The lymphatic system consists of lymph, lymph nodes, lymph vessels, the spleen, thymus, tonsils, bone marrow and skin-associated lymphoid tissues. The main cells of the lymphatic system are lymphocytes such as B cells, T cells, natural killer cells, and supporting cells that interact with and present antigens to lymphocytes. The lymphatic system protects the body from foreign materials, assists in fluid circulation, and transports dietary fats. The thymus gland aids in the maturation of T cells while the spleen filters blood and mounts an immune response to antigens. Lymph nodes are located around arteries and veins and filter lymph fluid draining tissues.

1. LYMPHOID TISSUES
Maj Dr Rishi Pokhrel
MBBS, MD
Lecturer, NAIHS
FAIMER Fellow, USA

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Lymphatic System-Organs

3. Lymphatic System
• Not a primary tissue type but a variety of connective
tissue.
• Consists of:
- lymph
- network of vessels
- lymph nodes and nodules, MALT
- tonsils
- spleen
- thymus gland
- bone marrow

4. CELLS OF LYMPHATIC SYSTEM
Chief cells are lymphocytes-
• B lymphocytes
• T lymphocytes
• Natural killer cells
• Supporting cells-
– interact with lymphocyte
– Present antigens to
Lymphocytes
• OTHER TYPE OF WBC’S
-monocyte
-macrophages
-neutrophils
-eosinophil
-basophils
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5. Formation & flow of lymph

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CLASSIFICATION
I. FUNCTIONAL
LYMPHOID ORGANS
CENTRAL PERIPHERAL
THYMUS
BONE MARROW
LYMPH NODE
SPLEEN
MALT, GALT

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II. MORPHOLOGICAL
LYMPHOID ORGANS
DISCRETE DIFFUSE
LN, SPLEEN
THYMUS, TONSIL
BM, PEYER’S PATCHES

9. FUNCTIONS
• protects body against foreign material - The site of clonal
production of immunocompetent lymphocytes and
macrophages in the specific immune response.
• assists in circulation of body fluids between cells and
bloodstream - Maintains pressure & volume of
extracellular fluid by returning excess water to the
circulation.
• transports dietary fats

10. THYMUS
• Introduction
• Gross anatomy
• development
• Histology
-Circulation
-Relation with
immunology
• Functions
• Age changes
• Recent advances
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11. THYMUS
• Bi-lobed organ
• Located in superior
mediasternum ant to heart
and great vessels.
• largest and most active
during prenatal period and
infancy
• after puberty it decreases
in size
• Capsule- incomplete septa
• No Afferent lymphatics

12. • composed of lymphatic tissue
• subdivided into lobules
• immature T cells originating in the bone
marrow migrate to thymus via blood
• in thymus, cells develop into mature T cells
for release into circulation
• thymic hormones aid in maturation of T cells
THYMUS

14. Development
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• 3rd Endodermal pouch

15. BLOOD THYMUS BARRIER
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Changes of Thymic Structure with Age
(involution)
• Largest at birth
• fully functional at 20 weeks of foetal life.
• progressive involution of adipose tissue.
– Accelerated by adrenal corticosteroids and sex hormones
• In juveniles:
– isolation of cortical compartments,
– reduction of cortical and medullary volume, and
– appearance of more, larger blood vessels,
• until the adult thymus is mainly dominated by fat.

17. Applied
• Myasthenia gravis
• DiGeorge syndrome-absent-thymus &
parathyroid ,defect in cardiac outflow tract
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Lymph Nodes

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• Capsule – Trabeculae, hilus-
collagenous framework
• Lymph flow
– Retculin Meshwork-sinuses
– Subcapsular Sinus
– Cortical Sinuses
– Medullary Sinuses
– Eff Lymph Ch

23. Location
• Present around large
arteries or veins
– Cervical LN
– Axillary LN
– Coeliac and mesenteric LN
– Inguinal LN

24. Applied anatomy
• Lymphadenitis
• Metastasis

25. The Spleen
• largest lymphatic organ
• In upper left quadrant of the
abdominal cavity.
• size of a cupped hand
• Functions
– filters the blood
– react immunologically to
blood-borne antigens,
– removes defective blood cells
– store blood cells &platelets
– hematopoiesis
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26. The Spleen
• Size: 1 X 3 X 5 inches
• Weight: 7 ounce
• Relation: 9-11 ribs in mid-
axillary line

27. LIGAMENTS
• Gastrosplenic ligament passes to greater curvature of
stomach (carries short gastric and left gastroepiploic vessels)
• Lienorenal ligament passes to posterior abdominal wall
(contains splenic vessels and tail of pancreas).

28. RELATIONS

29. RELATIONS
• Posteriorly- left dome of
diaphragm separating it
from pleura, left lung and
9th, 10th & 11th ribs
• Anteriorly- stomach
• Inferiorly- splenic flexure of
colon
• Medially- left kidney
• Tail of pancreas is related at
the hilum of spleen

30. BLOOD SUPPLY
• Splenic artery- largest
branch of coeliac axis
• Splenic vein joins
superior mesenteric
vein to form portal
vein

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STRUCTURE
• It has a thin fibrous capsule, to which peritoneum adheres.
• The fibrous septae of capsule extends into spleen as
trabeculae between which lies splenic pulp.
• Red pulp
– This has large numbers of red blood cells (RBCs).
– It consists of splenic sinuses, separated by splenic cords (of
Billroth)
• White pulp
– WBC, mainly lymphocytes around the central artery in a
cylindrical fashion -periarterial lymphatic sheath (PALS) of the
artery.

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STRUCTURE

34. CLINICAL ANATOMY
• During splenectomy, close relation of pancreatic tail to
the hilum and splenic pedicle must be remembered; it
is easily wounded.
• Stab wound of posterior left chest may penetrate
diaphragm and damage the spleen. Spleen is the
commonest organ ruptured by blunt trauma.
• Accessory spleens may occur near the hilum, in the tail
of pancreas, omentum, mesentery, ovary and even
testis.