10.11 Thymus

Question 1

Shortly after forming in the bone marrow, T cells migrate to _

Answer 1

Shortly after forming in the bone marrow, T cells migrate to thymus

Question 2

The majority of T cells undergo _ in the thymus

Answer 2

The majority of T cells undergo apoptosis in the thymus
* The thymus is a site of rigorous testing and most T cells don’t meet the standards
* The T cells that pass then leave the thymus and participate in the body’s immune response

Question 3

The thymus is a bilobed, encapsulated organ that is located in the _

Answer 3

The thymus is a bilobed, encapsulated organ that is located in the anterior part of the superior mediastinum

Question 4

The thymus is (in front/ behind) the sternum and (in front/ behind) the heart

Answer 4

The thymus is behind the sternum and in front of the heart

Question 5

The thymus changes colors from grayish-pink to yellow during maturation due to _

Answer 5

The thymus changes colors from grayish-pink to yellow during maturation due to infiltration of fat

Question 6

Describe the structure/ appearance of the thymus

Answer 6

Thymus:
* bilobular
* pyramidal shape
* surrounded by capsule

Question 7

Label the parts of the thymus

Answer 7

Cortex: thin, fibrous outer layer
Medulla: central region
Thymic corpuscles: keratinized epithelial reticular cells

Question 8

Blood comes into the thymus via the _ which is a branch from the internal thoracic artery

Answer 8

Blood comes into the thymus via the thymic artery which is a branch from the internal thoracic artery
* The thymic arteries flow along the interlobular septa and branch off into arterioles and capillaries

Question 9

The thymus is composed mostly of (T cells/ B cells)

Answer 9

The thymus is composed mostly of T cells

Question 10

The (medulla/ cortex) of the thymus appears darker because the T cells are closely packed together

Answer 10

The cortex of the thymus appears darker because the T cells are closely packed together
* Dark-blue basophilic appearance

Question 11

The medulla of the thymus is pale in appearance because it has fewer lymphocytes and more _ cells

Answer 11

The medulla of the thymus is pale in appearance because it has fewer lymphocytes and more epithelial cells

Question 12

Thymic corpuscles are also called _

Answer 12

Thymic corpuscles are also called Hassall corpuscles

Question 13

The _ is responsible for keeping antigens circulating in the bloodstream out of the thymus

Answer 13

The blood-thymus barrier is responsible for keeping antigens circulating in the bloodstream out of the thymus
* Keeps the antigens from disrupting normal T cell selection process in the thymus

Question 14

The blood-thymus barrier consists of two different parts _ (cells) and _ (capillaries)

Answer 14

The blood-thymus barrier consists of two different parts epithelial-reticular cells and thymic cortical capillaries

Question 15

The epithelial-reticular cells in the thymus are connected by _ which provide a net-like scaffolding for the thymus and prevent antigens from getting in

Answer 15

The epithelial-reticular cells in the thymus are connected by tight junctions which provide a net-like scaffolding for the thymus and prevent antigens from getting in

Question 16

The thymic cortical capillaries are (fenestrated/ nonfenestrated)

Answer 16

The thymic cortical capillaries are nonfenestrated so that the capillaries in the blood-thymus barrier are not permeable to antigens

Question 17

Naiive and immature T cells are produced in the _ –>
They then undergo positive and negative selection in the _ –> This makes them mature –>
They can then leave the thymus and bind antigen to become _ T cells or _ T cells

Answer 17

Naiive and immature T cells are produced in the bone marrow –>
They then undergo positive and negative selection in the thymus –> This makes them mature –>
They can then leave the thymus and bind antigen to become effector T cells or memory T cells

Question 18

The thymus produces hormones that facilitates T cell maturation called _

Answer 18

The thymus produces hormones that facilitates T cell maturation called thymosins

Question 19

_ and _ are thymosins that facilitate in T cell maturation in the thymus and play a role in promoting cell migration, angiogenesis, cell survival, stem cell differentiation, and modulation of cytokine production

Answer 19

Thymopoietin and serum thymic factor are thymosins that facilitate in T cell maturation in the thymus and play a role in promoting cell migration, angiogenesis, cell survival, stem cell differentiation, and modulation of cytokine production

Question 20

Fast growing malignancies of the thymus are called _ ; slow growing malignancies of the thymus are called _

Answer 20

Fast growing malignancies of the thymus are called thymomas ; slow growing malignancies of the thymus are called thymic carcinoma
* Half of patients with thymomas have myasthenia gravis

Question 21

_ is a consequence of normal loss of thymic cells that occurs throughout adulthood

Answer 21

Age-related thymic hypoplasia is a consequence of normal loss of thymic cells that occurs throughout adulthood
* We loss about 3% of our thymic cells each year
* Partially explains why older adults have reduced immune function

Question 22

_ is a rare congenital disorder that causes decreased immune response in children; involves failure of thymic development, hypoplasia of the parathyroid glands, and congenital heart disease

Answer 22

DiGeorge syndrome is a rare congenital disorder that causes decreased immune response in children; involves failure of thymic development, hypoplasia of the parathyroid glands, and congenital heart disease
* Some children develop low T cell counts
* Severe recurrent lung and sinus infections
* Sometimes need stem cell transplantation/ thymic transplantation