CHAPTER 10
Lymphoid System
189
Mucosa-Associated Lymphoid Tissue
Name
Location
Epithelial
Covering
Crypts
Capsule
Lymphatic
Nodules (Follicles)
Palatine tonsils (2)
Posterolateral walls
of the oral cavity
StratiF ed squamous
epithelium
(nonkeratinized)
Yes, deep and
branched crypts
divide tonsil into
lobules
Thick, incomplete
connective tissue
capsule; par-
tially covered by
epithelium
Each lobule
contains
numerous lymphatic
nodules, most having
a germinal center
Pharyngeal
(adenoid) tonsil (1)
Posterior roof of the
nasopharynx
PseudostratiF ed
ciliated columnar
epithelium
No, only epithelial
invagination
Thin, incomplete
connective capsule;
partially covered
by epithelium
Mostly diffuse
lymphoid tissues
and some lymphatic
nodules
Lingual tonsils (2)
Posterior fl oor of the
mouth (surface of
the posterior third of
the tongue)
StratiF ed squamous
epithelium
(nonkeratinized)
Yes, wide
nonbranched crypt;
duct of mucous
gland opens into
the crypt
No capsule;
partially covered
by epithelium
Rows of lymphatic
nodules supported
by connective
tissue
septa
TABLE 10-1
Tonsils
Figure 10-8A.
Pharyngeal tonsil, MALT.
H&E,
3
76; inset
3
184
MALT
refers to diffuse lymphatic tissues or aggregate lymphatic nod-
ules in the mucosa of the digestive, respiratory, and genitourinary
tracts. Comparable tissue is
GALT
in the gut and
BALT
in the respi-
ratory system. Tonsils are composed of aggregate lymphatic nodules
and belong to MALT. Tonsils include
pharyngeal
,
palatine
, and
lingual
tonsils
. The pharyngeal tonsil is located in the roof of the nasophar-
ynx (±ig. 10-6). It has epithelial invaginations, but no crypts, and is
covered by
pseudostratif ed columnar epithelium
. The pharyngeal ton-
sil traps bacteria and viruses and is one of the lymphoid organs that
provides an environment for lymphocytes to meet antigens. It mostly
consists of secondary nodules and a few primary nodules. A secondary
nodule is composed of a
germinal center
and
mantle zone
. Activated
B cells are found mainly in the germinal centers of secondary nodules
and inactivated B cells primarily in primary nodules.
Pseudostratified
Pseudostratified
columnar
columnar
epithelium
epithelium
Pseudostratified
columnar
epithelium
Pseudostratified
columnar
epithelium
Mantle
Mantle
zone
zone
Primary
Primary
nodule
nodule
Germinal
Germinal
center
center
Pseudostratified
Pseudostratified
columnar
columnar
epithelium
epithelium
Mantle
zone
Primary
nodule
Germinal
center
Pseudostratified
columnar
epithelium
Pseudostratified
columnar
epithelium
A
Germinal
Germinal
center
center
Large lymphocytes
Large lymphocytes
in germinal center
in germinal center
Mantle
Mantle
zone
zone
Mantle
zone
Stratified squamous
Stratified squamous
epithelium
epithelium
Germinal
center
Large lymphocytes
in germinal center
S
tr
t
r
a
tifie
t
if
ie
d
s
s
q
u
a
m
o
u
s
e
p
ith
it
h
e
liu
liu
m
Stratified squamous
epithelium
Stratified sq
uamous
ep
ithelium
B
Figure 10-8B.
Palatine tonsil, MALT.
H&E,
3
83; inset
3
750
(left);
3
197 (right)
Palatine tonsils
are paired and are located in the posterior and lateral
portions of the oral cavity. They have 10 to 20 crypts and the portion
facing the oral cavity is covered by
stratif
ed squamous epithelium
.
The nodules usually lie as a row beneath the epithelium and sur-
round each crypt. They safeguard the entrance of the respiratory and
digestive tracts against microbe invasion. They also function in the
recirculation of lymphocytes and provide sites for the lymphocyte
to interact with antigens. The
germinal center
of a nodule contains
large-sized B cells and antigen-presenting cells where B cells encoun-
ter antigens and continue to proliferate and develop into plasma
cells. The
mantle zone
of the nodule contains mostly small inactive
B cells. The peripheral region of the nodule contains mostly T cells.
Palatine tonsils are common sites for infection, such as
acute tonsil-
litis
, recurrent
tonsillitis
, or
tonsillar hypertrophy
due to lymphoid
hyperplasia.
Tonsillectomy
may be a choice in some children with
recurrent tonsillitis.
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