Anatomy

Question 1

Location of the thymus

Answer 1

In the superior mediastinum (and anterior until puberty)
Posterior to the sternum
Anterior to the pericardium

Question 2

What happens to the thymus after puberty

Answer 2

Undergoes involution

Question 3

Parts of the thymus gland

Answer 3

Cortex

Medulla

Question 4

In the thymus, is the cortex or medulla more cellular

Answer 4

Cortex is more cellular

Question 5

What cells are in the thymus

Answer 5

Lymphoid cells
Macrophages
Epithelial cells
Supporting cells

Question 6

How do epithelial cells in the thymus differ depending on location

Answer 6

In the cortex and outer medulla they form a continuous layer

In the deep medulla they are aggregated into Hassall’s corpuscles

Question 7

Describe T cell maturation

Answer 7

Immature T cells from bone marrow enters the thymus cortex and proliferate, mature and then move into the thymus medulla
From the medulla, mature T cells enter the circulation

Question 8

What is the lymphatic system

Answer 8

An ‘overflow system ‘ which:
Provides for the drainage of surplus tissue fluid and leaked plasma proteins into the bloodstream
Removes debris from cellular decomposition and infection

Question 9

What are lymphatic plexuses

Answer 9

Network of lymphatic capillaries that originate from the extracellular spaces of most tissue

Question 10

Where are blood capillaries found but not lymphatic capillaries

Answer 10

Teeth
Bone
Bone marrow
CNS

Question 11

Features of lymphatic vessels

Answer 11

Thin walls

Abundant lymphatic valves

Question 12

What are lymphoid organs

Give some examples

Answer 12

Organs that produce lymphocytes, for example:
Thymus
Red bone marrow
Spleen 
Tonsils
GALT (gut associated lymphoid tissue)

Question 13

Describe direction of lymphatic drainage

Answer 13

Superficial lymph nodes drain into deep lymph nodes
Deep lymph nodes join to form lymphatic trunks
Lymphatic trunks join to form the right lymphatic duct (right) or the thoracic duct (left)

Question 14

What does the right lymphatic duct drain into

Answer 14

Right venous angle - junction of right subclavian and right internal jugular veins

Question 15

What does the thoracic duct drain into

Answer 15

Left venous angle - junction of left subclavian and left internal jugular veins

Question 16

Main functions of lymph nodes

Answer 16

Filter for particulate matter and microorganisms (phagocytic cells in nodes)
Present antigens to the immune system

Question 17

Structure of lymph nodes

Answer 17

Fibrous capsule which have extensions called trabeculae 
3 components are:
Lymphatic sinuses
Blood vessels
Parenchyma

Question 18

What can the lymph node parenchyma be divided into

Answer 18

Cortex
Paracortex
Medulla

Question 19

How do B cells enter lymph nodes and what do they pass into

Answer 19

Via post capillary venules called high endothelial venules (HEV)
B cells are passed to follicles of the lymph node

Question 20

What happens to B cells from the circulation if they are not stimulated in the lymph node

Answer 20

Rapidly return to the circulation with the lymph

Question 21

What happens to B cells from the circulation if they are stimulated by antigenic material in the lymph node

Answer 21

They remain in the node, proliferate and undergo somatic hypermutation
High affinity antibodies to the antigen are selected for by follicular dendritic cells
Stimulated B cells then take up the antigen, process it and present it to T cells

Question 22

What are stimulated B cells within lymphoid follicles called

Answer 22

Follicle centre cells

Question 23

Forms of follicle centre cells

Answer 23

Centrocytes - cleaved nuclei

Centroblasts - several nuclei

Question 24

Difference between a primary and secondary lymphoid follicle

Answer 24

Secondary has a pale staining central area called the germinal centre (site of B cell proliferation)

Question 25

What surrounds the germinal centre of a secondary follicle

Answer 25

Mantle zone containing B cells to be transformed into plasma/memory cells and a few T cells

Question 26

What do T cells do when an antigen is presented to them

Answer 26

Promote development of B cell type producing complementary antibody by releasing cytokines (IL4) B cell -> Centrocyte -> Centroblast

Question 27

What happens to centroblasts after leaving the follicle

Answer 27

Move to the paracortex and medullary sinuses where they become immunoblasts

Question 28

What do immunoblasts give rise to

Answer 28

Plasma cells | Memory B cells

Question 29

What cells does the paracortex of a lymph node contain

Answer 29

Lymphocytes (mainly T) Supporting cells Accessory cells

Question 30

What's the predominant cell type in the lymph node medulla

Answer 30

Macrophages

Question 31

What structures are in the lymph node medulla

Answer 31

Blood vessels Medullary cords Medullary sinuses

Question 32

What cell type is predominant in medullary cords and what is the consequence of this

Answer 32

Plasma cells | Antibodies produced by the plasma cells pass from the medullary cords to the efferent lymphatic vessel

Question 33

How do lymphocytes enter the lymph nodes (give percentages)

Answer 33

10% from lymph via afferent lymph vessels | 90% from the blood via HEVs

Question 34

Describe the passage of lymph through a lymph node | How does this relate to immune response

Answer 34

Afferent lymphatics -> marginal sinus -> cortical sinus -> medullary sinus -> efferent lymphatics Macrophages remove particulate matter in the lymph Antigen presenting cells facilitate the immune response to antigens in lymph

Question 35

What is red pulp

Answer 35

Blood filtration system in the spleen

Question 36

What is white pulp

Answer 36

Part of the spleen with a similar structure to lymph nodes containing lots of T cells, B cells and accessory cells

Question 37

Function of red pulp

Answer 37

Removes old or damaged RBCs from the circulation

Question 38

Function of white pulp

Answer 38

Mounts an immune response to antigens within the blood

Question 39

Possible effects of a splenectomy

Answer 39

Enhanced susceptibility to infection, especially by streptococci pneumoniae, haemophillus influenza and meningococcus

Question 40

Where is GALT

Answer 40

Waldeyer's ring - includes tonsils and adenoids Peyer's patches Accumulates in appendix, large intestine, stomach (with age) and gut lamina propria

Question 41

What are peyer's patches

Answer 41

Aggregates of lymphoid tissue found in the small intestine which generate an immune response within the mucosa

Question 42

Features of peyer's patches

Answer 42

``` M cells (epithelial cells with microfolds) No HEVs ```

Question 43

Describe the immune response of peyer's patches

Answer 43

B cells stimulated by antigen Cells pass to mesenteric lymph nodes where the response is amplified Activated lymphocytes pass into the circulation via the thoracic duct Activated lymphocytes home into the gut to carry out final effector functions

Question 44

Consequence of lymphocytes (and some phagocytes) recirculating between lymphoid and non-lymphoid tissue

Answer 44

Helps lymphocytes (and some phagocytes) to be exposed to the antigens they recognise so they can be distributed to sites where they are needed

Question 45

Give examples of immune cells and their pattern of recirculation

Answer 45

Naive lymphocytes - from primary (where lymphocytes mature) to secondary (where lymphocytes interact to generate immune response) lymphoid tissue via blood Activated lymphocytes - from spleen, MALT and lymph nodes to blood, to other lymphoid and non-lymphoid tissue APCs (macrophages and dendritic cells) - carry antigen from the periphery to lymphoid tissue

Question 46

What does the pattern of recirculation depend on

Answer 46

State of activation Adhesion molecules expressed by endothelial cells Chemotactic molecules