Lymphoid Organs

Question 1

1. Describe the morphological characteristics of mesenchymal reticular cells.

Answer 1

a. Large cells
b. Has cytoplasmic processes that wrap around fibers (resembles dendritic cell)
c. Its cytoplasm is pale
d. nucleus is elongated and nucleolus is prominent

Question 2

What is function of reticular cell and its origin?

Answer 2

1.It is a fibroblastic cell, forming fibrils that support free cells in lymphoid tissue 2. phagocytosis (macrophage) 3. ferritin storage 4. antigen presentation (dendritic cell)

Question 3

Describe the structure of 3 basic types of Lymphoid Tissue

Answer 3

3Types: Loose, Dense, Nodular

• Loose: open meshwork of cells and fibers with reticular cells predominating
• Dense: dense meshwork of cells and fibers with lymphocytes predominating
• Nodular: tightly packed lymphocytes, spherical, lack a connective tissue capsule, B lymphocytes predominate when under antigenic challenge

Question 4

Describe a germinal center

Answer 4

• It is a tissue in lymph under antigenic challenge.
• There is a light zone, dark zone, and mantle zone
• The center aspect of nodule is paler and contains non-dividing B lymphocytes and T helper cells. Selection, differentiation, and apoptosis occurs in the light zone
• proliferation occurs in dark zone
• temporary storage of young plasma and memory B cells occurs in mantle zone

Question 5

Describe the flow of lymph through a lymph node

Answer 5

Blood>afferent lymphatic vessels >subscapular sinus> trabecular sinus >medullary sinus> hilum- efferent> blood via thoracic duct

Question 6

What is function of High Post-Capillary Venules

Answer 6

High Endothelial Venules bring lymph back to nodes via cell adhesion molecules

Question 7

Which regions of lymph nodes are T dependent?

Answer 7

The paracortical zone aka deep zone is T-dependent

Question 8

What are the key molecules in Homing?

Answer 8

selectins, integrins, immunoglobulin super family, carbohydrates

Question 9

Where can HEVs be seen?

Answer 9

Lymph nodes, tonsils, Peyer’s Patches

Question 10

What kind of tissue is in the medulla of lymph nodes?

Answer 10

dense lymphoid tissue

Question 11

What kind of tissue is in medullary sinus?

Answer 11

loose lymphoid tissue

Question 12

Tissue of trabeculae of lymph is…

Answer 12

Connective

Question 13

Capsule of lymph is made of…

Answer 13

dense irregular connective tissue

Question 14

What are the three functions of lymph nodes?

Answer 14

1. Production of B lymphocytes
2. Filtration of Lymph
3. Play role in the immune response to lymph-borne antigens

Question 15

To which lymphoid organ does the cytoreticulum belong? What is its function?

Answer 15

Cytoreticulum of the thymus gland forms a supporting framework for thymal epithelial reticular cells that allow secretion.

Question 16

The major functions of the thymus are.

Answer 16

1. T- lymphocyte development 2. development of the lymphoid system - other lymphoid organs

Question 17

What are the three major cell types in thymus?

Answer 17

1. thymocytes, 2. epithelial reticular cells 3. reticular cell of mesenchymal origin (dendritic cells)

Question 18

What are the major functions of the spleen?

Answer 18

1, production of lymphocytes

2. immune response to blood-borne antigens
3. storage of blood (including monocyte reservoir)
4. destruction of old erythrocytes

Question 19

Describe the histological organization of the spleen.

Answer 19

It lacks a cortex and medulla. It has a dense, irregular capsule with red (80%) and white (20%) pulp. plus traberculae arising from capsule. Capsule and trabeculae have small amounts of smooth muscle. Red pulp consist of splenic sinuses and cords.

Question 20

Where do red blood cells get destroyed and stored?

Answer 20

Splenic cords

Question 21

Where in the spleen are lymphatic nodules found?

Answer 21

In the PALS of the white pulp. PALS= periarterial lymphatic sheath, a T dependent area that surrounds central arteries

Question 22

Where is the marginal zone located and what flows through this region? What major function of the spleen is fulfilled here?

Answer 22

This area is located vetween the red and white pulp. Arterial blood flows through this region. Also present includes macrophages, dendritic cells, and lymphocytes.. This is the site of the immune response to blood-borne antigens.

Question 23

Blood flow through the spleen follows the following pattern:

Answer 23

Splenic artery > Trabecular artery > central artery > Penicillar artery > Capillary > Sinuses > Red Pulp vein >Trabecular Vein> Splenic Vein</p>

Question 24

what is th e open circulation theory?

Answer 24

penicillar arteries open into the splenic cords and the blood passes through the space between the cells to reach the sinusoids

Question 25

What is the closed circulation theory?

Answer 25

capillaries open directly into the sinusoids, forming a closed circulation in which the blood always remains inside the vessels.

Question 26

Discuss how the structure of the sinus wall facilitates the free exchange of
material between splenic sinuses and splenic cords

Answer 26

The sinus wall endothelium is made of elongated cells that are porous due to the spaces between them and the gaps in the basement membrane allowing free exchange between sinuses and cords.