LYMPHOID TISSUES

Maj Dr Rishi PokhrelMBBS, MD

Lecturer, NAIHSFAIMER Fellow, USA

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Lymphatic System-Organs

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

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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Formation & flow of lymph

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CLASSIFICATIONI. FUNCTIONAL

LYMPHOID ORGANS

CENTRAL PERIPHERAL

THYMUS

BONE MARROW

LYMPH NODE

SPLEEN

MALT, GALT

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II. MORPHOLOGICAL

LYMPHOID ORGANS

DISCRETE DIFFUSE

LN, SPLEENTHYMUS, TONSIL BM, PEYER’S PATCHES

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

THYMUS• Introduction• Gross anatomy• development• Histology -Circulation -Relation with

immunology• Functions• Age changes• Recent advances

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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

• 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

Development

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• 3rd Endodermal pouch

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.

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

Location

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

Applied anatomy

• Lymphadenitis• Metastasis

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 25

The Spleen

• Size: 1 X 3 X 5 inches• Weight: 7 ounce• Relation: 9-11 ribs in mid-

axillary line

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).

RELATIONS

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

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

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.

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