The Big Picture
Your immune system protects your body from harmful or unwanted substances. These threats include pollen, toxins, bacteria, viruses, and abnormal body cells.
Immunity means protection against a disease or condition. The body uses two main types of defence, nonspecific immunity and specific immunity.
The body also has different ways of gaining protection from disease. Some protection comes from genetics. Other protection develops naturally or through injections such as vaccines or immune globulin.
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Start Here If You’re Overwhelmed
Focus on these core ideas:
- Nonspecific immunity reacts to anything the body does not recognize as a normal body substance.
- The first line of defence uses mechanical barriers, chemical barriers, and reflexes.
- The second line of defence includes phagocytes, inflammation, and fever.
- Specific immunity protects against a certain disease or infection.
- Acquired immunity includes natural active immunity, natural passive immunity, and artificially acquired immunity.
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Course Notes: Key Ideas You Need to Know
What Immunity Means
Immunity means protection against a disease or condition. A person with immunity will not contract or be affected by that disease or condition.
The immune system protects the body from threats inside and outside the body. These threats include:
- pollens
- toxins
- bacteria
- viruses
- abnormal body cells, including cancer cells
The body has two main defence mechanisms:
- nonspecific immunity
- specific immunity
Nonspecific Immunity
Nonspecific immunity is the body’s reaction to anything it does not recognize as a normal body substance.
This type of defence has a first line and a second line.
First Line of Defence
The first line of defence includes barriers and reflexes.
- Mechanical barriers: Intact skin and mucous membranes form physical barriers.
- Chemical barriers: Tears, stomach acids, saliva, and perspiration act as chemical barriers.
- Reflexes: Coughing, sneezing, vomiting, and diarrhea help form part of this first defence.
Second Line of Defence
The second line of defence includes phagocytes, inflammation, and fever.
Phagocytes are white blood cells. They digest and destroy microorganisms and other unwanted substances.
Inflammation involves the release of histamine in an injured or irritated area. Histamine causes blood vessels to widen and brings more blood to the area. It causes redness, heat, and fluid leakage from the blood, which leads to swelling.
Fever stimulates phagocytosis. Phagocytosis means ingesting or engulfing other cells. Fever also decreases the ability of certain pathogens to multiply.
Specific Immunity
Specific immunity is the body’s ability to resist or overcome a certain disease or infection caused by a foreign agent, such as a pathogen or antigenic substance.
Special cells and substances take part in this type of immunity.
Antibodies
Antibodies are normal body substances that recognize abnormal or unwanted substances. They attack and destroy those substances.
Antigens
Antigens are abnormal or unwanted substances, usually proteins. They cause the body to produce antibodies that attack and destroy the antigens.
Lymphocytes
Lymphocytes are white blood cells that produce antibodies. Antibody production increases as the body responds to an infection.
Two types of lymphocytes described in these notes are B lymphocytes and T lymphocytes.
- B lymphocytes, or B cells: These cells cause the production of antibodies that circulate in plasma.
- T lymphocytes, or T cells: These cells destroy invading cells.
Killer T cells produce toxic substances near invading cells. Some T cells attract other cells that destroy the invaders.
What Happens When the Body Senses an Antigen
When the body senses an antigen, the immune system responds.
Phagocyte and lymphocyte production increases.
- Phagocytes destroy invaders by digesting them.
- Lymphocytes produce antibodies that attack and destroy unwanted substances.
- B cells produce antibodies that react to specific antigens.
Genetic and Acquired Immunity
Immunity to disease falls into two classifications:
- genetic immunity
- acquired immunity
Genetic Immunity
Genetic immunity protects a member of one species from diseases that affect another species.
For example, a cat does not catch chickenpox from a person.
Acquired Immunity
A person gets acquired immunity naturally or artificially.
Naturally Acquired Immunity
Natural immunity develops in two ways, active immunity and passive immunity.
Active Immunity
Active immunity develops after a person naturally acquires an illness.
For example, after a person gets chickenpox, the body develops antibodies that protect the person from getting it again.
Passive Immunity
Passive immunity is short-lived.
A mother passes this immunity:
- to the fetus through the placenta
- to the baby through breast milk
This protection lasts for about the first 6 months after birth.
Artificially Acquired Immunity
A person gets artificially acquired immunity through an injection of a vaccine or immune globulin.
Vaccine
A vaccine contains a small amount of an antigen-bearing substance, or pathogen. The injection stimulates the body to produce antibodies.
Immune Globulin
Immune globulin, also called immunoglobulin, comes from a donor who already has the antibodies.
The immune globulin gets injected into another person to provide passive immunity.
Exam Clue Words
- Certain: Specific immunity protects against a certain disease or infection. The word “certain” separates specific immunity from nonspecific immunity.
Fast Review
Use these points for a fast review before a quiz or exam.
- Immunity means protection against a disease or condition.
- Nonspecific immunity reacts to anything the body does not recognize as a normal body substance.
- The first line of defence includes mechanical barriers, chemical barriers, and reflexes.
- The second line of defence includes phagocytes, inflammation, and fever.
- Specific immunity protects against a certain disease or infection.
- Antibodies recognize and attack abnormal or unwanted substances.
- Antigens cause the body to produce antibodies that attack and destroy them.
- B cells cause antibody production, while T cells destroy invading cells.
- Genetic immunity protects one species from diseases that affect another species.
- Active immunity develops after naturally acquiring an illness.
- Passive immunity passes from mother to fetus through the placenta and from mother to baby through breast milk. It lasts about the first 6 months after birth.
- Artificially acquired immunity comes from an injection of a vaccine or immune globulin.
Final Pep Talk
There are several immunity terms to keep separate, so focus first on the big groups and then connect each one to its definition. A few short reviews will help those differences feel more familiar.