The Body Defenses - Chapter 12

Immunity is the body’s ability to resist or eliminate potentially harmful foreign materials or abnormal cells.

The immune system plays a key role in this. It:

defends against invading pathogens,

removes "worn-out" cells

identifies and destroys abnormal or mutant cells.

leads to allergies or autoimmune responses in the face of foreign antigens.

The primary pathogens are bacteria and viruses.

¬ Introduction

A. The lymphatic system is comprised of a network of:

1. Vessels that transport body fluids that closely follow the circulatory system

2. The cells and chemicals in those vessels

3. The organs and glands that produce them.

Three functions of the lymphatic system are:

1. Defense against disease.

2. Collection and transport of excess fluid from interstitial spaces

3. Transport of fats to the circulatory system through vessels called lacteals.


Lymph Formation and Function

Increasing pressure forces blood plasma into the interstitial space, and some of the fluid into lymphatic capillaries.


The same forces that move blood in veins (skeletal muscle contraction, breathing movements, and contraction of smooth muscle in the walls of lymphatic trunks) are the forces that propel lymph through lymphatic vessels.

The lymphatic system also has one-way valves that keep back-flow from occurring

A condition that interferes with the flow in lymph will result in edema.

¬ Lymphatic Pathways

Lymphatic pathways start as lymphatic capillaries that merge to form larger vessels that empty into the circulatory system.

¬ Lymph Nodes

A. Lymph nodes, which contain lymphocytes and macrophages, are located along lymphatic pathways.

B. Functions of a Lymph Node

1. These contain both lymphocytes and macrophages which remove bacteria and clean the lymph as it flows through the node.

Lymphatic Nodules

Concentrations of lymphatic tissue not surrounded by a capsule scattered throughout connective tissue of mucous membranes

Peyer’s patches in the ileum of the small intestine

Tonsils form ring at top of throat

adenoids (pharyngeal tonsil)

palatine tonsils (on each side wall)

lingual tonsil in the back of the tongue



Caused by mutation or abnormal activation of cellular genes that control cell growth and cells mitosis.

Most mutations eliminated by immune system

Characteristic of malignant tumors

Spread of disease from one organ to another

cancer cells travel via blood or lymphatic system

cells establish new tumors where lodge

Secondary tumor sites can be predicted by direction of lymphatic flow from primary site

Cancerous lymph nodes are firm, enlarged and nontender -- infected lymph nodes are not firm and are very tender


Cancers of lymphatic organs, especially lymph nodes

No known cause

Hodgkin’s disease

Non-Hodgkin’s lymphoma

Good survival rate with treatment

Chemotherapy, radiation therapy, bone marrow transplant

¬ Other Lymphatic Organs: Thymus and Spleen

A. The functions of the thymus and spleen are similar to those of lymph nodes.

B. Thymus

1. Contains lymphocytes, some of which mature into T lymphocytes (T cells) that leave the thymus to provide immunity.

C. Spleen

1. The spleen lies in the upper left abdominal cavity and is the body’s largest lymphatic organ.

2. The spleen resembles a large lymph node except that it contains blood instead of lymph.

3. The spleen filters the blood and removes damaged blood cells and bacteria.

¬ PART II: Body Defenses Against Infection

A. Diseases-causing agents, also called pathogens, can produce infections within the body.

B. The body has two lines of defense against pathogens: nonspecific defenses (innate or inborn) that guard against any pathogen, and specific defenses (acquired immunity) that mount a response against a very specific target.

  • 1. Specific defenses are carried out by lymphocytes that recognize a specific invader.
  • 2. Nonspecific and specific defenses work together to protect the body against infection.
  • ¬ Nonspecific Defenses

    A. Present at Birth

    1. Immediate protection wide variety of pathogens

    2. Come in three forms.-

    -External mechanical (skin, mucous)

    - Chemical (sebum, gastric juices, perspiration)

    -Internal nonspecific:

            Antimicrobial proteins

            NK cells, phagocytes

            Inflammation and fever

    B. External Mechanisms (Mechanical and Chemical)

    Skin – keratinized

    (i) is a barrier – sheds easily

  • (ii) is dry
  • (iii) has a low pH
  • (iv) has high salt concentrations
  • (v) possesses lysozyme (in sweat).
  • Mucous membranes

    Tears (i) wash away pathogens

  • (ii) contain lysozyme
  • Urine (i) washes away pathogens

  • (ii) has a low pH
  • (iii) has high salt concentrations
  • Vaginal lining: (i) mucous membranes

  • (ii) has a low pH
  • Saliva (i) digestive enzymes

    Stomach (i) has a low pH

  • (ii) digestive enzymes
  • (iii) mucous membranes
  • C. Internal, Non-specific

    NK cells, Macrophages and phagocytes

  • Recognize certain antigens, other surface markers, recognize cancer
  • Recognize, adhere, release perforin
  • D. Inflammation

    1. Inflammation, a tissue response to a pathogen, is characterized by

    a. redness

    b. swelling

    c. heat

    d. pain.

    2. Major actions that occur during an inflammatory response include:

    a. dilation of blood vessels;

    b. increase of blood volume in affected areas;

    c. invasion of white blood cells into the affected area;

    d. appearance of fibroblasts and their production of a sac around the area.

    E. Fever

    Abnormally high body temperature that occurs because the hypothalamic thermostat is reset

    Occurs during infection & inflammation

    bacterial toxins trigger release of fever-causing agents


    intensifies effects of interferons, inhibits bacterial growth, speeds up tissue repair

    5 Stages of Inflammatory Response

    1. Localized Vasodilation

  • Takes place due to release of histamine by tissue mast cells (basophil-like cell)
  • Histamine increases capillary permeability. antibodies and clotting factors escape into tissue fluid

    2. Localized Edema

  • As fluids deposit into tissue, the pressure balance between tissue fluid and plasma gets thrown off.
  • As a result, huge quantities of nutrients and fluid get released into the interstitial space
  • 3. Isolation of Invader

  • Fibrin clots surround the invader and prevent or slow down its escape
  • Toxins produced by invader also are localized and isolated
  • 4. Phagocyte migration

  • Within an hour, neutrophils and then monocytes arrive and leave blood stream

  • 5. Phagocytosis

  • Chemotaxis
  • attraction to chemicals from damaged tissues,
  • Adherence
  • attachment to plasma membrane of phagocyte
  • Ingestion
  • Engulfed by pseudopods
  • Digestion & killing
  • Merging with lysosome containing digestive enzymes
  • Exocytosis residual body
  • F. Tissue Repair. Finally, the inflammatory process repairs tissues

    Salicylates (aspirin) and glucocorticoid drugs suppress the inflammatory response.

    Salicylates also reduce fever by inhibiting the production of prostaglandins.

    Glucocorticoids suppress most aspects of the inflammatory response.

    Specific Resistance: Acquired Immunity

    A. Immunity is body’s ability to defend itself against specific foreign material or organisms

    - bacteria, toxins, viruses, cat dander, etc.

    Differs from nonspecific defense mechanisms

    -specificity----recognize own cells & non-self cells

    -memory----2nd encounter produces even more vigorous response

    B. Antigens

  • 1. Antigens are glycoproteins that function as I.D. tags on the surface of cells. These antigens help the body to recognize which cells belong to the body and which do not.
  • 2 Foreign antigens are attacked by two types of lymphocytes (T & B Lymphocytes)
  • C. Lymphocyte Functions

    T cells attack foreign, antigen-bearing cells, such as bacteria, by direct cell-to-cell contact, providing "cell-mediated immunity."

    B cells are the main warriors of immunity in body fluids

    They secretes antibodies

    Antibodies mark antigens for elimination

    Like T cells, some of the B cells become memory cells to respond to future encounters with the antigen

    D. Acquired Active Immune Responses

    1. When B or T cells become activated the first time, their actions constitute a primary immune response, after which some cells remain as memory cells.

    2. If the same antigen is encountered again, more numerous memory cells can mount a more rapid response, known as the secondary immune response. The ability to produce a secondary immune response may be long-lasting.

    Two Types of Acquired Active Immune Response:

  • 1. Naturally acquired active immunity occurs after exposure to the antigen itself.
  • 2. Artificially acquired active immunity occurs through the use of vaccines, without the person becoming ill from the disease.
  • E. Immunological Memory

  • 1. Allergic Reactions - Allergic reactions to allergens (substances that cause an allergic response in some people) are excessive immune responses that may lead to tissue damage, respiratory failure and/or death.
  • F. Transplantation and Tissue Rejection

  • 1. A transplant recipient's immune system may react with foreign antigens on the surface of the transplanted tissue, causing a tissue rejection reaction.
  • 2. Close matching of donor and recipient tissues can reduce the chances of tissue rejection
  • 3. Use of immunosuppressive drugs may reduce rejection, although the individual may be more susceptible to infection.
  • G. Autoimmunity

  • 1. In autoimmune disorders, the immune system manufactures antibodies against some of its own antigens.
  • 2. Autoimmune disorders may result from viral infection, faulty T cell development, or reaction to a nonself antigen that bears close resemblance to a self antigen.

    Rheumatoid Arthritis: An Auto-Immune Disease

    3. AIDS leaves the body defenseless

  • The AIDS virus attacks helper T Cells
  • This cripples immunity
  • Transmitted by exchange of body fluids
  • Usually fatal: attacks immune system
  • Prior to 1980s U.S. blood not screened for HIV
  • Sub-Sahara Africa: 25% of blood today not screened for HIV
  • AIDS takes about 10 years to develop after initial exposure to HIV
  • Not all HIV persons will develop AIDS
  • So far, AIDS is incurable
  • Drugs and vaccines offer hope for the future