lymphoid tissues l o

SMC, JSMU, MBBS, Blood module

1. Lecture outline and learning objectives
Semester – (I) ,WEEK -5 . Batch- II. (Lecture, Dr. Santosh Kumar)
Submitted by; Dr. Zafar H.Baloch
Learning objectives
•At the end of lecture student should know:
• Types of lymphoid tissue & lymphoid organs:
•Structure & function of
•( a) Lymph nodule
•( b) Lymph node
•(c) Thymus
•(d) Tonsil
•(e) Spleen.

2. Lecture outline
Lymphoid tissues
These are different structures in the body mainly composed of lymph cells and
reticular cells.
Lymphatic system gives organism immunity against injury by foreign substance or
organism.
Lymphoid tissue can be divided into:
1- Diffuse lymphoid tissue.
2- Nodular lymphoid organs:
a) Lymph nodule
b) Lymph node
c) Thymus
d) Tonsil
e) Spleen.
Diffuse Lymphoid Tissue
It is found throughout the body particularly in alimentary tract and respiratory
tract.
They are characterized by a loosely organized mass of lymphocytes.
Lymph Nodule
They are rounded masses of densely packed lymphocytes.

3. Each nodule contains light staining central area the germinal centre which is the
site of active lymphocyte proliferation.
Lymph nodules are found in the mucosa of small intestine and appendix.
They also form the basic structure of many lymphoid organs.
Single lymph nodule
Lymph Node
They are ovoid structure 1- 25 mm in size.
They are surrounded by connective tissue capsule made up of collagen fibers.
From the capsule trabeculae penetrate forming incomplete partition.
Gland substance is composed of cortex and medulla.
Lymph node section at low magnification
Cortex is separated from capsule by sub-capsular sinus.
Sub-capsular sinus is continuous with the sinuses inside the node.
In the cortex there are lymph follicles (lymph nodules) which are 0.2-1 mm in
diameter.
LYMPH NODE
These lymph follicles may or may not contain germinal centre.
Germinal center contain activated lymphocytes.
They are best developed in childhood.
Between the cortical follicle and medulla is paracorticular region. This region is
composed of loosely aggregated T-lymphocytes.
Medulla contains lymphocytes and plasma cells arranged in the form of cords
called medullary cords.

4. Afferent lymph vessels open along the convex surface in sub-capsular sinus.
Efferent lymphatics leave the node at hilum.
Artery also enters at the hilum while vein leaves at this point.
Most of the antigens and cell debris are filtered when the lymph passes through
the node.
Functions of Lymph Node
Lymph nodes are immunological filter of the lymph.
They produce lymphocytes.
Antibodies are also produced in lymph nodes in response to antigen.
TONSILS
Tonsils
These are masses of lymphoid tissue may be partially encapsulated as small
organs.
There are three such masses which are paired structures, palatine, pharyngeal
and lingual tonsil.
They all are located in the pharynx.
Palatine Tonsil
They are oval shaped bodies in oropharynx between glossopharyngeal and
pharyngopalatine arches.
Free surface is covered by stratified squamous epithelium which is continuous
with the epithelium of pharynx.
There is capsule of connective tissue over the attached or basal surface of
lymphatic tissue.
Epithelium of the crypt is infiltrated with lymphocytes.

5. In tonsillitis other blood cells like neutrophil are also found in tonsillar tissue.
At various places on the surface of tonsil deep indentations or pockets occur
which are known as crypts.
The crypts are 10~20 in number. Several secondary crypts arise from the primary
one.
Surrounding each crypt are lymphatic nodules as well as diffuse lymphatic tissue.
Lingual Tonsil
These are spherical aggregation of lymphatic tissue present on the dorsal surface
of tongue.
Wide mouth crypts are present which are lined by stratified squamous
epithelium.
Ducts of some lingual glands frequently open in these crypts.

6. In tonsillitis other blood cells like neutrophil are also found in tonsillar tissue.
At various places on the surface of tonsil deep indentations or pockets occur
which are known as crypts.
The crypts are 10~20 in number. Several secondary crypts arise from the primary
one.
Surrounding each crypt are lymphatic nodules as well as diffuse lymphatic tissue.
Lingual Tonsil
These are spherical aggregation of lymphatic tissue present on the dorsal surface
of tongue.
Wide mouth crypts are present which are lined by stratified squamous
epithelium.
Ducts of some lingual glands frequently open in these crypts.