10/20 Lymphoid Histology

Question 1

what is a primary lymphoid structure

Answer 1

where B (bone marrow) and T (thymus) cells become immunocompetent, specific to one antigen
migrate in blood to secondary lymphoid structures

Question 2

what is a secondary lymphoid structure

Answer 2

site where a foreign antigen is captured
immune response is mounted to trap and destroy antigen
actions: lymphocyte proliferation, B cell differentiation into plasma cells and then secrete of antibodies

Question 3

examples of secondary lymphatic structures

Answer 3

MALT (mucus-associated lymphatic tissue)
tonsils
lymph nodes
spleen

Question 4

cells/fibers found in secondary lymphatic structures

Answer 4

macrophages
dendritic cells
reticular cells and fibers

Question 5

what type of collagen is in reticular fibers

Answer 5

Type III

Question 6

what type of tissue is stroma

Answer 6

dense irregular CT

Question 7

what is the septa/trabeculae of lymphatic tissue

Answer 7

dense irregular CT, extends inward from capsule

Question 8

what lymphatic structure does NOT have reticular fibers

Answer 8

thymus

Question 9

fxn of reticular fibers

Answer 9

support lymphocytes

Question 10

three types of organization in lymphatic system

Answer 10

cortex/medulla
lymphoid nodules
white/red pulp

Question 11

what cells help t cells differentiate, and where are they located

Answer 11

epithelioreticular

all parts of the thymus

Question 12

how does the cortex of the thymus stain and why

Answer 12

dark staining

t cells are small and densly packed

Question 13

how does the medulla of the thymus stain and why

Answer 13

lighter

t cells are large and less densly packed

Question 14

what structure is unique to the thymus (specifically the medulla)

Answer 14

Hassall’s/thymic corpsucles, concentrically packed epithelioreticular cells, keratinized

Question 15

thymus degeneration

Answer 15

puberty to age 25
parenchyma replaced by adipose tissue
t cell proliferation and differentiate decreases

Question 16

failure of negative selction to occur can result in what

Answer 16

autoimmune conditions

Question 17

two types of selection during t cell differentiation

Answer 17

positive (failure to differentiate from lymphocytes in cortex)
negative (failure to further differentiate properly in medulla)

Question 18

what happens if the thymus is removed in early embryonic development

Answer 18

impaired cell-mediated immunity

Question 19

MALT

Answer 19

mucus associated lymphatic tissue
80% of lymphatic tissue
multiple types: diffuse lymphoid tissue, isolated lymphoid nodules, tonsils

Question 20

diffuse lymphoid tissues

Answer 20

lymphocytes and plasma cells diffusely arranged in LP

Question 21

isolated lymphoid nodules

Answer 21

transient, primary or secondary, in secondary: more b cells than t cells esp in germinal center

Question 22

tonsils

Answer 22

capture/mount immune response against antigens from mouth and nose

palatine
adenoids/pharyngeal
lingual

Question 23

why do tonsils easily become inflammed or infected

Answer 23

no clear border between epithelium and parenchyma

Question 24

fxn of lymph nodes

Answer 24

trap and destroy foreign antigens and particulate matter in lymph, recirculation of lymphocytes

Question 25

stroma of lymph nodes

Answer 25

capsule, septa, reticular fibers

Question 26

parenchyma of lymph nodes

Answer 26

cortex and medulla

Question 27

outer cortex of lymph nodes

Answer 27

lymphoid nodules, b cells, plasma cells, macrophages

Question 28

paracortex of lymph nodes

Answer 28

t cells, lymphoid tissue

Question 29

medullary cord of lymph nodes

Answer 29

b cells, plasma cells, macrophages

Question 30

medullary sinus of lymph nodes

Answer 30

spaces lined by epithelium that seperates medullary cords

Question 31

lymphatic flow in circulation

Answer 31

``` lymphatic capillaries (blind) larger lymphatic vessels lymph nodes even larger lymphatic vessels thoracic duct L internal jugular v ```

Question 32

lymph node flow

Answer 32

``` afferant lymphatic vessel cortical vessel trabecular sinus medullary sinus efferent medullary sinus (hilum) ---- lymphatic vessel ```

Question 33

how do lymphocytes enter lymph nodes

Answer 33

HEVs then diapedesis

Question 34

fxn of spleen

Answer 34

trap and destroy particulate matter/foreign antigens in blood hematopoesis during fetal life removes and phagocytoses damaged/old RBCs and platelets

Question 35

stroma of spleen

Answer 35

myofibroblasts mesothelium speta reticular fibers

Question 36

parenchyma of spleen

Answer 36

white pulp and red pulp

Question 37

white pulp

Answer 37

lymphatic tissue periarterial lymphatic sheath (PALS) surrounding central artery is rich in t cells splenic nodule, secondary lymphatic nodule, b cells marginal zone is white pulp

Question 38

red pulp

Answer 38

rich in RBCs splenic cords splenic sinuses: sinusoids

Question 39

blood flow in spleen

Answer 39

splenic a trabecular a central a blind capillaries deposit blood into red pulp (open system of circulation)

Question 40

Splenomegaly

Answer 40

enlargement of spleen due to infection, lymphoma, anemia susceptible to rupture due to relatively thin capsule, can be fatal due to bleeding into the abdominal cavity. Spleen may have to be removed

Question 41

consequences of splenectomy

Answer 41

Bone marrow and liver take over its role in removing RBCs from circulation High susceptibility to bacterial infections