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Immune System and Infectious Disease
Immune System:
 The network of cells, tissues, and organs that work together to protect the body against infectious
invaders.
 The organs involved in the immune system are called the lymphatic system and consist of:
o Thymus
o Bone Marrow
o Spleen
o Lymph Nodes
 These are important parts of the immune system because they produce or store leukocytes
Lymph System:
 Macrophages are a type of phagocyte that migrate through the body by using the lymphatic system.
Leukocytes:
 Leukocytes circulate through the blood and lymphatic system and there are two types:
o Phagocytes
 Cells that engulf and break down the invading organism
 Most common is neutrophils, which fight bacteria
o Lymphocytes:
 cells that allow the body to remember and recognize previous invaders and help the body
destroy them
 B-cells and T-cells find organisms identified by antibodies and destroys them
Lymphocyte Response:
 When foreign organisms (antigens) are recognized by the body B-cells produce antibodies
 Antibodies are proteins that are developed to lock onto specific antigens
 These antibodies will be present in your body for life, so the next time that antigen enters your body it is
destroyed very quickly
 That is how immunizations work, they introduce a weakened antigen into your body, so your body can
produce antibodies in case a stronger antigen returns
 Antibodies cannot destroy these antigens on their own, the T-cells destroy the antigens
Types of Immunity:
 Humans have three different types of immunity:
o Innate – immunity you are born with
o Adaptive – immunity that develops throughout our lives
o Passive – immunity that is borrowed from another person or source
 Innate Immunity:
o This includes lots of our external barriers that prevent antigens from ever entering our bodies
o Our skin prevent germs from entering our blood stream
o Secretions give the skin a pH between 3 and 5, acidic enough to prevent colonization of many
microbes and secretes lysozyme, which digests bacterial cell walls
o If there is a break in the skin, it will try to heal and blood flows outward preventing the infection
from getting inside
o Our breathing passages are covered in hairs and mucus that are meant to trap foreign organisms
and expel them from our bodies
o Organisms that enter through our mouth will either be killed by the chemicals in our saliva or the
acid in our stomach
 Adaptive Immunity:
o Adaptive immunity includes the antibodies we develop by being exposed to different diseases
throughout our lives and the vaccinations we receive
 Passive Immunity
o Sometimes we can borrow immunity from another source, but this does not usually last for very
long
o The most common example of this is when babies get antibodies from the mother’s breast milk,
which is one reason breast feeding is beneficial for babies
Inflammatory Response:
 Inflammatory response is when fluid and white blood cells leak out of the blood vessels and into the
tissues.
 The white blood cells fight the pathogens
 During an inflammatory response, the blood vessel get wider to increase the flow of blood to that area
 Because of the increase blood flow and the fluid leaking into the tissue, an inflamed area will look red
and swollen. Also, the inflamed area will feel warn to the touch.
 In some cases, the inflammatory response will result in you having a temperature. This high
temperature keeps pathogens from reproducing.
 Triggered by the release of histamines (which are sometimes released when harmless substances enter
the body causing an allergic reaction)
Infectious Diseases:
 a disease that can be passed from one organism to another (called antigens or pathogens)
 When you have an infectious disease, a pathogen has gotten into your body and harmed it
 Pathogens make you sick by damaging individual cells
 There are four major groups of pathogens
Bacteria:
 Bacteria are single cell organisms
 Bacteria are classified as PROKARYOTES
 Most bacteria cannot make their own food; they have to break down, or decompose, other living things
to obtain their energy
 Most bacteria do not cause diseases
 Bacteria are almost everywhere: air, food, water, soil.
 Example: Strep throat
Viruses:
 Virus – a nonliving particle consisting of a core of hereditary material surrounded by a protein coat.
 Viruses can reproduce ONLY inside a living cell.
 Examples: Flu, common cold
Fungi:
 Most fungi are multicellular
 Fungi obtain food by secreting enzymes onto the dead material outside of their bodies (external
digestion). The fungi then absorb the nutrients into their cells. Organisms that feed this way are called
SAPROPHYTES
 Example: Athlete’s foot
Protists:
 One cell organisms (unicellular) that have organelles
 Example: Malaria
Man-Made Defenses:
 PASTERUIZATION – a heating process that is used today to kill microorganisms in food products such
as milk
 ANTIBIOTICS – a chemical that is used to kill bacteria or slow their growth without harming your
body cells. Unfortunately, there is no way to cure viral diseases.
 VACCINE – introducing the body to a weaker or dead form of a pathogen, so we can generate
antibodies against that disease
Famous Fights Against Disease:
 Louis Pasteur
 Proved that microbes caused infectious disease.
 He showed these microbes were in the air.
 Food could avoid contamination by being heated in a flask that did no allow bacteria from the air
to get in.
 His methods led to development of pasteurization.
 Jonas Salk
 Invented the polio vaccine.
 In the 1950’s there was an outbreak of polio that killed over 3,ooo and left over 21,000
paralyzed.
 It was the first mass distributed vaccine that was safe for public use.
 It used a dead form of the virus, so people would generate antibodies to it without ever getting
sick
Spread of Disease:
 PERSON-TO-PERSON TRANSFER
o Diseases can be transferred by direct contact such as kissing and shaking hands
o Diseases can be transferred by indirect contact such as sneezing and coughing
 CONTAMINATED OBJECTS
o Food and water can become contaminated
o You can get ill by using contaminated objects such as towels and silverware
 ANIMAL BITES
o An infected animal can pass on pathogens through their bite
o Examples: rabies (dog, raccoon), Lyme disease (tick), malaria (mosquitoes in tropical areas)
 PATHOGENS FROM THE ENVIRONMENT
o Some pathogens live naturally in the soil and water
o Example: tetanus, botulism (causes food poisoning)
Super-Bugs:
 Antibiotics kill bacteria, but if antibiotics are not taken their full term too many bacteria are left alive, so
your immune system can’t kill the rest before they begin reproducing.
 The bacteria left are ones resistant to the antibiotic, which reproduce asexually creating identical copies
(also resistant to antibiotics).
 So, next time you take the antibiotic to kill the bacteria they are immune and won’t die.
Spread of Infection:
 The spread of
infectious can be
affected by several
factors:
o Amount of
time the person
is contagious
o How the
disease spreads
(STD, airborn,
through bodily
fluids, contact,
etc)
o Population
density
o Population Mixing
Non-Infectious Diseases:
 A disease that is not contagious (cannot be passed from person to person or animal to person)
 These are not caused by pathogens (germs)
o Heart Disease
o Cancer
o Arthritis
Autoimmune Diseases:
 An autoimmune disease occurs when the immune system attacks and destroys healthy body tissue.
 The causes of these disorders are unknown for the most part.
 We suspect some are caused by bacteria, some by drugs, and some people may just have a genetic
predisposition.
 Examples of autoimmune diseases are:
o Lupus
o Diabetes Type I
o Guillain-Barre Syndrome
HIV and AIDS:
 HIV (human immunodeficiency virus) – the virus that attacks the immune system causing patients to
become more and more vulnerable to infection
 AIDS (acquired immune deficiency syndrome) – this is the disorder that occurs after symptoms of the
virus begin to present themselves.
 This is an infectious disease because it is transmitted from person to person through bodily fluids.
 Tomorrow we will complete the AIDS Lab. You will learn more about this disease when you read the
pre-lab information.