Page 317 - Anatomy and Physiology of Farm Animals, 8th Edition

302 / Anatomy and Physiology of Farm Animals

ody defense is protection against of lymphocytes capable of removing
Binjury; immunity is protection against
VetBooks.ir foreign microorganisms or the harmful the potentially harmful cell (cellular
response), or both.
Inflammation can be defined as the
effect of antigenic substances (antigens).
Antigens are molecules that can stimulate response of tissues to injury. The classic
an immune response directed at that spe- signs of acute inflammation (swelling,
cific molecule, and in most cases antigens pain, heat, and redness) are produced
are either components of foreign cells or as a result of the injury and the tissue
secretions by microorganisms. While the response. Chronic inflammatory
ability to mount immune responses is part responses may not demonstrate these
of the body’s defenses, it is not the only classic signs. The desired outcome of the
means by which the body is defended. A response to injury is complete repair with
number of nonspecific defenses, general the restoration of tissues to their original
defense mechanisms that do not need to state. Obviously, this may or may not be
recognize specific antigens to be effective, possible, depending on the severity and
also protect the body against injury. type of injury and the ability of tissues to
Foreign refers to cells or substances that respond. While the effects of injury pro-
are not self. Self refers to cells and sub- duce local changes that initiate an inflam-
stances that are normal components of an matory response, cells attracted to the
animal’s body and that normally do not area of injury (e.g., leukocytes and
elicit an immune response. The ability to macrophages) also participate in inflam-
differentiate between foreign and self is a matory responses.
critical function of the immune system.
Autoimmune disorders occur when the
immune system erroneously identifies self Nonspecific Defenses
tissues or antigens as foreign and mounts
an inappropriate immune response. The Epithelia that cover surfaces exposed to the
immune system must also be able to iden- external environment function as protec-
tify and eliminate self cells that have tive barriers to prevent entry of injurious
changed so that they may be harmful. The agents, such as microbes and chemicals.
identification and elimination of these This barrier function can be enhanced by
altered cells is protection against the devel- epithelial secretions, such as hydrochloric
opment of cancers. acid in the stomach and nonspecific anti-
The immune system may be defined as microbial agents in saliva (e.g., lysozyme).
all of the structures and cells involved in Physical disruption of the barrier or loss of
providing immune protection. This is not epithelial function can provide an entry-
an anatomically defined system, as cells of way for injurious agents to reach the body
this system can be found throughout the fluids and possibly spread.
body in many tissues. Lymphocytes are the When microbes or injurious agents
primary cell type involved in an immune penetrate an epithelial barrier, their pres-
response, and the wide distribution of lym- ence and any tissue damage that they pro-
phocytes throughout the body provides duce initiates a response, inflammation.
them ready access to invading microorgan- The initial phases of this response are
isms and newly introduced antigens. immediate and similar regardless of the
Lymphocytes are not a uniform group of type or identity of the microbe or agent.
cells, and the different subtypes of lympho- Thus, these are nonspecific responses, or
cytes have specific roles in the overall gen- innate responses. The terms nonspecific
eration and regulation of an immune immune response and innate immune
response. However, in general, the primary response have also been used. A specific
responses are production of circulating or acquired immune response entails
antibodies (humoral response), generation identification of the specific microbe or