C H A P T E R 1 5
Introduction to the immune response and inflammation
229
myelocytes:
leucocyte-producing cells in the bone marrow that can develop into neutrophils, basophils, eosinophils, monocytes or
macrophages
non-self cells:
cells that are foreign; not identified as part of the organism itself
phagocytes:
neutrophils that are able to engulf and digest foreign material
phagocytosis:
the process of engulfing and digesting foreign pyrogens
pyrogen:
fever-causing substance
rubor:
redness, one of the four cardinal signs of inflammation; caused by activation of the inflammatory response
T cells:
lymphocytes programmed in the thymus gland to recognise self cells; may be effector T cells, helper T cells, or suppressor T cells
tumour:
swelling, one of the four cardinal signs of inflammation; caused by activation of the inflammatory response
Mucous membranes
Mucous membranes line the areas of the body that
are exposed to external influences but do not have the
benefit of skin protection. These body areas include the
respiratory tract, which is exposed to air; the gastro
intestinal (GI) tract, which is exposed to anything
ingested by mouth; and the genitourinary (GU) tract,
which is exposed to many pathogens from the perineal
and rectal area. Like the skin, the mucous membrane
acts as a physical barrier to invasion. It also secretes a
sticky mucous capable of trapping invaders and inacti
vating them for later destruction and removal by the
body.
In the conducting airways of the respiratory tract,
the mucous membrane is lined with tiny, hair-like
processes called cilia
.
The cilia sweep any captured
pathogens or foreign materials upwards towards the
mouth, where they will be swallowed. The cilia can also
move the captured material to an area causing irritation,
which leads to removal by coughing or sneezing.
In the GI tract, the mucous membrane serves as a
protective coating, preventing erosion of GI cells by the
acidic environment of the stomach, the digestive enzymes
of the small intestine and the waste products that accu
mulate in the large intestine. The mucous membrane
also secretes mucous that serves as a lubricant through
out the GI tract to facilitate movement of the food bolus
and of waste products. The mucous membrane acts as
a thick barrier to prevent foreign pathogens from pene
trating the GI tract and entering the body.
In the GU tract, the mucous membrane provides
direct protection against injury and trauma and traps
any pathogens in the area for destruction by the body.
Gastric acid
The stomach secretes acid in response to many stimuli.
The acidity of the stomach not only aids digestion, but
also destroys many would-be pathogens that are either
ingested or swallowed after removal from the respira
tory tract.
Major histocompatibility complex
The body’s last barrier of defence is the ability to distin
guish between self cells and foreign cells. All of the cells
T
he body has many defence systems in place to keep it
intact and to protect it from external stressors. These
stressors can include bacteria, viruses, other foreign
pathogens or
non-self cells
, trauma and exposure
to extremes of environmental conditions. The same
defence systems that protect the body also help to
repair it after cellular trauma or damage. Understand
ing the basic mechanisms involved in these defence
systems is important in order to be able to explain the
actions of the drugs that affect the immune system and
inflammation.
BODY DEFENCES
The human body can mount two types of immune
defences. The innate or natural (or non-specific)
immunity and the specific or acquired immunity. The
innate or natural immunity defences are factors that are
present in the body prior to exposure to a particular
infectious organism. The specific or acquired immune
defences occur only after exposure to substances called
antigens.
The body’s defences include barrier defences,
cellular defences, the inflammatory response and the
immune response. Each of these defences plays a major
role in maintaining homeostasis and preventing disease.
Barrier defences
Certain anatomical barriers exist to prevent the entry
of foreign pathogens and to serve as important lines of
defence in protecting the body. These barriers include
the skin and mucous membranes, gastric acid and the
major histocompatibility complex.
Skin
The skin is the first line of defence. The skin acts as
a physical barrier to protect the internal tissues and
organs of the body. Glands in the skin secrete chemi
cals that destroy or repel many pathogens. The top layer
of the skin sheds daily, which makes it difficult for any
pathogen to colonise on the skin. In addition, normal
bacterial flora of the skin help to destroy many disease-
causing pathogens.
