Thymus

Question 1

_____ is a primary lymphoid organ with an endocrine function?

Answer 1

thymus

Question 2

what is the site of thymus?

Answer 2

in the thoracic cavity behind the sternum .

Question 3

brief note on the size of the thymus.

Answer 3

the size of the thymus varies greatly with age . it starts to increase in size till puberty and then undergoes atrophy ( i.e. decrease in size ) after puberty but continues to produce lymphocytes.

Question 4

in thymus the capsule sends __ __ trabeculae that ____ subdivide the lobes into large number of lobules.

Answer 4

thin incomplete ; incompletely

Question 5

the outer part of the cortex contains ___ while the inner part contains ___ ( ___ )

Answer 5

lymphoblasts ; lymphocytes ( thymocytes )

Question 6

hassall’s corpuscles are present in which organ?

Answer 6

thymus

Question 7

hassall’s corpuscles are ___ structures .

Answer 7

acidophilic

Question 8

clarify the relation between age and the number of hassall’s corpuscles present in the thymus.

Answer 8

their number increases with age .

Question 9

the main cell types in both cortex and medulla are?

Answer 9

1. epethelial reticular cells
2. T - lymphocytes
3. macrophages

Question 10

origin of epethelial reticular cells and T - Lymphocytes

Answer 10

endoderm and mesodermal respectively

Question 11

write a note on functions of epithelial reticular cells in the thymus .

Answer 11

1. The nursing cells for lymphocytes during their differentiation. They form sheets to isolate the developing lymphocytes in the cortex from contact with antigens while they’re programmed.
2. They secrete thymic hormones & thymic factors which promotes T- cell differentiation and proliferation.

Question 12

explain the process undergone to form T - Lymphocytes.

Answer 12

stem cells ( formed in BM & travel to the thymus) > as lymphoblasts ( divide ) > small lymphocytes ( differentiate ) > thymocytes ( mature and undergo thymic education ) > T - cell markers .

Question 13

how do t - lymphocytes undergo elimination process?

Answer 13

1. elimination of non - functioning lymphocytes ( 80 % )
2. elimination of thymocytes that bind to self-antigen causing autoimmune disease.
3. the eliminated thymocytes die by apoptosis and are eliminated by macrophages.
4. some of the functioning thymocytes migrate to the medulla to 2ry lymphatic organs ( lymph nodes and spleen ) where they settle in the thymus dependant zone.

Question 14

the epethelial reticular cells of thymus do not produce ____ ?

Answer 14

reticular fibres

Question 15

one of the special features of thymus is that it has no ____ , ____ , ____ , ___ & ____.

Answer 15

no lymphoid nodules , no large lymphocytes , no B - lymphocytes , no plasma cells and no afferent lymphatic vessels.

Question 16

what is the wall which separates the developing t - lymphocytes in the cortex from the antigens in the circulating blood.

Answer 16

the blood thymic barrier

Question 17

______ does not possess a blood thymic barrier and absence of ____ in the thymus protects it also from circulating antigens.

Answer 17

medulla ; afferent lymphatics.

Question 18

functions of the thymus.

Answer 18

1. T - Lymphocytes proliferation and differentiation .

2. Thymic hormones secretion by reticular epithelial cells which stimulates maturation and activity of T - Lymphocytes.

Question 19

multiplication of helper & suppressor T - Lymphocytes is controlled by?

Answer 19

thymic humoral factor

Question 20

production T - cytotoxic cells is stimulated by?

Answer 20

thymopoietin

Question 21

lymphocyte production is stimulated by?

Answer 21

thymosin

Question 22

______ enhances the functions of various types of T - cells , especially suppressor cells

Answer 22

thymulin