MI 04a: Histology

Question 1

Thymus develops from (X) cells, derived from (Y), as well as from underlying (Z).

Answer 1

X = epithelial
Y = endoderm
Z = mesenchyme

Question 2

Epithelial reticulum (cytoreticulum) forms when cells of (X) spread apart, but remain connected via (Y).

Answer 2

X = epithelial cords
Y = desmosomes

Question 3

List the basic functions of epithelioreticular cells in (X) organ.

Answer 3

X = thymus

1. Stromal support
2. Barrier
3. Developmental support
4. Endocrine function
5. Hassall’s corpuscles

Question 4

What’s unique about the stroma of the thymus?

Answer 4

No reticular fibers; made up of cytoreticulum (stellate cells, linked via desmosomes)

Question 5

Blood-thymus barrier formed by (X) cells that envelop (Y) in (Z) part of thymus.

Answer 5

X = epithelioreticular
Y = continuous capillaries
Z = cortex

Question 6

(X) cells monitor development of thymocytes in thymus and play key role in selecting the useful thymocytes.

Answer 6

X = thymic nurse cells

Question 7

Thymic (X) cells secrete peptides that serve (paracrine/autocrine/endocrine) functions. How do these affect thymocytes?

Answer 7

X = hormone-secreting;
Paracrine and endocrine;

1. Differentiation
2. Expression of surface molecules

Question 8

Hassall’s corpuscles are characteristic of (X) part of (Y) organ. They’re composed of (round/flat) (Z) cells.

Answer 8

X = medulla
Y = thymus
Flat;
Z = epithelioreticular

Question 9

Thymocyte precursors migrate from (X) to thymus via (Y). What attracts them to thymus?

Answer 9

X = bone marrow
Y = systemic circulation

Thymotaxic factors (secreted by epithelioreticular cells)

Question 10

In thymus, precursors begin proliferation/differentiation in (X) and get progressively displaced (inward/outward) toward (Y).

Answer 10

X = cortex
Inward;
Y = medulla

Question 11

Only developing thymocytes with which characteristics survive selection?

Answer 11

Bind weakly to self-MHC molecules, but NOT autoreactive

Question 12

Surviving thymocytes enter (X) of thymus as (Y) cells.

Answer 12

X = medulla
Y = mature, naive T lymphocyte

Question 13

GALT found in (X). BALT found in (Y). CALT found in (Z).

Answer 13

X = gut
Y = bronci/trachea
Z = cutaneous tissue (dermis/epidermis)

Question 14

(X) tissue overlying MALT is modified and contains special cells, depending on location of the MALT. Give examples.

Answer 14

X = epithelial

1. M cells (GI tract)
2. Langerhans cells (epidermis)

Question 15

M cells are a type of (X) cells in (Y) location with (Z) function.

Answer 15

X = epithlial (modified)
Y = GI tract (overlying MALT)
Z = antigen-transport

Question 16

Langerhans cells are a type of (X) cells in (Y) location with (Z) function.

Answer 16

X = Dendritic (modified epithlium)
Y = epidermis (overlying MALT)
Z = antigen presenting

Question 17

In which type of epithelial structure would you find reticulated epithlium? What’s the purpose?

Answer 17

Stratified squamous (note: simple columnar epithlia don’t need this modification)

Modified with channels to allow passage of lymphocytes

Question 18

T/F: MALT has well-defined capsule.

Answer 18

False

Question 19

T/F: MALT has efferent lymphatic vessels.

Answer 19

True

Question 20

T/F: MALT has afferent lymphatic vessels.

Answer 20

False

Question 21

Lymphocytes leave MALT via (X).

Answer 21

X = efferent lymphatic vessels

Question 22

T/F: HEV found in all MALT and lymph nodes.

Answer 22

True

Question 23

HEV are special (X), whose walls are lined by (Y).

Answer 23

X = post-capillary venules
Y = unusual endothelial cells

Question 24

Function of HEV is to:

Answer 24

1. Bind lymphocytes (slow their flow)
2. Separate them from blood
3. Allow their migration (through wall) into specific lymph tissue

Question 25

Aside from lymphocytes, which cells/substances pass through HEV?

Answer 25

1. Macrophages | 2. Tissue fluid (draining out into circulation)

Question 26

Stroma of lymph nodes is composed of:

Answer 26

1. Reticular fibers (collagen type III) 2. Reticular cells 3. Endothelial cells and macrophages

Question 27

Macrophages in stroma of lymph node has which functions?

Answer 27

1. Phagocyte 2. APC 3. Contributes growth factors (supplements cytokine production by lymphocytes)

Question 28

Abs produced by plasma cells in medulla is released into (X), from which it passes out of lymph node via (Y).

Answer 28

``` X = medullary sinus Y = efferent lymphatics ```

Question 29

T cells in lymph node proliferate in which part of organ?

Answer 29

Paracortex

Question 30

Blood vessels are distributed in (X) part of lymph node, after entering and exiting at the organ's (Y).

Answer 30

``` X = cortex Y = hilus ```

Question 31

Where might you find HEV in lymph node?

Answer 31

Interfollicular area and in deep paracortex

Question 32

B and T cells enter lymph node via:

Answer 32

HEV

Question 33

Most lymphocytes leaving lymph nodes are (X) cells that (have/haven't) encountered antigen.

Answer 33

X = naive | Haven't

Question 34

Largest lymphoid organ in body.

Answer 34

Spleen

Question 35

Two key functions of spleen

Answer 35

1. Monitor blood/respond to blood-borne antigens | 2. Destruction of ineffective RBC/platelets

Question 36

(X) are encased by white pulp of spleen. What's the white pulp composed of?

Answer 36

X = central arteries; 1. PALS (T-cells) 2. Splenic follicles: marginal zone (macrophages and splenic sinuses) and germinal center (B cells)

Question 37

List pathway of closed circulation in spleen.

Answer 37

1. Trabecular artery 2. Central artery 3. Radial artery 4. Splenic sinus 5. Trabecular vein

Question 38

Red pulp of spleen composed of:

Answer 38

1. Splenic sinus | 2. Splenic cord (cords of BIllroth)

Question 39

List pathway of open circulation in spleen.

Answer 39

1. Trabecular artery 2. Central artery 3. Radial artery 4. Splenic cord (cord of Billroth) 5. Splenic sinus 6. Trabecular vein

Question 40

Most arterial blood flows through (open/closed) circulation of spleen. It's a (shorter/longer), (slower/faster) path.

Answer 40

Closed; | Shorter, faster

Question 41

The reason the open circulation of spleen exists is that (X) and (Y) are major sites for (Z).

Answer 41

``` X = sheathed capillaries (sheath of macrophages) Y = splenic cords Z = clearance of cell debris and old blood cells ```

Question 42

In spleen, atypical, elongate endothelial cells, called (X) cells, line (Y) and rest on encircling bands of (Z).

Answer 42

``` X = stave Y = splenic sinus Z = reticular fibers ```

Question 43

Blood cell monitoring in spleen: blood cells in (X) must traverse longitudinal interendothelial slits in order to reach (Y). Aged/inflexible/damaged RBCs have difficult time doing this.

Answer 43

``` X = splenic cord Y = splenic sinus lumen ```