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Defense Mechanisms

Three lines of defense protect the body
against foreign invasion:
 Physical or surface barriers
 Inflammation
 Immune response
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Inflammation
Non-specific cellular and vascular
reaction to tissue
 Repels and destroys invader; cleans up
debris to promote healing
 Requires blood supply

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Inflammatory Process

Signs and symptoms:
 Redness
 Heat
 Edema
 Pain
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Chronic Inflammation
Last two weeks or longer
 Acute inflammation lasts less than 10
days

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Inflammatory Exudates
Appearance and amount of exudate
(blood fluid) reveals acute or chronic
condition
 Serous exudate is clear serum-like fluid

 Acute state of inflammation
 Skin blisters and cold sores
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Inflammatory Exudates

Fibrinous exudate
 Indicates larger injury with severe
inflammation
 Commonly called scab
 Strep throat or bacterial pneumonia forming
a mesh-like lesion
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Inflammatory Exudates
Purulent exudate called “pus”
 Collection of pus is an abscess
 Accumulation of pus in body cavity is
empyema

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Inflammatory Lesions
Due to physical or pathologic injury
 Inflammatory lesions include:

 Abscesses
 Ulcers
 Cellulitis
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Tissue Repair and Healing
Ongoing process
 Tissue repair:

 Regeneration
 Fibrous connective tissue repair
 Scar formation
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Tissue Repair and Healing
Regeneration leads to normal function
 Fibrous connective tissue repair does
not

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Tissue Healing

Primary Union (First Intention)
 Involves approximating edges of wound
 Steps of primary healing:
○ Forms scab
○ 1 to 2 days, new capillaries begin to bridge
gap between wound edges
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Tissue Healing

Primary Union (First Intention)
 Steps of primary healing:
○ Fibroblast grows across deeper wound layers
forming granulation tissue
○ Scar forms
○ Example of primary healing is surgical incision
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Tissue Healing

Secondary Union (Secondary Intention)
 Larger, deeper wounds with more
inflammation than primary union
 Need more capillaries, fibroblasts, and
collagen
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Tissue Healing

Secondary Union (Secondary Intention)
 After a week, new soft red tissue called
granulation tissue is produced
 Scar tissue is formed
 Healing time is dependent on size of wound
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Delayed Wound Healing

Debridement (washing or cutting away
necrotic tissue and foreign material) may
be necessary
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Delayed Wound Healing

Factors affecting healing time:
 Age
 Size of wound
 Location
 Nutrition
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Delayed Wound Healing

Factors affecting healing time:
 Circulation
 Organism virulence
 Steroids
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Complications of Wound Healing
Poor or excessive scar formation
 Dehiscence - separation of tissue
margins
 Keloid - hard, raised scar
 Adhesions - fibrous bands of tissue that
attach to surfaces of adjacent organs as
scar tissue develops

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Infection
Invasion of microorganisms causing cell
or tissue injury
 Pathogenic - microorganisms causing
disease
 Opportunistic - normal flora become
pathogenic under certain conditions

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Infection

Conditions for flora to become
pathogenic
 Microorganisms gain access to body
through portal of entry
 Pathogen is resistant to defenses of host
 Number of invading microorganisms
 Condition of individual or host
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Frequency and Type of
Infection
Infectious diseases leading cause of
death in the world
 Identifying and tracking infectious
diseases is crucial

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Frequency and Type of
Infection

CDC - Centers for Disease Control and
Prevention provide these services in the
United States
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Frequency and Types of
Infection

Bacteria
 Primary or secondary disease
 Staphylococcus is bacterium on skin
 Streptococcus live on skin and in throat
 Escherichia coli, Kelbsiella, Pseudomonas,
Shigella, and Salmonella are common
enteric bacteria
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Frequency and Types of
Infection

Viruses
 Smallest infective organism
 Must be visualized by electron microscope
 Cannot reproduce or live outside cell
 Viral infections are not easily treated
 Antibiotics do not kill a virus but help prevent
secondary infections
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Frequency and Types of
Infections

Viruses
 Immunizations are effective in preventing
many viral diseases such as measles,
mumps, rubella, and smallpox
 Latent viruses lay dormant in cells and
replicate and cause symptoms during times
of stress
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Frequency and Types of
Infection

Fungi
 Microscopic plant-like organisms larger than
bacteria
 Only few are pathogenic
 Types of infections:
○ Tinea - skin
○ Candida - superficial infection of skin and
mucous membranes
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Frequency and Types of
Infections

Fungi
 Treated with antibiotics and antifungal
medications
 Often difficult to cure
 May require long-term therapy
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Frequency and Types of
Infections

Rickettsiae
 Microscopic organisms that are intermediate
between bacteria and viruses
 Must live in host cell like a virus
 Spread by fleas, ticks, mites, and lice
 Most common infection: Rocky Mountain
Spotted Fever
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Frequency and Types of
Infections

Protozoa
 Single-celled microscopic organisms
 Found in soil; live on dead or decaying
material
 Infection through bite of infected insect or
ingestion of spores
 Malaria is most common disease
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Frequency and Types of
Infections

Helminths
 Roundworms or flatworms
 Pinworms and tapeworms are most common
 Pinworms cause anal itching
 Tapeworms cause intestinal disease due to
inadequately cooked meat
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