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CHAPTER 13: LYMPHATIC AND IMMUNE SYSTEMS
LECTURE OUTLINE
13.1 The Lymphatic System
The lymphatic system consists of lymphatic vessels and the lymphoid organs. It is closely
associated with the cardiovascular system.
Lymphatic Vessels
Lymphatic vessels form a one-way system that begins with lymphatic capillaries that take
up excess tissue fluid. The fluid inside lymphatic vessels is called lymph.
Lymphoid Organs
The primary lymphoid organs are red bone marrow and the thymus gland. The secondary
lymphoid organs are the spleen and lymph nodes.
Primary Lymphoid Organs
Red bone marrow is the site of stem cells that are ever capable of dividing and
producing blood cells. The thymus gland is largest in children and shrinks as we
get older. Immature T cells migrate from the bone marrow through the blood
stream to the thymus, where they mature.
Secondary Lymphoid Organs
Lymphocytes migrate to the secondary lymphoid organs. Here they encounter
foreign molecules or cells, after which they proliferate and become
activated. The spleen filters the blood. Lymph nodes are packed with B and T
cells.
13.2 Innate and Acquired Immunity
Immunity is the body’s capability of removing or killing foreign substances, pathogens, and
cancer cells. Mechanisms of innate immunity are fully functional without previous exposure to
these substances, while acquired immunity is enhanced by exposure to specific antigens. An
antigen is any molecule that stimulates an immune response.
Innate Immunity
The four types of innate immunity include physical and chemical barriers, inflammation,
phagocytes and natural killer cells, and protective proteins.
Physical and Chemical Barriers
Skin and mucous membranes lining the respiratory, digestive, and urinary tracts
serve as mechanical barriers to entry of pathogens. The secretions of oil glands
in the skin contain chemicals that weaken or kill certain bacteria on the skin. The
stomach has an acid pH, which kills many types of bacteria or inhibits their
growth.
Inflammation
An inflamed area has four signs: redness, heat, swelling, and pain.
Phagocytes and Natural Killer Cells
Neutrophils and macrophages migrate to the area of tissue damage where they
engulf pathogens. Natural killer cells kill abnormal cells by cell-to-cell contact.
Protective Proteins
The complement system is composed of a number of blood plasma proteins that
form a membrane attack complex to destroy invading bacteria. Interferons are
proteins produced by virus-infected cells as a warning to noninfected cells.
Acquired Immunity
In acquired immunity, the body is able to distinguish “self” from “nonself”. Acquired
defenses primarily depend on the action of lymphocytes, which differentiate as either
B cells or T cells.
B Cells and Antibody-Mediated Immunity
When a B cell is activated by binding to a specific antigen, it is activated and
makes many copies of itself. Activated B cells become plasma cells that produce
antibodies.
Structure of an Antibody
Antibodies are also called immunoglobulins. They are typically
Y-shaped molecules with two binding sites for foreign antigens.
Types of Antibodies
There are five major classes of antibodies: IgG, IgM, IgA, IgD, and IgE.
T Cells and Cell-Mediated Immunity
T cells can only recognize an antigen when it is displayed to them by an antigenpresenting cell in conjunction with an MHC (major histocompatibility complex)
protein. There are two major types of T cells: helper T cells and cytotoxic T
cells. Helper T cells secrete various cytokines while cytotoxic T cells destroy the
target cell.
13.3 Active vs. Passive Immunity
In active immunity, the individual alone produces an immune response against an antigen; in
passive immunity, the individual is given prepared antibodies or cells via an injection.
Active Immunity
Active immunity usually develops naturally after a person is infected with a pathogen.
Immunization involves the use of vaccines to initiate immunity.
Passive Immunity
Passive immunity occurs when an individual is given prepared antibodies or immune
cells to combat a disease. This occurs naturally from mother to fetus.
Immune Therapies
Cytokines and Immunity
Cytokines are chemical messengers produced by T cells, macrophages, and other
cells. They regulate white blood cell formation and/or function. They may be
used as immunotherapeutic drugs in the future.
Monoclonal Antibodies
Monoclonal antibodies can be produced in vitro. Currently these are being used
for quick and certain diagnosis of various conditions. These may be used to treat
cancer.
13.4 Adverse Effects of Immune Responses
Allergies
Allergies are hypersensitivities to substances, such as pollen, food, or animal hair, that
ordinarily would do no harm to the body. An immediate allergic response can occur
within seconds of contact with the antigen and may result in anaphylactic shock, a lifethreatening problem. A delayed allergic response is initiated by memory T cells.
Blood-Type Reactions
The ABO blood system is the most important of the blood typing systems.
ABO System
The presence or absence of type A and type B antigens on red blood cells
determine a person’s blood type. Transfusion with the wrong type blood can be
fatal.
Rh System
Another important antigen in matching blood types is the Rh factor. A mismatch
can be fatal.
Tissue Rejection
The immune system is responsible for rejection of transplanted tissue. Organ rejection
can be controlled by administering immunosuppressive drugs.
13.5 Disorders of the Immune System
When a person has an autoimmune disease, cytotoxic T cells or antibodies mistakenly attack the
body’s own cells. Examples include myasthenia gravis, multiple sclerosis, and systemic lupus
erythematosus. In an immune deficiency, the immune system is unable to protect the body
against disease. Examples include AIDS and severe combined immunodeficiency disease
(SCID).