Lymphoid Organs Flashcards
- Describe the morphological characteristics of mesenchymal reticular cells.
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
What is function of reticular cell and its origin?
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)
Describe the structure of 3 basic types of Lymphoid Tissue
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
Describe a germinal center
- 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
Describe the flow of lymph through a lymph node
Blood>afferent lymphatic vessels >subscapular sinus> trabecular sinus >medullary sinus> hilum- efferent> blood via thoracic duct
What is function of High Post-Capillary Venules
High Endothelial Venules bring lymph back to nodes via cell adhesion molecules
Which regions of lymph nodes are T dependent?
The paracortical zone aka deep zone is T-dependent
What are the key molecules in Homing?
selectins, integrins, immunoglobulin super family, carbohydrates
Where can HEVs be seen?
Lymph nodes, tonsils, Peyer’s Patches
What kind of tissue is in the medulla of lymph nodes?
dense lymphoid tissue
What kind of tissue is in medullary sinus?
loose lymphoid tissue
Tissue of trabeculae of lymph is…
Connective
Capsule of lymph is made of…
dense irregular connective tissue
What are the three functions of lymph nodes?
- Production of B lymphocytes
- Filtration of Lymph
- Play role in the immune response to lymph-borne antigens
To which lymphoid organ does the cytoreticulum belong? What is its function?
Cytoreticulum of the thymus gland forms a supporting framework for thymal epithelial reticular cells that allow secretion.
The major functions of the thymus are.
- T- lymphocyte development 2. development of the lymphoid system - other lymphoid organs
What are the three major cell types in thymus?
- thymocytes, 2. epithelial reticular cells 3. reticular cell of mesenchymal origin (dendritic cells)
What are the major functions of the spleen?
1, production of lymphocytes
- immune response to blood-borne antigens
- storage of blood (including monocyte reservoir)
- destruction of old erythrocytes
Describe the histological organization of the spleen.
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.
Where do red blood cells get destroyed and stored?
Splenic cords
Where in the spleen are lymphatic nodules found?
In the PALS of the white pulp. PALS= periarterial lymphatic sheath, a T dependent area that surrounds central arteries
Where is the marginal zone located and what flows through this region? What major function of the spleen is fulfilled here?
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.
Blood flow through the spleen follows the following pattern:
Splenic artery > Trabecular artery > central artery > Penicillar artery > Capillary > Sinuses > Red Pulp vein >Trabecular Vein> Splenic Vein</p>
what is th e open circulation theory?
penicillar arteries open into the splenic cords and the blood passes through the space between the cells to reach the sinusoids
What is the closed circulation theory?
capillaries open directly into the sinusoids, forming a closed circulation in which the blood always remains inside the vessels.
Discuss how the structure of the sinus wall facilitates the free exchange of
material between splenic sinuses and splenic cords
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.
