Infectious Diseases & Immune System Review (Lecture Notes)

Question-and-answer flashcards covering key concepts from Infectious Diseases, Transmission, Immunity (innate and adaptive), vaccines, and antibiotic resistance as described in the notes.

What is an infectious disease?

A disease caused by a pathogen or external factor.

What is a non-infectious disease?

A disease caused by an internal factor within the body.

Define a pathogen.

An agent that can cause a disease.

Name the three main modes of pathogen transmission.

Airborne (droplets or dust), Vector-borne (via living vector), and Contact (direct or indirect via objects).

What does pathogenicity mean?

The potential of the pathogen to cause disease (likelihood).

How is the R number defined?

The average number of new infections caused by one infected person in a completely susceptible population.

Differentiate epidemic from pandemic.

Epidemic = widespread outbreak in a geographic area; Pandemic = widespread global outbreak.

List some factors that reduce the spread of infectious disease.

Antibiotics, vaccines, hygiene, and improved public awareness.

Give three disease-control strategies.

Control carriers (pesticides, DDT); Kill the pathogen (antibiotics, disinfectants); Herd immunity by mass immunisation.

What is quarantine?

Isolating those infected or possibly infected to prevent spread.

How can pathogens enter host cells via receptor-mediated endocytosis?

Pathogen binds to host cell receptors; cell membrane folds inward to form a vesicle; vesicle is digested and contents released into the cytoplasm.

What happens in viral membrane fusion?

Virus binds a receptor; viral envelope fuses with host cell membrane; virus enters the cell.

Name the innate immune system physical barriers.

Skin, eyes (tears), and blood components (platelets involved in clotting).

What role do tears play in innate defense?

They remove and inhibit growth of microorganisms.

How does the respiratory tract contribute to innate immunity?

Nose, trachea and bronchi have mucous membranes; mucus traps pathogens; cilia sweep them out; coughing/sneezing expels them.

What components in the digestive system help prevent infection?

Saliva enzymes and stomach acid (hydrochloric acid) help inhibit pathogens.

What role do gut bacteria play in immunity?

They help prevent colonisation by pathogens.

What are phagocytes and what do they do?

Neutrophils and macrophages; recognize and kill microbes by phagocytosis.

What are cytotoxic (killer) cells?

Natural killer (NK) cells; recognize and kill infected cells.

What are mast cells and basophils responsible for?

Inflammatory cells that release chemicals to recruit other immune cells.

What is the complement system?

A group of more than 30 blood proteins that attract and support white blood cells; some proteins destroy pathogen membranes.

What is inflammation?

A tissue response to injury or infection involving histamine release, increased blood flow and permeability, and recruitment of phagocytes and cytotoxic cells; causes swelling and redness.

What are the two main features of the acquired immune system?

Specificity and memory.

What are lymphocytes?

B cells and T cells; the effector cells of the adaptive immune system.

Where do B cells mature and where do they travel?

Mature in the bone marrow; travel to lymphoid tissues such as the spleen and lymph nodes.

Where do T cells mature?

In the thymus.

Name some lymphoid organs.

Bone marrow, thymus, spleen, tonsils, adenoids, appendix, and lymph nodes.

What is humoral immunity?

Involves B lymphocytes and antibodies.

What is cell-mediated immunity?

Involves T lymphocytes.

What do B cells do?

Produce antibodies (immunoglobulins) that neutralise pathogens.

What are plasma cells?

Specialised antibody factories that produce antibodies; long as activated.—(Note: produced 5–8 days after activation in notes)

What are memory B cells?

Long-lived B cells that remain in lymph tissues and provide faster immunity after re-exposure.

What are the four main types of T cells and their roles?

Helper T cells (activate B and cytotoxic T cells); Killer/cytotoxic T cells (destroy infected cells); Suppressor/regulatory T cells (regulate immune response); Memory T cells (long-lasting and help sustain immunity).

What is the function of helper T cells?

Recognise antigens on APCs and secrete interferon and cytokines to stimulate B cells and cytotoxic T cells.

What is the function of killer T cells?

Destroy abnormal body cells (virus-infected or cancer cells) by releasing perforin to lyse target cells.

What is the function of suppressor T cells?

Regulate the immune system to prevent damage after the pathogen is cleared.

What is the function of memory T cells?

Survive long-term and can stimulate memory B cells or killer T cells to provide rapid immunity upon re-exposure.

What is the role of antigen receptors on B and T cells?

Each carries customised receptors to recognize specific antigens and respond accordingly.

What are cytokines?

Signalling proteins (interleukins, growth factors, interferons) that coordinate immune responses.

What is antigen presentation (APCs)?

Antigen presenting cells display antigens to activate lymphoid cells.

How do humoral and cell-mediated immunity differ in terms of effector cells?

Humoral uses B cells to produce antibodies; cell-mediated uses T cells to destroy infected cells.

What is natural immunity: active vs passive?

Active: infection triggers antibody production; Passive: antibodies transferred (e.g., via breast milk/colostrum).

What is artificial immunity: active vs passive?

Active: vaccination stimulates antibody production; Passive: antibodies injected provide temporary protection.

What is colostrum?

First milk rich in antibodies passed from mother to baby.

What are the main types of vaccines mentioned?

Live attenuated, dead/inactivated, subunit, and mRNA vaccines.

What is herd immunity and its threshold as per notes?

Protection for the population achieved when about 80–85% are vaccinated.

How does antibiotic resistance develop according to the notes?

Dose 1 kills most; some resistant survive; dose 2 kills remaining non-resistant; resistant strains reproduce; natural mutations confer resistance and spread.

Name some classes of antibiotics and their targets.

Beta-lactams inhibit cell wall formation; Sulphonamides inhibit DNA synthesis; Aminoglycosides inhibit protein synthesis.

Why is antibiotic overuse a concern?

Over-prescription and use in livestock promote resistance.

What are some uses of antibiotics listed in the notes?

Transplants, dialysis, suppressed immune systems, surgery, and treatment of bacterial infections.

What is a key function of lysosomes in the innate immune system?

Degrade pathogens and cellular debris and act as signaling hubs to regulate immune cell metabolism and function.

What is the role of the viral capsid?

The protein coat that protects the virus’s genetic material.