IMMUNE AND HAEMATOLOGICAL TISSUES

Question 1

describe the location of blood cell formation from foetus to adult?

Answer 1

blood islands in yolk sac, then liver until shortly before birth, then spleen until bones are vascularised, bone marrow of long bones in children, bone marrow of pelvis, sternum, vertbrae in adults

Question 2

where are plasma proteins formed?

Answer 2

hepatocytes

Question 3

what are primary lymphoid tissues?

Answer 3

sites where lymphocytes mature and differentiate to express antigen receptors so they are functionally competent to recognise foreign antigens

Question 4

what are the 2 primary lymphoid tissues?

Answer 4

thymus (T lymphocytes) and bone marrow (B lymphocytes)

Question 5

where are B and T lymphocyte precursors formed?

Answer 5

bone marrow (different for maturing T cells)

Question 6

what are secondary lymphoid tissues?

Answer 6

specialised sites for turning on an acquired immune response

Question 7

what are the different types of secondary lymphoid tissue?

Answer 7

lymph nodes, spleen, Peyer’s patches and mucosal associated lymphoid tissue

Question 8

what are mucosal associated lymphoid tissues?

Answer 8

aggregates of lymphocytes in a reticular mesh e.g. Gut associated lymphoid tissue or Nasal associated lymphoid tissue

Question 9

where is the thymus found?

Answer 9

in the mediastinum between the sternum and the aorta

Question 10

where does the thymus originate from?

Answer 10

the embryo’s 3rd pharyngeal pouch

Question 11

when is the thymus most active and largest? why?

Answer 11

most active during childhood and largest during puberty. after puberty it involutes and the amount of lymphatic tissue decreases and adipocyte content increases

Question 12

what is the function of the thymus?

Answer 12

important in the maturation of T cells

Question 13

describe the histology of the thymus?

Answer 13

it has a medulla which is located centrally within each follicle and has increased amounts of epithelial cells. Hassall’s corpuscles are present in this region. the cortex is located peripherally within each follicle and is largely composed of lymphocytes supported by epithelial reticular cells.

Question 14

what are hassle’s corpuscles?

Answer 14

concentric arrangements of epithelia reticular cells

Question 15

what is the arterial supply of the thymus

Answer 15

anterior intercostal arteries and small branches from internal thoracic arteries.

Question 16

what is the venous set of up of the thymus?

Answer 16

the venous blood drains into the left brachiocephalic and internal thoracic veins

Question 17

describe the histology of a lymph node?

Answer 17

they are covered in a capsule which has extensions called trabeculae. inside the capsule is a supporting network of reticular fibres and fibroblasts. the outer cortex has lymphatic nodules (mostly B cells), the inner cortex consist of mainly T cells and dendritic cells, the medulla contains B cells, plasma cells and macrophages.

Question 18

what are the functions of the trabeculae of the lymph node?

Answer 18

compartmentalisation, provides support and provides a route for blood vessels into the interior of the node.

Question 19

what is the difference between a primary and secondary lymphatic nodule?

Answer 19

primary lymphatic nodules are mainly B cells whilst secondary nodules form in response to an antigen and are sites of plasma cell and memory cell formation.

Question 20

describe the pathway of lymph through the lymph node?

Answer 20

lymph enter through several afferent lymphatic vessels, enters sinuses in the node and then flow through trabecular sinuses which extend through the cortex, into the medullary sinuses which then extend through the medulla. the medullary sinus drain into 1 or 2 efferent lymphatic vessels.

Question 21

how are peyer’s patches structure different to lymph nodes?

Answer 21

they are not surrounded by a connective tissue capsule

Question 22

what special epithelial cells line the side of peers patches facing the intestinal lumen? why?

Answer 22

microfold cells

transcytosis of antigens

Question 23

what is the function of Peyer’s patches?

Answer 23

to analyse and response to pathogenic microbes in the ileum. antigens from microbes in the gut are absorbed via endocytosis by microfold cells. these antigens are passed to lymphoid tissue where they are absorbed by macrophages and presented to T lymphocytes and B lymphocytes. these lymphocytes can, if needed, trigger the immune response by producing pathogen-specific antibodies, turn into cytotoxic T lymphocytes and migrate through lymphatic vessels to alert the other cells of the immune system.

Question 24

where do lymphocytes enter lymph nodes?

Answer 24

at high endothelial venules and some enter via afferent lymphatics.

Question 25

what are the functions of the lymphatic system?

Answer 25

to drain excess interstitial fluid, transport dietary lipids and carry out immune responses.

Question 26

describe the vessel structure and organisation of the lymphatic system?

Answer 26

they begin as lymphatic capillaries between cells and are closed at one end, these then unite to form lymphatic vessels. at intervals along the lymphatic vessels, the lymph flows through lymph nodes.

Question 27

describe the key features of lymphatic capillaries?

Answer 27

have a one way structure that permits interstitial fluid to flow in only. they are attached to anchoring filaments that attach them to surrounding tissues. when excess interstitial fluid accumulates and causes swelling, the anchoring filaments are pulled which makes opening between cells even larger so more fluid can flow in.

Question 28

what are lacteals?

Answer 28

specialised lymphatic capillaries in the small intestine which carry dietary lipids into lymphatic vessels and then into the blood

Question 29

what are lymphatic trunks?

Answer 29

as lymphatic vessels exit lymph nodes and unite they form these trunks.

Question 30

what are the main lymphatic trunks?

Answer 30

lumbar (lower limbs/pelvis/kidneys/adrenal glands and abdominal wall), intestinal (stomach, intestines, pancreas, spleen and liver), broncho mediastinal (thoracic wall, lung and heart), subclavian (upper limbs) and jugular (head and neck).

Question 31

where does lymph from the lymph trunks pass in to?

Answer 31

the thoracic duct and right lymphatic duct. these then drain into the blood

Question 32

what is superficial lymphatic drainage?

Answer 32

drainage that follows superficial veins, flows into lymph nodes in axillary, inguinal or cervical areas where they then drain into deep lymphatics.

Question 33

what is deep lymphatic drainage?

Answer 33

drainage that follows main vessels. lymph from 75% of the body drains into the left brachiocephalic vein via the thoracic duct. lymph from the upper right quadrant enters the right brachiocephalic veins.