Page 831 - Fundamentals of anatomy physiology

818 Unit 4 Fluids and Transport Lymphatic Lymph
Figure 22–8 The Structure of a Lymph Node. ATLAS: Plate 70a vessel nodes

Efferent Lymph node
vessel artery and vein
Hilum

Lymph nodes

Trabeculae Medullary sinus
Medulla Outer cortex (B cells)
Cortex
Subcapsular space
Subcapsular
space Germinal center Outer cortex Capsule

Deep cortex
(T cells)

Dividing
B cell

Capsule Medullary cord Afferent
(B cells and vessel
plasma cells)

Dendritic cells

22 Nuclei of B cells

stimulate macrophages and lymphocytes in nearby lymph Capillary
nodes.
and phagocytes in the node in response to a minor, localized
To protect a house against intruders, you might guard infection. Chronic or excessive enlargement of lymph nodes
all the entrances and exits or place traps by the windows and is lymphadenopathy (lim-fad-e-NOP-a-the. ). This condition
doors. The distribution of lymphoid tissues and lymph nodes may occur in response to bacterial or viral infections, endocrine
follows such a pattern. The largest lymph nodes are located disorders, or cancer.
where peripheral lymphatics connect with the trunk, such as
in the groin, the axillae, and the base of the neck. These nodes The Thymus
are often called lymph glands. Because lymph is monitored in
these nodes, potential problems can be detected and dealt with The thymus is a pink, grainy organ located in the mediastinum,
before they affect the vital organs of the trunk. The mesenter- generally just posterior to the sternum (Figure 22–9a,b). In
ies of the gut also have aggregations of lymph nodes, located newborn infants and young children, the thymus is relatively
near the trachea and passageways leading to the lungs, and in large. It commonly extends from the base of the neck to the
association with the thoracic duct. These lymph nodes protect superior border of the heart. The thymus reaches its greatest
against pathogens and other antigens within the digestive and size relative to body size in the first year or two after birth. (The
respiratory systems. organ continues to increase in mass throughout childhood, but
the body as a whole grows even faster, so the size of the thymus
A minor injury commonly produces a slight enlargement relative to that of the other organs in the mediastinum gradu-
of the nodes along the lymphatic vessels draining the region. ally decreases.)
This sign is often called “swollen glands.” It typically indicates
inflammation in peripheral structures. The enlargement gener-
ally results from an increase in the number of lymphocytes