Immune and lymphatic system II Flashcards
Composition of Thymus
- Capsule
- Trabeculae
- Lobules
Composition of the Capsule of the Thymus
-Blood vessels
- Efferent lymphatics are present
—– NO AFFERENT LYMPHATICS PRESENT——
(therefore lymph does not circulate through the thymus)
- Extends Trabeculae (septa) into the parenchyma
Does the thymus contain afferent lymphatics
NO!!!!! (lymph does not circulate through the thymus)
The Trabeculae (Septa) of the thymus is composed of
delicate CT
What divides the thymus into incomplete lobules
Trabeculae (septa)
What is the function of the Trabeculae (septa) of the thymus
divides the thymus into incomplete lobules
Each lobule of the thymus is composed of
an outer, darker staining cortex and an inner, lighter staining medulla
The cortex of each lobule of the thymus is _____ staining
Dark
The cortex of thymus lobules stains densely with
basic dyes such as H and E
What is the cell population of the cortex of the thymus lobules
- Epithelial reticular cells, which secrete thymosin
- T cells in various stages of differentiation
Epithelial reticular cells in the cortex of thymus lobules secrete
Thymosin
Thymocytes (hematopoietic progenitor cells of the thymus) migrate from _____ to _____ areas
cortical areas to medullary areas
Blood vessels surrounded by continuous epithelial barrier in the thymus allows for
the thymus to maintain lymphopoiesis while segregated from antigens
The medulla of thymus lobules is ____ staining
light
The medulla of the thymus lobules is specialized to allow
entry channel into blood stream of mature lymphocytes
Capillary beds in the medulla of lobules in the thymus are
not sheathed by epithelial cells
Where are Hassall’s corpuscles found
in the medulla of thymus lobules
Whorls of highly keratinized medullary epithelial cells
Hassall’s corpuscles
Hassall’s corpuscles produce
cytokine thymic stromal lymphopoietin
What is the function of cytokine thymus stream lymphopoietin
stimulates thymic dendritic cells needed for the maturation of single positive T cells
The thymus is most developed at
puberty
At birth the thymus weighs
10-15 grams
at puberty the thymus weighs
30-40 grams
The thymus involutes during
adolescence
The thymus has no
lymph follicles (nodules)
No afferent lymph vessels
no lymph sinuses
Double negative T cells
- Lack cell surface molecules typical of mature T cells
- enter cortex from blood vessels
- proliferate in subcapsular area
Double negative T cells proliferate in
subcapsular area of the thymus
Double negative T cells enter the cortex of the thymus
from blood vessels
Double negative T Cells lack
cell surface molecules typical of mature T cells
Double positive T cells move to
outer cortex of thymus
Double positive T cells are confronted with _________ for ____ selection
epithelial cells with cell surface MHC classes I and II for clonal selection
Double positive T cells express
CD4 and CD8 coreceptors and TCR receptors
Single positive T cells move to the
inner cortex of the thymus
Single positive T cells express
TCR receptors and either CD4 or CD8 coreceptors
Clonal deletion is completed in the
medulla of the thymus lobules
What is the purpose of clonal deletion
to protect from autoimmune disease
