Immunology and Body Defenses

Glossary of Immune System Terms

• Bacteria: Single-celled microbes lacking a nucleus.
• Fungi: Organisms with complex cells that feed off living hosts.
• Microbes: Microscopic organisms including bacteria, viruses, fungi, and protozoa.
• Immune system: The body system that prevents and fights disease.
• Immunity: The body's ability to protect itself from infection.
• Disease: Any medical condition with specific symptoms.
• Pathogens: Microbes and other microscopic agents that cause disease.
• Infectious diseases: Diseases caused by pathogens.
• Infection: When pathogens enter the body and multiply.
• Non-infectious diseases: Diseases caused by lifestyle, environmental, or genetic factors, not pathogens.
• Pathogenic: Causing disease.
• Frequency: The number of waves that go by in one second.
• Pseudoscience: A claim presented as scientific but doesn't follow the scientific method.
• Cell: The smallest unit of life.
• B cell: Specialized white blood cells in the third line of defense.
• Clones: Identical copies of a B cell produced when an antibody finds its match.
• Memory cell: A B cell that remains in the bloodstream to recognize pathogens in the future.
• White blood cell: A blood component that helps protect the body from infection.
• Virus: A microscopic infectious agent made of genetic material and proteins.
• Contagious: When an infectious disease can pass from one person to another.
• Coronavirus: A type of virus that can cause diseases in mammals and birds, including COVID and the common cold.
• Non-contagious: A medical condition that cannot spread from person to person.
• Faeces: Solid waste that remains after food is digested.
• Epidemic: The rapid spread of a disease in a specific community or region.
• Endemic: The continual presence of a disease in a specific community or region.
• Pandemic: The rapid spread of a disease across multiple regions worldwide.
• First line of defence: The system of barriers to prevent pathogens from entering the body
  • Can be classified into chemical and physical barriers.
• Physical barriers: Stop pathogens from entering the body by blocking or trapping them such as skin and mucus.
  • Some physical barriers, such as cilia, actively push pathogens out.
• Chemical barriers: Kill pathogens before they can enter the body, stomach acid and enzymes found in tears, saliva, and mucus
• Cilia: Microscopic hairs on cells that line the airways.
• Enzyme: A substance that speeds up a chemical reaction, such as chemical digestion in the body.
• Second line of defence: The first general responses to infection.
• Membrane: A thin layer that forms a barrier.
• Phagocyte: A white blood cell that engulfs and destroys pathogens.
• Stomach acid: Kills many pathogens.
• Fever: An increase in core temperature above 38 degrees Celsius.
• Negative feedback loop: One change in a system causes another change in the opposite direction.
• Inflammation: Painful redness or swelling of part of the body.
• Core temperature: The temperature of the internal organs.
• Antibody: A protein that can identify and fight a specific pathogen.
• Polio: An infectious disease caused by a virus that mainly affects the nervous system and can cause loss of movement.
• Vaccination: A treatment that helps build immunity to an infectious disease.
• Paralysis: The inability to move parts of the body.

Microbes vs. Pathogens

• Microbes are abundant and diverse, living in nearly every environment, including on human skin.
• Microbes include bacteria, viruses, fungi, protozoa, and algae.
• Microbes in the human body can make up around 2kg of a person's weight.
• Not all microbes are harmful; some aid in digestion.
• Pathogens are microbes that cause diseases, with varying shapes and structures.
• Diseases caused by pathogens are infectious diseases like food poisoning, colds, measles, and COVID-19.

Types of Pathogens

• Bacteria: Unicellular organisms, examples include Salmonella (food poisoning).
  • Small, simple cells without a nucleus.
  • Cause disease by attacking cells, taking nutrients, or producing toxins.
• Viruses: Non-living entities, examples include the influenza virus (flu).
  • Consist of genetic material in a protein and fat layer.
  • Cause disease by entering cells to reproduce, causing them to burst and die.
  • Not always considered microbes.
• Fungi: Unicellular or multicellular organisms, examples include Microsporum (athlete's foot).
  • Complex cells that can't photosynthesize.
  • Cause disease by feeding off the host, sometimes producing toxins.

Infectious vs. Non-Infectious Diseases

• Infectious diseases occur when pathogens enter the body and multiply, damaging cells and causing symptoms.
• Infectious diseases can spread from person to person (contagious), or via vectors like mosquitoes.
• Non-infectious diseases are not caused by pathogens, instead by lifestyle, environmental, or genetic factors.
• Non-infectious diseases cannot spread from person to person.

Spread of Infectious Diseases

• Pathogens can spread through:
  • Shaking hands
  • Sharing drinks
  • Breathing saliva droplets (coughing or sneezing)
  • Exposure to infected feces or vomit
  • Touching contaminated surfaces
• Infectious diseases are compared by deadliness and contagiousness.
  • Contagiousness is measured by the average number of people an infected person transmits the disease to.

Classifying Disease Outbreaks

• Epidemic: Rapid spread of a disease in a specific community or region.
• Pandemic: Rapid spread of a disease across multiple regions or worldwide.
• Endemic: Continual presence of a disease in a specific community or region.

The Immune System and First Line of Defense

• The immune system prevents and fights both infectious and non-infectious diseases.
• The immune system has three lines of defense: barriers, general responses, and specific immunity.
• The system is made up of organs tissues and cells working together
• The first line of defense consists of barriers to prevent pathogens from entering the body.
• The barriers are classified as either physical or chemical.
• Pathogens must breach the first line of defense to cause infection.

First Line of Defense Mechanisms

• Skin: Acts as a barrier against most pathogens unless broken.
• Tears, saliva, and mucus: Trap pathogens for flushing or swallowing and contain enzymes that kill bacteria.
• Stomach acid: Kills many swallowed pathogens.
• Cilia: Microscopic hairs in airways that push mucus and trapped pathogens out.
• Urine flow: Flushes pathogens out of the bladder and urethra.
• Physical barriers: Block or trap pathogens such as skin and mucus.
• Chemical barriers: Kill pathogens with stomach acid and enzymes in tears, saliva, and mucus.

Second Line of Defense

• Occurs when pathogens bypass the first line of defense and enter the body.
• Consists of general responses to infection, treating all pathogens equally.

Second Line of Defense Mechanisms

• Fever: Increase in core body temperature to slow down or kill pathogens and speed up immune processes.
• Inflammation: Painful redness and swelling due to increased blood flow (containing white blood cells) to the infection site.
• Phagocytes: White blood cells that engulf and destroy pathogens.
• Pus forms due to the build-up of dead white blood cells.
• Yellow snot indicates a respiratory infection being fought by white blood cells.
• Relies on blood circulation to transport white blood cells to infected areas.

Comparing First and Second Lines of Defense

• Similarities:
  • Both are general ways the body protects against any type of pathogen.
  • Both are part of the immune system.
  • Both systems have more than one way to work.
• Differences:
  • The first line prevents infection, while the second line responds to infection.
  • The first line includes barriers, the second line includes phagocytes, inflammation, and fever.
  • The second line of defense fights pathogens once they are inside the body.

The Importance of Fever

• Damaged cells release chemicals that signal the brain to raise core body temperature.
• Shivering increases body temperature, while sweating decreases it.
• The body regulates temperature through a negative feedback loop.
• Negative feedback loops maintain core body temperature within narrow limits, preventing it from becoming too high or too low.

Controlling Inflammation

• Negative feedback loops are essential for controlling inflammation to prevent excessive damage.
• The loops act as a brake on the inflammatory response, preventing it from becoming excessive and causing more damage than good like death.

Third Line of Defense

• Provides immunity against specific pathogens.
• Roles include identifying and destroying specific pathogens and building long-lasting immunity.
• Made up of specialized white blood cells.
• Adapts to new threats and remembers them for future encounters.
• Requires time to identify the pathogen.
• A strength is that it can develop an effective weapon against a particular pathogen and remember that pathogen if it ever shows up in the body again..

How the Third Line of Defense Works

• The first encounter with a pathogen takes a few days for an attack to be mounted.
• B cells produce antibodies that bind to markers on pathogens.
• The first two lines of defence respond in a general way that treats all pathogens equally.
• Once an antibody binds to a pathogen, the B cell releases matching antibodies into the blood.
• B cells clone themselves to form an army to neutralize the pathogen.
• After the infection, some B cells remain as memory cells for future infections.
• Subsequent infections by the same pathogen trigger a faster and stronger response.
• The body becomes immune to the disease.

Third Line of Defense Summary

• B cells: Specialized white blood cells that make up the third line of defense.
• Antibodies: Proteins on B cell surfaces that bind to pathogens.
• Pathogen markers: Unique surface markers that only antibodies with matching shapes can bind to.
• Clones: Triggered by antibody-pathogen match, creating an army of new cells to produce millions of antibodies.
• Memory cells: Remain in the body after the pathogen is defeated, providing immunity if the pathogen reappears.

Immunity

• The third line of defence needs time to identify pathogens and produce antibodies.
• Immune amnesia (caused by measles) can have long-term health consequences, making individuals more susceptible to different infections because without antibodies you will be more open to different types of infections resulting in losing any antibodies that have been built up, and due to fighting different infections at the same time can be severed later in life if you haven't beaten them when you are younger.

Vaccinations

• A vaccination is a treatment that helps the body build immunity to an infectious disease.
• Most vaccinations are given by mouth as a nasal spray and injections.
• Involves introducing a dead or weakened pathogen into the body to stimulate an immune response.
• A substance that boosts the body’s immunity to a specific pathogen is called a vaccine.
• Relies on the third line of defense, triggering B cells to produce antibodies and memory cells.
• Helps build immunity in the same way as infection, but without the symptoms of disease.

How Vaccines work

• Vaccine contains dead or weakened pathogens.
• Triggers B cells to produce antibodies and memory cells that remain in the body.
• Allows the immune system to quickly identify and fight the pathogen in any future infection.
• Triggers an immune response.
• Antibodies are produced to fight infections.
• Vaccination works by introducing a dead or weakened pathogen into the body
• Being infected by the pathogens is likely to cause symptoms while a vaccination does not cause symptoms.

Vaccination Specificity

• Different vaccines are needed for each infectious disease because all pathogens are different and unique,
• Each antibody can bind to one pathogen using lock and key.
• Common myths include the high risk of side effects and autism, but they have been disproven.

Herd Immunity

• Vaccination rate is the percentage of vaccinated people. Infection rate is the percentage of unvaccinated people that are infected.
• Protects vulnerable people (babies, elderly, those with cancer) who can't be vaccinated.
• Achieved when enough people are vaccinated to prevent the spread of disease.
• Requires a high vaccination rate; a low rate can lead to outbreaks.
• Lower vaccination rates lead to higher infection rates.
• Members of community are affected by individuals/parents decisions not to get vaccinated..

Role of Vaccination Rate

• Vaccination protects individuals and the community because when a large portion of the community is vaccinated, it creates a barrier against the spread of disease.
• High-risk locations include childcare centers, retirement homes, and hospitals.

Vaccination rates and herd immunity

• As vaccination rates increase, infection rates decline for all 3 diseases.
• A new disease is more likely to spread quickly due as there isn't a known defense against it.
• Measles declines late on when the vaccination rate reaches around 60 per cent. They are different with different severities, how easily they can be transferred through people which is known as the infectious rate.
• Recommend a vaccination rate will be 75 per cent for Ebola and Polio and 85 per cent for Measles.

Explore the body's defense mechanisms against pathogens, including physical and chemical barriers. Learn about white blood cells, immune responses, and the importance of memory cells. Understand infectious agents, disease transmission, and pseudoscientific claims.