Lymphoid II

Question 1

How and where do naive lymphocytes enter lymph nodes?

Answer 1

They enter at the HEV through ligand receptor mediated specific surface interactions (with epithelial cells)

Question 2

When activated what do lymphocytes do?

Answer 2

Produce effectors and memory cells

Question 3

What two places might plasma cells mature?

Answer 3

In the lymph nodes or in the periphery

Question 4

In what part of the lymph nodes do plasma cells mature (if they mature in the nodes?)

Answer 4

In the medullary cords

Question 5

How does mature antibody escape the lymph node?

Answer 5

Through the sinuses and into the efferent lymphatic; syllabus only says “eventually to bloodstream”

Question 6

What type of plasma cells mature outside the lymph nodes? What type of cells are they specialized for?

Answer 6

Ones that secrete IgA antibodies; mucosal cells

Question 7

What are some examples of places where plasma IgA cells might go?

Answer 7

mammary and salivary glands

Question 8

What determines migration pattern of plasma cells?

Answer 8

Changes in receptor expression during activation

Question 9

Where do effector T cells disseminate to?

Answer 9

to the periphery, specifically areas where the antigen entered the body

Question 10

what happens to effector T cells during differentiation to affect their dissemination?

Answer 10

they gain receptors for peripheral post capillary venules and vessels in inflammatory sites

Question 11

what path do T cells take when searching for their antigen in the periphery?

Answer 11

through connective tissue and epithelia; if they don’t find their antigen then they proceed back into the lymphatic system going through secondary lymphatic organs

Question 12

What two general types of tissue are found in the spleen

Answer 12

red pulp and white pulp

Question 13

What is the red pulp?

Answer 13

it accounts for most of the tissue and has large amounts of blood

Question 14

What is the white pulp?

Answer 14

Accumulations of lymphoid tissue; stains basophilic in section; taken as a whole it makes up the largest lymphatic organ in the body

Question 15

What does the red pulp do?

Answer 15

filtration - removing foreign matter from the blood
removes organelles from reitculocytes
removes old or damaged erythrocytes

Question 16

Where do you find the marginal zone?

Answer 16

at the border of the white and red pulp

Question 17

which type of lymphatic vessel do you find in the spleen?

Answer 17

efferent lymphatics; because it does not have both, it does not filter lymph

Question 18

What’s special about the vasculature of the spleen?

Answer 18

Open system after capillaries, blood deposited into the extravascular space for filtration

Question 19

Where do you find the Largest vessels in the spleen?

Answer 19

in the connective tissue trabeculae

Question 20

where do you find white pulp in the spleen?

Answer 20

surrounding the central arteries; this is called the periarterial lymphatic sheath (PALS) and contains primarily T cells, but also has dendritic (APC) cells; also contains follicles

Question 21

what do you find in the follicles of the spleen? which type of pulp are they?

Answer 21

white pulp, B cells; these displace the central artery, have germinal centers and are found in less density in the elderly

Question 22

what do you find in the red pulp?

Answer 22

an anastomosing network of venous sinuses

Billroth’s strands (a.k.a. splenic cords)

Question 23

what characteristics of the venous sinuses do we need to know?

Answer 23

basement membranes; endothelial cells are long, plump and aligned parallel to direction of flow

Question 24

what’s special about Billroth’s strands?

Answer 24

reticular connective tissue between sinuses; sort of a web through which blood must flow to reach sinuses, contains macrophages and plasma cells; ALL blood cells go through

Question 25

what comprises the structural support for the spleen?

Answer 25

trabeculae made up of Type I collagen reticular fibers abundant in Billroth's strands and white pulp Note: not found within the blood sinuses (unlike lymphatic sinuses) 2nd note: basal lamina stains black in silver stain as well

Question 26

generally, what is the blood flow through the spleen?

Answer 26

central artery -> penicillar arteries -> very small capillaries -> EV space -> sinuses

Question 27

what is special about penicillar arteries?

Answer 27

they are surrounded by macrophages and plasma cells | found at the marginal zone

Question 28

what happens to the lymphocytes as they enter the EV space?

Answer 28

they are shunted to the white pulp to search for their antigen

Question 29

what special properties does the endothelium of the venous sinuses in the spleen have?

Answer 29

discontinuous basement membrane with thin slits that blood cells must crawl through to reenter circulation; macrophages and neutrophils hover just outside of the endothelium this serves to prevent damaged or old cells from reentering the circulation

Question 30

where do venous sinuses converge?

Answer 30

into the trabculae "central" vein

Question 31

what does collodial carbon reveal in animals?

Answer 31

Billroth's strands

Question 32

what is retrieved from RBC's if consumed by macrophages?

Answer 32

iron

Question 33

what happens to reticulocytes as they near the endothelium in the spleen?

Answer 33

their remaining organelles compressed into a pocket near the plasma membrane and are removed right before entering the circulation

Question 34

what type of organ is the thymus?

Answer 34

primary lymphoid organ

Question 35

what is produced in the thymus?

Answer 35

immunocompetent T cells

Question 36

what's special about the type of environment provided by the thymus (for T cells) and the bone marrow (for B cells)?

Answer 36

they are free of antigens; this means that the cells that they produce are immunocompetent by naive

Question 37

when does the thymus begin to involute? what is the function tissue replaced by?

Answer 37

puberty; fat cells;

Question 38

what is the tissue structure of the thymus?

Answer 38

septa (NOT TRABECULAE) divide the lobes into incomplete lobules; a darkly staining outer cortex and a lighter staining inner medulla, reflects density of lymphocytes

Question 39

what's another name for lymphocytes in the thymus?

Answer 39

thymocytes

Question 40

what do you find in the septa of the thymus?

Answer 40

larger vessels and connective tissue cells including numerous mast cells

Question 41

what provides the fine support structure of the thymus? what else do these cells produce?

Answer 41

highly stellate epithelial cells (epithelial reticular cells); factors essential for proper T cell development

Question 42

where does T cell maturation happen? what's the physical path taken by the T cells?

Answer 42

cortex; exit post capillary venules near the cortico-medullary junction and then migrate to the outer cortex

Question 43

what types of cells do you find in the thymus?

Answer 43

``` epithelial reticular cells thymocytes dendritic cells (at the C-M junction) macrophages Hassal's corpuscle ```

Question 44

what stages do developing T cells go through?

Answer 44

1st: proliferation 2nd: differentiation 3rd: development of specific receptors (antigen and migration control) (controlled by factors from epithelial reticular cells) 4th: selection and autoreactive cells (90% fail and are phagocytosed)

Question 45

how does the thymus limit exposure to antigens?

Answer 45

no afferent lymphatics; blood thymus barrier - composed of continuous tight junctions, zonula occludens, b/w endothelial cells; macrophage security surrounds that; wrapped by reticulocytes (also with zonula occludens)

Question 46

what is special about the medulla of the thymus?

Answer 46

little differentiation happens here composed primarily of epithelial reticular cells (fewer thymocytes) many connective tissue cells (macrophages, mast cells, plasma cells) no blood-thymus barrier here contains round epithelial cysts - Hassal's corpuscles

Question 47

where do you find Hassal's corpuscles?

Answer 47

medulla of the thymus

Question 48

aging effects on thymus?

Answer 48

``` functional decline (fewer T cells being produced) more autoimmune disorder decline in function of APC increase in latent disease activity THEREFORE, vaccinations are more important to the elderly ```

Question 49

DiGeorge Syndrome is associated how?

Answer 49

3rd & 4th pharyngeal pouch malformation that can result in thymus hypoplasia which results in lowered T cell effectiveness and counts