and secondary antibody responses? Why doesn’t the primary response prevent illness, whereas the secondary response does?

The first exposure of a B cell to an antigen for which it is specific causes the primary response.

The secondary response, or memory response, occurs when the immune system is exposed to an antigen against which it has already produced a primary response.

The secondary response includes the formation of new memory B cells, which protect against additional exposures to the antigen.

What type of lymphocyte is responsible for cell-mediated immunity? What does cell-mediated immunity involve?

T cells respond to endogenous antigens, and cytotoxic T cells can identify abnormal or infected cells of the body. Cell-mediated immunity involves delayed hypersensitivity reactions and the control of tumors.

How do cytoplasmic microorganisms stimulate cytotoxic T cells? What role do helper T cells play in this process?

Virally infected cells have viral antigens, tumor cells have tumor antigens, and tissue transplants have foreign antigens on their surfaces that can stimulate cytotoxic T-cell activity.

Without helper T cells, cytotoxic T-cell and B-cell activation is impaired, and adaptive immunity is impaired.

State the two main responses of cytotoxic T cells.

Cytotoxic T cells respond to endogenous antigens by inducing apoptosis and cytokine proliferation.

How is long-lasting immunity achieved in cell-mediated immunity?

The secondary response includes the formation of new memory B cells, which protect against additional exposures to the antigen. Memory B cells persist for many years— for life in some cases.

Distinguish between active and passive immunity.

Active immunity results when an individual is exposed to an antigen (either naturally or artificially), and the response of the individual’s immune system is the cause of the immunity.

Passive immunity occurs when another person or an animal develops immunity, and the immunity is transferred to a non-immune individual.

State four general ways of acquiring adaptive immunity. Which two provide the longest-lasting immunity?

1. active natural

2. active artificial

3. passive natural

4. passive artificial

Active immunity can persist for a few weeks to a lifetime. Passive immunity is not long-lasting.

What type of immunity occurs when a child is given the chickenpox vaccine? What type of immunity does a nursing baby contain?

Vaccination is a type of active artificial immunity.

A nursing baby contains passive natural immunity.

What type of immunity occurs when a person is given the rabies antisera? What type of immunity occurs if a person had the chickenpox as a child?

A person who was given the rabies antisera has passive artificial immunity.

If a person had the chickenpox as a child, they have active natural immunity.

What is immunotherapy? Give some examples.

Immunotherapy treats disease by altering immune system function or by directly attacking harmful cells.

For example, administering cytokines or other agents can promote inflammation and activate immune cells, which can help destroy tumor cells.