20.6 T lymphocytes mature in the thymus

What is the thymus?

a primary lymphoid organ where T lymphocytes mature

What is main function of the thymus?

maturation of T lymphocytes

What does “immunicompetent” mean?

able to recognize and defend against specific antigens

Where is the thymus located?

•inferior neck

•superior thorax

•deep to the sternum

•partially overlies the heart

What is the shape of the thymus?

bilobed

The thymus is most prominent during what stage of life?

infancy and childhood

When is the thymus most active?

during childhood

What happens to the thymus after puberty?

it gradually atrophies

What replaces much of the thymus in old age?

•fatty tissue

•fibrous tissue

Does the thymus completely stop functioning in adults?

NO, it continues producing T cells at a reduced rate

What structural unit make up the thymus?

thymic lobules

What vegetable is often used to describe the thymus organization?

cauliflower

Which region is the outer portion of a thymic lobule?

cortex

What cells dominate the cortex?

rapidly dividing T lymphocytes

Are lymphocytes densely packed or sparse in the cortex?

densely packed W

Which immune cell is scattered among cortical lymphocytes?

macrophages

Which regions is the inner portion of a thymic lobule?

medulla

Does the medulla contain more or fewer lymphocytes than the cortex?

fewer

What unique structure are found in the thymic medulla?

thymic corpuscles

What are thymic corpuscles?

concentric whorls of keratinized epithelial cells

Where are thymic corpuscles found?

medulla of the thymus

Function of the thymic corpuscles?

help develop regulatory T cells

Why are regulatory T cells important?

prevent autoimmune responses

Why does the thymus lack follicles?

it lacks B cells

Does the thymus directly fight antigens?

NO

What is the thymus’ role regarding antigens?

maturation only

Why must developing T cells be isolated from antigens?

to prevent premature activation

What type of stroma does the thymus contain?

epithelial tissue

What type of stroma do most other lymphoid organs contain?

reticular connective tissue

What is the blood-thymus barrier?

barrier that prevents bloodborne antigens from entering the thymus

Why is the blood-thymus barrier important?

protects developing T cells from premature exposure to antigens