Transcript Understanding Infection

Understanding
Infection
Chapter 2
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An infection is a response to a pathogen, or
disease-causing substance, that enters the
host’s body.
It results when tissue-destroying
microorganisms enter and multiply in the
body.
Some infections take the form of minor illness
Others result in a life-threatening condition
called sepsis, which causes widespread
vasodilation and multiple-organ-dysfunction
syndrome (MODS).
Infection-causing microbes
Four types of microorganisms can enter the
body and cause infection: viruses, bacteria,
fungi, and parasites.
Infection-causing microbes
 Viruses,
are microscopic genetic parasites
that may contain genetic material, such
as DNA or RNA. They have no metabolic
capability and need a host cell to
replicate.
 Viral hide-and-seek
 Viral infections occur when normal
inflammatory and immune responses fail.
 Some viruses surround the host cell and
preserve it; others kill the host cell on
contact.
Bacteria, are mono cells that
have no true nucleus and
reproduce by cell division.
Pathogenic bacteria contain
cell-damaging proteins that
cause infection, which may be:
•
exotoxins—released
during cell growth (cause fever
and aren’t affected by
antibiotics)
•
endotoxins—released
when the bacterial cell wall
decomposes; classified by their
shape, growth requirements,
motility, and whether they’re
aerobic or anaerobic
Infection-causing microbes
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Fungi
Fungi are nonphotosynthetic microorganisms that
reproduce asexually (by division).
They’re large and contain a true nucleus.
Fungi are classified as:
• yeasts—round, single-celled, anaerobes
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• molds—filament-like, multinucleated, aerobic.
There’s a fungus among us
Although fungi are part of the human body’s normal
flora, they can overproduce, especially when the
normal flora is compromised.
vaginal yeast infections can occur with antibiotic
treatment because normal flora are killed by the
antibiotic, allowing yeast to reproduce.
Infection-causing microbes
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Infections caused by fungi are called mycotic infections
because pathogenic fungi release mycotoxin.
Most of these infections are mild unless they become
systemic or the patient’s immune system is
compromised.
Parasites
Parasitic infections are uncommon except in hot, moist
climates.
Parasites are single-celled or multicelled organisms that
depend on a host for food and a protective
environment. Most common parasitic infections, such as
tapeworm and tick infestations, occur in the intestines.
Barriers to infection
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body has many built-in infection barriers:
the skin and
secretions from the eyes, nasal passages, prostate
gland, testicles, stomach, and vagina.
Most of these secretions contain lysozymes.
Other body structures, such as cilia in the pulmonary
airways that sweep foreign material from the breathing
passages, also offer infection protection.
Trillions of harmless inhabitants
 Normal
flora are harmless MOs that reside on and in
the body.
 They’re found on the skin and in the nose, mouth,
pharynx, distal intestine, colon, distal urethra, and
vagina.
 Many of these MOs provide useful, protective
functions ( intestinal flora help synthesize vitamin K,
which is important for blood- clotting)
The infection process
 Infection
occurs when the body’s defense
mechanisms break down or when certain
properties of MO (virulence)or toxin production,
override the defense system.
 Other factors that create a climate for infection
include:
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• poor nutrition
• stress
• humidity
• poor sanitation
• crowded living conditions
• pollution
• dust
• medications
• hospitalization (Nosocomial infection).
Enter, attach, and spread
 Infection
through:
direct contact,
 inhalation,
 ingestion, or
 an insect or animal bite.
The pathogen then attaches itself to a cell and releases
enzymes that destroy the cell’s protective membrane.
Next, it spreads through the bloodstream and lymphatic
system, finally multiplying and causing infection in the
target tissue or organ.
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results when a pathogen enters the body
Striking while there’s
opportunity
 Opportunistic
infections; infections that strike
people with altered, weak immune systems .
 For example, patients with acquired
immunodeficiency syndrome (AIDS) are plagued
by opportunistic infections such as Pneumocystis
carinii pneumonia