Immune III

Question 1

significance of thymus

Answer 1

is the site of T cell differentiation and maturation, removal of self reactive T cells (self tolerance()

Question 2

characteristic of thymus

Answer 2

1. cortex - T lymphocytes, macrophages, epithelial reticular cells
2. medulla - less densely packed differentiated T cells, reticular cells, hassall’s corpuscles
3. NO LYMPHOID NODULES
4. no reticular fibers but YES RETICULAR CELLS
5. mostly adipose in adults

Question 3

primary functions of thymus

Answer 3

1. maturation of T lymphocytes and migrates to paracortex of lymph nodes, periarteriolar lymphatic sheaths in spleen, interfollicular regions peyer patches
2. central tolerance - negative selection (prevents autoimmunity)

Question 4

where are T lymphocytes seen

Answer 4

1. paracortex lymph nodes
2. periarteriolar lymphatic sheaths in spleen
3. interfollicular regions in peyer’s patches

Question 5

embryonic origin of thymus

Answer 5

1. lymphoblasts in bone marrow = MESODERM

2. lymphatic epithelium = ENDODERM OF EMBRYONIC 3RD AND 4TH PHARYNGEAL POUCHES

Question 6

what is DiGeorge syndrome

Answer 6

thymic hypoplasia, severely depressed cell mediated immunity, failure of thymus to develop normally

Question 7

general histology of thymus

Answer 7

1. capsule
2. lobule
3. septa/trabeculae - see a lot of these, look like crypts but way more numerous
4. cortex *no nodules
5. medulla

Question 8

what are hassall’s corpuscles

Answer 8

flattened epithelial reticular cells, arranged concentrically to form a whorl filled with keratin and sometimes calcified

Question 9

cells of the thymic cortex

Answer 9

1. epithelial reticular cells
2. thymocytes
   3, macrophages

Question 10

function of epithelial reticular cells

Answer 10

1. separate cortex from CT capsule and septa
2. ensheath cortical capillaries BLOOD THYMUS BARRIER - GLUT1
3. secrete thymotaxin
4. secrete thymosin, serum thymic factor, thyompoeitin to stimulate T cell maturation

Question 11

what does thymotaxin do

Answer 11

attract precursor T cells from bone marrow to thymus

Question 12

defining characteristic of thymic medulla

Answer 12

hassall’s corpuscle

Question 13

describe epithelial reticular cells in thymic cortex

Answer 13

large, round, euchromatic nuclei with prominent nucleoli , eosinophilic cytoplasm, long cytoplasmic processes linked with desmosomes, invest themselves with endothelium of nonfenestrated capillaries - BLOOD THYMUS BARRIER

Question 14

structures of blood-thymus barrier

Answer 14

1. ERC - epithelial reticular cells and cytoplasmic processes
2. desmosomes
3. nonfenestrated capillary endothelium

Question 15

function of blood-thymus barrier

Answer 15

protect immature lymphocytes from foreign blood borne antigens and self antigens to block immune reaction

Question 16

characteristic of thymic medulla

Answer 16

1. cytoreticulum of ERC
2. differentiated T cells - less densely packed
3. Hassall’s Corpuscles - flattened ERC, whorl

Question 17

function of the spleen

Answer 17

1. filters blood, defense against blood borne pathogens

2. destruction of old RBC, recovers heme to be reused

Question 18

how does the spleen filter the blood

Answer 18

produces Ab and activated lymphocytes, removes microorganisms and inert particles

Question 19

features of spleen

Answer 19

1. dense CT capsule
2. trabeculae into splenic pulp, nerves arteries veins lymph vessels
3. NO CORTEX, NO MEDULLA, NO TRUE LOBULES
4. parenchyma = RBC, lymphocytes, macrophages, blood vessels in reticular cells/fibers

Question 20

composition of white pulp spleen

Answer 20

1. PERIARTERIAL WHITE PULP - mostly B lymphocytes next to PALS
2. PALS periarteriolar lymphoid sheaths OF T CELLS