Immune System and Disease

Chapter 31

PATHOGENS AND HUMAN ILLNESS 31.1

Key Concept

• Germs cause many diseases in humans

Germ Theory

• Microogranisms (microscopic particles) cause certain diseases – proposed by Louis

Pasteur – led to rapid

advances in understanding disease

Koch’s Postulates

• Support the germ theory

• Disease-causing agents are called pathogens

Pathogens

• Many different types

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

destroying cells

– release toxic chemicals

Pathogens

• Viruses: – genetic material

surrounded by a protein coat

– force host cells to make more viruses

– very small

Fungi

• Can be multicellular or single-celled – take nutrients

from host cells

– occur in warm and damp places

Protozoa

• Single-celled organisms – use host cells to complete their life cycles

– take nutrients from host cell

Parasites

• Multicellular organisms – grow and feed on a host

– possibly kill the host

Pathogens

• Different pathogens cause common infectious diseases

How Pathogens Enter the Body

• Can be transferred by direct or indirect contact

• Indirect: – does not require

touching an infected individual

– touching an infected surface

– breathing in infected air

How Pathogens Enter the Body

• Vectors: – carry a pathogen

and transmit it into healthy cells

• Direct: – requires touching an

infected individual: • kissing

• sexual intercourse

• hand shaking

tick

IMMUNE SYSTEM 31.2

Key Concept

• The immune system consists of organs, cells, and molecules that fight infections

The Immune System

• The body system that fights off infection and pathogens

• Many other tissues and systems help the immune system – Skin: a physical barrier to

infection. – Mucous membranes: trap

pathogens entering the body – Circulatory system:

transports immune cells

Immune Cells

• White blood cells (WBC’s) – attack infections inside the body

– phagocytes engulf and destroy pathogens

– T cells destroy infected cells

– B cells produce antibodies

Immune Proteins

• Fight off invading pathogens – Complement proteins weaken pathogen

membranes

– Antibodies make pathogens ineffective

– Interferons prevent viruses from infecting healthy cells

Immunity

• Prevents a person from getting sick – pathogens are destroyed

before sickness

• Passive immunity (occurs without an immune response):

– mother’s milk

– genetics

• Active immunity (occurs with an immune response)

IMMUNE RESPONSES 31.3

Key Concept

• The immune system has many responses to pathogens and foreign cells

Nonspecific Responses

• Are the same for every pathogen

• Ex: inflammation – blood vessels become leaky

– white blood cells move toward infection and damaged tissue

– characterized by swelling, redness, and pain

Nonspecific Responses

• Fever – blood temperature

increases

– low fevers stimulate white blood cells to mature

– high fevers can cause seizure, brain damage, and even death

Specific Responses

• Caused by immune cells

• Begin with antigen detection – antigens are surface

proteins on pathogens

– each pathogen has a different antigen

Specific Responses (1 of 2)

• Cellular Immunity – uses T cells to destroy infected body cells

Specific Responses (2 of 2)

• Humoral Immunity – uses B cells to produce antibodies

Memory Cells

• Produced by both Cellular and Humoral Immunity – specialized T and B cells

– provide acquired (active) immunity

Foreign Tissues

• Tissue rejection occurs in organ or tissue transplants

• Tissue rejection is the result of an immune respons – immune system detects protein markers on

the donor tissue

– makes antibodies against the donor’s tissue

IMMUNITY AND TECHNOLOGY 31.4

Key Concept

• Living in a clean environment and building immunity help keep a person healthy

Technology

• Many methods to control pathogens

• Antibiotics and antiseptics cause pathogens to burst

Technology

• Antiseptics: – kill pathogens outside the

body – do not target specific

pathogens • ex: vinegar, soap

• Antibiotics: • kill pathogens inside the body – target one specific bacterium

or fungus – not effective against viruses

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

Vaccines

• Artificially produce acquired immunity

• Control pathogens and disease – given to prevent illness

– contain the antigen of a weakened pathogen

Vaccination

• Provides immunity – stimulates a specific

immune response – causes memory cells to

be produced – allows immune system

to respond quickly to infection

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

DISEASES THAT WEAKEN THE IMMUNE SYSTEM

31.6

Key Concept

• When the immune system is weakened, the body cannot fight off disease

Leukemia

• Cancer of the bone marrow – characterized by immature white blood

cells

– causes weakened immune system

Leukemia

• Leads to opportunistic infections – occurs because

white blood cells cannot fight infections

– if immune system were healthy, would fight these infections

HIV

• Human immunodeficiency virus (HIV) is a retrovirus – targets the immune

system – attacks and weakens

the immune system – is transmitted by

mixing infected blood with a bodily fluid

HIV

• Leads to AIDS – HIV reproduces in

and destroys T cells

– the body cannot replace T cells fast enough

– T cells cannot help in immune responses

AIDS

• Acquired immune deficiency syndrome – several opportunistic infections

– very low amount of T cells