Page 146 - Textbook of Pathology, 6th Edition

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Chapter 6
Chapter 6 Inflammation and Healing

INFLAMMATION TYPES OF INFLAMMATION. Depending upon the defense
SECTION I
capacity of the host and duration of response, inflammation
can be classified as acute and chronic.
INTRODUCTION
A. Acute inflammation is of short duration (lasting less than
DEFINITION AND CAUSES. Inflammation is defined as 2 weeks) and represents the early body reaction, resolves
the local response of living mammalian tissues to injury due quickly and is usually followed by healing.
to any agent. It is a body defense reaction in order to eliminate
or limit the spread of injurious agent, followed by removal The main features of acute inflammation are:
of the necrosed cells and tissues. 1. accumulation of fluid and plasma at the affected site;
The agents causing inflammation may be as under: 2. intravascular activation of platelets; and
1. Infective agents like bacteria, viruses and their toxins, 3. polymorphonuclear neutrophils as inflammatory cells.
fungi, parasites. Sometimes, the acute inflammatory response may be
quite severe and is termed as fulminant acute inflammation.
2. Immunological agents like cell-mediated and antigen-
antibody reactions. B. Chronic inflammation is of longer duration and occurs
3. Physical agents like heat, cold, radiation, mechanical either after the causative agent of acute inflammation persists
trauma. for a long time, or the stimulus is such that it induces chronic
4. Chemical agents like organic and inorganic poisons. inflammation from the beginning. A variant, chronic active
5. Inert materials such as foreign bodies. inflammation, is the type of chronic inflammation in which
Thus, inflammation is distinct from infection—while during the course of disease there are acute exacerbations of
inflammation is a protective response by the body to variety activity.
of etiologic agents (infectious or non-infectious), while The characteristic feature of chronic inflammation is
infection is invasion into the body by harmful microbes and presence of chronic inflammatory cells such as lymphocytes,
General Pathology and Basic Techniques
their resultant ill-effects by toxins. Inflammation involves 2 plasma cells and macrophages, granulation tissue formation,
and in specific situations as granulomatous inflammation.
basic processes with some overlapping, viz. early inflam- In some instances, the term subacute inflammation is used
matory response and later followed by healing. Though both
these processes generally have protective role against for the state of inflammation between acute and chronic.
injurious agents, inflammation and healing may cause
considerable harm to the body as well e.g. anaphylaxis to ACUTE INFLAMMATION
bites by insects or reptiles, drugs, toxins, atherosclerosis, Acute inflammatory response by the host to any agent is a
chronic rheumatoid arthritis, fibrous bands and adhesions continuous process but for the purpose of discussion, it can
in intestinal obstruction. be divided into following two events:
As discussed earlier (Chapter 4), “immunity or immune I. Vascular events.
reaction” and “inflammatory response” by the host are both II. Cellular events.
protective mechanisms in the body—inflammation is the Intimately linked to these two processes is the release of
visible response to an immune reaction, and activation of mediators of acute inflammation, discussed just thereafter.
immune response is almost essential before inflammatory
response appears. I. VASCULAR EVENTS

SIGNS OF INFLAMMATION. The Roman writer Celsus Alteration in the microvasculature (arterioles, capillaries and
in 1st century A.D. named the famous 4 cardinal signs of venules) is the earliest response to tissue injury. These
inflammation as: alterations include: haemodynamic changes and changes in
rubor (redness); vascular permeability.
tumor (swelling);
calor (heat); and Haemodynamic Changes
dolor (pain). The earliest features of inflammatory response result from
To these, fifth sign functio laesa (loss of function) was changes in the vascular flow and calibre of small blood
later added by Virchow. The word inflammation means vessels in the injured tissue. The sequence of these changes
burning. This nomenclature had its origin in old times but is as under:
now we know that burning is only one of the signs of 1. Irrespective of the type of injury, immediate vascular res-
inflammation. ponse is of transient vasoconstriction of arterioles. With mild