BODY DEFENSES AGAINST INFECTION
The presence and reproduction of pathogens may cause
an infection. Pathogens include bacteria, complex single-
celled organisms, fungi, and viruses. An infection may
not immediately cause symptoms. The body has innate
c) and adaptive (speciF
c) defenses against
INNATE (NONSPECIFIC) DEFENSES
1. Species resistance
Each species is resistant to certain diseases that may
affect other species but is susceptible to diseases other
species may resist.
2. Mechanical barriers
a. Mechanical barriers include the skin and mucous
b. Intact mechanical barriers prevent entrance of
c. Hair traps infectious agents; and ﬂ
uids such as
tears, sweat, saliva, mucus, and urine wash away
organisms before they can F
3. Chemical barriers
a. Enzymes in gastric juice and tears kill some
b. Low pH in the stomach prevents growth of some
c. High salt concentration in perspiration kills some
d. Interferons stimulate uninfected cells to synthesize
antiviral proteins that block proliferation of
viruses, stimulate phagocytosis, and enhance
activity of cells that help resist infections and stiﬂ
e. Defensins make holes in bacterial cell walls and
f. Collectins provide broad protection against a wide
variety of microbes by grabbing onto them, easing
g. Activation of complement proteins in plasma
ammation, attracts phagocytes, and
4. Natural killer (NK) cells
Natural killer cells secrete perforins, which destroy
cancer cells and cells infected with viruses.
a. Inﬂ ammation is a tissue response to damage,
injury, or infection.
b. The response includes localized redness, swelling,
heat, and pain.
c. Chemicals released by damaged tissues attract
white blood cells to the site.
d. Clotting may occur in body ﬂ
uids that accumulate
in affected tissues.
e. Connective tissue may form a sac around the
injured tissue and thus aid in preventing the
spread of pathogens.
2. Obstruction of lymph movement
a. Any condition that interferes with the ﬂ ow of
lymph results in edema.
b. Obstruction of lymphatic vessels due to surgical
removal of lymph nodes causes edema in the
LYMPH NODES (PAGE 621)
1. Structure of a lymph node
a. Lymph nodes are usually bean-shaped, with
blood vessels, nerves, and efferent lymphatic
vessels attached to the indented region; afferent
lymphatic vessels enter at points on the convex
b. Lymph nodes are enclosed in connective tissue
that extends into the nodes and subdivides them
c. Nodules contain masses of lymphocytes and
macrophages and spaces through which lymph
2. Locations of lymph nodes
a. Lymph nodes aggregate in groups or chains along
the paths of larger lymphatic vessels.
b. They are in the cervical, axillary, supratrochlear,
and inguinal regions and in the pelvic,
abdominal, and thoracic cavities.
3. ±unctions of lymph nodes
a. Lymph nodes F
lter potentially harmful foreign
particles from the lymph before it is returned to
b. Lymph nodes are centers for the production of
lymphocytes that act against foreign particles.
c. They contain macrophages that remove foreign
particles from lymph.
THYMUS AND SPLEEN (PAGE 623)
a. The thymus is a soft, bilobed organ within the
b. It slowly shrinks after puberty.
c. It is composed of lymphatic tissue subdivided
d. Lobules contain lymphocytes.
e. T lymphocytes leave the thymus and provide
f. The thymus secretes thymosins, which stimulate
maturation of T lymphocytes.
a. The spleen is in the upper left portion of the
b. It resembles a large lymph node encapsulated
and subdivided into lobules by connective
c. Spaces in splenic lobules are F
lled with blood.
d. The spleen, which F
lters foreign particles
and damaged red blood cells from the blood,
contains many macrophages and lymphocytes.