Important words and
concepts from Chapter 16, Black, 1999 (3/28/2003):
by Stephen T. Abedon (abedon.1@osu.edu)
for Micro 509
at the Ohio State University
|
|
|
Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
are found below |
|
|
(1) Chapter title: Nonspecific Host Defenses and Host Systems
|
Prevention of entrance to the body |
· skin barrier · mucous membranes · one-way valves |
||
|
Removal by washing |
· washing of the eyes · washing of the mouth · washing of the respiratory tract · washing of the urogenital tract |
||
|
|
· antimicrobials of the skin · lysozyme made by the body · gastric juices |
||
|
Inhibition within the body |
--- |
· fever |
|
|
Specific resistance (next chapter) |
Cellular arm of the immune system |
--- |
--- |
|
Antibodies |
--- |
--- |
(a)
[nonspecific host defenses and
host systems (Google Search)] [index]
(a)
Host
defenses to pathogens may be divided categorically into specific host defenses
and non-specific ones
(b)
This
chapter considers the latter
(c)
[host defenses against disease
(Google Search)]
[a layperson’s guide to immunology (Paul Shen)] [index]
(3) Non-specific host defenses
(a)
"In
the case of many threats to an individual's well being, specific defenses
[e.g., antibodies or cellular immunity] do not need to be called on because the
body is adequately protected by its nonspecific defenses—those that act against
any type of invading agent. Often such defenses perform their function before
specific body defense mechanisms are activated."
(b)
Non-specific
host defenses include:
(ii)
Chemical barriers
(iii)
Cellular defenses
(iv)
Inflammation
(v)
Fever
(vi)
Molecular defenses
(c)
See Figure 16.10, A summary
of the body's nonspecific defenses
(d)
[non-specific host defenses,
constitutive defenses
(Google Search)]
[index]
(4) Physical barriers (mucous membranes)
(a)
Physical
barriers act to prevent pathogens from entering the body
(b)
Physical
barriers include the skin and mucous membranes
(c)
Physical
barriers additionally include the viscous mucous that covers mucous membranes,
giving these membranes their name
(d)
Movement
of substances out of the body additionally serve as physical barriers,
including the movement of mucous out of the lungs, the movement of urine down
the urethra and out of the body, vomiting, diarrhea, and even the movement of
blood out of a wound
(e)
Usually
physical barriers do a good job of preventing pathogens from entering the body
(f)
However,
some pathogens are capable of breaching these physical barriers, and sometimes
physical barriers are not functional or are not as present as one would otherwise
hope (e.g., cuts in the skin, drying out of mucous membranes, not voiding one's
bladder when necessary, etc.); for example:
(i)
A
number of viruses specifically infect mucous-membranes or via them {e.g., polio
virus (intestine), chickenpox (lungs)}
(ii)
A
number of viruses infect via skin abrasions (e.g., warts, smallpox, herpes,
hepatitis B, HIV)
(g)
[“Air begins its journey to the
respiratory system through the nose, which filters, warms, and moistens our
inhalations before they pass through the pharynx, larynx, and trachea into the
bronchi and the lungs. For this purpose, the external nose contains a septum
(the wall dividing the two nostrils) composed of cartilage and bone covered by
a layer of mucous membrane, and six or eight turbinates. ¶ The turbinates are
thin curlicues of bone, also covered by thick mucous membranes, that curve from
the outer part of the nose in toward the septum. Under the mucous membrane is
erectile tissue that is sensitive to temperature and causes tissues of the area
to swell with the influx of blood when there is an abundance of cold, dry, or
contaminated air. This narrows the passages and thus slows the incoming air,
allowing the turbinates to warm and humidify it. When the turbinates become
erect they give rise to large amounts of mucus, which is why noses tend to run
on cold days. ¶ The sticky mucous lining of the nose and nasal passages acts as
a filter, trapping bacteria and airborne dirt particles. The mucus is then
moved by the action of hair-like cilia either to the front of the nose where it
can be blown out, or to the back of the nose where it enters the throat and is
swallowed.” (Columbia University Home Medical Guide)]
(h)
[physical barriers to infection
(Google Search)]
[index]
(a)
Chemical
barriers are antimicrobial chemical defenses
(b)
These
defenses include lysozyme in sweat, tears, and saliva; the low pH of the lumen
of the stomach, etc.
(c)
[chemical barriers to infection
(Google Search)]
[index]
(a)
Various
blood cells as well as platelets play an active role in defending the body from
pathogen invaders
(b)
Platelets
are involved in blood clotting, which can serve as a barrier to pathogens
(c)
Various
white blood cells (a.k.a., leukocytes) are involved in phagocytosis (which
is essentially intracellular killing of pathogens) or an extracellular killing of pathogens
(d)
"Cellular
defense mechanisms usually prevent an infection from spreading or from getting
worse. However, sometimes these nonspecific defense mechanisms are overwhelmed
by sheer numbers of microbes or are inhibited by virulence factors that the
microbes possess. The pathogen can then invade other parts of the body."
(e)
["cellular defenses"
against infection (Google Search)] [index]
(a)
Cells
capable of effecting phagocytosis are called phagocytes
(b)
Included
among the phagocytes are the neutrophils and the macrophages
(c)
Typically
neutrophils serve as a first line of defense at the site of a wound whereas
macrophages serve as a second, much larger line of defense
(d)
Ideally,
the act of phagocytosis results in the ingestion and
subsequent killing of the pathogen
(e)
This
ideal is not always achieved, and in such cases the interior of the phagocyte
can serve as a immunologically protected zone within a body
(f)
[phagocytes (Google Search)] [index]
(a)
These
are the macrophages that migrate to a wound to effect cellular defenses against invading pathogens
(b)
[wandering macrophages
(Google Search)]
[index]
(a)
These
cells remain within tissues, essentially waiting, ideally futilely, for
breaches in the physical and chemical barriers that bring pathogens to them
(b)
[fixed macrophages (Google Search)] [index]
(a)
Phagocytosis
is the engulfing of debris or pathogens
(b)
Phagocytosis
occurs in four steps
(i)
The
phagocyte must first find the pathogen (or cell debris) meaning that it comes
into physical contact with it (chemotaxis)
(ii)
The
phagocyte must then chemically adhere to the pathogen (adherence)
(iii)
Next,
the pathogen is ingested (endocytosed into a
phagosome)
(iv)
Finally,
ideally, the pathogen in digested intracellularly (digestion)
(c)
See Figure 16.3,
Phagocytosis of two bacterial cells by a neutrophil
(d)
[phagocytosis (Google Search)] [index]
(a)
The
phagocytes find wounds or infections by following chemical signals released from
cells present at the site
(b)
Mostly
these chemicals are soluble proteins and phagocytes follow the protein gradient
(up the gradient) to the site
(c)
Some
pathogens avoid cellular defenses by interfering with
chemotaxis
(d)
[chemotaxis and phagocytosis (Google Search)] [index]
(12) Adherence (engulfment, ingestion, phagosome)
(a)
Phagocytes adhere to pathogens by
adhering to specific chemicals found on the surface of pathogens (many, most,
all? of these chemicals are actively placed there by the body, e.g., complement or antibodies)
(b)
A
means of interfering with adherence is via the secretion of a capsule (by a
bacterium) which prevents the chemical attachment of the phagocyte to the pathogen
(c)
Given
successful attachment, ingestion of the pathogen by the phagocyte follows
(d)
The
vesicle in which the pathogen is now present, within the phagocyte following
ingestion/engulfment, is called a phagosome
(e)
[adherence and phagocytosis,
engulfment and phagocytosis,
ingestion and phagocytosis,
phagosome (Google Search)] [index]
(13) Digestion (phagolysosome)
(a)
Ideally,
ingestion
of the pathogen is followed by the digestion (destruction) of the pathogen
(b)
Destruction
involves the use of digestive enzymes, e.g., by the fusing the phagosome with a
lysozome (thus forming a phagolysosome)
(c)
Digested
pathogens are subsequently secreted by a mechanism of exocytosis
(d)
Some
pathogens avoid digestion and some can even replicate within the phagocyte
(e)
This
avoidance may be accomplished either by resisting digestion (e.g., via
protection from capsule of acid-fast cell envelopes) or by releasing toxins
that actively destroy the phagocyte before digestion proceeds
(f)
[digestion and phagocytosis,
phagolysosome (Google Search)] [index]
(a)
Pathogens
may be filtered from lymph at lymph nodes where phagocytes actively
phagocytize
pathogens
(b)
Lymph
nodes can swell when actively battling an infection so consequently swollen
lymph nodes serve as an indicator for serious systemic infection
(c)
[lymph nodes (Google Search)] [index]
(a)
The
spleen is an organ that, serving a similar purpose to the blood as lymph nodes
serve for lymph, actively remove pathogens from blood via phagocytosis
effected by phagocytes present within the spleen
(b)
[spleen (Google Search)] [index]
(a)
Extracellular
killing is employed particularly against virus-infected cells and helminths
(b)
Extracellular
killing is accomplished by the secreting of chemical toxins
(c)
This
secretion is either into the vicinity of helminths, or is directed against
virus-infected cells, which are sacrificed to stop the viral-infected cell from
making additional viral progeny
(d)
This
killing of host cells to kill viruses is one way that viral infections effect
their damage upon their hosts
(e)
[extracellular killing
(Google Search)]
[index]
(a)
The
inflammation of tissues is a defensive response that serves to protect damaged
tissues against infection (or a worsening of an existing infection)
(b)
The
four indications of the occurrence of localized inflammation are
(i)
Warming
of the area
(ii)
Reddening
of the area
(iii)
Swelling
of the area
(iv)
Pain
in the area (e.g., to touch)
(c)
The
goal of inflammation is to
(i)
Kill
pathogens (kill)
(ii)
Remove
tissue debris (clean)
(iii)
Repair
damaged tissue (repair)
(d)
Inflammation
results from local histamine release from damaged cells which causes
vasodilation (a widening of blood vessels), an increase in blood flow to the
area that accounts for the warming, swelling, and redness associated with
inflammation
(e)
The
chemicals produced upon cellular injury, along with inducing inflammation,
additionally attract neutrophils and ultimately attract wandering macrophages