The Lymphoid System

Question 1

What are the steps in the production of lymphoid cells?

Answer 1

Haematopoietic stem cells - precursor lymphoid cells - maturation in bone marrow or thymus - secondary lymphoid organs

Question 2

What cells mature in the bone marrow?

Answer 2

B cells

Question 3

What cells mature in the thymus?

Answer 3

T cells

Question 4

What are the central (primary) lymphoid tissues?

Answer 4

Bone marrow and thymus

Question 5

What are the peripheral (secondary) lymphoid tissues?

Answer 5

Lymph nodes, spleen, tonsils, epithelio-lymphoid tissues, bone marrow

Question 6

What are some functions of the lymphatic system?

Answer 6

Returns lymph to circulation = important in fluid homeostasis and preventing oedema
Permits cell traffic, cell trapping and interaction of cells and molecules with cells of the immune system

Question 7

How are lymph node groups identified?

Answer 7

Distinct groups can be palpated = cervical, axillary, inguinal
Major groups can be viewed radiologically (e.g para-aortic)

Question 8

How is lymph drainage by nodes arranged?

Answer 8

Groups of nodes drain particular territories

Question 9

What are lymph nodes?

Answer 9

Small oval bodies up to 2cm in size that are located along the course of lymphatic vessels

Question 10

What are lymphatic vessels?

Answer 10

Blind ending vascular channels that collect fluid from tissues and return to bloodstream

Question 11

What do lymphatic vessels allow?

Answer 11

Passive movement of fluid = valves ensure direction of flow

Question 12

What drains lymph through the capsule of lymph nodes?

Answer 12

Afferent channels = drain through capsule and into peripheral sinus

Question 13

Where does the efferent vessel of the lymph node drain to?

Answer 13

Cisterna chyli/thoracic duct
Left jugular, subclavian or bronchomediastinal trunks
Right jugular, subclavian or bronchomediastinal trunks

Question 14

Where does lymph drain into the venous system?

Answer 14

At the junction of the left or right subclavian and jugular veins

Question 15

Where do the arterial and venous vessels serving the lymph node enter/exit from?

Answer 15

At the hilum

Question 16

Where is lymph filtered in the lymph node?

Answer 16

Filtered within the node parenchyma before returning to the bloodstream = traffic of cells between lymph and node parenchyma

Question 17

How is the lymphoid system involved in the immune response?

Answer 17

Houses cells of innate immune system = traffics APCs to link innate and adaptive systems
Seat of adaptive immune response

Question 18

What lymphocytes are present in the lymphoid system that serve in the immune response?

Answer 18

B cells
T cells = T helper cells, T cytotoxic cells
Natural killer cells

Question 19

What are some features of the B cells involved in the lymphoid system?

Answer 19

Associated with follicles and germinal centres = interfollicular, plasma cells (mainly in medulla)

Question 20

What immune cells does the lymphoid system conatin?

Answer 20

Lymphocytes, macrophages, antigen presenting cells (APCs), dendritic cells, endothelial cells

Question 21

What are some CD numbers associated with B and T cells?

Answer 21

CD20 is associated with B cells

CD3 is a T cell marker

Question 22

What are some causes of lymphadenopathy?

Answer 22

Local inflammation = infection, vaccination
Systemic inflammation = viral infection, autoimmune
Malignancy = metastatic, leukaemia/lymphoma
Others = sarcoidosis, Castleman’s, IgG4 related

Question 23

How should regional lymphadenopathy be examined for?

Answer 23

Examine the territory that drains the particular group of nodes

Question 24

What is associated with some causes of superficial inflammation causing regional lymphadenopathy?

Answer 24

Lymphangitis = red lines extending from an inflamed lesion, may be first sign of underlying malignancy

Question 25

What is generalised lymphadenopathy a sign of?

Answer 25

A systemic inflammatory process or widespread malignancy = lymphoma/leukaemia are high on differentials (check FBC)

Question 26

What are the different processes that cause lymph nodes to be enlarged?

Answer 26

Predominant B cell response = autoimmune, infection Predominant phagocytic response = draining a tumour site Predominant T cell response = viral infections, drugs

Question 27

Where is the spleen loacted?

Answer 27

High in left upper quadrant of abdomen = usually non-palpable unless substantially enlarged

Question 28

What are the two surfaces of the spleen?

Answer 28

Diaphragmatic and visceral

Question 29

What structures is the visceral surface of the spleen in contact with?

Answer 29

Left kidney, gastric fundus, tail of pancreas, splenic flexure of colon

Question 30

What is the vasculature of the spleen?

Answer 30

Supplied by splenic artery = branch of coeliac axis | Drained by splenic vein = joins with superior mesenteric vein to form portal vein

Question 31

What effect does a disease spleen have on the likelihood of rupture?

Answer 31

Diseased spleen is more likely rupture

Question 32

Is the spleen encapsulated?

Answer 32

Yes

Question 33

What does the parenchyma of the spleen contain?

Answer 33

Red pulp = contains sinusoids and cords | White pulp = contains CD4+ T cells

Question 34

What are some features of splenic sinusoids?

Answer 34

Fenestrated with a lining of endothelial cells | Supported by hoops of reticulin

Question 35

What do splenic cords contain?

Answer 35

Macrophages and some fibroblasts | Cells in transit = RBC, WBC, PC and some CD8+ T cells

Question 36

What are some of the functions of the spleen?

Answer 36

Detects, retains and eliminates unwanted, foreign or damaged red material Facilitates immune response to blood-borne antigens

Question 37

What does the white pulp of the spleen comprise?

Answer 37

Peri-arteriolar lymphoid sheath (PALS) = contains CD4+ T cells and is expanded by lymphoid follicles

Question 38

How does the white pulp of the spleen trigger an immune response?

Answer 38

Antigen reaches white pulp via blood and APCs in the white pulp present antigen to immune reactive cells = T and B cell responses can then occur

Question 39

What are some of the features associated with splenomegaly?

Answer 39

Dragging sensation in LUQ, discomfort with eating, pain (if ischaemia present), hypersplenism

Question 40

What is the triad of hypersplenism?

Answer 40

Splenomegaly, fall in one or more cellular components of blood, correction of cytopenias by splenectomy

Question 41

What are some causes of splenomegaly?

Answer 41

Infection = TB, EBV, malaria, typhoid Congestion and haematological disease Inflammatory conditions = SLE, rheumatoid Storage disease = Gaucher's, Niemann-Pick disease Others = amyloid, tumours, cysts

Question 42

What are some causes of congestion that lead to splenomegaly?

Answer 42

Hepatic cirrhosis, cardiac failure, portal or splenic vein thrombosis

Question 43

What haematological disease cause splenomegaly?

Answer 43

Lymphoma and leukaemia, haemolytic anaemia, ITP, myeloproliferative disorders

Question 44

What is hypersplenism associated with?

Answer 44

Conditions that cause splenomegaly

Question 45

What is the diagnostic test for hypersplenism?

Answer 45

Splenectomy

Question 46

What must be considered in patients with hypersplenism and bone marrow failure?

Answer 46

May have to balance productivity of spleen with its role in excessive removal of circulating blood cells

Question 47

What are the causes of hyposplenism?

Answer 47

Most commonly due to splenectomy | Others = Coeliac, sickle cell disease, sarcoidosis, iatrogenic

Question 48

What is mostly responsible for the features of hyposplenism?

Answer 48

Reduced red pulp function = Howell-Jolly bodies, other red cell abnormalities

Question 49

What can be an additional feature of hyposplenism?

Answer 49

Immune deficiency = especially if spleen is removed in childhood