The lymph node Flashcards
about Lymphatic nodules / Lymphoid follicles :
1. Shape& Size……………..
2. Site……….
3. Contain………..
1.Unencapsulated aggregations of
lymphocytes in a follicle & 1mm-1 to 2 cm
2.
- Lymphoid organs ( lymph node,
spleen , tonsils)
- In the connective tissue under
the epithelium of mucous
membranes (covering or lining)
3.
1) B lymphocytes
2) APCs (MQ and dendritic cells)
3) Reticular cells for support
4) Follicular dendritic cells
illustrate Types of Lymphatic nodules
- Primary lymphatic nodules
(homogenous density) :
* oval, rounded, pyramidal.
* Homogenous (no germinal center).
* Formed primarily of B
lymphocytes - Secondary Lymphatic nodules
(develop when nodule is exposed to Ag)
* Dark periphery and pale central region ( Germinal center)
a. Germinal center
b. Mantle zone
When primary nodule activated, lymphocytes proliferate in central region forming ……………..
germinal center
illustrate Germinal center of LN
- Lighter stained area in the center of the 2ry lymphatic nodules after
2nd exposure to the Ag. - Light stain →proliferating lymphocytes
& plasmablasts have large vesicular
euchromatic nuclei. - Represents the proliferating and
differentiation of B lymphocytes into plasma cells →antibodies. - It contains:
1. Activated B lymphocytes
2. Macrophages
3. Follicular dendritic cells
4. Few plasma cells
number of follicular dendritic cells and
macrophage increase after ………….
intense response to an Ag
illustrate mental zone
- The Mantle zone :
- Outer ring of small lymphocyte that
encircles the germinal center. - The outcome of immune reaction in
the lymph nodule :
Plasma cells
memory cell
illustrate Site of LN
- Along course of lymphatic vessels
- Abundant in axilla, groin and
mesentries.t
illustrate Surfaces of lymph node
a. Convex surface…where afferent lymphatic vessels enter
b. Concave surface (Hilum):
where efferent lymphatic leaves & entry and exit of blood vessels.
in LN both afferent and efferent
lymphatic vessels are provided
with ……………
valves
illustrate Structure of the Lymph Node
- Stroma:
- Capsule : dense irregular C.T
- Trabeculae: septa arising from capsule dividing node into incomplete compartments
- Reticular C.T. (reticular cells and reticular fibers):
*Network of reticular cells & fibers
*Attached to the septa and inner surface of the capsule.
* Support the parenchyma - Parenchyma:
- Cortex (outer and paracortex)
- Medulla
illustrate Cells of reticular meshwork
- Reticular cells
- Dendritic cells
- Macrophages
- Follicular dendritic cells
illustrate Reticular cells
- Fibroblasts –like cells.
- Its long cytoplasmic processes wrap around the reticular fibers →isolate
these structural component from the parenchyma. - Function:
- Synthesize and secrete type III collagen (reticular fibers) & the associated ground substances →stroma.
- Express surface molecules & produce substances that attract T cells, B cells, and dendritic cells
illustrate Dendritic cells
- They are bone marrow derived antigen presenting cells.
- Have dendrites that give the cells their name.
- Monitor local environment for foreign substances.
- High affinity to capture & process antigens.
illustrate Macrophages
- They are phagocytic & less efficient antigen presenting cells.
- High affinity of endocytosis and digestion of internalized material
illustrate Follicular dendritic cells
- Arise from pericytes and vascular smooth muscles.
- Site: In germinal center of lymph nodules.
- Multiple thin, hair like cytoplasmic
processes → interdigitate between B cells - Function: efficient in trapping antigens & retain them on its surface for long time where they can be recognized by specific B lymphocyte.
* N.B. Antigen is not endocytosed or processed
→ not a phagocytic cell
→ not APC
Cortex consist of (1.outer cortex and Paracortex) of Parenchyma of Lymph node .
illustrate each one
- The outer cortex:
a) Lymphoid nodules: Primary &Secondary
b) Cortical lymphatic sinuses:
- Spaces filled with Lymph
beneath the capsule surrounding the lymphatic nodules and trabeculae.
They include: - Subcapsular sinus: between capsule and cortical nodule
- Cortical sinus: surround the lymphoid cortical nodules
- They are Lined by discontinuous endothelial cells and partly with
reticular cells & macrophages - Deep paracortical region ( inner cortex):
- Indistinct, present between the cortex and medulla
- Composed mainly of T- lymphocytes
- Known as Thymus – dependent area of lymph node
- Has many specialized high endothelial post-capillary venules
- Site where lymphocytes leave blood to enter lymph node
between the high endothelial cells.
- B cells go to outer cortex &T cells remain in paracortex.
Deep paracortical region ( inner cortex): contains antigen presenting cells which migrate to it to activate T helper cells. T cells proliferate and
differentiate into memory and effector cells passes to medullary sinuses then to efferent lymphatic vessels to area of
antigenic activity
Paracortical region (Inner Cortex) contain :……..
a. Mainly T helper lymphocytes (thymus
dependent zone)
b. High endothelial post capillary venules
illustrate the struct and func of High endothelial post capillary venules
- Lined by cubical or low columnar
cells. - Both B and T lymphocytes leave blood
and enter the lymph node between the
high endothelial cells. - Also present in appendix, tonsils and
payer’s patches but not in Spleen. - Function:
Have receptors for T and B lymphocytes
→ signal lymphocytes to leave the
circulation. - B lymphocytes→ outer cortex
- T helper lymphocytes → remain in
paracortex
illustrate struct of Medulla of Lymph Node
- Surrounded by the cortex except at the hilum.
- It is composed of:
a) Medullary cords:
- branch and anastomose
- Mostly B cells, some T cells, plasma cells, macrophages,
dendritic cells, reticular cells.
b) Medullary sinus:
- Irregular spaces between the medullary cords.
- Lined by endothelial cells, reticular cells and fibers.
- Drain into efferent lymphatic vessel
what’s the Function of Lymph Node ?
- Filtration of lymph → by macrophage
→ defend against the spread of
microorganisms and tumor cells - Facilitate production of plasma cells
(secreting antibodies) merging with
the bloodstream. - Maintain and activate B and T
lymphocytes
list Blood supply of the lymph node
- Artery enter hilum & pass in the medulla within the trabeculae & form Medullary capillary beds.
- Small arteries Continue into cortex forming capillary network surrounding lymphatic nodules.
- Venous capillaries descend from the cortex to form high endothelial Postcapillary venules then large veins in the trabeculae & leave the LN at the hilum
- During Infection & antigenic stimulation, there is enlargement of lymph node. Most of lymph nodules are ………with active germinal
center. - In case of cancer, malignant cells reach lymph nodes, then they ………….. through efferent lymphatics and blood vessels
- secondary type
- spread to distant parts of body
