Immune System Flashcards

Pathogens

• Pathogens are disease-causing agents that disrupt normal physiology.

• They can be cellular (bacteria, fungi, parasites) or non-cellular (viruses, prions).

• Viruses insert genetic material into host cells to multiply.

• Prions are infectious proteins with abnormal folding.

• Bacteria reproduce quickly and compete with host cells.

• Fungi colonize body surfaces.

• Parasites feed on a host (microparasites/protozoa or macroparasites/helminths).

Immune System - Lines of Defense

• First line: Surface barriers prevent pathogen entry.

• Second line: Non-specific defenses activated after infection.

• Third line: Specific responses target antigens from pathogens.

Surface Barriers

• Physical barriers: obstruct access (e.g., skin, mucous membranes).

• Chemical barriers: hinder survival via chemical compounds (e.g., gastric secretions, sweat).

• Microbiological barriers: Natural flora prevent colonization.

Clotting

• Restores intact external layer when surface barriers are penetrated.

• Initiated by clotting factors from damaged cells/platelets.

• Prothrombin converts to thrombin, fibrinogen to fibrin, forming a clot.

Innate Immune System

• Non-specific defense; responds the same way every time.

• Phagocytic leukocytes internalize and digest pathogens.

• Phagocytes recruited by chemotactic chemicals.

• Lymphatic system filters fluid (lymph) and removes pathogens.

• Antigen-presenting cells (APCs) transport antigens to lymphocytes.

Adaptive Immune System

• Specific defense; recognizes specific antigens.

• Produces heightened response upon re-exposure (immunological memory).

• Lymphocytes in lymph nodes are principal components.

Antigens

• Molecular markers on pathogen surfaces.

• Targeted by antibodies.

Lymphocytes

• B and T lymphocytes recognize specific antigens.

• Clonal selection/expansion: lymphocyte activated to divide & form clones.

• Helper T cells coordinate adaptive response, activate B lymphocytes.

• B cells form plasma cells (produce antibodies) and memory cells.

Antibodies

• Proteins produced by B lymphocytes specific to an antigen.

• Y-shaped molecules with variable regions for antigen specificity.

• Facilitate pathogen destruction via opsonization, etc.

Memory Cells

• Produced when B and T lymphocytes divide.

• Enable faster, more potent secondary immune response.

• Provide immunological memory and immunity.

Immunodeficiency

• Compromised or absent immune system.

• HIV infects helper T lymphocytes, leading to AIDS.

• Transmitted via bodily fluids.

Antibiotics

• Target prokaryotic features in bacteria.

• Antibiotic resistance develops via mutations and gene transfer.

Vaccination

• Injection of attenuated pathogens/antigenic fragments to provide active acquired immunity.

• Initiates primary response and memory cell production.

• Secondary response prevents disease symptoms upon exposure.

Herd Immunity

• Indirectly protects non-vaccinated individuals when a large percentage of population is immune.

• Limits pathogen spread.

Outbreaks

• Epidemic: outbreak in a community/region.

• Pandemic: outbreak across a wider geographical area.