196
UNIT 3
Organ Systems
Lymphocytes
Lymphocytes
Macrophage
Macrophage
Lymphocytes
Macrophage
Luman of
Luman of
central artery
central artery
Lumen of
central artery
Endothelial
Endothelial
cells
cells
T cells
T cells
T cells
Endothelial
cells
Central artery
Central artery
PALS
PALS
Central artery
PALS
PALS
PALS
PALS
PALS
PALS
PALS
B
Figure 10-15B.
Periarterial lymphatic sheath, spleen.
H&E stain,
3
564; insets
3
1,727
The
central artery
, which helps to maintain the
lymphatic sheath
, continues through
the white pulp and branches before supplying the
marginal sinuses
(capillaries). Its
distal branches supply the red pulp. The central artery carries lymphocytes into
the marginal sinuses in the
marginal zone
, where B cells encounter antigens. Naive
B cells become memory B cells and plasma cells, which produce antibodies.
T cells
migrate to the central artery region and form multiple layers that surround that
artery to form the
PALS
. T cells interact with antigen-presenting cells (
inset
shows a
macrophage
) and receive antigens. Active T cells undergo proliferation to increase
their population (Fig. 10-5A).
Figure 10-15A.
Splenic circulation.
The
splenic artery
enters the spleen at the hilum and
branches into
trabecular arteries
, which follow the
trabeculae into the white pulp where they become the
cen-
tral artery
. Lymphatic tissue that immediately surrounds
the central artery is called the
PALS
. The central artery
passes through the white pulp and gives rise to two routes
of capillaries: (1) those which supply sinuses (
marginal
sinuses
) around the lymphatic nodule; (2) those which
supply sinuses in the red pulp. The central artery leaves
the white pulp and forms several
penicillar arterioles
(not
surrounded by PALS). The branches of the penicillar arte-
rioles are called
terminal arterial capillaries
, which either
give rise directly to the
splenic sinuses
(
closed circulation
)
or terminate as open-ended vessels within the splenic
cord of the red pulp (
open circulation
). Open circula-
tion allows blood passing through the splenic cord to be
± ltered by macrophages before the blood cells enter the
sinuses. The aggregation of the macrophages surround-
ing the terminal arterial capillaries is called the
sheath of
macrophages
or the
Schweigger-Seidel sheath
.
Open
circulation
Pulp
vein
Sheath of
macrophages
Macrophage
Splenic
cord
Splenic
sinuses
Penicillar
arterioles
Closed
circulation
Central
artery
Marginal
sinuses
Splenic nodule
Trabecular
artery and vein
Germinal
center
PALS
A
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