The objective of this lecture is to present the basic mechanisms of diseases of humans, including organisms, route of entry, and course of development of infections.
 | Viral |
| Bacterial |
| Fungal |
| Protozoan |
| Genetic |
| Nutritional |
| Poisons |
| Trauma |
2.2.1. parasite - an organism that lives at the expense of another; may be harmful or harmless
2.2.2. pathogen - a parasitic organism that causes harm to its host
2.2.3. virulence - degree of pathogenicity
2.2.4. infection - growth of microorganisms in host; not necessarily synonymous with disease
2.3.1. Animal bodies are favorable environments for survival and growth of microbes: pH, temperature, osmotic potential, organic food
2.3.2. Body has numerous mechanisms to retard microbial growth
2.3.3. Infections often start at mucous membranes (25-1)
2.3.4. Microbes abundant on outside world: skin, oral cavity, stomach, intestine, respiratory tract, genitourinary tract (25-2)
| Representative microorganisms in the normal flora of humans (25-3) |
2.3.5. Microbes normally not found inside organs, blood, lymph, internal body cavities
3.1.1. Potentially good environment for growth of organisms: pH, substrates, nutrients
3.1.2. Antimicrobial enzymes (e.g. lysozyme and lactoperoxidase) inhibit microbes
3.1.3. Species of Streptococcus colonize teeth to form plaque (25-4)
3.1.4. Dental carries
| Species of Streptococcus produce lactic acid (dissolved enamel) |
| 80-90% of individuals in U.S. and W. Europe have teeth colonized by S. mutans |
3.1.5. Other anaerobes involved in bone loss (periodontal disease, gingivitis, and abscess)
3.2.1. Stomach is barrier because of low pH and digestive enzymes
a. acid-tolerant lactobacilli and streptococci
3.2.2. High number of bacterial in small intestine (105-107 per gram)
3.2.3. Flora differ in intestines of different animals but are mostly strict anaerobes
3.2.4. Intestinal microbes (25-5)
| biochemical/metabolic contributions of intestinal microorganisms (25-6) |
| carry out important metabolic functions |
| inhibit growth and metabolism of foreign organisms (mostly by competition) |
| are resistant to natural defenses of host |
3.3.1. Normal flora are staphylococci, streptococci, diptheroid bacilli, and Gram-neg. cocci
3.3.2. Other pathogens (causing strep throat, diphtheria, pneumonia are also present in low numbers but can’t compete with resident organisms and are reduced by body defenses
3.3.3. Enter via air and particles
3.3.4. Mucous removal removes lots of organisms
3.4.1. Low numbers of microbes in urethra of men (25-7) and women and vagina of women (25-8)
3.4.2. Changes is pH or immune response can allow these organisms to multiply or secondary infections of yeast.
| Major adherence factors used to facilitate attachment of microbial pathogens to host tissues (25-11) |
| e.g. intestine is resistant to colonization (some bacteria with colonization factor antigens) overcome this to attach |
4.7.1. Factors: Exotoxins and extracellular virulence factors produced by certain bacteria pathogenic for humans (25-12)
| hyaluronidase - tissue deterioration |
| collagenase (gangrene) - tissue |
| streptokinase - lysis of fibrin (coats and isolates bacteria) clots |
| coagulase - coagulate fibrin |
| hemolysis - lyse blood cells |
| lecithinases - lyse cell membrane |
| phospholipases - lyse cellmembranes |
| leukocidins - destroy white blood cells |
4.7.2. Classification of toxins
| basic properties of exotoxins and endotoxins (25-13) |
| exotoxin, e.g., botulism |
- enterotoxin, e.g. staphylococcal
| endotoxin, e.g., salmonellosis |
4.7.3. Examples
| botulism (25-14) |
| tetanus (25-15) |
| cholera (a) (25-16) (b) (25-17) |
(GM1 - intestinal ganglioside)
| endotoxin (25-18) |
4.7.4. Involves invasiveness and toxigenicity
4.7.5. Attenuated - organisms that have lost their virulence
5.1. Animals vary in susceptibility to diseases.
| some diseases like rabies affect lots of organisms |
| others like anthrax causes different symptoms in different animals (e.g. not pathogenic to birds). |
5.2.1. More common in old and young
| young have limited flora and limited immunity |
| old more susceptible to respiratory infections, immunity is diminished |
| high physical activity increases disease |
| affects hormonal activity in a manner that increases disease |
| malnutrition - all diseases |
| sucrose - tooth decay |
| flatus caused by mixing wrong foods |
| vitamin and mineral supplements |
| intact skin; mucous membranes at other body surfaces |
| infection-fighting chemicals in tears, saliva, etc. |
| normally harmless bacterial inhabitants of body surfaces that out compete pathogenic visitors |
| flushing effect of tears, saliva, urination, and diarrhea |
5.6.1. Tissue specificity as a factor in infectious disease (25-20)
- Salmonella and Shigella can colonize intestine
| surgery |
| injections |
| catheterization |
| habits: smoking, alcohol, drug use, not enough sleep, poor nutrition |
| redness - vasodilation, increased blood flow to site |
| warmth - vasodilation, greater flow of blood carrying more metabolic heat to site |
| swelling - capillaries made more permeable so plasma and leukocytes leak out; also vasodilation |
| pain - increased fluid pressure and local chemical signals stimulate nociceptors (pain receptors) |
| normal variation is 1.0 - 1.5oC |
| hypothalmus resets body thermostat to increase rate of body defenses |
| defined as abnormal increase in body temperature |
| caused by pyogenic microorganisms |
| accelerates phagocytic and antibody responses |
6.1. What are six general causes of disease?
6.2. What is the difference between a disease and an infection?
6.3. What are the major barriers against pathogens at the bodies surfaces?
6.4. Discuss the mechanism of dental caries? How can you prevent it?
6.5. What are at least five useful functions of normal bacteria associated with the human body?
6.6. How do pathogens get past the surface barriers of the body.
6.7. What is the difference between exotoxins, endotoxins, and enterotoxins? Give specific examples of each.
6.8. Describe the difference between pathogenic, virulence, and bacteremia.
6.9. How do age, stress, diet, surgery, injection catheterization and bad habits (smoking, alcohol, drug use, not enough sleep) influence susceptibility to invasion by pathogens?
6.10. Describe the steps of the inflammatory response. How does this response ward off infection and its spreading?
| inflamatory response | parasite | peridontal disease |
| infection | endotoxin | gangrene |
| pathogenesis | exotoxin | botulism |
| virulence | enterotoxin | tetanus |
| bacteremia | lysozyme | attenuated |
Human Biology - The Biology Project, Biology, University of Arizona
Activities, Problems sets, and Tutorials: Human Genetics; DNA Forensics; Human Reproduction; Sexually Transmitted Diseases; Blood Types
