Lymphatic Tissue

8/6/2019 Lymphatic Tissue

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Lymphatic Tissue

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List the cells that are found in lymphatic tissue

List the precursor cells of different types of cellsmentioned above

Classify lymphatic tissue

Describe the non encapsulated lymphatic tissue

List the capsulated lymphatic tissue

State the general distribution of lymph nodes in

the body

State the mechanism of filtration of lymph in thefollowing lymph node

spleen

thymus


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Lymphatic System

Lymphatic vessels Lymphatic tissue

Lymph vessels contain transudate formed from

capillaries Lymph

Lymph contain fluid plasma, few granulocytes,Lymphocytes.

Red blood cells and platelets are not present.


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Blood capillary

Arteriole

Lymphatic capillary

Interstitial

fluid

Tissue cell

Venule

Relationship of lymph capillaries to tissue and blood

capillaries


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Basic structure of lymphatic tissue-

framework of reticulin fibres

reticular cells

Infiltrated with lymphocytes, macrophages and

plasma cells in some.

Lymphatic tissues are classified according tohow they present in the body.

Non-encapsulated Encapsulated


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Non-encapsulated

Diffuse Lymphatic tissue

Solitary lymphoid nodules (follicles)

Aggregated lymphoid follicles

Encapsulated

Lymph node Thymus

Spleen

All lymphocytes originate in the bone marrow.T lymphocytes mature further in the thymus.

B lymphocytes leave the bone marrow as mature

cells.


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Bone marrow and thymus are - primary or

central lymphoid organs.Lymphocytes migrate from these organs to the

blood and peripheral lymphoid organs such as

spleen, lymph nodes, solitary nodules, and

aggregated nodules.

Diffuse type uniformly distributed lymphocytes

under the wet epithelia of respiratory and

alimentary tracts. This area of lymphocytes is not

sharply demarcated.


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Solitary lymph nodules primary nodules

secondary nodules.

Seen under wet epithelia, in the lamina propria

Non capsulated spherical mass ofdensely

packed lymphocytes.Secondary follicles are with germinal centres.

It is an area of active proliferation of lymphocytes.

appear only after birth

in the lymph nodule and around- B lymphocytes

Area between nodules- T lymphocytes


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Aggregated lymph nodules (follicles)

Tonsil

Peyers patches

Appendix

At the oro-pharyngeal isthmus palatine tonsillingual tonsil

pharyngeal tonsil

They form a circle of lymphatic tissue-Waldeyers ring


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Aggregated lymphoid follicles are covered by an

epithelium.

Palatine tonsil-

located between two pillars of fauces.

semi capsulated

primary crypts epithelium dips into the tonsil.

secondary crypts- lateral extension of the

crypts.

**Lingual tonsil smaller and more numerouslocated at the base of the tongue

crypts are broad and shallow.


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Pharyngeal tonsil

single tonsil upper posterior part of the pharynx.

covered by pseudo stratified columnar ciliatedepithelium.

Appendix collection of lymphoid follicles undersimple columnar epithelium

Peyers patches

In the lamina propria of the ileum on the anti-mesenteric border.


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Peyers patch


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Lymph node-

encapsulated bean shaped organs. distributed throughout the body along lymph

vessels.

found in axilla ,groin, along great vessels,

thorax, abdomen.

convex surface, concave depression -hilum

arteries and nerves enter and veins and efferent

lymph vessels leave at the hilum. thick connective tissue capsule and trabeculae.

system oflymph sinuses.


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Each lymph node contains -outer cortex

inner cortex

medulla

lymph sinuses

Net work of reticularfibres

Reticular cells

Macrophages


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Outer cortex

reticular cells and fibres

lymphocytes in follicles primary or secondary

follicles.

germinal centres in secondary follicles have

stem cells, lymphoblasts and macrophages.

is a site ofactive B lymphocyte production

peripheral area of the follicle B lymphocytes


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Inner cortex paracortex- few or none follicles

T lymphocytes are present.

they generally not present as follicles.

Medulla

medullary cords branched extensions of innercortex which contain B lymphocytes and some

plasma cells.

medullary sinuses containing lymph.


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Section of a lymph node


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Lymph sinuses-

endothelial lined lymph spaces contain net work of reticulin fibres to slow the flow

of lymph.

afferent lymph vessels enter the sinus beneath

the capsule - Subcapsular sinus

along trabeculae trabecular (cortical)

sinuses

in the paracortex - paracortical sinuses

in the medulla - Medullary sinuses

efferent


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M-Macrophages

E- margin of sinus

Subcapsular sinus


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Lymphocytes leave the lymph nodes by

efferents and enter the blood circulation All lymph formed in the body drains back into

blood.

Lymphocytes return to the lymph nodes by

leaving the blood through specific blood vessels

Post capillary orhigh endothelial venules.

These venules have an unusual endothelial

lining of tall cuboidal cells. Lymphocytes are capable of traveling between

these cells.


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They are present in other lymphoid organs such

as appendix, peyers patches, and tonsils but not

in the spleen.

Read

the circulation of lymph

Functions of lymph node Recirculation of lymphocytes


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Spleen- is the largest accumulation of lymphoid

tissue in the body.

Situated in left hypochondrium in relation to 9th

10th 11th ribs posteriorly.

Is an important organ of defence against

microorganisms. Is a site of destruction of erythrocytes.

Is a site of production of activated lymphocytes.

Is an important immunologic blood filter.

Is an antibody forming organ.


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Spleen

Diaphragm

Tail of

Pancreas

Left Kidney

ColonInferior

mesenteric

vein

Renal vein

Splenic vein

Splenicartery

Oesophagus

( cut)

Spleen related structures


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Structure- capsule

Connective tissue septa ortrabecualae dividethe paranchyma- splenic pulp in to incomplete

compartments.

Hilum on the medial surface contain number oftrabeculae which carry nerves and blood

vessels.

Veins derived from paranchyma, lymphvessels originate in the trabeculae.

No lymphatic vessels in the paranchyma.


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Splenic pulp red pulp

white pulp

Red pulp - splenic cords and sinusoids

Loose network of reticular cells.

Reticular fibres.

Macrophages

B and T lymphocytes

Plasma cells

Many blood cells granulocytesplatelets

erythrocytes


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Structure of the spleen


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A-

Centralartery

Section ofSpleen


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White pulp- Periarteriolar lymphatic sheath

(PALS)

Lymphatic nodules

Lymphocytes surrounding the central artery-

T lymphocytesLymphocytes in the nodule B lymphocytes

Marginal zone marginal sinuses - large

number of antigens


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Splenic artery Trabecular arteries

enters the paranchymaCentral arteries/ white pulp arteries

Surrounded

by sheath oflymphocytes

PALS

Along the course

number of nodules

Radial arteries

Outside white pulp

Penicillar arteries

Ellipsoid arteries near

the termination

Capillaries

Beyond

ellipsoid

Open

Closed


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Thymus

Lympho -epithelial organ situated in themediastinum.

Two types of cells- epithelial reticular cells

derived from endoderm of third pharyngeal arch.

Lymphocytes derived from stem cells of bone

marrow

Large at birth and increases rapidly upto two

years.Less rapidly upto about puberty.

Has two lobes.


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Thyroid

Thymus

Heart

Left Lung

Diaphragm

Right Lung

Subclavian vein

Subclavian artery

Internal jugularvein

Common carotid artery

Vagus Nerve


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Capsule

Trabeculae divide the gland into incompleteirregular lobules.

Cortex 1. extensive population of T

lymphocytes

2. dispersed epithelial reticular cells

3. few macrophages are seen near the

capsule, perivascular region, and

cortico-medullary region

S f


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CX-Cortex

C-Capsule

Medulla

Septa

Section of Thymus


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Thymic Cortex

Capsule

BM-Basement

membrane ofepithelial cell

Endothelium

Macrophages


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Hassalls

corpuscle

Medulla


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C- Capsule

Cx - Cortex

M-Medulla


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Medulla

lymphocytes are not numerous

pink in H&E due to eosinophilic cytoplasm of

epithelial-reticular cells

thymic orHassalls corpuscles- degeneratingepithelial reticular cells.


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Epithelial -reticular cells

Form a frame work of irregular interconnected

sheets.

Continous sheet deep to the capsule, against

trabeculae and around blood vessels.

Forms a mesh work in the medulla. They are large, irregular eosinophilic cells with

large nuclei.

Forms a component of the haemo-thymic barrier

which prevents certain substances entering thethymus to keep the thymus free of antigens..


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Components of the haemo-thymic barrier.

Endothelium of the capillary

Basement membrane

Connective tissue

Basement membrane of epithelial reticular cells

Epithelial reticular cells.

Functions

Differentiation of T lymphocytes into

immunologically competent T- Lymphocytes. Maintenance of T lymphocytes in the circulation.


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Essential for the normal development of

lymphatic tissue.

Control of lymphopoiesis

Hormone thymosine controls lymphocyte

production.

Cells are educated to differentiate self fromnon-self.

Read the blood supply of the thymus


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Objectives Lymphatic Tissues

List the cells that are found in the lymphatic

tissues. List the precursor cells of the different types of

cells mentioned above.

Classify lymphatic tissues.

State the general distribution of lymph nodes inthe body.

Explain the term Peyers patch.

State the mechanism of filtration of lymph in the

Lymph node,S

pleen and the Thymus.

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Lymphatic Tissue

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