CHAPTER 12
THE LYMPHATIC SYSTEM AND BODY DEFENSES
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Introduction
a. Without the lymphatic system, our cardiovascular system would stop working and our immune
system would be hopelessly impaired.
b. Two main parts to the lymphatic system:
i. Lymphatic Vessels
ii. Lymphoid Tissues and Organs
c. Functions:
i. Lymphatic Vessels – transport fluids that have escaped from the blood back to the blood
ii. Lymphoid Organs – house phagocytic cells and lymphocytes which play roles in body
defenses and resistance to disease
Lymphatic Vessels
a. Function = pick up excess tissue fluid which is called LYMPH and return it back to the
bloodstream
b. The lymphatic vessels form a one-way system and lymph flows only toward the heart.
Lymph Nodes
a. 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
b. As lymph is transported toward the heart, it is filtered through thousands of lymph nodes.
i. 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
ii. Lymphocytes are located in the lymph nodes and respond to foreign substances.
c. When we have an infection, most of us have swollen glands. This swelling is a result of the
trapping function of the nodes.
i. Lymph nodes can sometimes be overwhelmed by the foreign particles they are trying to
destroy.
ii. 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
a. Spleen - blood rich organ that filters and cleanses blood of bacteria, viruses, and other debris
b. Thymus Gland – produces thymosin which functions in the programming of lymphocytes to
carry out their protective roles in the body.
c. Tonsils – trap and remove bacterial entering the throat. They sometimes become congested with
bacteria and become red, swollen, and sore = TONSILLITIS
d. Peyer’s Patches of the Intestine – capture and destroy bacteria before they enter the intestine
Body Defenses - 2 systems:
a. Nonspecific Body Defenses
i. Responds immediately to protect the body from all foreign substances
ii. Provided by skin and mucous membranes
iii. Prevents entry and spread of microorganisms throughout the body
b. Specific Body Defenses
i. Also known as the IMMUNE SYSTEM
ii. Mounts the attack against particular foreign substances.
iii. It protects us from most bacteria, viruses, transplanted organs or graft, and even our own
cells that have turned against us.
iv. The resulting resistance to disease = IMMUNITY
Nonspecific Body Defenses
a. Surface Membrane Barriers – THE BODY’S FIRST LINE OF DEFENSE
i. Provided by the skin and mucous membranes
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ii. These 2 membranes produce a variety of protective chemicals
1. The acid pH of skin secretions inhibits bacterial growth.
2. The mucosa of the stomach secretes hydrochloric acid which kills pathogens.
3. Saliva and lacrimal fluid contain lysozyme which destroys bacteria.
4. Mucus in the digestive and respiratory tract trap microorganisms.
b. Cells and Chemicals – THE BODY’S SECOND LINE OF DEFENSE
i. Phagocytes – engulfs foreign particles or pathogens that make it through the membrane
barriers
ii. 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
iii. Inflammatory Response – triggered whenever body tissues are injured
1. Four Cardinal Signs of an Inflammation Response:
a. Redness
b. Heat
c. Swelling
d. Pain
2. Advantages of the Inflammatory Response:
a. Prevents the spread of damaging agents to nearby tissues
b. Disposes of cell debris and pathogens
c. Sets the stage for repair
iv. Antimicrobial Chemicals
1. 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.
2. Interferon – a protein that binds to viruses and hinders the ability of viruses to
multiply within the cells
v. Fever – a response to invading microorganisms and speeds up the repair processes
Specific Body Defenses: The Immune System
a. Overview:
i. The immune system is a functional system that recognizes foreign molecules and acts to
inactivate or destroy them.
ii. The immune system’s response to a threat is called the IMMUNE RESPONSE.
iii. Two important parts to immunity:
1. Humoral Immunity: provided by antibodies present in the body’s “humors,” or
fluids
2. Cellular Immunity: provided by lymphocytes that defend the body
b. Antigens - any substance capable of exciting our immune system and provoking an immune
response
c. Cells of the Immune System
i. Lymphocytes:
1. Originate in red bone marrow
2. Two types of lymphocytes:
a. B cells – oversee humoral immunity & produce antibodies
b. T cells – oversee cellular immunity & do not produce antibodies
3. Both B cells and T cells migrate to the lymph nodes where their encounters with
antigens will occur
ii. Macrophages
1. Originate in the bone marrow
2. Job = engulfs foreign particles and place a “signal flag” on their surfaces so that
the B cells and T cells can recognize them
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d. Humoral Immune Responses
i. Active Immunity:
1. Naturally acquired during bacterial and viral infection, during which we may
develop the symptoms of the disease and suffer a little.
2. Artificially acquired when we receive VACCINES.
ii. Passive Immunity:
1. Naturally acquired when the mother’s antibodies cross the placenta and enter the
fetal circulation.
2. Artificially acquired when we receive IMMUNE SERUM (rabies, tetanus,
antivenom)
e. Antibodies – also known as IMMUNOGLOBULINS - Secreted in response to antigens
f. Organ Transplants and Grafts
i. Organ transplants and grafts are a desirable treatment option.
ii. However, they have had mixed success because the immune system can reject the
transplant or the graft.
iii. If a graft is taken from the same person or an identical twin, it is almost always
successful.
iv. If a graft or transplant is taken from an animal and given to a human, it is NEVER
successful.
v. 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.
vi. After surgery, to prevent rejection, the patient receives immunosuppressive therapy.
This consists of corticosteroids to suppress inflammation, various drugs, radiation and Xray therapy. Immunosuppressive therapy suppresses the immune system for a period of
time and it cannot protect the body against other foreign agents.
g. Disorders
i. Allergies – the immune system causes tissue damage as it fights off a threat to the body
ii. Immunodeficiencies – the production and function of the immune cells is abnormal
1. AIDS – acquired immune deficiency syndrome
iii. Autoimmune Diseases – the immune system loses its ability to distinguish good from bad
1. Multiple Sclerosis – destruction of the white matter of the brain and spinal cord
2. Grave’s Disease – the thyroid gland produces too much thyroxine
3. Rheumatoid Arthritis – destruction of the joints
Developmental Aspects
a. The thymus gland is the first lymphatic organ to appear in the embryo.
b. Development of immune response occurs around the time of birth.
c. Stress appears to interfere with normal immune response.
d. Efficiency of the immune response declines in old age, and infections, cancer,
immunodeficiencies, and autoimmune diseases become more prevalent.