Download MBBS Lymphatic System Lecture PPT

LYMPHATIC SYSTEM
INTRODUCTION

? Lymphatic system is also called as immune system.

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? This system consists of following structures
? Lymphatic vessels:-- Thin walled vessels collect

lymph and drain into vein.

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? Specific lymphatic organ:-- Lymphatic tissue

surrounded by capsule, e.g. Lymph node, spleen

and thymus.

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? Lymphatic tissue found within tissue of other

organ:-- Not surrounded by capsule, e.g. Tonsil,

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peyer's patches.


Components of the Lymphatic System

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? Lymph Tissue fluid drained
24-

by lymphatic vessels.

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3
Consists of tissue fluid, proteins,

fat & particulate matters.

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? Lymphatic Vessels

? Lymphatic Capillaries

? Lymphatic Vessels

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? Lymphatic Trunks

? Lymphatic Ducts

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? Lymphatic Organs

? Thymus

? Lymph Nodes

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? Spleen

? Tonsils

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? Lymphatic cells
? The specific immune response is evoked by

lymphocytes.

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? Lymphocytes are of two types, B and T.

? They are derived from common stem cells in the

bone marrow.

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? B lymphocytes mature and become

immunocompetent in the bone marrow.
? T lymphocytes mature and become

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immunocompetent in thymus and migrate to

other peripheral lymphoid organ.

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? The defence mechanism mediated by B

lymphocytes is called humoral immune response.

? The defence mechanism mediated by T

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lymphocytes is called cellular immune response
% of lymphocytes in various lymphoid organ

B lymphocytes

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T lymphocytes

Bone marrow

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90

10

Thymus

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0

100

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Lymph node

40

60

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Spleen

55

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45

Blood

30

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70
LYMPH NODE

? GENERAL FEATURE--

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? Oval or bean shaped situated along the course of

lymphatic vessels.

? They serve as filter of lymph, removing particulate

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matter and bacteria, thereby localising and

preventing the spread of infection.

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? Lymph node usually found in groups e.g. axilla,

inguinal region, root of lung.
? COMPONENTS/STRUCTURE--
? Stroma : Connective tissue framework

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-Capsule
-Trabeculae
-Reticular stroma

? Parenchyma : Lymphoid tissue

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-Cortex
-Paracortex (inner cortex)
-medulla

? Connective tissue framework--

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? Capsule and trabeculae-
*Lymph node is surrounded by a thin connective

capsule which sends trabeculae into the interior.

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*Beneath the capsule is the subcapsular sinus.

*The subcapsular sinus receives afferent lymphatic

vessels and is continuous with trabecular sinus.

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*Trabecular sinus becomes continuous with the

medullary sinus.

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? Reticular stroma-
*Made of reticular fibre and phagocytic reticular cells.
*Gives structural supports to lymphoid cells.
? Parenchyma-
? Cortex ? Peripheral part of the lymph node situated deep to

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the capsule.

? It contains
1.Subcapsular sinus

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2.Lymphatic nodules- with or without germinal centres formed

mainly of B lymphocytes.

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a)Primary nodule-lymphatic nodule without germinal centre.
b)Secondary nodule-nodule with germinal centre.

? The germinal centre contains large lymphoblast with more

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cytoplasm and lighter nuclei as compared to periphery of

nodule.
? Paracortex-
? It is the inner cortical zone, does not have

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precise boundary with outer cortex.

? Contains mainly T lymphocytes and called

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thymus-dependent zone.

? The dense lymphoid tissue in the paracortex

becomes continuous with medullary cords.

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? Medulla-
? Has two components, medullary cords and

medullary sinuses.

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? Medullary cords- are branching and

anastomosing cords of lymphoid tissue

contains mainly B lymphocytes, few plasma

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cells and macrophages.

? Medullary sinuses- drain into the efferent

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lymphatic vessels found at the hilum.

Flow of lymph through lymph node

Afferent lymphatic vessels

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Subcapsular sinus

Trabecular sinus

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Medullary sinus

Efferent lymphatic vessels
SPLEEN

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? GENERAL FEATURES--
? Spleen is the largest lymphoid organ.
? Present in the left hypochondrium.
? COMPONENTS/STRUCTURE--
? A)Connective tissue framework

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? Capsule
? Trabeculae
? Reticular stroma
? B)parenchyma
? White pulp

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? Red pulp
? Connective tissue framework--
? Capsule-
? Covers the spleen completely.
? Lies deep to the peritoneum.

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? Formed by dense collagenous connective tissue and

few smooth muscle fibres.

? Trabeculae-

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? Given off from the capsule into the substance of

spleen.

? Reticular stroma-

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? Made of reticular fibres and associated phagocytic

reticular cells.
? Parenchyma--
? The interior of spleen shows rounded white/grey

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areas surrounded by red matrix.

? These grey area are called white pulp and the dark

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red matrix called red pulp.

? White pulp--is the lymphatic tissue sheath that

surrounds the central artery (eccentric position)

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? It contains lymphocytes and macrophages in a

reticular connective tissue meshwork.
? This peri-arterial lymphatic sheath also contain

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lymphatic nodules with germinal centre.

? These nodules are called splenic nodules or

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malpighian corpuscles.

? Lymphocytes in white pulp is T while in nodule B

lymphocytes.

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? Red pulp-- consist of network of inter-

anastomosing splenic cords.

? Splenic cords-- made up of reticular cells and

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reticular fibres containing B and T lymphocytes,

macrophages, plasma cells, RBC, and granulocytes.

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? These splenic cords are also called as "cords of

Billroth".
Splenic Circulation

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? Blood enters via splenic artery at hilus
? Splenic artery trabecular arteries (within

trabeculae).

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? Trabecular arteries central arteries(covered by a

peri-arterial lymphatic sheath) [ PALS].

? Central artery terminate into straight vessels called

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penicilli.

? Penicilli shows localiszed thickening (ellipsoid)

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Penicilli continue as arterial capillary.
? The mode of blood flow between arterial capillaries

and splenic sinuses is not clear.

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? Two different theories open and closed circulation

have been proposed.

? According to "closed circulation theory" arterial

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capillaries open directly into splenic sinuses that drain

into tributaries of splenic vein.

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? According to "open circulation theory" the arterial

capillaries open and pour their blood into splenic cord

of red pulp.

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? Pulp veins drain into trabecular veins.
? Trabecular veins drain into splenic vein at the hilus.
Splenic Cords and Splenic Sinusoids
Open and Closed Circulation in Spleen

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Spleen
Functions of the spleen

? Filtration of blood.
? Storage of blood.

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? Formation of blood cells during fetal life.
? Aged and abnormal RBCs are destroyed in the

spleen.

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? Immune response.
THYMUS

? Covered by a capsule which extends to form

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Trabeculae.

? Trabeculae extends inwards to forms

numerous incomplete lobules (lobulated

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appearance).

? Each lobule consists of dark staining outer

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cortex and a light staining inner medulla.
? Cortex contains densely packed lymphocytes (No

lymphatic nodules).

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? Medulla contains fewer lymphocytes but more

epithelial reticular cells.

? Medulla also contains Thymic (Hassall's)

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Corpuscles.

? Thymic (Hassall's) Corpuscles are oval structures

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consisting of round whorls of flattened epithelial

cells.
Thymus
Function of thymus

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? Maturation of T lymphocytes.
? Mature T lymphocytes then carried from

thymus to the lymph node, spleen, and other

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lymphatic tissues.

? Thymopoietin induces T cell production and

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maturation.

? Thymosin supports T cell activities.
? Thymus gets atrophied after puberty.
PALATINE TONSIL

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? Collection of lymphoid tissue in mucosa of

oropharyngeal isthmus.

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? Consist of lymphatic nodules within diffused

lymphoid tissue .

? Lateral surface is covered by capsule.

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? Medial surface is pitted by 10-20 tonsillar crypts,

lined by stratified squamous non-keratinised

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epithelium.

? It has only efferent vessels.
? Infection of tonsil is called tonsillitis.

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? Function
? Production of lymphocytes.
? Immunological responses.