1. Chapter 5
Mechanisms of Disease

2. Objectives Define the terms health and disease
List and describe the basic mechanisms of disease and risk factors associated with disease
List and describe five categories of pathogenic organisms and explain how they cause disease

3. Objectives
Distinguish between the terms benign and malignant as they apply to tumors
Describe the pathogenesis of cancer
Outline the events of the inflammatory response and explain its role in disease

4. Studying Disease 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—the study of the factors that cause a disease

5. Studying Disease Disease terminology
Idiopathic—refers to a disease with an unknown cause
Signs and symptoms—the objective and subjective abnormalities associated with a disease
Pathogenesis—the pattern of a disease’s development
What are examples of “signs” of a disease? Signs are objective abnormalities such as a change in blood pressure, temperature, pulse, or respiratory rate.
What are examples of “symptoms” of a disease? Symptoms are subjective and can be felt only by the patient; examples include nausea or pain.

6. Studying Disease Patterns of disease
Epidemiology is the study of occurrence, distribution, and transmission of diseases in human populations
Endemic diseases are native to a local region
Epidemics occur when a disease affects many people at the same time
Epidemiologists are physicians or medical scientists who study patterns of disease occurrence in specific groups.
Where might an epidemiologist be employed? In a hospital, health departments, the CDC, research facilities, or infection control efforts.

7. Studying Disease Patterns of disease, cont’d
Pandemics are widespread, perhaps global, epidemics
Discovering the cause of a disease is difficult because many factors affect disease transmission
Disease can be fought through prevention and therapy (treatment)
Give examples of an endemic, an epidemic, and a pandemic. Endemic is a disease that is native to a local region. Epidemic is a disease that affects many individuals at the same time within a defined geographic region. Pandemic is an epidemic that has spread throughout the world.

8. Pathophysiology Mechanisms of disease
Pathophysiology—the study of underlying physiological aspects of disease
Genetic mechanisms
Infectious mechanism (pathogenic organisms and particles)
Neoplastic mechanism (tumors and cancer)
Traumatic mechanism (physical and chemical agents)
What is a parasite? A parasite is an organisms that lives in or on another organism to obtain its nutrients.
Give examples of genetic conditions. (See Appendix A, Table 11, p. A-15)
Give examples of pathogenic organisms. (See Appendix A, Table 6)

9. Pathophysiology Mechanisms of disease, cont’d
Metabolic mechanism (endocrine imbalances or malnutrition)
Inflammatory mechanism
Autoimmunity
Inflammation
Degeneration
Give examples of malnutrition as a result of deficiency diseases. (See Appendix A, Table 10.)

10. Pathophysiology Risk factors (predisposing conditions) Genetic factors
Age
Lifestyle
Stress
Environmental factors
Preexisting conditions

11. 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

12. Pathophysiology Mechanisms of disease Physical and chemical agents
Autoimmunity
Inflammation
Degeneration
Give examples of conditions caused by physical agents. (See Appendix A, Table 7.)
Give examples of autoimmune diseases. (See Appendix A, Table 9.)

13. Pathophysiology Risk factors (predisposing conditions) Genetic factors
Age
Lifestyle
Stress
Environmental factors
Preexisting conditions
Personal activities (lifestyle) can add risk for certain diseases (e.g., smoking and cancer).
Physical, psychological, or emotional stress can cause disorders such as headaches, depression, increased blood pressure, and heart disease.
Some organisms or parasites survive only in very specific climates. We are at risk for those conditions only if we live in those climates (e.g., tropical parasites).
What is the difference between a primary and secondary condition? A primary condition is a preexisting condition that can put a person at risk for developing a secondary condition.

14. Diversity of pathogenic viruses
Diversity of pathogenic viruses. Some viruses are relatively large; others are extremely tiny. A human hair would be 8 meters thick if drawn at the same scale as the particles depicted here. (Barbara Cousins.)

15. Pathogenic Organisms Types of organisms and particles 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
Many organisms cause disease. Microscopic organisms are called microbes.
Although viruses are not technically living, they have a genetic code and multiply.
How is a person most likely to contract a virus from an infected individual? Contact with blood or body fluids or infected animals can introduce viruses into one’s body.
Give examples of common viruses and discuss the method of transmission. HIV is spread by contact with blood or body fluids through sexual contact, sharing of needles or syringes, and exposure of the fetus before birth. SARS is spread through respiratory or other fluids shed through droplets or the airborne particles.

16. Pathogenic Organisms Types of organisms and particles 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)
Prions cause diseases such as “mad cow disease” and brain degenerative diseases.
What is “mad cow disease”? Mad cow disease is bovine spongiform encephalopathy, a very rare, fatal degeneration of brain tissue and progressive loss of nervous system function.

17. Prion. This pathogenic protein particle is the cause of variant Creutzfeldt- Jakob disease (vCJD), a degenerative, fatal condition of the brain. (Travis J: Drugs counter mad cow agent in cells, Science News 160 (7): 100, 2001, © Fred Cohen.)

18. Pathogenic Organisms Types of organisms and particles Bacteria
Tiny cells without nuclei
Secrete toxins, parasitize host cells, or form colonies
Classification
By growth requirements
Aerobic—require oxygen
Anaerobic—require no oxygen
Bacteria can be aerobic or anaerobic. What is the difference? Aerobic bacteria require oxygen for metabolism; anaerobic bacteria require an absence of oxygen for metabolism.

19. Pathogenic Organisms Types of organisms and particles Bacteria
Classification
By staining properties (depend on composition of cell wall)
Gram-positive
Gram-negative
Different bacteria stain differently. Some are gram positive and others are gram negative. What is the difference in the staining properties? The compounds in the cell’s walls either stain purple by Gram’s staining technique (Gram positive) or do not stain purple by Gram’s staining technique (gram-negative).
Another type of microbe similar to bacteria is archaea. What unique features do archaea offer? They thrive in extremely harsh environments that are very hot, very acid, or very salty. So far, no archaea have been found that infect humans.

20. Pathogenic Organisms Types of organisms and particles Bacteria
Classification
By shape and size
Bacilli—rod-shaped cells
Cocci—round cells
Curved or spiral rods
Small bacteria—obligate parasites
Spores—nonreproducing forms of bacteria that resist unfavorable environmental conditions
Why are small bacteria sometimes called “obligate parasites”? They can only reproduce inside other living cells.
Give examples of diseases caused by bacilli, cocci, curved, or spiral rod, or small bacterium. (Refer students to Table 5-2)

21. Streptococci bacteria
Streptococci bacteria. As this scanning electron micrograph shows, individual spherical bacteria (cocci) may adhere to each other to form chains. (David M. Phillips/Visuals Unlimited.)

22. Pathogenic Organisms Types of organisms and particles Fungi
Simple organisms similar to plants but lacking chlorophyll
Yeasts—small, single-celled fungi
Molds—large, multicellular fungi
Mycotic infections—often resist treatment
What are some examples of fungi? (Refer students to Table 5-3)

23. Examples of pathogenic fungi. Electron micrographs and drawings
Examples of pathogenic fungi. Electron micrographs and drawings. A, Scanning electron micrograph of yeast cells. Yeasts commonly infect the urinary and reproductive tracts. B, This electron micrograph shows Aspergillus organisms, a mold that can infect different parts of the body where it forms characteristic “fungus balls.” (Micrographs: David M. Phillips/Visuals Unlimited.)

24. Pathogenic Organisms Types of organisms and particles Protozoa
Large one-celled organisms that have organized nuclei
May infest human fluids and parasitize or destroy cells
What are pseudopodia and which group of protozoa possess pseudopodia? Amoebas have “false feet” that pull them along.

25. Pathogenic Organisms Types of organisms and particles Protozoa
Major groups
Amoebas—possess pseudopodia
Flagellates—possess flagella
Ciliates—possess cilia
Sporozoa (coccidia)—enter cells during one phase of a two-part life cycle; borne by vectors (transmitters) during the other phase
What are flagella? Whip-like extensions that move flagellates along.
What are cilia? Short hair-like extensions that move ciliates along.
What are some examples of diseases caused by protozoa? (Refer students to Table 5-4)

26. Naegleria fowlerii. N. fowlerii is an emerging pathogen in the southern United States. It is found in warm, fresh-water ponds, lakes, streams, and warm springs. The organism enters the body by swimming up the nose and invading the brain through the thin ethmoid bone. It causes a fatal central nervous system infection. (From Schuster FL, Visvesvara GS: Free-living amoebae as opportunistic and non-opportunistic pathogens of humans and animals, Int J Parasitol 39(9): , 2004.)

27. Pathogenic Organisms Types of organisms and particles
Pathogenic animals
Large complex multicellular organisms
Parasitize or otherwise damage human tissues or organs

28. Pathogenic Organisms Types of organisms and particles
Pathogenic animals
Major groups
Nematodes—roundworms
Platyhelminths—flatworms and flukes
Arthropods—these are often vectors of disease
Parasitic mites, ticks, lice, fleas
Biting or stinging wasps, bees, mosquitoes, spiders
What is a vector? An organism that spreads disease to other organisms.
What are some examples of arthropods? (Refer students to Table 5-5)

29. Prevention and Control
Mechanisms of transmission
Person-to-person contact
Can be prevented by education
Can be prevented by using aseptic technique
Environmental contact
Can be prevented by avoiding contact
Can be prevented by safe sanitation practices
Review methods of transmission.

30. Prevention and Control
Mechanisms of transmission
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
Give examples of diseases transmitted by person-to-person, environmental contact, opportunistic invasion, and vector. (1) Person-to-person contact: rhinovirus, hepatitis B, C, AIDS; (2) environmental contact: pathogens spread through contaminated food, water, soil, or surfaces; (3) opportunistic invasion: changes in the body’s environment allow organisms usually found on the skin and mucous membranes to create a problem; (4) vector: an arthropod such as a deer tick that spreads Lyme disease, or mosquitoes that spread malaria; see Table 5-5.

31. Prevention and Control
Other prevention and treatment strategies
Vaccination—stimulates immunity
Chemicals—destroy or inhibit pathogens
Antibiotics—natural compounds derived from living organisms
Synthetic compounds (e.g., ACV and AZT)
What is a vaccine? A vaccine is a dead or attenuated pathogen given to stimulate immunity.
Discuss the four aseptic techniques that help to prevent the spread of pathogens. See Table 5-6.
Which method (sterilization, disinfection, antisepsis, or isolation) is most effective? Sterilization
When we wash our hands, which method of prevention are we using? Disinfection

32. Tumors and Cancer Neoplasms (tumors)—abnormal growths of cells
Benign tumors remain localized
Malignant tumors spread, forming secondary tumors
Metastasis—cells leave primary tumor and start a secondary tumor at new location

33. Tumors and Cancer 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
Benign tumors are usually encapsulated and grow slowly.

34. 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—bone marrow tumor
Fibrosarcoma—cancer of fibrous tissue
What are malignant tumors from the epithelial tissues generally called? Cancer
What are malignant tissues that arise from the connective tissue generally called? Sarcomas
What does the term “metastasize” mean? Cells migrate from one tumor through lymphatic or blood vessels to another site.

35. Tumors and Cancer
Causes of cancer—varied and still not clearly understood
Cancer involves hyperplasia (growth of too many cells) and anaplasia (development of undifferentiated cells)
Cancer is a type of neoplasm that involves uncontrolled cell division.
Discuss with students “hyperplasia” and “anaplasia” cell division. Hyperplasia is a process that produces too many cells; anaplasia is a process that produces abnormal, undifferentiated tumor cells.

36. Tumors and Cancer Causes of cancer
Factors that play a role in causing 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 change in genetic “machinery”
Give an example of each identified cause of cancer on the slide. Genetic factor: basal cell carcinoma (skin), breast cancer, neuroblastoma (nerve)
Carcinogen: benzene – an industrial product
Age – young people: leukemia; older adults: colon cancer (accumulated cell damage)
Injury: skin cancer from sunlight; lung cancer from breathing asbestos fibers
Viruses: human papillomavirus: HPV – cervical cancer in women, penile cancer in men; vaccine now available against some strains of HPV for women

37. Tumors and Cancer Pathogenesis of cancer Signs of cancer
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
Early detection is critical. With early detection, care can begin before metastasis occurs.
What is the name of the medical specialist who diagnoses and treats cancer? Oncologist

38. Medical images of tumors
Medical images of tumors. A, A mammogram showing carcinoma of a breast duct. B, CT scan of the brain showing a tumor in the left hemisphere. C, MR image of the brain showing a tumor in the left hemisphere. D, Sonogram showing a transverse view of an abdominal tumor. IVC, inferior vena cava; L, liver; M, mass; RK, right kidney. (A, From LeTreut AL: Mammography, St Louis, 1991, Mosby., B, Courtesy Williams AL, Haughton VM: Cranial computed tomography, St Louis, 1985, Mosby., C, Courtesy Runge VM: Enhanced magnetic resonance imaging, St Louis, 1989, Mosby.)

39. Tumors and Cancer
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
Causes of death by cancer—secondary infections, organ failure, hemorrhage, and undetermined factors
What is a Papanicolaou test? A screening procedure to identify abnormal cells in the cervix.
Cancer cells can produce abnormal substances or trigger production of abnormal substances. These substances show up as “tumor markers.” Tumor markers are often evident with prostate, ovarian, and bone cancers.
What method is used to classify a tumor on the basis of size and the extent of spread? Staging
What method is used to assess how a tumor is likely to change, based on the degree of cell abnormality, and to assess prognosis? Grading

40. Tumors and Cancer Treatments Surgery Chemotherapy (chemical therapy)
Radiation therapy (radiotherapy)
Laser therapy
Immunotherapy
New strategies (e.g., rational drugs that target specific molecules, enzymes, or receptors )
How are “rational drugs” used in chemotherapy? Rational drugs target only specific molecules, enzymes, or receptors unique to cancer cells. They affect only cancer cells and ignore normal cells.

41. Inflammation
Inflammatory response—reduces injury to tissues, thus maintaining homeostasis
Signs—redness, heat, swelling, and pain
Inflammation mediators (histamine, prostaglandins, and kinins)
Some cause blood vessels to dilate, increasing blood volume (redness and heat); white blood cells travel quickly to injury site
The inflammatory response is a series of processes that attempt to reduce injury to tissues, thus helping to maintain homeostasis.
Discuss each stage of the inflammatory response with the students.
Inflammation mediators can cause blood vessels to dilate or to increase blood vessel permeability. They also can attract white blood cells to an injury site. Chemotaxis
What are some examples of inflammation mediators? Histamine, prostaglandins, and kinins

42. Typical inflammatory response to a mechanical injury
Typical inflammatory response to a mechanical injury. A, A splinter damages tissue and carries bacteria into the body. Blood vessels dilate and begin leaking fluids, causing swelling and redness. B, White blood cells are attracted to the injury site and begin to consume bacteria and damaged tissue cells. A fibrous capsule separates the injury site from surrounding tissue.

43. Inflammation
The inflammatory response reduces injury to tissues, thus maintaining homeostasis
Inflammation mediators (histamine, prostaglandins, and kinins)
Some increase blood vessel permeability (causing swelling or edema and pain); white blood cells move easily out of vessels; irritant is diluted; and exudate accumulates
Some attract white blood cells to injury site (chemotaxis)
What is pus? Accumulation of white blood cells, dead bacterial cells, and damaged tissue cells at the site of an infection.

44. Inflammation Inflammatory diseases
Inflammation can be local or systemic (body-wide)
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 its causes damage to tissues
What is the difference between acute and chronic inflammation? Acute inflammation is an immediate, protective response that promotes elimination of an irritant and subsequent tissue repair. Chronic inflammation, whether local or systemic, always damages affected tissues.
How does a “fever” assist the body in inflammatory disease? Increased temperature often kills or inhibits pathogenic microbes.