Chapter 6

Mechanisms of Disease

Learning Objectives for Lesson 6.1: Mechanisms of Disease and Pathogenic Organisms

  • Explain the study of disease:

    • Includes disease terminology and patterns of disease.

  • List and describe:

    • Basic mechanisms of disease and risk factors associated with disease.

    • Six categories of pathogenic organisms and how they cause disease.

Studying Disease (1 of 2)

  • Disease terminology:

    • Health: Physical, mental, and social well-being—not merely the absence of disease.

    • Disease: An abnormality in body function that threatens health.

    • Etiology: Study of the factors that cause a disease.

Studying Disease (2 of 2)

  • More disease terminology:

    • Idiopathic: Refers to a disease with an unknown cause.

    • Signs and symptoms: Objective (observable) and subjective (reported by the patient) abnormalities associated with a disease.

    • Pathogenesis: Pattern of a disease’s development.

Patterns of Disease (1 of 2)

  • Epidemiology: 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.

Patterns of Disease (2 of 2)

  • Pandemics: Widespread, possibly global, epidemics.

  • Challenges in disease discovery: Discovering the cause of a disease is difficult because many factors affect disease transmission.

  • Fight against diseases: Disease can be fought through prevention and therapy (treatment).

Pathophysiology (1 of 3)

  • Mechanisms of disease:

    • Pathophysiology: Study of underlying physiological aspects of disease.

    • Genetic mechanisms: Pathological changes due to genetic factors.

    • Infectious mechanisms: Involvement of pathogenic organisms and particles.

    • Neoplastic mechanisms: Tumors and cancer development.

    • Traumatic mechanisms: Result from physical and chemical agents affecting health.

Pathophysiology (2 of 3)

  • More mechanisms of disease:

    • Metabolic mechanisms:

    • Endocrine imbalances

    • Malnutrition

    • Inflammatory mechanisms:

    • Autoimmunity

    • Inflammation

    • Degeneration

Pathophysiology (3 of 3)

  • Risk factors associated with disease:

    • Genetics

    • Age

    • Lifestyle

    • Stress

    • Environment

    • Preexisting conditions

Pathogenic Organisms

Viruses

  • Characteristics:

    • Microscopic, intracellular parasites that consist of a nucleic acid core surrounded by a protein coat.

    • Invade host cells to commandeer organelles and raw materials.

  • Classification:

    • By shape, nucleic acid type, 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 (polio)

Prions (1 of 2)

  • Definition: Pathogenic protein molecules that convert normal proteins to abnormal forms, causing abnormal functions that produce disease; may be hereditary.

  • Examples of diseases:

    • Bovine Spongiform Encephalopathy (BSE)

    • Variant Creutzfeldt-Jakob disease (vCJD)

Prions (2 of 2)

  • References:

    • Travis J: Drugs counter mad cow agent in cells, Science News 160(7):100, 2001.

Bacteria

  • Characteristics:

    • Tiny cells without nuclei.

    • May secrete toxins, parasitize host cells, or form colonies.

  • Classification:

    • By growth requirements:

    • Aerobic: Require oxygen.

    • Anaerobic: Require no oxygen.

Bacteria Classification (1 of 2)

  • By staining properties (depend on composition of cell wall):

    • Gram-positive

    • Gram-negative

Bacteria Classification (2 of 2)

  • By shape and size:

    • Bacilli: Rod-shaped cells.

    • Cocci: Round cells.

    • Curved or spiral rods.

    • Small bacteria: Obligate parasites.

    • Spores: Non-reproducing forms that resist unfavorable environmental conditions.

Fungi

  • Characteristics:

    • Simple organisms similar to plants but lacking chlorophyll.

  • Types:

    • Yeasts: Small, single-celled fungi.

    • Molds: Large, multicellular fungi.

  • Mycotic infections: Often resist treatment.

Protozoa

  • Definition: Large one-celled organisms with organized nuclei.

  • Function: May infest human fluids and parasitize or destroy cells.

Major Groups of Protozoa

  • Amebas: Possess pseudopodia for movement.

  • Flagellates: Possess flagella for locomotion.

  • Ciliates: Possess cilia for movement.

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

Pathogenic Animals

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

Major Groups of Pathogenic Animals

  • Nematodes: Roundworms.

  • Platyhelminths: Flatworms and flukes.

  • Arthropods: Often serve as vectors of disease such as:

    • Parasitic mites, ticks, lice, fleas.

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

Learning Objectives for Lesson 6.2: Understanding Pathogen Prevention and Control, Cancer, and Inflammation

  • List and describe ways pathogens can spread, as well as prevention and control measures.

  • Distinguish between the terms benign and malignant.

  • Describe the pathogenesis of cancer.

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

Prevention and Control (1 of 2)

  • Mechanisms of transmission:

    • Person-to-person contact:

    • Can be prevented by education and using aseptic techniques.

    • Environmental contact:

    • Can be prevented by avoiding contact and implementing safe sanitation practices.

Prevention and Control (2 of 2)

  • Mechanisms of transmission:

    • Opportunistic invasion:

    • Prevented by avoiding changes in skin and mucous membranes and cleansing of wounds.

    • Transmission by a vector:

    • Prevented by reducing vector populations and minimizing exposure to them.

Prevention and Treatment Strategies

  • Vaccination: Stimulates immunity against pathogens.

  • Drug therapy: Aims to destroy or inhibit pathogens.

    • Antibiotics: Natural compounds derived from living organisms; resistance is an important consideration.

    • Antiviral drugs: Aim to inhibit viral reproduction and slow the progression of viral infections.

Tumors and Cancer (1 of 3)

  • Neoplasms (tumors): Abnormal growths of cells.

    • Benign tumors: Remain localized.

    • Malignant tumors: Spread, forming secondary tumors.

    • Metastasis: Process where cells leave primary tumor and begin secondary tumors at new locations.

Tumors and Cancer (2 of 3)

  • Classification of tumors:

    • Benign epithelial tumors:

    • Papilloma: Fingerlike projection.

    • Adenoma: Glandular tumor.

    • Nevus: Small, pigmented tumor.

    • Benign connective tissue tumors:

    • Lipoma: Adipose (fat) tumor.

    • Osteoma: Bone tumor.

    • Chondroma: Cartilage tumor.

Tumors and Cancer (3 of 3)

  • Malignant tumors:

    • Carcinomas (malignant epithelial tumors):

    • Melanoma: Cancer involving melanocytes.

    • Adenocarcinoma: Glandular cancer.

    • Sarcomas (connective tissue cancers):

    • Lymphoma: Cancer of lymphatic tissues.

    • Osteosarcoma: Bone cancer.

    • Myeloma: Bone marrow tumor.

    • Fibrosarcoma: Cancer of fibrous tissue.

Causes of Cancer (1 of 2)

  • Overview: Causes of cancer are varied and still not fully understood.

    • Cancer involves hyperplasia (growth of excessive cells) and anaplasia (development of undifferentiated cells).

Causes of Cancer (2 of 2)

  • Factors influencing cancer:

    • Genetic factors: e.g., oncogenes (cancer genes).

    • Carcinogens: Chemicals that alter genetic activity.

    • Age: Changes in cell activity over time or accumulated effects of cell damage.

    • Environment: Chronic exposure to damaging substances.

    • Viruses: Cause changes in genetic “machinery.”

Pathogenesis of Cancer

  • Signs of cancer:

    • Early identification through various detection methods:

    • Self-examination

    • Diagnostic imaging:

      • Radiography (mammogram and computed tomography [CT] scan).

      • Magnetic resonance imaging (MRI).

      • Ultrasonography.

    • Biopsy:

      • e.g., Pap smear.

    • Blood tests.

Staging, Grading, and Complications

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

  • Grading: Assessing the likely pattern of a tumor’s development.

  • Cachexia: Syndrome including appetite loss, weight loss, and general weakness associated with cancer.

  • Causes of death by cancer:

    • Secondary infections, organ failure, hemorrhage, and undetermined factors.

Cancer Treatment

  • Methods:

    • Surgery: Removal of malignant tissues.

    • Chemotherapy (chemical therapy): Use of drugs to kill cancer cells.

    • Radiation therapy (radiotherapy): Use of high-energy rays to destroy cancer cells.

    • Laser therapy: Focused light technology to remove tumors.

    • Immunotherapy: Enhancing the immune response against cancer cells.

    • New strategies: Rational drugs targeting specific molecules, enzymes, or receptors involved in cancer progression.

Inflammation (1 of 2)

  • Inflammatory response: Reduces injury to tissues, maintaining homeostasis.

  • Signs of inflammation: Redness, heat, swelling, and pain.

  • Inflammation mediators:

    • Histamine, prostaglandins, and kinins.

    • Some cause blood vessels to dilate, increasing blood volume leading to redness and heat; and aid white blood cells’ movement to injury sites.

Inflammation (2 of 2)

  • Mechanism of inflammatory mediators:

    • Increase blood vessel permeability leading to swelling (edema) and pain.

    • Allow white blood cells to move easily out of vessels, dilute irritants, and allow for exudate accumulation.

    • Attract white blood cells to injury sites (chemotaxis).

Typical Inflammatory Response to Mechanical Injury

  • Bacteria introduced (e.g., by a splinter penetration).

  • White blood cell migration through blood vessel walls, followed by phagocytizing bacteria to clear infection.

Inflammatory Disease

  • Nature of inflammation: Can be local (specific area) or systemic (bodywide).

  • Fever: High body temperature due to resetting the body’s thermostat; helps destroy pathogens and enhances immunity.

  • Chronic inflammation: Can become a disease in itself, as it damages tissues over time.