Viruses and Immune System

Rhinovirus

A virus that infects the mucus membranes of the respiratory tract, causing a cold.

Why don't we become immune to the common cold?

Over 100 different rhinoviruses exist, and they mutate quickly.

Why are viruses considered non-living?

They cannot reproduce on their own and require a host cell.

Virus Structure

Small, non-cellular structures containing their own genetic material.

Why can't antibiotics fight viruses?

Antibiotics target living processes; viruses are non-living.

How does penicillin kill bacteria?

It interferes with the bacteria's ability to build a cell wall.

Bacteria Characteristics

Living organisms with a metabolism, DNA, and the ability to reproduce independently.

Viral Life Cycle: Step 1

The virus attaches to the host cell.

Viral Life Cycle: Step 2

The virus injects its genetic material into the host cell.

Viral Life Cycle: Step 3

The virus uses host cell machinery to build new viruses.

Viral Life Cycle: Step 4

Host cell lysis occurs, releasing new viruses to infect other cells.

What causes the symptoms of viral illness?

The body's own immune system responding to the virus.

Nonspecific External Barriers

The first line of defense, including skin and mucous membranes.

Innate Immune Response

Nonspecific internal defenses including phagocytes, natural killer cells, inflammation, and fever.

Adaptive Immune Response

A specific defense mechanism involving cell-mediated and humoral immunity.

Skin Defense Mechanisms

Sloughing of dead cells and anti-microbial chemicals in sweat and oils.

Mucus and Cilia Defense

Mucus destroys/washes microbes; cilia sweep mucus out of the lungs.

Inflammation Benefits

Dilutes toxins, local heat kills bacteria, and attracts phagocytes.

Fever Benefits

Systemic heat kills temperature-sensitive bacteria and boosts immune efficiency.

Phagocytes

Cells that engulf foreign invaders and alert the immune system.

Acquired Immunity

Immunity gained when the immune system forms a chemical memory of a microbe.

Antibody

Proteins produced by the immune system to tag and destroy invasive microbes.

Antigen

Any protein used by the immune system to recognize self versus non-self.

Steps after invader destruction

Immune response halts, memory cells form, and rapid future defense is established.

How is a cold transmitted?

Viruses reach respiratory mucus membranes via hands, surfaces, or airborne droplets.

Cold vs. Flu: Fever

Fever is rare with a cold, but characteristic with the flu.

Cold vs. Flu: Fatigue

Fatigue is mild with a cold, but lasts 2 to 3 weeks with the flu.

Allergy

An immune system reaction to harmless foreign antigens like pollen or food.

Autoimmune Disorder

A condition where the immune system attacks the body's own self proteins.