Thymus Flashcards
Production of B lymphocytes occurs primarily in the ____. Production of T lymphocytes occurs primarily in the ____.
Bone Marrow
Thymus
Carrying out immune responses generally occurs in ____.
Secondary lymphoid organs and lymphoid tissue
Examples of secondary lymphoid organs
lymph nodes
spleen
tonsils
MALT
mucosa-associated lymphoid tissue
In hollow organs lymphoid tissue is most often found in the layer called the _____.
Lamina propria
GALT
gut associated lymphoid tissue
Daughter cells differentiate into ____ and _____ .
Effector cells
Memory cells
Thymus begins to develop at about the ___ week of gestation.
5th
Thymus develops from the endodermal epithelium of the ___________.
3rd pharyngeal pouch
Where does the thymus fuse across?
The midline in the thorax
Thymus is initially composed of only _______ called _______.
Epithelial cells
Thymic Epithelial Cells (TECs)
TECs are connected by ______.
desmosomes
Capusle of Thymus is made up of ______.
Denser irregular CT with collagen 1 and reticular fibers
Where thymocyte precursors enter the thymus.
Corticomedullary boundary
Where thymocytes leave the thymus
via postcapillary venules at the corticomedullary junction OR via lymphatics
the blood-thymus barrier in the cortex consists of:
- capillary endothelial cells
- basal lamina of endothelial cells
- A perivascular space containing CT cells and fibers
- basal lamina of the TECs
- A continuous layer of Type 1 TECs joined by tight junctions
blood-thymus barrier is _______ in the medulla
leakier
Positive selection occurs in the _____
cortex
Negative selection occurs mainly in the _____
medulla
What identifies TECs as epithelial cells rather than connective tissue cells?
tonofibrils composed of cytokeratin
TEC secreted cytokine that induces thymocyte division
TECK and SDF-1
Type 5 TECs form ____ corpuscles in the medulla
Hassall’s
Cortical TECs
Type 1
Type 2 (nurse cells)
Type 3
Medullary TECs
Type 4
Type 5
Type 6
