The lymph node

Question 1

about Lymphatic nodules / Lymphoid follicles :
1. Shape& Size……………..
2. Site……….
3. Contain………..

Answer 1

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

Question 2

illustrate Types of Lymphatic nodules

Answer 2

1. Primary lymphatic nodules
   (homogenous density) :
   * oval, rounded, pyramidal.
   * Homogenous (no germinal center).
   * Formed primarily of B
   lymphocytes
2. Secondary Lymphatic nodules
   (develop when nodule is exposed to Ag)
   * Dark periphery and pale central region ( Germinal center)
   a. Germinal center
   b. Mantle zone

Question 3

When primary nodule activated, lymphocytes proliferate in central region forming ……………..

Answer 3

germinal center

Question 4

illustrate Germinal center of LN

Answer 4

• 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

Question 5

number of follicular dendritic cells and
macrophage increase after ………….

Answer 5

intense response to an Ag

Question 6

illustrate mental zone

Answer 6

• 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

Question 7

illustrate Site of LN

Answer 7

• Along course of lymphatic vessels
• Abundant in axilla, groin and
  mesentries.t

Question 8

illustrate Surfaces of lymph node

Answer 8

a. Convex surface…where afferent lymphatic vessels enter
b. Concave surface (Hilum):
where efferent lymphatic leaves & entry and exit of blood vessels.

Question 9

in LN both afferent and efferent
lymphatic vessels are provided
with ……………

Answer 9

valves

Question 10

illustrate Structure of the Lymph Node

Answer 10

1. 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
2. Parenchyma:
   - Cortex (outer and paracortex)
   - Medulla

Question 11

illustrate Cells of reticular meshwork

Answer 11

1. Reticular cells
2. Dendritic cells
3. Macrophages
4. Follicular dendritic cells

Question 12

illustrate Reticular cells

Answer 12

1. Fibroblasts –like cells.
2. Its long cytoplasmic processes wrap around the reticular fibers →isolate
   these structural component from the parenchyma.
3. 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

Question 13

illustrate Dendritic cells

Answer 13

1. They are bone marrow derived antigen presenting cells.
2. Have dendrites that give the cells their name.
3. Monitor local environment for foreign substances.
4. High affinity to capture & process antigens.

Question 14

illustrate Macrophages

Answer 14

1. They are phagocytic & less efficient antigen presenting cells.
2. High affinity of endocytosis and digestion of internalized material

Question 15

illustrate Follicular dendritic cells

Answer 15

1. Arise from pericytes and vascular smooth muscles.
2. Site: In germinal center of lymph nodules.
3. Multiple thin, hair like cytoplasmic
   processes → interdigitate between B cells
4. 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

Question 16

Cortex consist of (1.outer cortex and Paracortex) of Parenchyma of Lymph node .
illustrate each one

Answer 16

1. 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:
2. Subcapsular sinus: between capsule and cortical nodule
3. Cortical sinus: surround the lymphoid cortical nodules
   - They are Lined by discontinuous endothelial cells and partly with
   reticular cells & macrophages
4. 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.

Question 17

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

Question 18

Paracortical region (Inner Cortex) contain :……..

Answer 18

a. Mainly T helper lymphocytes (thymus
dependent zone)
b. High endothelial post capillary venules

Question 19

illustrate the struct and func of High endothelial post capillary venules

Answer 19

• 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

Question 20

illustrate struct of Medulla of Lymph Node

Answer 20

1. Surrounded by the cortex except at the hilum.
2. 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

Question 21

what’s the Function of Lymph Node ?

Answer 21

• 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

Question 22

list Blood supply of the lymph node

Answer 22

• 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

Question 23

1. During Infection & antigenic stimulation, there is enlargement of lymph node. Most of lymph nodules are ………with active germinal
   center.
2. In case of cancer, malignant cells reach lymph nodes, then they ………….. through efferent lymphatics and blood vessels

Answer 23

1. secondary type
2. spread to distant parts of body