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8/6/2019 Lymphatic Tissue
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Lymphatic Tissue
The Open note Project : www.facebook.com/groups/opennote
About the Open Note Project : http://biy.ly/open-note
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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.