6. Histo - Lymphoid

8/4/2019 6. Histo - Lymphoid

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2. Peyers patch (mucousmembrane of ileum)

3. Appendix (mucousconnective tissue, mucousmembrane)

General Structure

A. Stroma- framework- capsule, trabeculae,

septa, reticularnetwork

B. Parenchyma- cellular part- made up of

lymphocytes,monocytes, plasmacells, macrophages

Lymph NodeAggregates of lymphoid

tissue in the course of thelymphatic vessels

Location - axilla, inguinal area,cervical, mesentery

StructureRounded or kidney-shaped

organ with a slight indentation(hilus) where the blood vesselsenter and leave the organStroma of lymph node

Capsule

Trabeculae

Network of reticularfibers and cells

ParenchymaCellular part responsible for

the function of the organ

A. Cortex (peripheral)- lymphatic nodules

- germinal center (ofFlemming)

- lymphocytes :nodular

C. Medulla (central)- medullary cords- lymphocytes : in

cords (medullarycords)

Lymphatic SinusesSpaces within the lymph

node for passage of lymph duringlymph filtration

1. SubcapsularPrimary or marginal;beneath capsule andnodule

2. CorticalSecondary; space betweentrabeculae and nodule

3. MedullarySpace between medullarycords and trabecula

Functions1. Filtration of lymph (from

intercellular spaces in CT)2. Production of lymphocytes3. Immune defense

(secondary; macrophages)

Filtration of Lymph

Lymph Afferent lymph vessel

Convex part of lymph node

Sinuses Efferent vessels athilus (with valves directed awayfrom node)

Spleen

Largest lymphoid organLocation- left hypochondriac

regionA. Stroma

Capsule : fibro-muscular,smooth muscle


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Trabeculae : splenic lobule,structural and functionalunit of spleenNetwork of reticular fibersand cells

B. Parenchyma splenic pulp1. White pulp

Lymphocytes :diffused or in nodulesForms the PALS (peri-arterial lymphoidsheath) whichsurrounds thearteriesCentral artery :artery within thenodule

2. Red pulpBilroths or spleniccord and venoussinuses (spacesbetween the cords),not lymph sinuses

Blood VesselsSplenic artery : arteries

which supply the spleen

Spelnic artery Passestrabeculae, become trabecular

arteries Reaches dm of 2 mm,artery enters white pulp, acquireslymphoid sheath (PALS), now

known as central artery

Reaches dm of 25 micra Artery

enters red pulp Becomes apenicillar artery or a penicillus ofRuysch.Penicillar Artery Segments

1. Pulp arteriole longest part2. Sheathed artery covered

by the sheath of Schweiger-Seidel, constitute thesplenic ellipsoid (sheathand sheathed artery)

3. Terminal branches dilation : ampulla of Thoma

Functions of the Spleen

1. Filtration of blood; bloodfilter

2. Blood reservoir, due tovenous sinuses

3. Iron storage4. Production of lymphocytes

(nodules in white pulp)5. Immunologic defense

(macrophages)

ThymusBroad, flat, bilobed mass of

lymphoid tissue found justbeneath the upper part of thesternum, a primary lymphoidorgan

First lymphoid organ

seeded by lymphocytes from thebone marrow

The lymphocytes are honedin the thymus

A. Stroma1. Capsule2. Septa3. Trabeculae end at the cortico-medullary junction

B. Parenchyma

1. CortexLymphocytes arediffused2. MedullaLymphocytes arediffusedFound here : Hassalls orthymic corpuscle - nestof epithelioid cellscontaining kerato-hyaline granulesarranged concentrically

Functions1. Production of lymphocytes primary function2. Immunedefense presence ofplasma cells andmacrophages


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TonsilsOne of the MALTAccumulation of lymphoid

tissue in the lamina propria of theupper part of the respiratory anddigestive tractsTypes

1. Pharyngeal or Adenoid only one, located at thedorsal midline part of thenasopharynx

2. Palatine or Faucial two,the left and right, located inthe glossopalatine arch orthe pharyngopalatinearches

3. Lingual located at the rootof the tongue

These tonsils guard theopening of the upper part of therespiratory and digestive tract orthroat and form a ring-likestructure along with other smallercollections of lymphoid tissue(includes solitary nodules) in thelamina propria of the throat, all ofthese form the

Ring of WaldeyerBasic Structure

Tonsils are covered byepithelium (type depends onlocation), infiltrated withlymphocytes

Epithelium invaginates,goes down to the lamina propriato form crypts known as thetonsillar crypts

Tonsillar crypts containdesquamated epithelial cells anddegenerated/degeneratinglymphocytes to form the salivarycorpusclesCapsule

Only located on one side,opposite to the lining epithelium,not entire tonsil is covered

Half will be covered by theconnective tissue capsule, whilethe exposed part is covered byepitheliumTypical lymphatic nodules

A nodule with a darkperipheral part and a pale center(germinal center)

Present in the tonsils, butlymphatic sinuses are absentDifferentiationBases Adenoid Fauci

alLingual

Epithelium

Pseudostratifiedciliatedepitheliumwith goblet

cells

Stratifiedsquamous

Stratifiedsquamous

Crypts Shallow pseudocrypt

Deepandbranching

Deepandbranching

Associatedglands

Sero-mucous

Mucous Mucous

Openingof glans

Surface oftonsil

Surfaceorupperpart ofcrypt

Bottomof crypt

Infectio

n

Not

common

Very

common

Rare

Peyers PatchAccumulations of lymphoid

tissues or aggregates of nodulesfound in the lamina propria of theileum opposite its mesentericattachment

Collection of lymphoidtissues will be only on one side ofthe organ, the side opposite its

attachmentContains typical lymphatic

nodules but no lymphatic sinusesThere will be infiltration of

the overlying epithelium, sincethe lining epithelium of the smallintestine is simple columnar, the


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Peyers patch will be covered bysimple columnar epitheliumFunctions

1. Production of lymphocytes2. Immune defense

Confluent Nodules of theAppendix

Collection of lymphoidtissue found in the lamina propriaof the appendix all around itslumen

Contains typical lymphaticnodules but no lymphatic sinuses

Covering epithelium issimple columnarFunctions

1. Production of lymphocytes2. Immune defense

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6. Histo - Lymphoid