192
UNIT 3
Organ Systems
Figure 10-11A.
Lymph node.
H&E,
3
43
Lymph nodes
are bean shaped and are the only lymphoid
organs that have afferent lymphatic vessels (Fig. 10-9). This
is a cross section of a lymph node. (1) The
cortex
is the
peripheral region of the lymph node and consists of a row of
nodules. (2) The
medulla
stains lighter and is located at the
center area; it is composed of medullary sinuses and medul-
lary cords (Fig. 10-11B,D). (3) The
paracortex
lies between
the cortex and the medulla. Lymph nodes are the major sites
to ±
lter incoming lymph and are the sites for lymphocytes to
meet antigens.
Figure 10-11B.
Lymph node.
H&E,
3
100
The
subcapsular sinus
carries lymph from
afferent lymphatic
vessels
into the node by passing through
peritrabecular sinuses
to the
medullary sinuses
. The nodules in the cortex consist of a
germinal center
(loosely packed large B cells) and a
mantle zone
(containing tightly packed small B cells). T cells mainly reside
in the
paracortex
region where they interact with antigen-
presenting cells; lymphocytes enter the lymph node through
HEVs in the paracortex region (Fig. 10-12A,B).
Figure 10-11C.
Germinal center, lymph node.
H&E,
3
658
The
germinal center
is composed of activated B cells in various
stages of maturation. Cell size and nuclear shape are varied.
The large immature cells with round nucleus and dispersed
euchromatin are
lymphoblasts
and
plasmablasts
. They dif-
ferentiate into memory B cells and plasma cells. The germinal
center also contains
follicular dendritic
(
antigen-presenting
)
cells
, which help pass antigens to B cells. They are dif±
cult to
recognize in H&E stain.
Figure 10-11D.
Medullary sinuses and cords, lymph node
.
H&E,
3
658
A
medullary sinus
surrounded by a
medullary cord
is shown
here.
Medullary sinuses
carry lymph to where antigens are
removed by
macrophages
from slow-fl
owing lymph. The
medullary cords
contain B cells, plasma cells, dendritic cells,
and macrophages held within a network of reticular ±
bers.
Medullary cord
Medullary cord
Medullary
Medullary
cord
cord
Medullary cord
Lumen of the
Lumen of the
medullary sinus
medullary sinus
Lumen of the
medullary sinus
Medullary
cord
Macrophages
Macrophages
Macrophages
Medullary cord
Medullary cord
Medullary cord
Lymphocytes in the
Lymphocytes in the
medullary sinus
medullary sinus
Lymphocytes in the
medullary sinus
D
Lymphatic
nodules
Medulla
lla
Medulla
Paracortex
Paracortex
Paracortex
Cortex
Cortex
Cortex
A
Subcapsular sinus
Subcapsular sinus
Subcapsular sinus
Peritrabecular
Peritrabecular
sinus
sinus
Peritrabecular
sinus
Medullary
Medullary
cords
cords
Medullary
cords
Germinal
Germinal
center
center
Germinal
center
Medullary
Medullary
sinuses
sinuses
Medullary
sinuses
Medullary
Medullary
sinuses
sinuses
Medullary
sinuses
Paracortex
Paracortex
Paracortex
Mantle
Mantle
zone
zone
Mantle
zone
B
Lymphoblast
Lymphoblast
Lymphoblast
Small
Small
lymphocytes
lymphocytes
Small
lymphocytes
Lymphoblast
Lymphoblast
Lymphoblast
C
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