Lymphatic Organs & Tissue Flashcards by Lindsay Kirkpatrick

Lymph nodes

Small bean shaped encapsulated lymphatic organs located along the pathway of lymphatic vessels

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2 types of lymphatic vessels

Afferent & efferent lymphatic vessels

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Afferent lymphatic vessels

Bring lymph into lymph node

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Efferent lymphatic vessels

Brings lymph away from lymph node at the hilum

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Hilum

Concave depression on the concave surface, serves as an entrance/exit for blood & lymphatic vessels & nerves

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Supporting elements of lymph nodes

Capsule
Trabeculae (CT septa)
Reticular tissue

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lymph nodes

Capsule is composed of…

dense irregular CT

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lymph nodes

Trabeculae (CT septa)

CT extensions from the capsule that extend into the lymph node forming a supportive framework

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lymph nodes

Reticular tissue

Reticular cells & fibers form a fine supporting meshwork

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General architecture of lymph node

Parenchyma divided into cortex & medulla

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lymph nodes

Parenchyma is divided into ____ and ____

Cortex & medulla

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lymph nodes

Subcapsular sinus

Immediately below the capsule, receives lymph from afferent lymphatics

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lymph nodes

Cortical (trabecular) sinuses

Branching from the subcapsular sinus among the lymphatic nodules within Trabeculae

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Lymphatic (lymphoid) nodules

Round aggregations of lymphocytes, mostly B lymphocytes (B cells)

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2 types of lymphatic nodules

Primary & secondary lymphatic nodules

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Primary lymphatic nodule immune function

Currently no immune response

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Secondary lymphatic nodule immune function

Immune response to antigen presentation

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Secondary lymphatic nodules structure

paler germinal centre of proliferating lymphocytes (mostly B cells) surrounded by corona (mantle) of smaller mature B lymphocytes

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Lymphatic nodules may transition into ____

Diffuse lymphatic tissue - random lymphocyte arrangement between nodules
(Not bound by CT)

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lymph nodes

Paracortex

Deeper extension of the cortex, no lymphatic nodules, diffuse lymphatic tissue, mostly T cells

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lymph nodes

High endothelial venules (HEVs) are located in the ____

Paracortex

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lymph nodes

Paracortex contains mostly ____

T cells

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High endothelial venules (HEVs)

Specialized post capillary venules, entry point for most circulating lymphocytes

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lymph nodes

2 major components of medulla

Medullary cords
Medullary sinuses

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# lymph nodes Medullary cords

Branched, cord-like masses of reticular fibers containing mostly B lymphocytes, and plasma cells. T lymphocytes, macrophages and dendritic cells

# lymph nodes Medullary cords contain branched cord-like masses of ____

Reticular fibers

# lymph nodes Medullary cords contains mostly ____

B lymphocytes

# lymph nodes Medullary sinuses

- Dilated lymphatic vessels with discontinuous endothelium, extending from cortical sinuses - converge & empty into into efferent lymphatic vessel at the hilum

# lymph nodes Medullary sinuses extend from the ____

Cortical sinuses

Medullary sinuses converge & empty into the ____ at the ____

Efferent lymphatic vessel at the hilum

Thymus location

Bi-lobed organ in the superior mediastinum, anterior to the heart

Thymus function

Site of T-cell differentiation (into thymocytes) & proliferation

Only ____ reside in the thymus

T lymphocytes

General architecture of thymus

- CT capsule surrounding thymus - Trabeculae (CT septa) extending from capsule into parenchyma, separating tissue into completely separate thymic lobules

Epithelioreticular cells

Features of reticular cells & epithelial cells - supportive cells, no true CT fibers within a thymic lobule

Epithelioreticular cells function

- line capsule, Trabeculae & surround microvasculature, forming **blood-thymus barrier** - form cytoreticulum to support thymocytes

Blood-thymus barrier

Prevents exposure of thymocytes (T cells) to antigens

# thymus Cortex

Each lobule has an outer darker staining region, more densely packed thymocytes (T cells)

# thymus Medulla

Paler staining (fewer thymocytes), Epithelioreticular cells more visible

# thymus Hassall’s corpuscles (thymic corpuscles) are located in the ____

Medulla

Hassall’s corpuscles

- Larger aggregates of concentrically wrapped Epithelioreticular cells, contain keratohyalin granules - thought to produce factors (interleukins) that promote T cell development

Hassall’s corpuscles are thought to produce ____

Factors (interleukins) that promote T cells development

What are the specialized post Capillary venules located in the Paracortex of a lymph node, that act as an entry point for most circulating lymphocytes?

HEVs

Functions of spleen

- filter blood & react immunologically to blood-borne antigens (white pulp & red pulp) - main site of destruction & removal of old, damaged & abnormal RBCs & platelets AND storage of extra RBCs (red pulp)

# spleen General architecture

CT capsule - surrounds spleen Trabeculae (CT septa) - contain myofibroblasts Hilum - splenic artery enters here

# spleen Functions of Trabeculae (CT septa)

- support trabecular arteries - myofibroblasts help release RBC storage pool when necessary

# spleen Where does the splenic artery enter?

Hilum

# spleen Parenchyma consists of ____ & ____

Red pulp & white pulp

# spleen What is White pulp

Lymphatic nodules (primary or secondary, mainly B lymphocytes)

White pulp contains a ____

Central artery

# spleen What Branches from trabecular arteries?

**Central artery** - splenic a. - trabecular aa. - **central aa.** - penicillar arterioles - sinusoids

# spleen Periarterial lymphatic sheath (PALS)

- Cylindrical aggregation of lymphocytes around the central artery - mainly T lymphocytes in initial formation of white pulp

# spleen Red pulp is made up of…

Splenic cords (billroth cords) Splenic sinusoids (sinuses)

# spleen Splenic cords (billroth cords)

Reticular tissue containing large numbers of stored RBCs, macrophages & lymphocytes, and plasma cells & dendritic cells

# spleen Splenic sinusoids (sinuses)

Sinusoidal capillaries, site where senescent RBCs are removed

# spleen Penicillar arterioles: 1/2 are ____ 1/2 are ____

- 1/2 open ended: dumping blood into stroma of splenic cords - 1/2 are typical closed circulation

Diffuse & Mucosa-Associated Lymphatic Tissue includes…

- MALT - mucosa associated lymphatic tissue (eg. GALT, BALT) - tonsils - Peyer’s patches (ileum) - appendix

3 tonsils

- palatine tonsils - pharyngeal tonsils (adenoids) - lingual tonsils

What are tonsils?

- 3 irregular masses of lymphoid tissue in the oral cavity & nasopharynx - cells encounter antigens entering mouth & nose

Immune cells in the tonsils are…

Not permanent - lymphocytes come and go as necessary to accommodate immune response

Lymphocytes in appendix

Lymphocytes dispersed diffusely throughout CT of mucosa or aggregated into nodules

Immune cells of appendix are…

Not permanent - lymphocytes come & go as necessary to accommodate immune response