The Immune System

The Immune System

High School

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Learning Objectives

• Define the immune system and its primary functions in defending the body.

• Identify different types of pathogens and describe the body's three lines of defense.

• Differentiate between active, passive, natural, and artificial immunity.

• Recognize common immune system disorders like allergies and autoimmune diseases.

Key Vocabulary

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Pathogen

A disease-causing agent, like a virus or bacteria, that invades the body and causes illness.

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Antigen

A foreign substance or toxin that triggers a defensive immune response from the body.

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Antibody

A protein made by B cells that identifies and neutralizes foreign invaders like bacteria and viruses.

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Immunity

The body's ability to resist a particular infection through the action of specific antibodies or cells.

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Phagocytosis

The process where certain white blood cells ingest harmful foreign particles, bacteria, and dead cells.

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Vaccine

A substance used to stimulate antibody production and provide immunity against one or several diseases.

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What is the Immune System?

• The immune system is your body's defense against invaders called pathogens.

• ​It's a complex network of cells, organs, and tissues working together.

• It produces special proteins called antibodies to fight off infections and diseases.

• It also helps with fluid recovery in tissues and absorbing lipids (fats).

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Solved Example 1
A patient with a bacterial infection is given an antibiotic treatment. If the initial bacterial count is 500,000 and the antibiotic kills 90% of the bacteria every 4 hours, what is the bacterial count after 12 hours?

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
A patient with a bacterial infection is given an antibiotic treatment. If the initial bacterial count is 500,000 and the antibiotic kills 90% of the bacteria every 4 hours, what is the bacterial count after 12 hours?

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Step 2: Solve for the Unknown

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Solved Example 1
A patient with a bacterial infection is given an antibiotic treatment. If the initial bacterial count is 500,000 and the antibiotic kills 90% of the bacteria every 4 hours, what is the bacterial count after 12 hours?

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Step 3: Evaluate the Answer

• The calculation correctly applies this decrease over the three 4-hour intervals in the 12-hour period.

• The final answer of 500 bacteria is a logical result of the exponential decay.

Multiple Choice

Besides immunity, what are two other main functions of the immune system?

• Oxygen transport and cell respiration

• Digestion and hormone production

• Fluid recovery and lipid absorption

• Nerve signaling and muscle contraction

What Are Pathogens?

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Viruses

• ​These are very small infectious agents with a protein coat.

• ​​They contain genetic material for making more copies of themselves.

• ​Viruses must invade a host cell in order to reproduce.

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Bacteria

• ​Bacteria are single-celled organisms that can cause various illnesses.

• ​​Some cause harm by directly destroying the body’s cells.

• ​Others release harmful chemicals that are known as toxins.

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Parasites

• ​Parasites are multicellular organisms that live on a host.

• ​​They grow and feed on their host, often causing harm.

• ​Other pathogens include fungi and various types of toxins.

Multiple Choice

How do bacteria primarily cause illness in the body?

• By coating healthy cells with a protein layer

• By destroying cells or releasing toxins

• By growing and feeding on a host

• By forcing host cells to make more of them

The Body's Lines of Defense

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First Line of Defense

• ​This line of defense consists of external physical barriers to block pathogens.

• ​​The skin acts as a tough and protective outer shield for the body.

• ​Mucous membranes trap pathogens in the nose and throat passages.

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Second Line of Defense

• ​This involves non-specific cells that fight any invader that gets past.

• ​​Natural Killer Cells perform a process called immune surveillance within the body.

• ​They attack and destroy bacteria, viruses, and even body cancer cells.

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Third Line of Defense

• ​This is a highly specific response targeting particular pathogens.

• ​​It uses specialized cells to mount a focused attack on the invader.

• ​It produces a lasting memory of the invader for future immunity.

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Solved Example 2
In a lab, 500 bacteria are present in a culture. If the bacteria double every hour, how many bacteria will be present after 4 hours of growth?

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Step 1: Analyze and Sketch the Problem

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Solved Example 2
In a lab, 500 bacteria are present in a culture. If the bacteria double every hour, how many bacteria will be present after 4 hours of growth?

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Step 2: Solve for the Unknown

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Solved Example 2
In a lab, 500 bacteria are present in a culture. If the bacteria double every hour, how many bacteria will be present after 4 hours of growth?

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Step 3: Evaluate the Answer

• The calculation correctly applies the principle of exponential growth, doubling the bacteria count for each hour.

• The final count of 8,000 bacteria is consistent with the initial conditions and the growth rate.

Multiple Choice

Which of the following is part of the first line of defense against pathogens?

• Skin and mucous membranes

• Natural Killer Cells

• Antibodies and B cells

• Inflammation and fever

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Antigens and Antibodies

Antigens

• Antigens are foreign substances that trigger a response from the immune system.

• They are protein markers found on the surface of pathogens, like bacteria and viruses.

• These markers help the immune system identify and target harmful invading cells.

Antibodies

• Antibodies are proteins produced by the immune system to fight off specific antigens.

• These specialized proteins are created by a type of white blood cell called B cells.

• They have specific binding sites that lock onto antigens to neutralize the pathogen.

Multiple Choice

What is the primary role of an antibody?

• To act as a marker on the surface of a pathogen

• To create a universal response to all invaders

• To bind with specific antigens to neutralize them

• To destroy the body's own "good" cells

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Types of Immunity

Active Immunity

• Your body produces its own antibodies when it is exposed to a pathogen.

• Natural immunity develops after you get sick from an infection and then successfully recover.

• Artificial immunity is acquired through vaccination, introducing a harmless version of a pathogen.

Passive Immunity

• You gain temporary immunity by receiving antibodies that were produced from another source.

• A baby gets natural passive immunity from its mother through the placenta or breastmilk.

• Artificial passive immunity is an emergency measure, like an injection of immune serum.

Multiple Choice

Getting a vaccine to protect against the flu is an example of what type of immunity?

• Natural active immunity

• Artificial passive immunity

• Natural passive immunity

• Artificial active immunity

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Non-Specific Responses: Inflammation and Fever

Inflammation

• A local defensive response to tissue injury, like a cut or infection.

• It works to limit the spread of pathogens, remove debris, and start tissue repair.

• The four main signs are redness, swelling, heat, and pain.

Fever (Pyrexia)

• An abnormal elevation in the body's temperature, often due to infection.

• A moderate fever helps white blood cells work better and can slow pathogen growth.

• A person with a fever is called febrile, while one without is afebrile.

Multiple Choice

Which of the following is NOT a primary purpose of inflammation?

• To limit the spread of pathogens

• To remove debris of damaged tissue

• To initiate tissue repair

• To lower the body's temperature

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Key Organs of the Immune System

Tonsils & Lymph Nodes

• Tonsils are located at the back of the mouth to guard against ingested or inhaled germs.

• Inflammation of the tonsils due to infection is a common condition that is called tonsillitis.

• Lymph nodes are small glands that filter out pathogens, which causes them to swell during an infection.

Spleen & Other Parts

• The spleen is the body's largest lymphatic organ that filters blood and recycles old red blood cells.

• It also plays a crucial role by storing the body's white blood cells and platelets for future use.

• Other parts include the thymus, appendix, and bone marrow where many new immune cells are produced.

Multiple Choice

Which organ is the largest in the lymphatic system and serves to filter blood and store white blood cells?

• Tonsils

• Thymus

• Appendix

• Spleen

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When the Immune System Malfunctions

Allergies

• An allergy is an immune response to a typically harmless substance called an allergen.

• The immune system mistakenly identifies it as a threat, which causes inflammation.

• A severe, life-threatening allergic reaction is known as anaphylaxis.

Autoimmune Diseases

• This is a condition where the immune system mistakenly attacks the body’s own healthy cells.

• White blood cells, which are meant to fight infection, are responsible for this attack.

• Multiple sclerosis (MS), which attacks nerve cells, is one of over 80 types of these diseases.

Multiple Choice

What is the fundamental cause of an autoimmune disease?

• A pathogen becomes resistant to antibiotics

• A harmless allergen triggers a response called anaphylaxis

• The body fails to produce any white blood cells

• The immune system attacks the body's own healthy cells

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Diseases and Medical Interventions

Diseases

• HIV is a virus that attacks and weakens the immune system, the body's defense.

• This makes a person vulnerable to infections that a healthy immune system could defeat.

• Leukemia is a cancer of the bone marrow that leads to abnormal white blood cells.

Medical Interventions

• Vaccines contain an antigen, which stimulates a specific immune response and creates memory cells.

• This allows the body to quickly fight off a future infection by that same pathogen.

• Antibiotic resistance happens when bacteria evolve to become resistant to antibiotic medications over time.

Multiple Choice

How do vaccines work to protect against illness?

• By strengthening the first line of defense like the skin.

• By directly attacking and destroying any virus that enters the body.

• By creating memory cells that enable a fast response to a future infection.

• By supplying the body with a temporary dose of antibodies.

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Common Misconceptions About the Immune System

Misconception	Correction
Vaccines can give you the disease they are supposed to prevent.	Vaccines use a weakened or inactive pathogen to train your immune system.
Fevers are always harmful and should be suppressed immediately.	A moderate fever is a natural immune response that helps fight infection.
Antibiotics are effective against all infections, including colds and the flu.	Antibiotics only work against bacterial infections, not viruses that cause colds and flu.
A stronger immune response is always better.	An overactive immune system can lead to allergies and autoimmune diseases.

Multiple Choice

Based on their mechanism, what is the key difference between how active and passive immunity are acquired?

• Active immunity is only acquired from vaccines, while passive immunity is only acquired from natural exposure.

• Active immunity is temporary, while passive immunity is lifelong.

• Active immunity involves your own body producing antibodies, while passive immunity involves receiving them from another source.

• Active immunity fights bacteria, while passive immunity fights viruses.

Multiple Choice

Why is it necessary to get a new influenza vaccine each year?

• The vaccine is an antibiotic, which loses effectiveness over time.

• The body's memory cells for influenza only last for one year.

• The influenza virus mutates very quickly, creating new antigens.

• The vaccine provides passive immunity, which is only temporary.

Multiple Choice

A person develops Multiple Sclerosis (MS), a disease where the immune system attacks the myelin sheath of nerve cells. Analyze this situation and classify the type of disease.

• It is an opportunistic infection because the immune system is weakened.

• It is an allergy because the body is overreacting to an external allergen.

• It is a result of antibiotic resistance because a bacteria is no longer treatable.

• It is an autoimmune disease because the immune system is attacking the body's own healthy cells.

Multiple Choice

Predict the most likely outcome for a person infected with HIV who then contracts a common bacterial infection, compared to a healthy individual.

• The person with HIV will recover faster because their immune system is already on high alert.

• The person with HIV will likely have a much more severe and prolonged illness because their immune system is compromised and cannot fight the bacteria effectively.

• Both individuals will have the exact same response and recovery time.

• The person with HIV will be completely immune to the bacterial infection.

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Summary

• The immune system is a network that defends the body against pathogens.

• The body's defense has three lines: external, non-specific, and specific responses.

• Immunity can be active or passive, and acquired naturally or artificially.

• Key components include white blood cells, B cells, T cells, and lymph nodes.

• Immune system malfunctions can cause allergies and autoimmune diseases.

• Vaccines stimulate the immune system to create memory cells for future protection.

Poll

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