Histology of the Lymphoreticular System

Question 1

What are the organs of the lymphoreticular system?

Answer 1

Thymus, lymph node, mucosa-associated lymphoid tissue (MALT), spleen

Question 2

The immune system provides highly specific responses to what specifically?

Answer 2

To antigens with the destruction of the antigen

Question 3

What was the original definition of an antigen?

Answer 3

Any molecule that binds specifically to an antibody

Question 4

What does the term antigen now also refer to?

Answer 4

Any molecule or molecular fragment that can be bound by a major histocompatability complex (MHC) and presented to a T helper cell

Question 5

What is the function of a MHC - major histocompatability complex?

Answer 5

The function of MHC molecules is to bind peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T cells.

Question 6

What are the the types of lymphocytes?

Answer 6

B lymphocytes and t lymphocytes

Question 7

What is the function of the b lymphocytes?

Answer 7

To produce antibodies

Question 8

What is the function of the t lymphocytes?

Answer 8

They have several subtypes and act as suppressor cells, cytotoxic cells and helper cells

Question 9

What are antigen presenting cells?

Answer 9

They include macrophages and the b lymphocytes control the activation of the t cells. An antigen-presenting cell is a cell that displays antigen complexed with major histocompatibility complexes (MHCs) on their surfaces

Question 10

Why are the b lymphocytes called b lymphocytes?

Answer 10

Because they are formed from a stem cell, into a pre-b cell and the pre-b cell matures into a fully functional b cell in the red bone marrow

Question 11

Why are the t lymphocytes called t lymphocytes?

Answer 11

Because they are formed from a stem cell into a pre t cell in the red bone marrow. but then the pre-t cell matures into a fully functional t cell in the thymus

Question 12

Roughly what percentage of white blood cells in circulation are lymphocytes?

Answer 12

20-50%

Question 13

The number of lymphocytes in circulation increase in response to what?

Answer 13

In response to a viral infection

Question 14

How would you describe lymphocytes under a microscope

Answer 14

they have a round/oval nuclei with dense chromatin and nucleoli which are not usually visible and often very little cytoplasm

Question 15

How does the size of a lymphocyte compare to the size of red blood cells?

Answer 15

red blood cells are about 7 microns in diameter - about the size of a lymphocyte nucleus

Question 16

What are the two types of lymphocytes?

Answer 16

t and b

Question 17

what are the three types of t lymphocyte?

Answer 17

t helper cells, cytotoxic t cells and suppressor t cells

Question 18

what do t helper cells do

Answer 18

they help other lymphocytes perform functions

Question 19

what do cytotoxic t cells do

Answer 19

they kill virally infected and malignant cells

Question 20

what do suppressor t cells do

Answer 20

they switch off the immune system when the stimulating antigen is removed

Question 21

what do b lymphocytes do

Answer 21

they produce antibodies following maturation to plasma cells

Question 22

what is a plasma cell

Answer 22

a fully differentiated B-lymphocyte (white blood cell) which produces a single type of antibody.

Question 23

what types of cells are included in the antigen presenting cells category

Answer 23

macrophage monocyte type cells and dendritic cells

Question 24

what do antigen presenting cells do?

Answer 24

the antigen is taken up by the apc and processed. processed antigen is then bound to a major histocompatability complex and the mhc-peptide complex is exposed to the outside world

Question 25

how would you describe the dendritic cell morphology

Answer 25

finger like projections

Question 26

what are the four organs of the lymphoid system

Answer 26

thymus, lymph nodes, mucosa-associated lymphoid tissue, spleen

Question 27

what is the thymus

Answer 27

a flattened lymphoid organ

Question 28

where is the thymus located

Answer 28

in the upper anterior mediastinum and lower part of the neck

Question 29

when is the thymus most active and when does it undergo involution

Answer 29

most active during childhood, heaviest at puberty and then undergoes involution

Question 30

what does the thymus consist of

Answer 30

its got a right and left lobe, its got septae and its made of lobules

Question 31

what function does the thymus have in terms of t lymphocytes

Answer 31

the thymus is involved in the development of immunocompetent t lymphocytes from t cell precursors derived from bone marrow

Question 32

what types of hormones would the thymus release

Answer 32

secretion of hormones which regulate t cell maturation, proliferation and function

Question 33

why does the thymus allow the proliferation of clones of mature naive t cells

Answer 33

to supply the lymphocyte pool

Question 34

what does the thymus originate as

Answer 34

the thymus originates as epithelial outgrowths which merge in the midline forming an organ with fine lobules

Question 35

the epithelium originally forming the thymus develops into what to house what

Answer 35

the epithelium develops into a sponge like structure containing numerous interconnecting spaces which are colonised by immature t cells

Question 36

what is in the centre of the epithelial meshwork making up the thmus

Answer 36

in the centre the epithelial meshwork is coarser with a smaller lymphocyte population so the gland has an outer cortex and a less cellular central medulla

Question 37

*label this thymus

Answer 37

there

Question 38

what do the epithelial cells provide the thymus with

Answer 38

a strong mechanical framework

Question 39

what is the function of the cortical epithelial cells / nurse cells

Answer 39

they enevelope multiple lymphocytes promoting t cell differentiation and proliferation

Question 40

what forms hassal's corpuscles

Answer 40

groups of keratinised epithelial cells

Question 41

are hassal's corpuscles eosinophillic or basophillic

Answer 41

eosiophilic structures

Question 42

what are APC cells in the thymus called

Answer 42

thymic interdigitating cell

Question 43

in adults where do the t cell precursors enter

Answer 43

at the cortico-medullary junction

Question 44

once the t-cell precursors have entered the thymic cortico-medullary junction what happens

Answer 44

they begin a highly ordered differentiation programme which is linked to migration through the thymic stroma

Question 45

where are mature lymph nodes found

Answer 45

distributed throughout the body in aggregates, present along the larger regional vessels of the lymphovascular system

Question 46

lymph nodes occur in groups, give some examples

Answer 46

neck, axillae, groins, lung hila and para-aortic areas

Question 47

list four functions of the lymph nodes

Answer 47

1. non specific filtration of particulate matter and micro organisms from lymph 2. interaction of circulating lymphocytes with antigen containing lymph 3. activation and proliferation of b cells 4. aggregation, activation and proliferation of t cells

Question 48

*label this lymph node

Answer 48

there ya go

Question 49

what three types of cells are present in lymph nodes

Answer 49

lymphoid cells, immunological accessory cells and stromal cells

Question 50

how would you describe the lymph node and the function of lymph nodes

Answer 50

small bean shaped organs situated on the course of lymphatics so lymph draining back to bloodstream passes through one or more lymph nodes

Question 51

in the inactive state what is the size of a lymph node

Answer 51

only a few mm in size

Question 52

what is the outer and central area of a lymph node described as

Answer 52

the outer part is highly cellular and called the cortex | the central area is less cellular, called the medulla

Question 53

what is a lymph node surroudned by

Answer 53

a collagenous capsule from which trabeculae extend for a variable distance into the node

Question 54

what do afferent lymphatic vessels divide into and where

Answer 54

they divide into branches outside the node and pierce the capsule to drain into a narrow space

Question 55

when the afferent lymphatic vessels divide into branches outside the node and pierce the capsule to drain into a narrow space, what is this narrow space called?

Answer 55

the subcapsular sinus which encircles the lymph node beneath the capsule