Histology of lymphatic system

Question 1

what is immune system

Answer 1

-Differentiates between self (own) and foreign structures specificity
- Immune response - fights against pathogens
- Remember antigens over long period of time

Question 2

what cell of the immune system

Answer 2

– Lymphocytes :T, B
– Antigen presenting cells (APC): Dendritic cells, macrophages

Question 3

what difference lymphocytes T and B cells

Answer 3

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

Question 4

lymphatic system includes?

Answer 4

 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

Question 5

lymphoid tissue is divided into two :

Answer 5

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

Question 6

lymphoid organ central(primary) :

Answer 6

where lymphoid precursor cells undergo antigen independent proliferation and differentiation
– T cells in thymus
– B cells in bone marrow

Question 7

lymphoid organs peripheral (secondary) :

Answer 7

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

Question 8

what is mucosa associated lymphoid tissue (MALT)

Answer 8

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

Question 9

Palatine tonsil microscopy

Answer 9

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

Question 10

lymph node

Answer 10

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

Question 11

two type of lymphatic vessel serve the lymph node :

Answer 11

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

Question 12

lymph node structure, microscopic

Answer 12

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.

Question 13

what division cortex lymph nodes

Answer 13

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)

Question 14

medulla in lymph node consist of ?

Answer 14

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

Question 15

how filtration of lymph

Answer 15

Subcapsular sinus and trabecular lymphatic sinuses
Communicate with the medullary sinuses

Question 16

what lymph node function

Answer 16

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

Question 17

spleen

Answer 17

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

Question 18

what is white pulp in spleen

Answer 18

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

Question 19

what spleen -red pulp

Answer 19

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

Question 20

what the splenic microcirculation

Answer 20

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

Question 21

what are the spleen functions

Answer 21

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

Question 22

different between lymph node and spleen

Answer 22

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

Question 23

what is thymus

Answer 23

Present in thorax
2 lobes connected by fibrous tissue.
Fully formed & Functional at birth
After puberty, mostly replaced by adipose tissue
Lymphoepithelial Organ

Question 24

what is thymus features

Answer 24

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

Question 25

what is hassall’s corpuscles in thymus

Answer 25

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

Question 26

what are the functions of thymus

Answer 26

• 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