Primary and secondary lymphoid organs discussed. PPT is useful to Students studying X, XI, XII and B.Sc., M.Sc., Life Sciences. The teachers can also use the PPt.
1. Dr. P. VEERAMUTHUMARI,
Assistant Professor of Zoology,
V.V.Vanniaperumal College for Women,
Virudhunagar – 626 001
veeramuthumari@vvcollege.org;muthusdream@gmail.com
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2. LYPHOID ORGANS
The lymphoid organs in the human
body includes the spleen, lymph nodes,
bone marrow, thymus and lymph tissue.
The lymphatic system is a network
of tissues and organs that help to clear
toxins, waste and other unwanted materials
present in the human body. The
primary function of the lymphatic system is
to transport lymph, a fluid containing
infection to fighting with white blood cells,
throughout the body.
https://www.google.com/search?q=define+ly
mphoid+organs&source=lnms&tbm=isch&sa
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3. PRIMARY LYMPHOID ORGANS
(a) Bone marrow
(b) Thymus
In primary lymphoid organs, immature lymphocytes
differentiate to mature ones into an antigen sensitive
lymphocytes and after maturation, lymphocytes migrate to
secondary lymphoid organs.
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4. (a) Bone Marrow:
It is the main lymphoid organ, where all the lymphocytes and all the body cells are
produced and T-lymphocytes are developed.
Bone marrow is soft, gelatinous tissue that fills the medullary cavities, the centers
of bones. such as hip and thigh bones. The two types of bone marrow are red bone
marrow, known as myeloid tissue, and yellow bone marrow, or fatty tissue.
The major function of bone marrow is to generate blood cells. Bone marrow
contains two main types of stem cells. Hematopoietic stem cells, found in red
marrow, are responsible for the production of blood cells.
The stem cells that carry oxygen through out the body, the white blood cells that
fight infections, and initiate the platelets that help with blood clotting.
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5. (b) Thymus:
It is a lobed organ, The thymus is a small, irregular-shaped gland in the top part
of the chest, just under the breastbone and between the lungs. It is located in
an area of the body called the mediastinum. The thymus is part of both the
lymphatic system and the endocrine system.
It is large at the time of birth but with age, the size keep on reducing and
becomes very small by attaining puberty. Growth and maturation of T-
lymphocytes takes place in thymus only. Both bone marrow and thymus
provide micro-environments for the development and maturation of T-
lymphocytes.
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6. SECONDARY LYMPHOID ORGANS
These organs provide the sites for the interaction of
lymphocytes with the antigen, which then proliferate to become
effector cells.
These are of following types:
(a) Spleen
(b) Lymph nodes
(c) Mucosal associated Lymphoid Tissue (MALT)
Peyer’s patches of small intestine and appendix are also some
of the secondary lymphoid organs.
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7. (a) Spleen:
Spleen, organ of the lymphatic system located in the left side of the abdominal
cavity under the diaphram, the muscular partition between the abdomen and
the chest. It is a large bean-shaped organ containing lymphocytes and
phagocytes. It filters the blood by trapping the pathogens in it. The white
pulp of the spleen contains typical lymphoid elements, such as plasma cells,
lymphocytes, and lymphatic nodules, called follicles in the spleen.
Germinal centre in the white pulp serve as the sites
of lymphocyte production.
Similar to the lymph nodes, the spleen
reacts to microorganisms and other
antigens that reach the bloodstream by
releasing special phagocytic cells known as
macrophages. Splenic macrophages reside
in both red and white pulp, and they serve
to remove foreign material from the blood
and to initiate an immune reaction that
results in the production of antibodies.
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8. (b) Lymph Nodes:
These are small solid structures located at different points along the
lymphatic system. Their function is to trap the microorganisms or other
antigens, that enter the lymph and tissue fluid. Therefore, the antigens
trapped in the lymph nodes are responsible for the activation of
lymphocytes present there and cause the immune response.
Lymph nodes- These are small, bean-
shaped structures which produce and
store cells, specialized in fighting
infections. They are a part of
the lymphatic system. The lymphatic
system is part of the vascular system
and an important part of the immune
system, composed of a large network of
lymphatic vessels that carry a clear fluid
called lymph directionally towards the
heart.
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9. (c) Mucosal Associated Lymphoid Tissue (MALT):
The mucosa-associated lymphoid tissue (MALT), also called mucosa-associated lymphatic
tissue, is a diffuse system of small concentrations of lymphoid tissue found in various
submucosal membrane sites of the body, such as the gastrointestinal tract, nasopharynx, thyroid,
breast, lung, salivary glands, eye, lining of main tracts in the body like respiratory, digestive,
urogenital tracts and skin. It constitutes about 50% of the lymphoid tissue in human body.
MALT is populated by lymphocytes such as T cells and
B cells, as well as plasma cells and macrophages, each
of which is well situated to encounter antigens passing
through the mucosal epithelium. In the case of intestinal
MALT, M cells are also present, which sample antigen
from the lumen and deliver it to the lymphoid tissue.
There are three types of situations in which MALT is
present- Tonsils, Appendix and Small intestine area.
Peyer's patches are small masses of lymphatic tissue
found throughout the ileum region of the small intestine.
Also known as aggregated lymphoid nodules, they form
an important part of the immune system by monitoring
intestinal bacteria populations and preventing the growth
of pathogenic bacteria in the intestines.
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