The lymphatic organs

D r . S a m a r A s k e rD r . S a m a r A s k e r

LYMPH NODE

Kidney shape

Along the course of

lymphatic vessels to filter

lymph from any organism.

In groups allover the body

e.g. Neck, axilla, thorax,

abdomen& groin.

It is divided intoCortex (outer part).Medulla (inner part).

Formed of 1- Stroma 2- Parenchyma

Lobe

Lobule

Lobule

StromaStroma

Capsule:Capsule: Dense C. T Dense C. T cells = fibroblast cells = fibroblast Fibers collagenous & elastic Fibers collagenous & elastic Is thickened at the Is thickened at the hilum due to smooth ms hilum due to smooth ms covered covered

with adipose CT.with adipose CT.Reticular fibres: Reticular fibres: cells & fibres in the background stained cells & fibres in the background stained

brown with {Ag}. brown with {Ag}.

Trabeculae:Trabeculae: C. T septaC. T septa

cells & Fiberscells & Fibers

descend fromdescend fromthe cortex into thethe cortex into thedeep surface of thedeep surface of thecapsule. capsule.

They divide theThey divide thecortex into regularcortex into regularCompartmentCompartment

In the medulla In the medulla they branch to they branch to divide it into divide it into irregular areas. irregular areas.

ParENcHYMParENcHYMaa

In the cortex: • formed of cortical Lymph follicles either

primary or secondary.

• 1ry lymph follicle:Rounded , oval or pyramidal

Aggregation of

Small lymphocytes lymphocytes mainly mainly BB

and few T and few T ++ Antigen Antigen

presenting cells & reticularpresenting cells & reticular

cells.cells.

When exposed to specificWhen exposed to specific

antigen, some of theantigen, some of the

lymphocyteslymphocytes will activated will activated & &

become become medium-sized & collect medium-sized & collect

in the centre to form palein the centre to form pale

germinal centregerminal centre

Secondary follicleFollicles with darkperiphery (smalllymphocytes) & palegerminal centre containing

Activated B lymphocytesPlasmablastsPlasma cellsSome T- cellsMacrophagesReticular cells

The thymus dependent Zone:

• the deep part of the cortex

(between cortex &medulla.

• It contains T- lymphocytes

which migrated from the

thymus and post capillary

venules which are lined with

cubical epithelium. Through

which lymphocytes enter &

leave the lymph node.

The cortical lymph The cortical lymph

sinuses:sinuses:

Occupy the area Occupy the area

between the cortical between the cortical

follicles, capsule & follicles, capsule &

trabeculae. Lined with trabeculae. Lined with

endothelial cells & endothelial cells &

macrophages . Contain macrophages . Contain

B lymphocytes , plasma B lymphocytes , plasma

cells & macrophagescells & macrophages

In the medulla: formed of

Medullary cords

irregular aggregation of

B lymphocytes

plasma cells

may be continous with

cortical follicle.

Medullary sinuses.

Spaces () medullary cords

lined with epithelial cells + macropages

Contain lymph received from cortical sinuses

Circulation of lymph :

• Aff lymph vessels enter through the outer convex border & poor into the cortical then the medullary sinuses & drain into efferent lymph vessels which come out from hilum

Cells in lymph nodeStromal cells Parenchymal cells:

Fibroblast

&

Reticular

cells

B lymphocytes

cortex & medulla

Activated B lymphocytes + Plasmablasts

in the germinal centre

plasma cells & macrophages

Endothelial cells l ining the sinuses

Function oF Lymph

node

Filtration of lymph from any antigen by the macrophages.

Formation of lymphocytes in the germinal centre.

Immunological function:

B- lymphocytes

plasmablasts

plasma cells

Humeral immunity

T helper cell

Cell mediated immunity

T- killer cells

direct destruction of the antigens.

The spleenSingle intra abdominal hemo

lymphatic organ. To fi l ter the blood from any

organism

a- Capsule: Thick C. T. formed of

fibroblast collagen & elastic fibers containing smooth muscle fibres.

Is covered by peritoneum.

Stroma:

b-Trabeculae:They arise from the hilum of spleen may be from the capsule .Formed of Thick C. T. containing smooth muscle fibres.

Divide the spleen into irregular compartments.The capsule and trabeculae contain blood vessels and nerves.

Reticular CT : formed of cells & fibres in the bacheground stained only with si lver{Ag} stain.

ParenchymaIn fresh sections it

shows white spots on red background i.e devided into: White pulp & red Pulp

White pulp= (Malpighian corpuscle):

Rounded or oval scattered

foll icles with an arteriole on

one side called central

arteriole or follecular arteriole.

Formed of reticular CT in which

cells are arranged around the

arteriole into 4 concentric

zones:

1. Thymus dependent zone: periarterial lymphatic sheath (PALS) contain

T- lymphocytes around the central arteriole

2-Germinal center: pale area contain activated large B lymphocytes,

plasmablasts, plasma cells & macrophages.

Foll icular zone= corona: dark contain B lymphocytesMarginal zone : at the periphery contain: T& B lymphocytes plasma cells & macrophages.

Red Pulp:Formed of :

Splenic cords

Blood sinusoids.

Splenic cords= Bil lroth cords

The areas between the white pulp &

bl. Sinusoids contain

blood cells:

(RBCs, WBCs ,lymphocytes , monocyts)plasma cellsMacrophage.

Blood sinusoids. Irregular blood spaces

lined with fenestrated

endothelial cells & non-

continuous basement

membrane For easy passage

of blood cells to the blood.

Macrophages appear in the

wall of the sinusoids to engulf

any foreign bodies

Filtration

Formation Storage

DestructionBlood

Functions

Immuonological

Functions1. Filtration of blood from any organism by

macrophages

2. Formation of blood cells : in embryo & lymphocytes in germinal center

3. Storage of blood cells & platelets.

4. Destruction of RBCs& storage of iron.

5. Immuonological function the reticular cells trap the antigen & present it to lymphocytes---- humeral & cell mediated immunity.

Lymph node

spleen

number multiple Single

Function Filteration of lymphImmunity

Filtration& stores of blood Immunity

Lymph node spleenCapsule Thin, covered with fat

Smooth ms only at hilum.,

Thick covered with peritoneum

rich in smooth muscle

Trabeculae Thin arise from the capsule

Thick arise from the hilum

Lymph node spleenParenchyma

Cortex & medulla Cortex = lymph follicle & lymph sinus

The follicles have no arteriol.

Medulla = Medullary cords & Medullary

sinuses.

White pulp & red pulpWhite pulp = lymph follicle

no sinuses. The follicle contain arteriole.

Red pulp = splenic cords & blood sinusoids.

Cells lymphocytes + macrophages + plasma.

macrophages + plasma cells + WBCs +RBCs

Tonsils

Partially capsulated lymphatic tissue

3 sites:Palatine tonsils

Lingual tonsil

Pharyngeal Tonsil

Palatine tonsilsPalatine tonsils

Two oval masses of Two oval masses of lymphatic tissue under the lymphatic tissue under the mucous membrane of oro-mucous membrane of oro-pharynx. pharynx.

Lymphatic t issue of two kinds:

Lymph fol l icle with or without germinal center

Diffuse lymphatic t issue:

Lymphocytesplasma cellsmacrophage.

Each tonsils is coveredEach tonsils is covered with with stratif ied squamous epithelium stratif ied squamous epithelium which dips into the underlying which dips into the underlying lymphatic t issue to crypts. lymphatic t issue to crypts.

mucous glands mucous glands deep to the deep to the fol l icle fol l icle their their ducts open to ducts open to the surface & the surface & not in the base not in the base of the crypt so of the crypt so inflammation is inflammation is common common

Incomplete capsule:separates the tonsils from the underlying structure.Salivary corpuscle:Lymphocyte which pentrate the epith. To appear in the saliva.

Lingual tonsil:At the base of the tongueSecondary follicle & diffuse lymphatic. Non keratinised str. Sqam.epth which form crypt.mucous glands mucous glands open open into the base of the crypt.into the base of the crypt.

Pharyngeal Tonsil

Single mass of lymphoid tissue under nasopharynex.Covered with pseudo stratified columnar ciliated epith. with goblet cellsFolded with no cryptFunction :at the beginning of the respiratory &digestive systems so protect from bacteria & produce Ab.