Lymphoid System Flashcards
What are the two major types of lymphocytes and their associated immunological responses?
T-Lymphocytes- Cell-mediated immunity
B-Lymphocytes- humoral immunity (B-cells differentiate into plasma cells and secrete antibodies)
Lymphocytes are “recirculating, Immunocompetent” cells. What does this mean?
Recirculating- travel through blood/lymphatic vessels and lymphoid tissue.
Immunocompetent- Ability to recognize a single foreign antigen
Recirculation ensures that the “correct” immunocompetent lymphocytes will detect an antigen, regardless of location of infection.
What’s the difference in Primary and secondary lymphoid tissue?
Primary- lymphocytes differentiate into T&B cells
Secondary- Foreign antigens are captured/controlled here. (Positioned near common sites of foreign antigen presence)
Where do T-cells mature?
Thymus
Where do B-cells mature?
Bone Marrow
Areas of loose connective tissue where large members of lymphocytes and plasma cells are present are called?
Diffuse Lymphatic Tissue
What are some common locations of diffuse lymphatic tissue?
Digestive, Respiratory, Urogenital tracts
If a foreign antigen gets past the epithelium of the digestive system, where will lymphocytes intercept it?
Lamina Propria immediately deep to the epithelium
A discrete concentration of lymphocytes contained in a meshwork of reticular cells is called?
An Isolated lymphatic nodule/follice
Where are isolated lymphatic nodules generally located?
Digestive, Respiratory, Urogenital tracts
What are the 2 types of isolated lymphatic nodules?
Primary lymphatic nodule- oval accumulations of small lymphocytes beneath the epithelium.
Secondary lymphatic nodule- Lighter central region with large lymphocytes (mostly Bcells) and dark outer region of small lymphocytes
When do secondary lymphatic nodules form?
After antigen exposure - location of immune response (high B-cell concentration = more antibody secretion)
What are PERMANENT aggregates of lymphoid nodules called?
Aggregated lymphoid nodules.
Examples: Peyer’s Patches/Appendix, tonsils,
Where are Peyer’s Patches located?
Ileum, on ONE SIDE of intestinal wall.
What does MALT stand for?
Mucosal Associated Lymphoid Tissue. Constitutes 85% of lymphoid tissue in the body, because mucosa are the most common site of entry for microorganisms.
What permanent aggregated lymphoid structures capture and mount immune responses to antigens entering through the mouth and nose?
Tonsils
Name the 3 kinds of tonsils.
1) Pharyngeal- roof of pharynx
2) Palatine (“the tonsils”) - either side of pharynx
3) Lingual- base of tongue
What type of epithelium lines the tonsils? (think mucosa)
Non-keratinized stratified squamous epithelium
Why do tonsils become infected easily?
Deep crypts- no clear border between epithelium and parenchyma
What is the stroma and parenchyma of a lymphoid organ?
Stroma- supporting framework (generally CT/reticular fibers)
Parenchyma - functional part of an organ
Lymphoid nodules generally contain which 3 types of cells?
B-cells, Plasma Cells, and Macrophages
In lymph nodes, where are B-cells located?
Outer cortex in nodules
In lymph nodes, where are T-cells located?
Paracortex
How do lymphocytes get into the lymph nodes?
Postcapillary venules inside lymph node are lined with HIGH CUBOIDAL CELLS which have surface receptors that specifically recognize lymphocytes.
These venules are more specifically called HEVs (high endothelial venules)
The spleen parenchyma contains white and red pulp. What is the difference?
White pulp: lymphatic tissue
Red pulp: RBCs
Splenic lymphatic nodules are also called:
Malpighian corpuscles
Explain the open circulation of the spleen.
The splenic artery enters the spleen and sends branches out into the trabeculae (dense irregular CT from stroma). Once in the parenchyma, the artery is called the central artery. Central artery is surrounded by white pulp - periarterial lymphatic sheath, and splenic lymph nodules. Central artery runs into red pulp, etc etc… and they end blindly in the red pulp, dumping the blood into the spleen.
How does blood exit the spleen?
Blood contents are dumped into splenic tissue, and RBCs re-enter circulation through VENOUS SINSUSES by squeezing through the elongated epithelial cells. Only healthy RBCs can get through, and macrophages pick out impurities.
In the spleen, where are the T-cells? B cells?
T-cells are in the periarterial lymphatic sheath surrounding the central artery.
B-cells are in the splenic lymphoid nodules
WTF is a cord of Billroth?
Strands of lymphatic tissue in the red pulp.
What are the functions of the spleen?
1- Trap and mount immune responses against blood antigens.
2- Remove and phagocytose old RBCs and platelets
3- Remove iron from Hemoglobin and store it.
4- Hematopoeisis of FETUS
If the spleen is removed, what takes over its role of removing damaged RBCS from the bloodstream?
Bone Marrow
Where to T-cells develop?
Thymus
What does the Thymus have instead of nodules?
Lobules
What provides the structural framework for the Thymus?
Epithloireticular cells - form a continuous epithelium but are pushed aside as thymus develops. Retain their desmosomal junctions and their processes support the structure of the Thymus.
Do epithelioreticular cells secrete reticular fibers?
No.
What DO ecpithelioreticular cells secrete?
Soluble factors that promote T -cell differentiation.
Differentiated T-cells are located in what part of the Thymus?
medulla
