Histology of lymphatic system Flashcards
what is immune system
-Differentiates between self (own) and foreign structures specificity
- Immune response - fights against pathogens
- Remember antigens over long period of time
what cell of the immune system
– Lymphocytes :T, B
– Antigen presenting cells (APC): Dendritic cells, macrophages
what difference lymphocytes T and B cells
T cells
•Thymus-processed lymphocytes
•2 subdivisions based on expression of specific surface markers.
CD4 - Helper T cells
CD8 - Cytotoxic T cells
B cells
•Function of B cells is production of antigen-specific antibody (immunoglobulin).
•Once activated B cells terminally differentiate into plasma cells
lymphatic system includes?
Lymph capillaries – Thin walled, collect lymph. Absent in cornea, hair, nail & bone marrow.
Lymph – transudate from blood, contains same proteins as in plasma, in smaller amounts.
Lymphocytes are suspended in lymph.
Lymphoid tissues & organs
Lymph capillaries unite to form larger lymph vessels which drain into vein
lymphoid tissue is divided into two :
Encapsulated: connective tissue capsule spleen, thymus, lymph nodes
Unencapsulated (or partly encapsulated)
Tonsils, Peyer’s patches, lymphoid nodules in GI tract, Respiratory tract, Urinary & Reproductive tracts
lymphoid organ central(primary) :
where lymphoid precursor cells undergo antigen independent proliferation and differentiation
– T cells in thymus
– B cells in bone marrow
lymphoid organs peripheral (secondary) :
where functional lymphocytes go - including lymph nodes, spleen, MALT (mucosa associated lymphoid tissue) - lymphoid nodules of Gastro intestinal (Peyer’s patches),Respiratory & Urogenital systems
• Lymphocytes contact antigens and divide and differentiate into effector B cells and T cells
• Memory cells form & circulate for years to provide extended
what is mucosa associated lymphoid tissue (MALT)
Gut associated lymphoid tissue.
Tonsils – Palatine tonsil, Pharyngeal tonsil, Lingual tonsil & Tubal
tonsil.
In GIT – Solitary lymphoid follicles & Aggregated lymphoid follicles (Peyer’s patches) seen.
‘B’ lymphocytes present in GIT, mature into plasma cells & produce IgA antibodies
Palatine tonsil microscopy
Lymphoid follicles
Mucosa are invaginated into crypts which are covered by Stratified squamous non-keratinised epithelium(oral cavity)
Mucous acini open into the crypts.
Desquamated epithelial cells & bacteria seen in the lumen of crypts.
Reticulated epithelium , basal lamina discontinuous
Interdigitating dendritic cells - APCs
Lymphoid tissue
Germinal centers
Mantle zones
Reticulated Crypt epithelium – IgG - & IgA – producing B
lymphocytes, T cells & APCs
lymph node
Lymph nodes are small encapsulated organs located along the pathway of lymphatic vessels
Serve as filters through which lymph percolates on its way to the blood vascular system
two type of lymphatic vessel serve the lymph node :
Afferent lymphatic vessels
-convey lymph towards the node
-enter at various points on the convex surface Efferent lymphatic vessels
-convey lymph away from the node
-leave at the hilum
lymph node structure, microscopic
Covered by capsule
The parenchyma is divided into a cortex and medulla
The cortex forms the outer portion of the node except at the hilum.
It consists of a
dense mass of lymphatic tissue
lymphatic sinuses (subcapsular & trabecular)
The medulla is the inner part of the lymph node.
what division cortex lymph nodes
Outer part of the cortex is called the superficial (nodular) cortex
-Contains lymphatic nodules
-In an active lymph node, nodules contain germinal center (Majority of cells within germinal center are B-lymphocytes)
Inner portion of the cortex is called the deep cortex (paracortex).
-is free of nodules
-This region contains most of the T cells in the lymph node
-Most of the lymphocytes (about 90%) enter the node through the walls of postcapillary venules (High Endothelial Venules)
medulla in lymph node consist of ?
Consists of cords of lymphatic tissue (Medullary cords) separated by lymphatic sinuses called medullary sinuses
The medullary cords contain reticular cells, lymphocytes (mostly B lymphocytes), macrophages, dendritic, and plasma cells
The medullary sinuses converge near the hilum, where they drain into efferent lymphatic vessels
how filtration of lymph
Subcapsular sinus and trabecular lymphatic sinuses
Communicate with the medullary sinuses
what lymph node function
Phagocytosis of particulate material by phagocytotic cells
All antigens have the opportunity to be presented to B lymphocytes, to T helper cells, and to T cytotoxic lymphocytes for these cells to initiate an immune response.
An important site of lymphocyte proliferation (especially of B cells in the germinal centers) as well as of transformation of B lymphocytes into plasma cells
spleen
Largest lymphatic organ
The spleen filters blood and reacts immunologically to
blood-borne antigens
The spleen is enclosed by a dense connective tissue capsule from which trabeculae extend into the parenchyma of the organ
No afferent lymphatics
The substance of the spleen is divided into white pulp and red pulp
what is white pulp in spleen
Consists of lymphatic tissue, mostly lymphocytes
Within white pulp, there is presence of central artery
Lymphocytes that aggregate around the central artery constitute the periarterial lymphatic sheath (PALS)
In cross sections, the PALS appears circular and may resemble a lymphatic nodule
The presence of the central artery (occupies an eccentric rather than a central position) however, distinguishes the PALS from typical lymphatic nodules
The lymphocytes of the PALS (similar to deep cortex of lymph nodes) are chiefly T lymphocytes
The nodules usually contain germinal centers, which, as in other lymphatic tissues, develop as B cells proliferate after their activation
Enlarged nodules are called splenic nodules or Malpighian corpuscles
what spleen -red pulp
Appears red because it contains large numbers of red blood cells
Consists of splenic sinuses separated by splenic cords (cords of Billroth)
Splenic cords contain a meshwork of reticular cells and reticular fibers
The highly permeable splenic sinuses are special sinusoidal vessels lined by rod-shaped endothelial cells
what the splenic microcirculation
Splenic artery
Trabecular artery
Central artery
Penicillar arteriole
Sheathed capillaries
Sheathed capillaries then empty directly into the reticular meshwork of the splenic cords – Open circulation
what are the spleen functions
The spleen performs both immune and hemopoietic functions
Activation and proliferation of B and T lymphocytes;
Production of antibodies against antigen present in circulating blood
Removal and destruction of senescent, damaged, and abnormal erythrocytes and platelets
Retrieval of iron from erythrocyte hemoglobin
Formation of erythrocytes during early fetal life
different between lymph node and spleen
Lymph node
Subcapsular and Trabecular lymphatic sinuses – present
Afferent lymphatics – Present
Parenchyma – Cortex and
medulla
No artery in lymphatic nodules in cortex
Spleen
Subcapsular and Trabecular lymphatic sinuses – Absent
Afferent lymphatics – Absent
Parenchyma – Red pulp and
White pulp
Central artery present in PALS
what is thymus
Present in thorax
2 lobes connected by fibrous tissue.
Fully formed & Functional at birth
After puberty, mostly replaced by adipose tissue
Lymphoepithelial Organ
what is thymus features
Capsule- which sends septa that divide the lobes into Thymic lobules.
Cortex – High concentration of lymphocytes, Basophilic, Small lymphocytes
Medulla- Lymphocytes are less in
number and larger, stains lightly
Hassall’s corpuscles in medulla.
Trabeculae does not form true lobules
Cortical caps over portions of continuous medullary tissue
what is hassall’s corpuscles in thymus
Small, round structures in medulla
Central core- epithelial cells & macrophages that have degenerated-form a pink staining hyaline mass.
Around this mass epithelial cells arranged concentrically
what are the functions of thymus
• Immature lymphocytes from bone marrow reach Thymus
• Undergoes antigen independent proliferation and differentiation
• FormsT-lymphocytes
• Enters circulation and occupy the thymus dependent areas of secondary lymphoid organs
• Confers Cell mediated Immunity
