31.1 Pathogens and Human Illness

KEY CONCEPTGerms cause many diseases in humans.

31.1 Pathogens and Human Illness

Germ theory states that microscopic particles cause certain diseases.

• Germ theory proposes that microorganisms cause diseases.– proposed by Louis Pasteur– led to rapid advances in understanding disease

31.1 Pathogens and Human Illness

• Disease-causing agents are called pathogens.

• Koch’s postulates support the theory.

31.1 Pathogens and Human Illness

There are different types of pathogens.

• Bacteria are single-celled organisms. – cause illness by destroying

cells – release toxic chemicals

31.1 Pathogens and Human Illness

• Viruses are genetic material surrounded by a protein coat.– force host cells to

make more viruses – very small

31.1 Pathogens and Human Illness

• Fungi can be multicellular or single-celled.

– take nutrients from host cells– occur in warm and damp places

31.1 Pathogens and Human Illness

• Protozoa are single-celled organisms.

– use host cells to complete their life cycles– take nutrients from host cell

31.1 Pathogens and Human Illness

• Parasites are multicellular organisms.

– grow and feed on a host – possibly kill the host

31.1 Pathogens and Human Illness

• Different pathogen cause common infectious diseases.

31.1 Pathogens and Human Illness

Pathogens can enter the body in different ways.

• Pathogens can be transferred by direct or indirect contact.• Indirect contact does not require touching an infected

individual.

– touching an infected surface– breathing in infected air

31.1 Pathogens and Human Illness

• Vectors carry a pathogen and transmit it into healthy cells.

• Direct contact requires touching an infected individual. Includes: – kissing– sexual intercourse – hand shaking

tick

31.1 Pathogens and Human Illness

KEY CONCEPT 31.2The immune systems consists of organs, cells, and molecules that fight infections.

31.1 Pathogens and Human Illness

Many body systems protect you from pathogens.

• The immune system is the body system that fights off infection and pathogens.

• Many other tissues and systems help the immune system.– Skin is a physical barrier to infection.– Mucous membranes trap pathogens entering the body.– The circulatory system transports immune cells.

31.1 Pathogens and Human Illness

Cells and proteins fight the body’s infections.

• White blood cells attack infections inside the body.– Phagocytes engulf and destroy pathogens. – T cells destroy infected cells.– B cells produce antibodies.

31.1 Pathogens and Human Illness

• Three types of proteins fight off invading pathogens.

– Complement proteins weaken pathogen membranes.– Antibodies make pathogens ineffective. – Interferons prevent viruses from infecting healthy cells.

antibody

pathogens

31.1 Pathogens and Human Illness

Immunity prevents a person from getting sick from a pathogen.

• In all immunity, pathogens are destroyed before you get sick.

• Passive immunity occurs withoutan immune response.– mother’s milk– genetics

• Active immunity occurs after aspecific immune response

31.1 Pathogens and Human Illness

KEY CONCEPT 31.3The immune system has many responses to pathogens and foreign cells.

31.1 Pathogens and Human Illness

Many body systems work to produce nonspecific responses.

• Nonspecific responses are the same for every pathogen.• In inflammation, blood vessels become leaky.

– white blood cells movetoward infection anddamaged tissue

– characterized by swelling, redness, and pain

capillary wallextracellular space

white blood cell

31.1 Pathogens and Human Illness

• In fever, body temperature increases.

– High fevers can cause seizure, brain damage, and even death.

– Low fevers stimulate white blood cells to mature.

31.1 Pathogens and Human Illness

Cells of the immune system produce specific responses.

• Specific immune responses begin with the detection of antigens.– Antigens are surface proteins on pathogens.– Each pathogen has a different antigen.

virus

antigens

31.1 Pathogens and Human Illness

pathogen

antigens

T cell

receptors activated T cells

antigens

memory T cells

• There are two specific immune responses.– Cellular immunity uses T cells to destroy infected body

cells.

31.1 Pathogens and Human Illness

• There are two specific immune responses.– Humoral immunity uses B cells to produce antibodies.

memory B cells

activated B cells

antibodies

B cell

T cell

pathogen

31.1 Pathogens and Human Illness

• Both responses produce memory cells.

– specialized T and B cells– provide acquired (active) immunity

B cellT cell

31.1 Pathogens and Human Illness

The immune system rejects foreign tissues.

• Tissue rejection occurs in organ or tissue transplants.• Tissue rejection is the result of an immune response.

– immune system detects protein markers on the donor tissue

– makes antibodies against the donor’s tissue

31.1 Pathogens and Human Illness

KEY CONCEPT 31.4Living in a clean environment and building immunity help keep a person healthy.

31.1 Pathogens and Human Illness

Many methods are used to control pathogens.

• Antibiotics and antiseptics cause pathogens to burst.

31.1 Pathogens and Human Illness

• Antiseptics kill pathogens outside of the body.– do not target specific pathogens– examples include vinegar and soap

• Antibiotics kill pathogens inside the body.– target one specific bacterium or fungus– not effective against viruses

31.1 Pathogens and Human Illness

• Antibiotic resistance can cause medicines to become ineffective.– Some bacteria in a population have genes that make

them immune to antibiotics.– These bacteria spread the gene, making the antibiotics

useless.

A bacterium carriesgenes for antibioticresistance on a plasmid.

A copy of the plasmid is transferredthrough conjugation.

Resistance is quicklyspread throughmany bacteria.

31.1 Pathogens and Human Illness

Vaccines artificially produce acquired immunity.

• Vaccines also control pathogens and disease.– given to prevent illness– contain the antigen of a weakened pathogen

31.1 Pathogens and Human Illness

• Vaccination provides immunity.– stimulates a specific

immune response

– allows immune system to respond quickly to infection

– causes memory cells to be produced

– has such a fast response, a person will not get sick

A memory B cell isstimulated when the real pathogen binds to it.

2

The B cell quickly activates and makes antibodies that fight the pathogens before you get sick.

3

Antigens in a vaccinetrigger an immune response, and memory B cells are made.

1memory B cells

31.1 Pathogens and Human Illness

KEY CONCEPT 31.5An overactive immune system can make the body very unhealthy.

31.1 Pathogens and Human Illness

Allergies occur when the immune system responds to harmless antigens.

• An allergy is an response to a harmless antigen.• Allergies are caused by allergens.

– Allergens are antigens that cause an allergic reaction.– Allergens cause inflammation responses.

31.1 Pathogens and Human Illness

• There are many different allergens. – food, e.g. peanuts,

milk, wheat, etc.– airborne, e.g. pollen,

dust mite feces, mold, etc.

– chemical, e.g. nickel, medicine, bee stings, etc.

31.1 Pathogens and Human Illness

• Allergens can cause anaphylaxis. – Anaphylaxis is an extreme inflammation response.– Blood vessels and airways become too porous.– If not treated immediately, anaphylaxis can cause death.

31.1 Pathogens and Human Illness

In autoimmune diseases, white blood cells attack the body’s healthy cells.

• Autoimmune diseases are failures of the immune system.– White blood cells cannot recognize healthy cells.– White blood cells attack healthy body cells.– Tissues fail because of attack.

31.1 Pathogens and Human Illness

• There are over 60 autoimmune diseases.

31.1 Pathogens and Human Illness

KEY CONCEPT 31.6When the immune system is weakened, the body cannot fight off disease.

31.1 Pathogens and Human Illness

Leukemia is characterized by abnormal white blood cells.

– characterized by immature white blood cells – causes weakened immune system

• Leukemia is cancer of the bone marrow.

31.1 Pathogens and Human Illness

• Leukemia leads to opportunistic infections.– occur because white blood cells cannot fight infections– if immune system were healthy, would fight these

infections

31.1 Pathogens and Human Illness

HIV targets the immune system.

• The human immunodeficiency virus (HIV) is a retrovirus. – attacks and weakens the

immune system– is transmitted by mixing

infected blood with a bodily fluid

31.1 Pathogens and Human Illness

• HIV infection leads to AIDS.

HIV

T celldeadT cell

antibody

activatedB cell

– HIV reproduces in and destroys T cells.– The body cannot replace T cells fast enough.– T cells cannot help in immune responses.

31.1 Pathogens and Human Illness

• AIDS is acquired immune deficiency syndrome. – several opportunistic infections– very low amount of T cells