Micro. MedTerm Study Guide

Viruses

• Definition: Microscopic parasites, non-living organisms.

• Composition: Made up of either DNA or RNA.

• Replication: Cannot multiply independently; must infect a host cell to replicate.

Viral Processes

• Penetration: The initial step involves bonding to the host cell; this process requires intimate contact with the host.

• Lytic Cycle:

  • Description: This cycle involves viral replication that leads to the destruction of the host cell, a process known as lysis.

  • Example: A host cell may burst from overcrowding, akin to bursting a water balloon.

• Lysogenic Cycle:

  • Description: In this cycle, viral DNA integrates into the host's chromosomes, allowing the virus to be passed to daughter cells without immediate lysis.

  • Characterization: The virus essentially hides within the cell's DNA.

Prions

• Definition: Abnormally folded proteins that are associated with neurodegenerative diseases.

Bacteria

• Bacterial Shapes:

  • Bacilli: Rod-shaped bacteria; often represented as a pair of circles.

  • Streptobacilli: These bacteria form chains.

  • Staphylococcus: This type forms clusters or stacks, resembling grapes.

• Endospore Forming Bacteria:

  • Characteristics: These bacteria are resistant to heat and are relevant in cases such as Clostridium difficile (C-Diff).

Immunology

• Definition: The scientific study of the genetic, biological, and physical characteristics of the immune system.

Key Terms

• Immunity: The body's ability to respond to foreign substances by recognizing, fighting, and remembering them.

• Antigens: Substances that bind to the components of the immune system, particularly white blood cells.

• Allergens: Substances that cause allergic reactions, such as pollen and egg whites.

• Autoantigens: Proteins that are interpreted as non-self by the immune system, potentially leading to autoimmune responses.

Transplants (Grafts)

• Autografts: Tissues transplanted from one part of an individual to another part of the same individual.

• Isografts: Transplants that occur between identical twins.

• Allografts: Transplants obtained from another person, not genetically identical.

• Xenografts: Transplants that occur between different species; for example, a heart valve from a pig.

Antibodies

• Function: Specialized proteins that fight infections within the body.

Lymphatic System

• Lymphatic Vessels: Structures that drain lymph into larger lymphatic vessels, playing a critical role in the immune response.

Body Defenses

• First Line of Defense: Physical barriers such as:

  • Skin

  • Mucous membranes

  • Ciliary escalators

  • Tears

  • Saliva

  • Urine flow

• Second Line of Defense: Mechanisms such as phagocytosis (cell eating), where the body removes unwanted substances.

• Pyrexia (Fever): A systemic response to inflammation or infection that is regulated by the hypothalamus.

Types of Immunity

• Active Immunity: This arises from direct exposure to a pathogen.

  • Naturally Acquired: Immunity developed after illness and recovery from an infection.

  • Artificially Acquired: Immunity gained when the body produces antibodies responding to vaccinations.

• Passive Immunity: This is an indirect type of immunity in which an individual is exposed to antibodies.

  • Naturally Acquired: Maternal antibodies passed to infants through breastfeeding.

  • Artificially Acquired: Antibodies that are infused via vaccines.

• Herd Immunity: This refers to immunity within a population as a result of a significant portion of individuals being immune.

Hypersensitivity & Autoimmune Disorders

• Hypersensitivity Reactions: Immune responses triggered by allergens.

• Delayed Hypersensitivity: A type 4 allergy that requires 24 hours or more to develop.

• Examples of Autoimmune Disorders:

  • Myasthenia Gravis: An autoimmune condition that leads to muscle weakness.

  • Multiple Sclerosis: A chronic autoimmune disorder that causes demyelination of the central nervous system (CNS).

  • Graves' Disease: An autoimmune disorder where the immune system attacks the body’s own thyroid gland.

  • Systemic Lupus Erythematosus (SLE): An autoimmune disorder that targets healthy tissues leading to chronic inflammation.

  • Rheumatoid Arthritis: An autoimmune disorder that specifically attacks the cells surrounding the joints.

• Immune Senescence: The gradual deterioration of the immune system that occurs with aging.

Symbiotic Relationships

• Mutualism: A relationship where both organisms benefit.

• Commensalism: A relationship where one organism benefits while the other is neither helped nor harmed.

• Parasitism: A relationship where one organism benefits at the expense of another (e.g., ringworms, tapeworms).

• Amensalism: A relationship in which one organism inhibits the growth and survival of another without being affected itself.

Pathogens & Infection

• Pathogens: Microorganisms that are capable of causing infections.

• Contamination: The presence of microbes on or within the body, such as cases with C-Diff.

Portal of Entry

• Definition: The specific site where pathogens enter the host, commonly through mucous membranes.

• Exogenous Source: Microbes originating from outside the body.

• Endogenous Source: Microbes that are already present within the body.

• Normal Flora: Naturally occurring microorganisms that typically do not cause harm.

Steps of Infection

1. Adhesion: The infection begins with the attachment of pathogens to host cells.

2. Colonization: The pathogens multiply within the host.

3. Invasion: Pathogens penetrate the tissues of the host.

4. Evasion of Host Defense: Pathogens develop mechanisms to survive the immune response.

5. Toxins: Pathogens may produce toxins that damage the host's tissues (toxigenic).

6. Portal of Exit: Pathogens exit the host to potentially infect other individuals.

Types of Infection

• Local Infection: Confined to a specific area.

• Focal Infection: Localized infection that can spread to other areas.

• Systematic Infection: Widespread infection affecting the entire body.

• Mixed Infection: Presence of multiple types of pathogens simultaneously.

• Acute Infection: Characterized by rapid onset and severe symptoms.

• Chronic Infection: Persistent infection with less severe symptoms.

• Primary Infection: The first infection a person experiences.

• Secondary Infection: Follows after an initial (primary) infection.

Epidemiology

• Definition: Study of how, where, and why diseases occur.

• Prevalence: The total number of existing cases of a condition in a population at a given time.

• Incidence: The updated number of new cases within a specified timeframe.

• Endemic: A disease or condition characteristic of a specific population or area, e.g., flu, pneumonia.

• Sporadic Disease: Occurs occasionally or sporadically, e.g., measles.

• Epidemic: An increase in the number of cases in a specific area.

• Pandemic: An outbreak that spreads across multiple countries or worldwide, e.g., COVID-19, swine flu.

Transmission of Infections

• Animal Reservoirs: Zoonotic diseases transmitted from animals to humans.

• Vector: Organisms, often insects or mosquitos, that transmit pathogens.

• Direct Contact: Transmission from person to person through physical interaction.

• Indirect Contact: Transmission via contaminated objects such as tissues, towels, or bedding.

• Droplet Transmission: Spread of pathogens through respiratory droplets produced when an infected person sneezes or coughs.

• Airborne Transmission: Pathogens that travel through dust particles in the air.

Prevention Strategies

• Vaccinations: Providing immunity against specific pathogens.

• Proper Hand Hygiene: Regular handwashing to prevent infection transmission.

• Infection Control in Healthcare: Protocols in medical settings to prevent healthcare-acquired infections (nosocomial infections).

• Reminder: It is crucial to ALWAYS wash hands before and after any contact.

Mycology (Fungi)

• Definition: The study of fungi.

• Types of Fungi:

  • Yeasts: Single-celled fungi.

  • Molds: Multicellular fungi forming filamentous structures.

  • Fleshy Fungi: Includes mushrooms and similar structures.

• Dimorphic Fungi: Fungi that can exist in two forms, typically yeast and mold forms.

• Penicillium: A type of mold that produces penicillin, an important antibiotic.

Other Microorganisms

• Algae: Photosynthetic, aquatic organisms that can cause food poisoning, illustrated by shellfish poisoning and phenomena such as red tide.

• Protozoans: Eukaryotic, unicellular organisms that lack a cell wall and require moist environments to survive.

• Helminths: Worms that can be found in blood, feces, or urine, including flatworms and roundworms.

  • Transmission: Can be inhaled or ingested and are typically treated with antiparasitic medications.

• Eukaryotic Organisms: The category encompasses bacteria, fungi, protozoans, algae, and helminths, representing diverse forms of life.