The document summarizes the primary and secondary lymphoid organs of the immune system. The primary lymphoid organs, where immune cells develop, are the bone marrow and thymus. The bone marrow produces immune cells, while the thymus matures T cells. Secondary lymphoid organs, where immune responses are coordinated, include the spleen, lymph nodes, tonsils, Peyer's patches, and skin tissue. These organs filter pathogens and allow immune cells to interact.

1. Organ of Immune System
Mrs. Praveen Garg
VITS College, Satna

2. INTRODUCTION
• The human immune system (and those of most mammals) is composed of
physical barriers (skin and mucus), innate and adaptive cells, chemical
messengers (cytokines), and primary and secondary lymphoid tissue.
• The organs and tissues of the immune system are divided into the two types:
• Primary (or generative) lymphoid organs
• Secondary (or peripheral) lymphoid organs
• The primary lymphoid organs consist of the Bone marrow and thymus and are
the sites where cells of the innate and adaptive immune system are generated
and produced.
• The secondary lymphoid organs include the spleen, lymph nodes, and
epithelial and mucosa-associated lymphoid tissues (MALT) such as Peyer
patches in the small intestine.

3. • These secondary lymphoid tissues are the anatomic site for coordination of the
adaptive immune response.
• The cellular components of the innate immune response—
neutrophils, eosinophils, basophils, and monocytes—leave the bone marrow as
mature, functional cells.
• In contrast, the cellular components of the adaptive immune response require
further development in specific anatomic sites.
• T-cell precursors leave the BM and migrate to the thymus, where they develop
their antigen receptor, the TCR.
• Although B cells leave the BM with a functional BCR/Ig, they require further
maturation following interaction with T cells and antigen in secondary
lymphoid organs, such as the spleen or lymph nodes.

4. Primary Lymphoid organ

5. BONE MARROW
• Bone marrow is a sponge-like tissue found inside the bones.
• Most immune system cells are produced, multiply in bone marrow. These
cells move to other organs and tissues through the blood.
• At birth, many bones contain red bone marrow, which actively creates
immune system cells.
• Over the course of our life, more and more red bone marrow turns into fatty
tissue.
• In adulthood, only a few of our bones still contain red bone marrow,
including the ribs, breastbone and the pelvis.
• It is the blood cell 'factory'. Healthy bone marrow releases blood cells into
the bloodstream when they are mature and when required.
• Without bone marrow, our bodies could not produce the white cells we need
to fight infection, the red blood cells we need to carry oxygen, and the
platelets we need to stop bleeding.

7. • The two types of bone marrow are red bone marrow, known as myeloid
tissue, and yellow bone marrow, or fatty tissue.
• The bone marrow contains two types of stem cells, mesenchymal and
hematopoietic.
• Red bone marrow consists of a delicate, highly vascular fibrous tissue
containing hematopoietic stem cells. These are blood-forming stem cells.
• Yellow bone marrow contains mesenchymal stem cells, also known as
marrow stromal cells. These produce fat, cartilage, and bone.
• Stem cells are immature cells that can turn into a number of different types
of cell.
• Hematopoietic stem cells in the bone marrow give rise to two main types of
cells: myeloid and lymphoid lineages.
• These include monocytes, macrophages, neutrophils, basophils, eosinophils,
erythrocytes, dendritic cells, and megakaryocytes or platelets, as well as T
cells, B cells, and natural killer cells.

8. • The different types of hematopoietic stem cells vary in their regenerative
capacity and potency.
• Some are multipotent, oligopotent or unipotent as determined by how many
types of cell they can create.
• Pluripotent hematopoietic stem cells have the following properties:
• Renewal: They can reproduce another cell identical to themselves.
• Differentiation: They can generate one or more subsets of more mature
cells.
• The process of development of different blood cells from these pluripotent
stem cells is known as hematopoiesis.11
• It is these stem cells that are needed in bone marrow transplant.

9. THYMUS
• The thymus gland, located behind your sternum and between your lungs, is
only active until puberty.
• After puberty, the thymus starts to slowly shrink and become replaced by fat.
• Thymosin is the hormone of the thymus, and it stimulates the development
of disease-fighting T cells.
• This gland-like organ reaches full maturity only in children, and is then
slowly transformed to fatty tissue.
• Special types of immune system cells called lymphocytes (T cells) mature in
the thymus.
• These cells coordinate the processes of the innate and adaptive immune
systems.
• T cells move through the body and constantly monitor the surfaces of all
cells for changes.
• T cells that successfully develop MHC immune receptors of the body.

11. • Abnormalities of the thymus can result in a decreased number of T cells and
autoimmune diseases such as autoimmune polyendocrine syndrome type
1 and myasthenia gravis.
• These are often associated with cancer of the tissue of the thymus,
called thymoma, or tissues arising from immature lymphocytes such as T
cells, called lymphoma.
• Removal of the thymus is called thymectomy.
• The thymus consists of two lobes, merged in the middle, surrounded by a
capsule that extends with blood vessels into the interior.
• The lobes consist of an outer cortex rich with cells and an inner less
dense medulla. The lobes are divided into smaller lobules 0.5-2mm diameter,
and divided from the capsule along septa.
• The cortex is mainly made up of thymocytes and epithelial cells.

12. LYMPHATIC SYSTEM
• The lymphatic system, or lymphoid system, is an organ system in
vertebrates that is part of the circulatory system and the immune system.
• It is made up of a large network of lymph, lymphatic vessels, lymph nodes,
lymphatic or lymphoid organs, and lymphoid tissues.
• The primary function of the lymphatic system is to transport lymph, a fluid
containing infection-fighting white blood cells, throughout the body.
• It also maintains fluid balance and plays a role in absorbing fats and fat-
soluble nutrients.
• Lymph circulates through the body in a similar way to blood.
• These nodes swell in response to infection, due to a build-up of lymph fluid,
bacteria, or other organisms and immune system cells.
• It maintains the balance of fluid between the blood and tissues, known as
fluid homeostasis.

14. • Around 2 liters of fluid leak from the cardiovascular system into body tissues
every day.
• The lymphatic system is a network of vessels that collect these fluids, or lymph.
Lymph is a clear fluid that is derived from blood plasma.
• The properties of the lymph vessel walls and the valves help control the
movement of lymph. However, like veins, lymphatic vessels have valves inside
them to stop fluid from flowing back in the wrong direction.
• The vessels branch through junctions called lymph nodes. These are often
referred to as glands, but they are not true glands as they do not form part of the
endocrine system.
• In the lymph nodes, immune cells assess for foreign material, such as bacteria,
viruses, or fungus.
• Lymph nodes are not the only lymphatic tissues in the body. The tonsils, spleen,
and thymus gland are also lymphatic tissues.

15. Secondary Lymphoid organ

16. Secondary lymphoid
organs (SLOs) includes:
• lymph nodes
• Spleen
• Peyer’s patches
• mucosal tissues such as the
nasal-associated lymphoid
tissue
• adenoids
• tonsils

18. LYMPH NODES
• A small bean-shaped structure that is part of the body's immune system.
• Lymph nodes filter substances that travel through the lymphatic fluid, and
they contain lymphocytes (white blood cells).
• lymph nodes, also called lymph glands, play a vital role in your body's ability
to fight off infections.
• They function as filters, trapping viruses, bacteria and other causes of illnesses
before they can infect other parts of your body.
• Lymph nodes are located in many parts of the body, including the neck,
armpit, chest, abdomen (belly), and groin.
• There are hundreds of lymph nodes throughout the body.
• A lymph node is enclosed in a fibrous capsule, which extends inside a lymph
node to form trabeculae and is made up of an outer cortex and an inner
medulla.

20. SPLEEN
• The spleen is an organ in the upper left part of the abdomen, protected by the rib
cage, to the left of the stomach. The spleen varies in size and shape between
people, but it’s commonly fist-shaped, purple, and about 4 inches long.
• Old red blood cells are recycled in the spleen, and platelets and white blood cells
are stored there. The spleen also helps fight certain kinds of bacteria that cause
pneumonia and meningitis.
• The spleen are secondary lymphoid organs that play key roles in: Filtering out
and destroying unwanted pathogens; Maintaining the population of mature
lymphocytes (which are white blood cells) to enable the adaptive immune
response to begin.
• The spleen is a soft organ with a thin outer covering of tough connective tissue,
called a capsule.
• The spleen also produces compounds called opsonins, such as properdin and
tuftsin, that help the immune system.
• The spleen receives blood through the splenic artery, and blood leaves the spleen
through the splenic vein. Although the spleen is connected to the blood vessels of
the stomach and pancreas, it is not involved in digestion.

21. Spleen Conditions
• Enlarged Spleen (Splenomegaly): An enlarged spleen, usually caused by viral
infection, liver disease, blood cancers (lymphoma and leukemia), or other
conditions.
• Ruptured spleen: A ruptured spleen can cause serious life-threatening internal
bleeding and is a life-threatening emergency. An injured spleen may rupture
immediately after an injury, or in some cases, days or weeks after an injury.
• Sickle cell disease: In this inherited form of anemia, abnormal red blood cells
block the flow of blood through vessels and can lead to organ damage, including
damage to the spleen. People with sickle cell disease need immunizations to
prevent illnesses their spleen helped fight.
• Thrombocytopenia (low platelet count): An enlarged spleen sometimes stores
excessive numbers of the body’s platelets. Splenomegaly can result in abnormally
few platelets circulating in the bloodstream where they belong.

22. • The spleen contains two
main regions of tissue
called white pulp and red
pulp.
• Red pulp: Contains
venous sinuses (cavities
filled with blood), and
splenic cords (connective
tissues containing red
blood cells and white
blood cells).
• White pulp: Mostly
consists of immune cells
(T cells and B cells).

23. TONSILS
• The tonsils are small masses of lymphoid tissue that ring the pharynx (the
throat), where they are found in the mucosa.
• Their job is to trap and remove any bacteria or other foreign pathogens
entering the throat.
• They carry out this function so efficiently that sometimes they become
congested with bacteria and become red, swollen, and sore, a condition called
tonsilitis.
• The tonsils are found in three location: lingual at the base of the tongue,
palatine at the side of the back of the mouth and pharyngeal (adenoids) in the
roof the nasopharynx.
• All tonsils conatain lymphocytes, macrophage, granulocytes and mast cells.

24. • Peyer's patches are small masses of lymphatic tissue found throughout the
ileum region of the small intestine. Also known as 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.
• Peyer’s patches contain a variety of immune cells, including macrophages,
dendritic cells, T cells, and B cells.
• The macrophages of Peyer’s patches are in an ideal position to capture and
destroy bacteria, thereby preventing them from penetrating the intestinal wall.
• Peyer’s patches and the tonsils are part of the collection of small lymphoid
tissues referred to as mucosa-associated lymphatic tissue (MALT).
• MALT acts as a mucosal membrane lining present in digestive, respiratory, and
urogenital system area.
• These membrane surface are defended by a group of lymphoid tissue and
collectivelly known as MALT.
PEYER’S PATCHES

25. Cutaneous Associated lymphoid tissue
• The skin is an important barrier to the external environment and provide
innate immnity.
• The epidermal layer of the skin is composed largely of specialized epithelial
cells called keratinocytes.
• These cells produce number of cytokines that induce a local inflammatory
response.
• Keratinocytes ccells express class II MHC molecule and function as antigen
presenting cells.

26. THANK YOU