Chapter 6: Mechanisms of Disease

Chapter 6: Mechanisms of Disease

Mrs. Sweeney

Learning Objectives

Lesson 6.1: Mechanisms of Disease and Pathogenic Organisms

  • Explain the study of disease, including disease terminology and patterns of disease.

  • List and describe the basic mechanisms of disease and risk factors associated with disease.

  • List and describe six categories of pathogenic organisms and explain how they cause disease.

Studying Disease

Disease Terminology

  • Health:

    • Defined as physical, mental, and social well-being—not merely the absence of disease.

  • Disease:

    • An abnormality in body function that threatens health.

  • Etiology:

    • The study of the factors that cause a disease.

Additional Terminology

  • Idiopathic:

    • Refers to a disease with an unknown cause.

  • Signs and Symptoms:

    • Signs: Objective abnormalities associated with a disease.

    • Symptoms: Subjective abnormalities reported by the patient.

  • Pathogenesis:

    • The pattern of a disease’s development.

Patterns of Disease

Epidemiology

  • Epidemiology:

    • The study of occurrence, distribution, and transmission of diseases in human populations.

  • Endemic Diseases:

    • Diseases that are native to a local region.

  • Epidemics:

    • Occur when a disease affects many people at the same time.

  • Pandemics:

    • Widespread, perhaps global epidemics.

  • There are many factors affecting disease transmission, making it difficult to discover causes.

  • Disease can be combated through prevention and therapy (treatment).

Pathophysiology

Mechanisms of Disease

  • Pathophysiology:

    • Study of the underlying physiological aspects of disease.

  • Basic mechanisms of disease include:

    • Genetic mechanisms

    • Infectious mechanisms: Pathogenic organisms and particles.

    • Neoplastic mechanisms: Tumors and cancer.

    • Traumatic mechanisms: Physical and chemical agents.

    • Metabolic mechanisms: Such as endocrine imbalances and malnutrition.

    • Inflammatory mechanisms: Including autoimmunity, inflammation, and degeneration.

Risk Factors

  • Risk Factors:

    • Genetics

    • Age

    • Lifestyle

    • Stress

    • Environment

    • Preexisting conditions

Pathogenic Organisms

Viruses

  • Viruses:

    • Microscopic, intracellular parasites consisting of a nucleic acid core with a protein coat.

    • They invade host cells and utilize host organelles and raw materials for replication.

    • Classification is based on shape, type of nucleic acid, and method of reproduction.

  • Examples of Viruses:

    • DNA viruses:

    • Vaccinia virus (cowpox)

    • RNA viruses:

    • Paramyxovirus (mumps)

    • Herpes simplex virus (fever blister)

    • HIV (AIDS)

    • Rhinovirus (common cold)

    • Adenovirus (respiratory virus)

    • Poliovirus (poliomyelitis)

Prions

  • Prions:

    • Pathogenic protein molecules that convert normal proteins into abnormal proteins, disrupting normal functions and potentially being inherited.

    • Associated with rare degenerative disorders of the nervous system, such as:

    • Bovine spongiform encephalopathy (BSE)

    • Variant Creutzfeldt-Jakob disease (vCJD)

Bacteria

  • Bacteria:

    • Tiny cells without nuclei that can secrete toxins, parasitize host cells, or form colonies.

  • Classification of Bacteria:

    • By growth requirements:

    • Aerobic: Requires oxygen for growth.

    • Anaerobic: Does not require oxygen.

    • By staining properties (based on the composition of cell walls):

    • Gram-positive

    • Gram-negative

    • By shape and size:

    • Bacilli: Rod-shaped cells.

    • Cocci: Round cells.

    • Curved or spiral rods

    • Spores: Nonreproducing forms of bacteria that resist unfavorable environmental conditions.

Fungi

  • Fungi:

    • Simple organisms similar to plants but lacking chlorophyll.

    • Yeasts: Small, single-celled fungi.

    • Molds: Large, multicellular fungi.

    • Mycotic infections: Often resist treatment.

Protozoa

  • Protozoa:

    • Large, one-celled organisms that contain organized nuclei and may infest human fluids to parasitize or destroy cells.

  • Major Groups of Protozoa:

    • Amebas: Possess pseudopodia.

    • Flagellates: Have flagella.

    • Ciliates: Possess cilia.

    • Sporozoa (coccidia): Enter host cells during one phase of a two-part life cycle and are borne by vectors during the other phase.

Pathogenic Animals

  • Pathogenic Animals:

    • Large, complex multicellular organisms that parasitize or damage human tissues or organs.

  • Major Groups of Pathogenic Animals:

    • Nematodes: Roundworms.

    • Platyhelminths: Flatworms and flukes.

    • Arthropods: Often serve as vectors of disease, including:

    • Parasitic mites, ticks, lice, fleas.

    • Biting or stinging wasps, bees, mosquitoes, spiders.

Learning Objectives

Lesson 6.2: Understanding Pathogen Prevention and Control, Cancer, and Inflammation

  • List and describe ways pathogens can be spread, alongside prevention and control measures.

  • Distinguish between benign and malignant tumors.

  • Describe the pathogenesis of cancer.

  • Outline the events of inflammatory response and explain its role in disease.

Prevention and Control

Mechanisms of Transmission

  • Person-to-person contact: Preventable through education and aseptic techniques.

  • Environmental contact: Preventable by avoiding contact and practicing safe sanitation.

  • Opportunistic invasion: Prevented by avoiding changes in skin and mucous membranes and through proper wound care.

  • Transmission by vectors: Preventable by reducing vector populations and contact with vectors.

Prevention and Treatment Strategies

  • Vaccination: Stimulates immunity against diseases.

  • Drug therapy: Destroys or inhibits pathogen growth.

    • Antibiotics: Natural compounds derived from living organisms; crucial consideration of antibiotic resistance.

    • Antiviral drugs: Inhibit viral reproduction and slow down the progression of viral infections.

Tumors and Cancer

Neoplasms (Tumors)

  • Defined as abnormal growths of cells categorized as:

    • Benign tumors: Remain localized, not usually harmful.

    • Malignant tumors: Spread and form secondary tumors, known as metastasis, where cells leave the primary tumor to establish secondary tumors in new locations.

Classification of Tumors

  • Benign Epithelial Tumors:

    • Papilloma: Fingerlike projections.

    • Adenoma: Glandular tumor.

    • Nevus: Small pigmented tumor.

  • Benign Connective Tissue Tumors:

    • Lipoma: Adipose (fat) tumor.

    • Osteoma: Bone tumor.

    • Chondroma: Cartilage tumor.

  • Malignant Tumors:

    • Carcinomas: Malignant epithelial tumors, such as:

    • Melanoma: Involves melanocytes.

    • Adenocarcinoma: Glandular cancer.

    • Sarcomas: Cancers of connective tissue, including:

    • Lymphoma: Lymphatic cancer.

    • Osteosarcoma: Bone cancer.

    • Myeloma: Bone marrow tumor.

    • Fibrosarcoma: Cancer of fibrous tissue.

Causes of Cancer

  • Cancer causes are varied and not fully understood, particularly concerning:

    • Hyperplasia: Growth of too many cells.

    • Anaplasia: Development of undifferentiated cells.

  • Contributing factors include:

    • Genetic Factors: Such as oncogenes (cancer genes).

    • Carcinogens: Chemicals altering genetic activity.

    • Age: Changes in cell activity over time.

    • Environment: Chronic exposure to damaging substances.

    • Viruses: Cause changes in genetic “machinery.”

Pathogenesis of Cancer

  • Cancer detection methods include:

    • Self-examination: Personal medical checks for abnormalities.

    • Diagnostic Imaging:

    • Radiography: Includes mammograms and CT scans.

    • Magnetic Resonance Imaging (MRI).

    • Ultrasonography.

    • Biopsy: E.g., Pap smears for histological analysis.

    • Blood Tests: Check for markers related to cancer.

Staging, Grading, and Complications

  • Staging: Classifying tumors by size and extent of spread.

  • Grading: Assessing likely tumor development patterns.

  • Cachexia: A syndrome including appetite loss, weight loss, and general weakness that complicates cancer cases.

  • Causes of Death by Cancer: Complications such as secondary infections, organ failure, hemorrhage, and undetermined factors.

Cancer Treatment

  • Surgery: Removal of tumors.

  • Chemotherapy: Chemical treatment aimed at cancer cells.

  • Radiation Therapy: Radiation to kill cancer cells.

  • Laser Therapy: Using lasers for precision in targeting tumors.

  • Immunotherapy: Harnesses the immune system to fight cancer.

  • New Strategies: Such as rational drugs targeting specific molecules, enzymes, or receptors.

Inflammation

Inflammatory Response

  • Inflammatory response: A process reducing injury to tissues, thus maintaining homeostasis.

  • Signs of Inflammation:

    • Redness, heat, swelling, and pain.

  • Inflammation Mediators: Include histamine, prostaglandins, and kinins.

    • Some mediators cause blood vessel dilation (results in redness and heat).

    • Promote rapid white blood cell travel to injury sites.

Mediators and Effects

  • Some inflammation mediators increase blood vessel permeability (causing swelling or edema and pain).

  • White blood cells move easily out of vessels to combat pathogens; irritants are diluted, and exudate accumulates.

  • Certain mediators attract white blood cells to the injury site (chemotaxis).

Response to Injury

  • Example of a typical inflammatory response involves:

    • Introduction of bacteria via splinter, leading to white blood cells migrating through blood vessel walls to phagocytize bacteria, thus combating infection.

Inflammatory Disease

  • Inflammation can be either local or systemic (bodywide).

  • Fever: High body temperature as a response to infection; results from a resetting of the body’s “thermostat”; helps destroy pathogens and enhances immunity.

  • Chronic inflammation can become a disease itself as it can damage tissues.

Questions?

Additional queries regarding the mechanisms of disease or specific topics can be addressed as needed.