Lymphatic organs of body • Lymphoid organs are the organs, in which lymphocytes can differentiate and proliferate. • They are part of lymphatic system. • The lymphatic system is part of circulatory system and a vital part of the immune system, comprising a network of lymphatic vessels that carry a clear fluid called lymph (from Latin, lympha meaning "water" directionally towards the heart. • Unlike the cardiovascular system, the lymphatic system is not a closed system. • HISTORY – • Hippocrates and Aristotle described lymph as white fluid. • Gasparo aselli an Italian anatomist discovered lymphatic vessels in 1622. • Van hook in 1652 demonstrated the presence of cisterna chyli and thoracic duct in humans. • William hunter in the late 18th century was the first to describe the functions of lymphatic system. • Olof Rudbeck of Swedish university described that lymphatic system constitute a circulatory system separate from blood circulation and this fact was accepted by Royal society of London.

1. Lymphatic organs of body
• Lymphoid organs are the organs, in which lymphocytes can differentiate and
proliferate.
• They are part of lymphatic system.
• The lymphatic system is part of circulatory system and a vital part of the immune
system, comprising a network of lymphatic vessels that carry a clear fluid
called lymph (from Latin, lympha meaning "water" directionally towards the heart.
• Unlike the cardiovascular system, the lymphatic system is not a closed system.
• HISTORY –
• Hippocrates and Aristotle described lymph as white fluid.
• Gasparo aselli an Italian anatomist discovered lymphatic vessels in 1622.
• Van hook in 1652 demonstrated the presence of cisterna chyli and thoracic duct in
humans.
• William hunter in the late 18th century was the first to describe the functions of
lymphatic system.
• Olof Rudbeck of Swedish university described that lymphatic system constitute a
circulatory system separate from blood circulation and this fact was accepted by
Royal society of London.

2. LYMPHOID ORGANS
Primary or Central
Lymphocytes are produced and undergo development and are supplied to secondary
organs.
• Thymus
• Bone marrow
Secondary or peripheral organs
Lymphocytes are activated to participate in specific immune response.
• Lymph nodes
• Spleen
• Tonsils
BONE MARROW
Bone marrow contains two types of cells multipotent stem cells
NON – LYMPHOID STEM CELLS
• Differentiate in bone marrow.
• Including Erythrocytes, Granulocytes, Monocytes & Platelets.
LYMPHOID STEM CELLS
• Differentiate in bone marrow & then migrate to lymphoid tissue.
• Including B & T lymphocytes.

3. LYMPHOCYTES
• T- lymphocytes ( 75-80 %)-
based on Function divided into
 T - helper cells (with CD 4 coreceptors)
 T - cytotoxic cells (with CD 8 coreceptors)
 Memory T Cells
 Suspensor cells
 NK T cells
• B- lymphocytes
 plasma cells
 memory cells
THYMUS
• Primary organ of Lymphatic System.
• Unpaired organ.
• Consists of 2 pyramidal lobes.
• Delicate & finely lobulated surface.
• Located in mediastinum.

4. • Extending
Upwards - into neck as far as lower edge of thyroid gland
Downwards - as far as fourth costal cartilage
• Largest at puberty and weighs 35 to 40 gms - Pinkish grey.
• Gradually atrophies in old age- yellowish in colour ( fat).
FUNCTIONS OF THYMUS
• Thymus contains lobes divided into lobules.
• Each lobule – cortex ( immature T lymphocytes, Macrophages)
– medulla ( T lymphocytes, thymic corpuscels)
1) Processing the “T’’ Lymphocytes
2) Endocrine functions of Thymus
They Secretes Hormones namely
A) Thymosin
B) Thymin
C) Thymic Humoral Factor
D) Thymulin
SPLEEN
• Located in left hypochondrium, directly below diaphragm, above left kidney &
descending colon & behind fundus of stomach.
• Roughly ovoid shape (Depend on species)
• Varies in size in diff individuals
• Same individuals differs in size from time to time
Hypertrophy in infections
Atrophies in old age
• Surrounded by fibrous capsule
• Its extensions run inwardly roughly dividing the organ into compartments
WHITE PULP and RED PULP ( Splenic cords & sinusoids).
FUNCTIONS OF SPLEEN

5. • DEFENSE : as the blood passes through sinusoids of spleen, microorganism from
the blood are destroyed
• HEMOTOPOIESIS : monocytes & lymphocytes complete development in spleen
• Worn – out RBC & platelets are destroyed
• Acts as a RESERVOIR of blood (200-350 ml )
• Main source of circulating antibody in the body.
TONSIL
• Tonsil are located under mucous membrane and back of throat.
• There are depression of surface epithelium around which aggregate of lymph
nodule are grouped called CRYPTS.
• Intratonsillar crypt Peritonsillar abscess begins in this cleft
• It is a collection of pus between fibrous capsule of the tonsil usually at its upper
pole and the superior constrictor muscle of pharynx.
LINGUALTONSILS
• Hyperplasia is the most common abnormality of the lingual tonsil.

6. • Lingual tonsils sit on the base of the tongue and extend to the vallecula and do
have a capsule.
• Can be visualized by indirect mirror or flexible laryngoscopy.
• Clinically, infection is marked by erythema and enlargement of tonsillar tissue.
• Although the lymphoid tissue in Waldeyer's ring tends to decrease with advancing
age, the lingual tonsil may increase in size. Important cause of lingual tonsil
hypertrophy is the occurrence of compensatory hyperplasia following
adenotonsillectomy
LYMPH NODES
• A normal young adult body contains some 400-450 lymph nodes.
• Head and neck -- 60-70
• Arms/superficial thorax – 40
• Legs/superficial buttocks – 30
• Thorax – 100
• Abdomen/pelvis – 230

7. • Small oval or bean shaped body
• Range from 10 to 20 mm in diameter.
• Positioned along the course of lymph vessel.
• Slight depression called HILUS (blood vessels enter & leave through it)
•

8. MICROSCOPIC STRUCTURE OF LYMPH NODES
• Each lymph node is enclosed by a fibrous capsule
• It consist of Capsule, Cortex, Medulla.
• Fibrous septa or trabeculae extend from covering capsule toward centre of node.
• Cortical nodule packed lymphocytes surrounded by less dense area Germinal
Center
• Cortical nodules within cortex separated from each other by trabeculae
• MEDULLA is composed of Sinuses & Medullary Cords
•
CELL ZONES IN LYMPH NODES
• ZONE 1 - is a region of loosely packed cells, predominantly small lymphocytes,
macrophages and occasional plasma cells.
• ZONE 2 - is a denser region internal to zone 1,composed mainly of small
lymphocytes and macrophages

9. • ZONE 3 - comprises the germinal centers of follicles, its cells include large
lymphoblast, dendritic cells and macrophages
•
FUNCTIONS OF LYMPH NODESDEFENSE
• As lymph passes through lymph Node reticuloendothelial cells remove
microorganisms & other injurious particles
• HEMATOPOIESIS Site for final stage of maturation of lymphocytes & monocytes
that have migrated from bone marrow