CHAPTER 12 THE LYMPHATIC SYSTEM AND BODY DEFENSES

Introduction  Without the lymphatic system, our cardiovascular system would stop working and our immune system would be hopelessly impaired.  Two main parts to the lymphatic system Lymphatic Vessels Lymphoid Tissues and Organs  Functions: Lymphatic Vessels – transport fluids that have escaped from the blood back to the blood Lymphoid Organs – house phagocytic cells and lymphocytes which play roles in body defenses and resistance to disease

Lymphatic Vessels  Function = pick up excess tissue fluid which is called LYMPH and return it back to the bloodstream  The lymphatic vessels form a one-way system and lymph flows only toward the heart.

Lymph Nodes  Function = help protect the body by removing foreign material such as bacteria and tumor cells from the lymphatic stream and by producing lymphocytes that function in the immune response  As lymph is transported toward the heart, it is filtered through thousands of lymph nodes. Inside the lymph nodes are MACROPHAGES = engulf and destroy bacteria, viruses, and other foreign substances in the lymph before it is returned to the blood Lymphocytes are located in the lymph nodes and respond to foreign substances.

Lymph Nodes  When we have an infection, most of us have swollen glands. This swelling is a result of the trapping function of the nodes. Lymph nodes can sometimes be overwhelmed by the foreign particles they are trying to destroy. If there are large numbers of bacteria or viruses trapped in the lymph nodes, the nodes become inflamed and tender to the touch.

Other Lymph Organs  Spleen - blood rich organ that filters and cleanses blood of bacteria, viruses, and other debris  Thymus Gland – produces thymosin which functions in the programming of lymphocytes to carry out their protective roles in the body.  Tonsils – trap and remove bacterial entering the throat. They sometimes become congested with bacteria and become red, swollen, and sore = TONSILLITIS  Peyer’s Patches of the Intestine – capture and destroy bacteria before they enter the intestine

Body Defenses - 2 systems:  Nonspecific Body Defenses Responds immediately to protect the body from all foreign substances Provided by skin and mucous membranes Prevents entry and spread of microorganisms throughout the body

Body Defenses – 2 systems:  Specific Body Defenses Also known as the IMMUNE SYSTEM Mounts the attack against particular foreign substances. It protects us from most bacteria, viruses, transplanted organs or graft, and even our own cells that have turned against us. The resulting resistance to disease = IMMUNITY

Nonspecific Body Defenses  Surface Membrane Barriers – THE BODY’S FIRST LINE OF DEFENSE Provided by the skin and mucous membranes These 2 membranes produce a variety of protective chemicals The acid pH of skin secretions inhibits bacterial growth. The mucosa of the stomach secretes hydrochloric acid which kills pathogens. Saliva and lacrimal fluid contain lysozyme which destroys bacteria. Mucus in the digestive and respiratory tract trap microorganisms.

Nonspecific Body Defenses  Cells and Chemicals – THE BODY’S SECOND LINE OF DEFENSE Phagocytes – engulfs foreign particles or pathogens that make it through the membrane barriers Natural Killer Cells – defensive cells that can kill cancer cells and virus-infected body cells by releasing chemicals in the membrane of the foreign body

Inflammatory Response  Triggered whenever body tissues are injured  Four Cardinal Signs of an Inflammation Response: Redness Heat Swelling Pain  Advantages of the Inflammatory Response: Prevents the spread of damaging agents to nearby tissues Disposes of cell debris and pathogens Sets the stage for repair

Antimicrobial Chemicals  Complement – a group of plasma proteins that circulate in the blood in an inactive state. It becomes active when it attaches to foreign cells and becomes a factor in the fight against the foreign bodies.  Interferon – a protein that binds to viruses and hinders the ability of viruses to multiply within the cells

Fever  A response to invading microorganisms and speeds up the repair processes

Specific Body Defenses: The Immune System  The immune system is a functional system that recognizes foreign molecules and acts to inactivate or destroy them.  The immune system’s response to a threat is called the IMMUNE RESPONSE.

Two important parts to immunity:  Humoral Immunity: provided by antibodies present in the body’s “humors,” or fluids  Cellular Immunity: provided by lymphocytes that defend the body

Antigens  Any substance capable of exciting our immune system and provoking an immune response

Cells of the Immune System  Lymphocytes: Originate in red bone marrow Two types of lymphocytes: B cells – oversee humoral immunity & produce antibodies T cells – oversee cellular immunity & do not produce antibodies Both B cells and T cells migrate to the lymph nodes where their encounters with antigens will occur  Macrophages Originate in the bone marrow Job = engulfs foreign particles and place a “signal flag” on their surfaces so that the B cells and T cells can recognize them

Humoral Immune Responses  Active Immunity: Naturally acquired during bacterial and viral infection, during which we may develop the symptoms of the disease and suffer a little. Artificially acquired when we receive VACCINES.  Passive Immunity: Naturally acquired when the mother’s antibodies cross the placenta and enter the fetal circulation. Artificially acquired when we receive IMMUNE SERUM (rabies, tetanus, antivenom)

Antibodies  Also known as IMMUNOGLOBULINS - Secreted in response to antigens

Organ Transplants and Grafts  Organ transplants and grafts are a desirable treatment option.  However, they have had mixed success because the immune system can reject the transplant or the graft.  If a graft is taken from the same person or an identical twin, it is almost always successful.  If a graft or transplant is taken from an animal and given to a human, it is NEVER successful.

Organ Transplants and Grafts  The most common graft is taken from a recently deceased person. Before it is attempted, the ABO blood type must be determined and must match.  After surgery, to prevent rejection, the patient receives immunosuppressive therapy. This consists of corticosteroids to suppress inflammation, various drugs, radiation and X-ray therapy. Immunosuppressive therapy suppresses the immune system for a period of time and it cannot protect the body against other foreign agents.

Disorders  Allergies – the immune system causes tissue damage as it fights off a threat to the body  Immunodeficiencies – the production and function of the immune cells is abnormal AIDS – acquired immune deficiency syndrome  Autoimmune Diseases – the immune system loses its ability to distinguish good from bad Multiple Sclerosis – destruction of the white matter of the brain and spinal cord Grave’s Disease – the thyroid gland produces too much thyroxine Rheumatoid Arthritis – destruction of the joints

Developmental Aspects  The thymus gland is the first lymphatic organ to appear in the embryo.  Development of immune response occurs around the time of birth.  Stress appears to interfere with normal immune response.  Efficiency of the immune response declines in old age, and infections, cancer, immunodeficiencies, and autoimmune diseases become more prevalent.