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Studying Disease Disease terminology Health: physical, mental, and social well-being—not merely the absence of disease or infirmity Disease: a structural or functional change within the body that is judged to be abnormal Minor abnormalities that cause no problems are considered variations of the normal state (A)etiology: the study of the factors that cause a disease Pathophysiology: the study of underlying physiological features of disease Idiopathic: a term that refers to a disease with an unknown cause Iatrogenic: its origin an inadvertent outcome of medical treatment Nosocomial: having its origin in the hospital environment Signs and symptoms—the objective and subjective abnormalities associated with a disease Pathogenesis—the pattern of a disease’s development Patterns of disease Epidemiology* is the study of the occurrence, distribution, and transmission of diseases in human populations Endemic diseases are native to a local region Epidemics occur when a disease affects an unusually large proportion of the population at the same time Patterns of disease Pandemics are widespread, perhaps global, epidemics Discovering the cause of a disease is difficult because many factors affect disease causation Disease can be fought through prevention and therapy (treatment) *HS320: Principles of Epidemiology Mechanisms of Disease Genetic mechanisms Abnormalities in the genetic makeup of the individual or genetic abnormalities acquired in utero Pathogenic organisms and particles: Infectious agents Tumors and cancer Physical and chemical agents: Injury due to external forces or agents Malnutrition Autoimmunity: Overreaction or unwanted reactions of the immune system Inflammation: Vascular and cellular response to injury Degeneration: Sub-lethal cell injury Physical Determinants of Health* Genetic factors Age Lifestyle Stress Environmental factors Preexisting conditions *Note: all of the above risk factors need to be considered with respect to their relationship to the social determinants of health, discussed in detail in HS200: Social Determinants of Health Pathogenic Organisms Viruses Microscopic, intracellular parasites that consist of a nucleic acid core with a protein coat Invade host cells and pirate organelles and raw materials Classified by shape, nucleic acid type, and method of reproduction Prions Pathogenic protein molecules Convert normal proteins to abnormal proteins, causing abnormal functions that produce disease; may be passed on to offspring Cause rare, degenerative disorders of the nervous system such as BSE (Bovine Spongiform Encephalopathy) and vCJD (variant Creutzfeldt-Jakob disease) Bacteria Tiny cells without nuclei Secrete toxins, parasitize host cells, or form colonies Classification By function Aerobic: require oxygen Anaerobic: require no oxygen By staining properties Gram-positive Gram-negative Classification By shape and size Bacilli: rod-shaped cells Cocci: round cells Curved or spiral rods Small bacteria: obligate intracellular parasites Spores: nonreproducing forms of bacteria that resist unfavorable environmental conditions Fungi Simple organisms similar to plants but lacking chlorophyll Yeasts: small, single-celled fungi Molds: large, multicellular fungi Mycotic infections often resist treatment Protozoa Large, single-celled organisms having organized nuclei May infest human fluids and parasitize or destroy cells Major groups Amoebas: dynamic shape; possess pseudopodia Flagellates: possess flagella Ciliates: possess cilia Sporozoa: enter cells during one phase of a two-part life cycle; borne by vectors (transmitters) during the other phase Pathogenic animals (metazoa) Large, complex multicellular organisms Parasitize or otherwise damage human tissues or organs Major groups Nematodes: roundworms Platyhelminths:flatworms and flukes Arthropods: Parasitic mites, ticks, lice, fleas, bedbugs; Biting or stinging wasps, bees, mosquitos, spiders; Often vectors of disease Prevention and Control Mechanisms of transmission Person-to-person contact Can be prevented by education Can be prevented by using aseptic techniques Environmental contact Can be prevented by avoiding contact Can be prevented by safe sanitation practices Opportunistic invasion Can be prevented by avoiding changes in skin and mucous membranes Can be prevented by cleansing of wounds Transmission by a vector Can be prevented by reducing the population of vectors and reducing contact with vectors Prevention and Control Other prevention and treatment strategies Vaccination: stimulates immunity Chemicals that destroy or inhibit pathogens Antibiotics: natural compounds derived from living organisms Synthetic compounds (for example, ACV and AZT) Tumors and Cancer Neoplasms (tumors): abnormal growths of cells Benign tumors remain localized Malignant tumors spread, forming secondary tumors Metastasis: cells leave a primary tumor and start a secondary tumor at a new location Tumors and Cancer Classification of tumors Benign, epithelial tumors Papilloma: a fingerlike projection Adenoma: a glandular tumor Nevus: a small, pigmented tumor Benign, connective tissue tumors Lipoma: an adipose (fat) tumor Osteoma: a bone tumor Chondroma: a cartilage tumor Tumors and Cancer Classification of tumors Carcinomas (malignant epithelial tumors) Melanoma: involves melanocytes Adenocarcinoma: glandular cancer Sarcomas (connective tissue cancers) Lymphoma: lymphatic cancer Osteosarcoma: bone cancer Myeloma: a bone marrow tumor Fibrosarcoma: cancer of fibrous tissue Tumors and Cancer What causes the wide variety of cancers is still not clearly understood All cancers involve uncontrolled cell division and in some instances prolonged cell lifespan Factors known to play a role in causing cancer Genetic factors: oncogenes (cancer genes) Carcinogens: chemicals that alter genetic activity (e.g. mutagens) Age Environment Viruses Pathogenesis of cancer Early detection is (likely) important Methods of detecting cancers Self-examination Diagnostic imaging: radiography (e.g., mammogram and CT scan), magnetic resonance imaging (MRI), ultrasonography Biopsy (e.g., Pap smear) Blood tests Tumors and Cancer Cachexia: a syndrome including appetite loss, weight loss, and general weakness Causes of death by cancer: secondary infections, organ failure, hemorrhage, and undetermined factors Treatments Surgery Chemotherapy (chemical therapy) Radiation therapy (radiotherapy) Laser therapy Immunotherapy New strategies (for example, vaccines) Inflammation The inflammatory response Signs: redness, heat, swelling, and pain Inflammation mediators (e.g. histamine) Some cause blood vessels to dilate, increasing blood volume (redness and heat), allowing white blood cells to travel quickly to the site of injury Some increase blood vessel permeability (causing edema and pain), allowing white blood cells to move easily to the site of injury Accumulated fluid (inflammatory exudate) dilutes the irritant at the site of injury; these fluids are removed from inflamed tissues via lymphatic vessels, which pass it through lymph nodes that remove dead cells and pathogens Some attract white blood cells to the site of injury White cells move to the site of injury by chemotaxis, where they phagocytize foreign cells and dead or damaged host cells “Pus” is a combination of dead tissue, bacterial cells, white blood cells, and foreign matter Inflammatory diseases Inflammation can be local or systemic (body-wide), acute or chronic Fever—high body temperature caused by a resetting of the body’s “thermostat”–destroys pathogens and enhances immunity Chronic inflammation can constitute a disease itself because it causes damage to tissues