Chapter-4:  Mechanisms of Disease

 

I.                    Studying Disease

A.     Disease Terminology

1.      Health – physical, mental, and social well-being – not merely the absence of disease

2.      Disease – an abnormality in body function that threatens health

3.      Etiology – the study of the factors that cause a disease

4.      Idiopathic – refers to a disease with an unknown cause

5.      Signs and Symptoms – the objective and subjective abnormalities associated with a disease.

6.      Pathogenesis – the pattern of a disease’s development

B.     Patterns of Disease

1.      Epidemiology is the study of occurrence, distribution, and transmission of diseases in human populations.

2.      Endemic diseases are native to a local region

3.      Epidemics occur when a disease affects many people at the same time.

4.      Pandemics are widespread, perhaps global, epidemics

5.      Discovering the cause of a disease is difficult because many factors affect disease transmission

6.      Disease can be fought through prevention and therapy (treatment.)

II.                 Pathophysiology

A.     Mechanisms of disease

1.      Pathophysiology – the study of underlying physiological aspects of disease

2.      Genetic mechanisms

3.      Pathogenic organisms

4.      Tumors and cancer

5.      Physical and chemical agents

6.      Autoimmunity

7.      Inflammation

8.      Degeration

B.     Risk Factors (predisposing conditions)

1.      Genetic Factors

2.      Age

3.      Lifestyle

4.      Stress

5.      Environmental Factors

6.      Pre-existing conditions

III.               Pathogenic Organisms

A.     Types of Organisms

1.      Viruses

a.       Microscopic, intracellular parasites that consist of a nucleic acid core with a protein coat.

b.      Invade host cells and pirate organelles and raw materials

c.       Classified by shape, nucleic acid type, and method of reproduction

2.      Bacteria

a.       Tiny cells without nuclei

b.      Secrete toxins, parasitize host cells, or form colonies

c.       Classification

                                                                                                                                       i.      By function

1.      Aerobic – require oxygen

2.      Anaerobic – require no oxygen

                                                                                                                                     ii.      By staining properties (composition of cell wall)

1.      Gram-Positive

2.      Gram-Negative

                                                                                                                                    iii.      By shape and size

1.      Bacilli – rod shaped cells

2.      Cocci – round cells

3.      Curved or spiral rods

4.      Small bacteria – obligate parasites

d.      Spores – non-reproducing forms of bacteria that resists unfavorable environmental conditions

3.      Fungi

a.       Simple organisms similar to plants but lacking chlorophyll.

b.      Yeasts – small, single-celled fungi.

c.       Molds – large, multi-cellular fungi.

d.      Mycotic infections – often resist treatment

4.      Protozoa

a.       Large, one-celled organisms having organized nuclei

b.      May infest human fluids and parasitize or destroy cells

c.       Major groups

                                                                                                                                       i.      Amoebas – possess pseudopodia

                                                                                                                                     ii.      Flagellates – possess flagella

                                                                                                                                    iii.      Ciliates – possess cilia

                                                                                                                                   iv.      Sporozoa (coccidia) – enter cells during one phase of a two-part life cycles; borne by vectors (transmitters) during the other phase.

5.      Pathogenic Animals

a.       Large, complex, multi-cellular organisms

b.      Parasitize or otherwise damage tissues or organs

c.       Major groups

                                                                                                                                       i.      Nematodes – round worms

                                                                                                                                     ii.      Platyhelminths – flatworms and flukes

                                                                                                                                    iii.      Arthropods

1.      Parasitic mites, ticks, lice, and fleas

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

3.      Are often vectors of disease

B.     Prevention and control

1.      Mechanisms of transmission

a.       Person-to-person contact

                                                                                                                                       i.      Can be prevented by education

                                                                                                                                     ii.      Can be prevented by using aseptic technique

b.      Environmental contact

                                                                                                                                       i.      Can be prevented by avoiding contact

                                                                                                                                     ii.      Can be prevented by safe sanitation practices

c.       Opportunistic invasion

                                                                                                                                       i.      Can be prevented by avoiding damage to skin and mucus membranes

                                                                                                                                     ii.      Cab be prevented by cleansing of wounds

d.      Transmission by a vector

                                                                                                                                       i.      Can be prevented by reducing the population of vectors and reducing contact with vectors

2.      Other prevention and treatment strategies

a.       Vaccination – stimulates immunity

b.      Chemicals – destroy or inhibit pathogens

                                                                                                                                       i.      Antibiotics – natural compounds derived from living organisms

                                                                                                                                     ii.      Synthetic Compounds (for example ACV and AZT)

IV.              Tumors and Cancer

A.     Neoplasms (tumors) – abnormal growths of cells

1.      Benign tumors remain localized

2.      Malignant tumors spread, forming secondary tumors

3.      Metastasis – cells leave a primary tumor and start a secondary tumor at a new location

4.      Classification of Tumors

a.       Benign epithelial tumors

                                                                                                                                       i.      Papilloma – fingerlike projection

                                                                                                                                     ii.      Ademona – glandular tumor

                                                                                                                                    iii.      Nevus – small, pigmented tumor

b.      Benign connective tissue tumors

                                                                                                                                       i.      Lipoma – adipose (fat) tumor

                                                                                                                                     ii.      Osteoma – bone tumor

                                                                                                                                    iii.      Chondroma – cartilage tumor

c.       Carcinomas (malignant epithelial tumors)

                                                                                                                                       i.      Melanoma – involves melanocytes

                                                                                                                                     ii.      Adenocarcinoma – glandular cancer

d.      Sarcomas (connective tissue cancers)

                                                                                                                                       i.      Lymphoma – lymphatic cancer

                                                                                                                                     ii.      Osteosarcoma – bone cancer

                                                                                                                                    iii.      Myleloma – bone marrow tumor

                                                                                                                                   iv.      Fibrosarcoma – cancer of fibrous tissue

B.     The causes of cancer – varied and still not understood

1.      Cancer involves hyperplasia (growth of too many cells) and anaplasia (development of undifferentiated cells)

2.      Factors known to play a role in causing cancer:

a.       Genetic Factors (for example, oncogenes – cancer genes)

b.      Carcinogens – chemicals that alter genetic activity

c.       Age

d.      Injury

e.       Viruses

C.     Pathenogenesis of Cancer

1.      Early detection is important

2.      Methods of detecting cancers

a.       Self examination

b.      Diagnostic Imaging – radiography (for example, mammogram and CT scan), magnetic resonance imaging (MRI), ultrasonography

c.       Biopsy

d.      Blood tests

3.      Staging – classifying tumors by size and extent of spread

4.      Grading – assessing the likely pattern of a tumor’s development

5.      Cachexia – syndrome including appetite loss, weight loss, and general weakness

6.      Causes of death by cancer – secondary infections, organ failure, hemorrhage, and undetermined factors

7.      Treatments:

a.       Surgery

b.      Chemotherapy

c.       Radiation Therapy

d.      Laser Therapy

e.       Immunotherapy

f.        New Strategies (for example – vaccines)

V.                 Inflammation

A.     The inflammatory Response – reduces injury to tissues, thus maintaining homeostasis

1.      Signs – redness, heat, swelling, and pain

2.      Inflammation mediators (histamines, prostaglandins, and kinins)

a.       Some cause blood vessels to dilate, increasing blood volume (redness and heat) – white blood cells travel quickly to injury site

b.      Some increase blood vessel permeability (causing swelling, edema, and pain) – white blood cells move easily out of vessels, irritant is diluted, and exudates accumulates.

c.       Some attract white blood cells to injury site (chemotaxis)

B.     Inflammatory Diseases

1.      Inflammation can be local or systemic (body-wide)

2.      Fever – high body temperature caused by a resetting of the bodies “thermostat” – destroys pathogens and enhances immunity.

3.      Chronic Inflammation can constitute a disease itself because it causes damage to tissues.