"Microscopic Anatomy Lymphoid Organs Ira Ames" GABY

Question 1

Where are immune responses initiated and generated?

Answer 1

Within the lymphoid organs

Question 2

Extralymphoid tissues & organs

Answer 2

GI
respiratory
urinary
reproductory tract
skin
blood
lymph
wandering lymphocytes

Question 3

Lymphocyte recirculation

Answer 3

1. Connects the three components of the immune system: primary, secondary, extralymphoid
2. Permits continuous immune surveillance and ensures rapid response to antigens

Question 4

Lymphocyte types:

Answer 4

B cells
T cells
Null cells (NK cells)

Question 5

What do cells & fibers of reticular connective tissue do for lymphocytes?

Answer 5

Form a sponge-like meshwork that supports the lymphocytes

Question 6

Types of reticular tissue in hematopoietic organs

Answer 6

Lymphoid tissue:
free cells are largely lymphocytes

Myeloid tissue:
free cells are developing erythrocytes & granular leukocytes
(bone marrow)

Question 7

Reticular (dendritic) cell

Answer 7

• Most reticular cells are of mesenchymal origin
• Large cells numerous cytoplasmic processes
• Processes wrap around reticular fibers

Question 8

Functions of Reticular Cells (of mesenchymal origin)

Answer 8

• Synthesis and maintenance of the extracellular matrix
• Phagocytosis
• Trophic role in blood cell formation
• Storage place of ferritin
• Antigen processing and presentation

Question 9

Lymphoid tissue from a lymph node

Answer 9

Loose: reticular cells
Dense: lymphocytes

Question 10

Unstimulated primary nodule lymphoid tissue (spleen)

Answer 10

Compact
Spherical
Lack a c.t. capsule
Consist mostly of B lymphocytes

Question 11

Stimulated secondary lymphatic nodules (lymph node)

Answer 11

Capsule
Subcapsular sinus
Germinal center contains numerous activated B lymphocytes

Question 12

When do secondary lymphatic nodules appear?

Answer 12

During 1ry antigenic response and involute in about 4 weeks

Question 13

What happens to activated B lymphocytes within the germinal center (GC) in the secondary lymphatic nodule under antigenic stimulation?

Answer 13

proliferation 
selection 
apoptosis
differentiation
storage

Question 14

Lymph nodes

Answer 14

A series of in-line filters in the lymphatic system

Question 15

Components of the lymphoid node –> cortex

Answer 15

Loose lymphoid tissue: subcapsular & peritrabecular sinuses

Lymphatic nodules: primary and/or secondary contain mostly B lymphocytes

Question 16

Components of the lymphoid node –> medulla

Answer 16

Dense lymphoid tissue: medullary cords populated largely by B lymphocytes & plasma cells

Loose lymphoid tissue: medullary sinuses (numerous reticular cells)

Question 17

Does the structure of the sinuses facilitate the filtering function of the nodes?

Answer 17

YES

Question 18

Key Molecules in Lymphocyte Homing

Answer 18

selectins
integrins
carbohydrates (sugars & mucins)
immunoglobulin superfamily members (ICAM, VCAM, etc.)

Question 19

Where can high endothelial venules (HEV) be observed?

Answer 19

Lymph nodes
tonsils
Peyer’s patches

*not in spleen or thymus

Question 20

Medical Relevance of HEVs

Answer 20

• play a role in lymphocyte recirculation
  (contribute to specificity)
• decrease in number with age
  (immunologic function down with age)

-implicated in metastasis of lymphoid malignancies (lymphomas)

Question 21

Functions of lymph nodes

Answer 21

Filtration of lymph

Production & selection of B lymphocytes

Immune response to lymph-borne antigens

Question 22

Components of the lymphoid node –> deep cortex

Answer 22

paracortex
tertiary cortex

Located between the cortex and the medulla

location of HEVs
most lymphocytes are

Question 23

Fetal thymus

Answer 23

Well developed at birth, and reaches its maximum size within the first year of life

Dual embryological origin:
1. epithelial lining of 3rd & 4th
branchial pouches
2. Surrounding mesenchyme

Develops early!!

Question 24

Adult thymus

Answer 24

Atrophy begins by the age of two. Much of the parenchyma is replaced by connective tissue.

Question 25

Principle Cell Types Within the Thymus

Answer 25

Thymocytes (thymic lymphocytes):
predominate in cortex
proliferate selection apoptosis
travel to other lymphoid organs

Epithelial reticular cells derived from endoderm of 3rd & 4th branchial pouches
(desmosomes & tonofilaments)

Question 26

Unlike mesenchymal reticular cells, epithelial reticular cells: ___

Answer 26

1. are not normally phagocytic
2. do not make reticular fibers
3. not antigen-presenting cells

Question 27

Functions of Epithelial Reticular Cells

Answer 27

Secretion

Provide supporting framework (cytoreticulum)

Form Hassall’s corpuscles

Contribute to blood-thymus barrier

Question 28

Spleen

Answer 28

1. filtration of blood
2. immunodefense

white pulp (20%) –> PALS + lymphatic nodules

red pulp (80%) –> splenic cord & splenic sinus

capsule

Question 29

Blood Flow Through the Spleen

Answer 29

Splenic artery
Trabecular arteries 
Central arteries 
Penicillar arteries 
Capillaries 
Sinuses
Red pulp veins 
Trabecular veins 
Splenic vein

Question 30

Most blood follows the ___ circulatory route within the spleen

Answer 30

Open (blood flows from caps. into cords
before it enters sinuses)

*as supposed to closed (blood flows directly from caps. into sinuses)

Question 31

Functions of the Spleen

Answer 31

1. production of lymphocytes 2. immune response to blood-borne antigens
2. destruction of old erythrocytes (by macrophages)
3. storage of blood (especially the cells and platelets)
   * A reservoir of monocytes that can be rapidly released to regulate inflammation

Question 32

Tonsils

Answer 32

Aggregates of lymphoid tissue lying beneath the epithelium in the upper pharynx

Question 33

Functions of tonsils

Answer 33

Detection and response to pathogens in the oral cavity Production of lymphocytes