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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