Flashcards in Chapter Three - Thymus & Spleen Deck (70)
Is the thymus a primary or secondary lymphoid organ?
At what age do we see that little functioning of the thymus is left?
About 25 years of age
Is the thymus larger in a child or an adult?
When does involution of the thymus begin?
What is the pattern of the involution process of the thymus?
1st - septa
2nd - cortex
3rd - medulla
What is the important function of the thymus?
Establish immunocompetent T cells
What two steps are involved in the thymus establishing immunocompetent T cells?
Being able to distinguish self from non self antigens and to develop self-tolerance
What is a thymocyte?
T lymphoblast in the thymus
What makes up the thin capsule of the thymus?
Dense irregular connective tissue
What makes up the lobules of the thymus?
Peripheral cortex and a central medulla
What is the term for the support tissue of the thymus?
What makes up the stroma of the thymus?
Capsule, septa, adipose, microstroma
What is the microstroma of the thymus?
Thymic epithelial cells (TECs)
What is another name for thymic epithelial cells?
Epithelioreticular cells or epithelial reticular cells
How many types of TECs are there?
What are the functions of the thymic epithelial cells?
Support using cytoplasmic processes (NOT reticular fibers), secrete thymic hormones and cytokines, form thymic corpuscles (Hassall's bodies), important component to the blood-thymic barrier, function as an APC
What are the functions of the hormones and cytokines that can be secreted by TECs?
Influence T cell maturation, division, and activities (immunity elsewhere in the body too)
What type of TEC are the thymic corpuscles (Hassell's bodies)?
Where can thymic corpuscles be found?
In the medulla
What is the function of the thymic corpuscles?
Secrete cytokines to influence local dendritic cells and the development of some T cells
What type of TEC is found in the blood-thymic barrier?
TEC type I
What makes up the perivascular component of the blood-thymic barrier?
Connective tissue with many macrophage to destroy foreign molecules
What is the function of the blood-thymic barrier?
To prevent T cells from physically contacting foreign antigens
What part of the thymus contains a high cell concentration?
What cells make up the cortex of the thymus?
T lymphocytes, macrophages, TEC types I, II, and III
What part of the thymus contains a lower cell density?
Where are T lymphoblasts produced?
What cell types are found in the medulla of the thymus?
Fewer but large T cells, macrophages, dendritic cells (APC), and TEC types IV, V, and VI
When the T lymphocytes first enter the thymus, are they immunocompetent?
No; they are immunoINcompetent