causes lymph to accumulate in lymph nodes, allowing more time for its
MALT (mucosa-associated lymphoid tissue) is lymphoid
tissue found in the mucosa of the digestive, respiratory, and genitouri-
nary tracts. It includes tonsils, Peyer’s patches, and the appendix.
spleen cleanses the blood, stores breakdown products of RBCs, stores
platelets and monocytes, and is thought to be a site of erythrocyte pro-
duction in the fetus.
±e thymus develops ﬁrst.
Review Questions 1.
Case Study 1.
±e red streaks radiating from Mr. Hutchinson’s ﬁnger
indicate that his lymphatic vessels are inﬂamed. ±is inﬂammation may
be caused by a bacterial infection. If Mr. Hutchinson’s arm had exhibited
edema without any accompanying red streaks, the problem would likely
have been impaired lymph transport from his arm back to his trunk, due
to injury or blockage of his lymphatic vessels.
Mr. Hutchinson’s arm
was placed in a sling to immobilize it, slowing the drainage of lymph from
the infected area in an attempt to limit the spread of the infection.
Hutchinson’s low lymphocyte count indicates that his body’s ability to ﬁght
infection by bacteria or viruses is impaired. ±e antibiotics and additional
staﬀ protection will protect Mr. Hutchinson until his lymphocyte count
increases again. Gloving and gowning also protect the staﬀ caring for Mr.
Hutchinson from any body infection he might have.
recovery may be problematic, as he probably already has an ongoing bacte-
rial infection and his ability to raise a defense to this infection is impaired.
Check Your Understanding 1.
±e innate defense system is always ready
to respond immediately, whereas it takes considerable time to mount the
adaptive defense system. ±e innate defenses consist of surface barriers
and internal defenses, whereas the adaptive defenses consist of humoral
and cellular immunity, which rely on B and T lymphocytes.
barriers (the skin and mucous membranes) constitute the ﬁrst line of
Opsonization is the process of making pathogens more sus-
ceptible to phagocytosis by decorating their surface with molecules that
phagocytes can bind. Antibodies and complement proteins are examples
of molecules that act as opsonins.
Our own cells are killed by NK cells
when they have been infected by viruses or when they have become
Redness, heat, swelling, and pain are the cardinal signs of
inﬂammation. Redness and local heat are both caused by vasodilation of
arterioles, which increases the ﬂow of blood (warmed by the body core) to
the aﬀected area. ±e swelling (edema) is due to the release of histamine
and other chemical mediators of inﬂammation, which increase capillary
permeability. ±is increased permeability allows proteins to leak into
the interstitial ﬂuid (IF), increasing the IF osmotic pressure and draw-
ing more ﬂuid out of blood vessels and into the tissues, thereby causing
swelling. ±e pain is due to two things: (1) the actions of certain chemi-
cal mediators (kinins and prostaglandins) on nerve endings, and (2) the
swelling, which can compress free nerve endings.
±ree key character-
istics of adaptive immunity are that it is speciﬁc, it is systemic, and it has
A complete antigen has both immunogenicity and reactivity,
whereas a hapten has reactivity but not immunogenicity.
particularly MHC proteins, mark a cell as self.
Development of im-
munocompetence of a B or T cell is signaled by the appearance on its
surface of speciﬁc and unique receptors for an antigen. In the case of a B
cell, this receptor is a membrane-bound antibody. (In T cells, it is simply
called the T cell receptor.)
±e T cell that would survive is (c), one that
recognizes MHC but not self-antigen.
Dendritic cells, macrophages,
and B cells can all act as APCs. Dendritic cells are most important for T
In clonal selection, the antigen does the selecting. What
is being selected is a particular clone of B or T cells that has antigen recep-
tors corresponding to that antigen.
±e secondary response to an an-
tigen is faster than the primary response because the immune system has
system, increasing heart rate, in an attempt to restore blood pressure.
±e external carotid arteries supply most of the tissues of the head except
for the brain and orbits.
±e cerebral arterial circle (circle of Wil-
lis) is the arterial anastomosis at the base of the cerebrum.
unpaired arteries that emerge from the abdominal aorta are the celiac
trunk, the superior and inferior mesenteric arteries, and the median sac-
You would palpate the popliteal artery behind the knee, the
posterior tibial artery behind the medial malleolus of the tibia, and the
dorsalis pedis artery on the foot. (See also Figure 19.12.)
arteries help supply the brain, but the vertebral veins do not drain much
blood from the brain.
±e internal jugular veins drain the dural ve-
nous sinuses. Each internal jugular vein joins a subclavian vein to form a
A portal system is a system where two capillary
beds occur in series. In other words, in a portal system, a capillary bed is
drained by a vein that leads into a second capillary bed. ±e function of
the hepatic portal system is to transport venous blood from the digestive
organs to the liver for processing before it enters the rest of the systemic
circulation. ±is plays an important role in defense against absorbed
toxins or microorganisms and also allows direct delivery of absorbed
nutrients to the liver for processing.
±e leg veins that o²en become
varicosed are the great and small saphenous veins.
between arteries and veins are (1) arteries run deep while veins are both
deep and superﬁcial, (2) venous pathways are more interconnected than
arterial pathways, and (3) the brain and digestive systems have unique
venous drainage systems, whereas their arterial supply patterns are not
substantially diﬀerent from those of other organs.
±e foramen ovale
and the ductus arteriosus both bypass the fetal lungs. ±e ductus venosus
bypasses the fetal liver.
Varicose veins, atherosclerosis, and hyperten-
sion are associated with aging.
Review Questions 1.
(1)b, e, g; (2)c; (3)i; (4)f, h; (5)d;
Case Study 1.
±e tissues in Mr. Hutchinson’s right leg were deprived of
oxygen and nutrients for at least one-half hour. When tissues are deprived
of oxygen, tissue metabolism decreases and eventually ceases, so these tis-
sues may have died due to anoxia.
Mr. Hutchinson’s vital signs (low BP;
rapid, thready pulse) indicate that he is facing a life-threatening problem
that must be stabilized before other, less vital problems can be addressed. As
for surgery, he may be scheduled for open reduction of his crushed bone,
depending upon the condition of the tissues in his crushed right leg. If tis-
sue death has occurred in his leg, he may undergo amputation of that limb.
Mr. Hutchinson’s rapid, thready pulse and falling blood pressure are
indications of hypovolemic shock, a type of shock resulting from decreased
blood volume. Because his blood volume is low, his heart rate is elevated to
increase cardiac output in an eﬀort to maintain the blood supply to his vital
organs. Mr. Hutchinson’s blood volume must be increased as quickly as
possible with blood transfusions or intravenous saline. ±is will stabilize his
condition and allow his physicians to continue with his surgery.
Check Your Understanding 1.
Lymph is the ﬂuid inside lymphatic ves-
sels. It enters lymphatic vessels from interstitial ﬂuid. Interstitial ﬂuid,
in turn, is a ﬁltrate of blood plasma.
±e right lymphatic duct receives
lymph from the right upper arm and the right side of the head and tho-
rax. ±e thoracic duct drains lymph from the rest of the body.
movement is driven by the contraction of adjacent skeletal muscles,
pressure changes in the thorax during breathing, the pulsations of nearby
arteries, and contraction of smooth muscle in the lymphatic vessel walls.
(Valves in lymphatic vessels prevent backﬂow of lymph.)
follicles are solid, spherical bodies consisting of tightly packed reticular
ﬁbers and lymphoid cells, o²en with a lighter-staining central region.
±ey are regions where B cells predominate.
Having fewer eﬀerents