Histology-Lymphoid Tissue

Question 1

What are encapsulated lymphoid tissues?

Answer 1

Thymus
Lymph Nodes
Spleen
Tonsils

Question 2

Describe X-linked Agammaglobulinemia

Answer 2

• X-linked

- Lack of B cells (B cells don’t mature)

Question 3

What cells form the supporting framework of lymphoid organs?

Answer 3

Reticular Cells: synthesize reticular fibers

Question 4

What is peyer’s patch (GALT)?

Answer 4

Large lymphoid nodules that exudate into submucosa of ileum.

Question 5

What are Microfold (M) cells?

Answer 5

Specialized cells that endocytose antigens and transfer them to lymphocytes and macrophages in GALT.

Question 6

Both afferent & efferent lymphatic vessels exist in

Answer 6

Lymph Nodes

• Have multiple afferent lymphatic vessels but only one efferent lymphatic vessel.

Question 7

Describe Lymph Node

Answer 7

1. Cortex: mainly B cells
2. Paracortex: mainly T cells
   - has high endothelial venules
   - Is thymus dependent region
3. Medulla: composed of medullary cords & sinuses

Question 8

What is high endothelial venules?

Answer 8

Venules where circulating lymphocytes in the blood (90%) enter the lymph nodes here by diapedesis.

• made of simple CUBOIDAL epithelium

Question 9

Describe components of Medullary Cords & Medullary Sinuses

Answer 9

Medullary Sinuses (lighter): contain macrophages and reticular fibers (Type III collagen)

Medullary Cords (darker): contain a few lymphocytes and plasma cells.

Question 10

Benign swollen lymph nodes are

Answer 10

less than 1.5 cm, soft and movable

Question 11

Where is virchow’s node located and what does it suggest?

Answer 11

It’s an enlarge, hard node located in the left supraclavicular node.

It suggests abdominal metastasis.

Question 12

How is thymus different from lymph node?

Answer 12

Thymus has no hilum and lymphoid nodules.

Question 13

Describe Thymus

Answer 13

1. Cortex: Maturing T cells
   - Positive selection occurs
   - Most T cells die here
   - contains blood-thymus barrier
2. Medulla: Matured T cells
   - Negative selection occurs
   - contains hassall corpuscles

Question 14

What is blood-thymus barrier?

Answer 14

The barrier that makes an immunologially protected region, ensuring that antigens escaping the bloodstream do not reach developing T cells in the cortex.

Question 15

What are hassall corpuscles

Answer 15

Whorl-like epithelial cells in thymic medulla that increase in number with age. Unkown function.

Question 16

What hormone depress T cell formation in the thymus?

Answer 16

adenocorticosteroids

Question 17

what causes DiGeorge syndrome?

Answer 17

Lack of cell-mediated immunity due to congenital absence of thymus and parathyroid gland.

Triad: Cardiac defects, hypocalcemia, hypoplasia of thymus

Question 18

What are the main functions of Spleen?

Answer 18

Filters blood and clear damaged RBCs

Question 19

How is spleen different from thymus and lymph node?

Answer 19

Spleen has no cortex/medulla.

Question 20

What secondary lymphoid tissues don’t have afferent lymphatic vessels?

Answer 20

Thymus & Spleen

Question 21

Describe Spleen

Answer 21

1. White Pulp
   - Includes lymphoid nodules (B cells)
   - Includes central arterioles surrounded by PALS (T cells)
2. Red Pulp
   - Splenic sinusoids (contains endothelial cells called stave cells)
   - Splenic Cords (loose CT with plasma cells, blood cells, and macrophages)

Question 22

What is the main function of tonsils?

Answer 22

Filtration of foreign antigens transported across epithelium.

• No cortex/medulla
• only lymphoid nodules