W1 Anatomy of the Haematopoietic System

Question 1

what are the haematopoietic organs in embryos?

Answer 1

aggregations of blood cells in the yolk sac

Question 2

where is bone marrow found?

Answer 2

within the medullary cavity and interstitial spaces of spongy bone

Question 3

what is the site of most blood cell formation in adults?

Answer 3

bone marrow

Question 4

describe red bone marrow:

Answer 4

haematopoietic function, richly vascularised - all bone marrow in young animals is red

Question 5

describe yellow bone marrow:

Answer 5

predominantly fat, conversion from red to yellow happens in larger spaces first - dormant haematopoietic potential

Question 6

what fluid is filtered out of capillaries?

Answer 6

interstitial fluid

Question 7

what happens to lymph once it drains into lymphatic vessels?

Answer 7

travels through progressively larger vessels until emptied back into venous circulation, may pass through lymph nodes

Question 8

what lymphatic duct drains into the left branches of the vena cava?

Answer 8

thoracic duct

Question 9

what are primary lymphatic organs?

Answer 9

organs where lymphocytes are formed and mature

Question 10

where do T cells have to go to fully mature (after originating in bone marrow)?

Answer 10

the thymus

Question 11

what do secondary lymphatic organs do?

Answer 11

act as filters that monitor content of extracellular fluids (lymph, tissue fluid, blood), they are also where lymphocytes are activated

Question 12

what happens to lymphocytes in a secondary lymphatic organ?

Answer 12

antigen-dependent proliferation and differentiation into antigen-disposal cells or memory cells

Question 13

does lymph flow at low or high pressure? why?

Answer 13

low pressure - lymphatics are thin walled, readily collapse

Question 14

what does elevations in venous pressure do to lymph flow?

Answer 14

disrupts it (does have valves to prevent backflow)

Question 15

where do efferent vessels in lymph nodes originate from?

Answer 15

in the central medulla - leave from the indented hilar region

Question 16

how are pig lymph nodes different?

Answer 16

the cortical tissue is central, the afferent vessels penetrate near hilus and the efferent emerge from the periphery (inside out/back to front)

Question 17

what are haemal nodes?

Answer 17

not in all species (more common in cattle and sheep), they contain blood sinuses (vascular structures modified by focal collections of lymphocytes - presumed to have a similar function to the spleen

Question 18

how do mucosal associated lymphoid tissue (MALT) differ from lymph nodes?

Answer 18

absence of capsule, close relationship to epithelial surface, positioned at origin of the lymphatic drainage pathway - unlike lymph nodes

Question 19

name three MALT:

Answer 19

any three of:
pharyngeal (tonsils)
palatine (tonsils)
larynx
intestine (peyer’s patches)
prepuce
vagina

Question 20

where are peyer’s patches commonly found?

Answer 20

mostly in the ileum and jejunum (lamina propria and submucosa)

Question 21

how are peyer’s patches distinguishable?

Answer 21

by the lack of villi covering them

Question 22

where is the spleen found?

Answer 22

in the left cranial part of the abdomen attached to the greater curvature of the stomach - exact positioning depends on blood content/stomach filling

Question 23

what ligament attaches the spleen to the stomach?

Answer 23

the gastrosplenic ligament

Question 24

what is the shape of the spleen in cats/dogs, pigs, cattle and horses?

Answer 24

cats/dogs = dumbbell shaped
pigs = stap-like
cattle = broad oblong shape
horses = hooked shape

Question 25

what is the spleen vascularised by?

Answer 25

the splenic artery and vein

Question 26

describe the vascular supply to the spleen in ruminants, horses/pigs and dogs/cats:

Answer 26

ruminants = pass undivided through confined hilus horses/pigs = run along organ branching at intervals cats/dogs = divide as approach organ

Question 27

describe the capsule of the spleen:

Answer 27

capsule extends trabeculae into the interior, very muscular in some species (contractions under sympathetic influence to change volume)

Question 28

what functions does the spleen have?

Answer 28

blood storage, blood filter, destruction of old red blood cells and production of lymphocytes

Question 29

what is the parenchyma of the spleen divided into?

Answer 29

red and white pulp

Question 30

the thymus produces huge numbers of what?

Answer 30

T cells

Question 31

the thymus has a great size in juveniles, what happens as it gets older?

Answer 31

importance - gradually involutes until puberty, regression starts at the cervical/cranial end, the lymphoid structure is replaced by fat

Question 32

where does the buds of the thymus grow?

Answer 32

down the neck alongside the trachea - fuses with the pericardium and travels with the heart caudally

Question 33

what does the capsule of the thymus house?

Answer 33

blood vessels, nerves and efferent lymphatics

Question 34

the thymus has a dense cortex of rapidly dividing what?

Answer 34

thymocytes (developing T cells)

Question 35

are the T cells is the medulla of the thymus dividing or non-dividing?

Answer 35

non-dividing (fewer T cells = weaker staining (histology))

Question 36

what is the blood-thymus barrier in capillaries for?

Answer 36

to protect T cells from exposure to antigens in the blood

Question 37

do birds have lymph nodes?

Answer 37

no - apart from ducks and geese that have two primitive pairs (cervicothoracic pair (near thyroid) and lumbar pair (near kidneys))

Question 38

describe the bursa fabricius in birds:

Answer 38

dorsal diverticulum in the proctodeum, contains folds of lymphoid tissue (thick wall in domestic fowl, thin and sac-like in psittacines and passerines), reaches max size before sexual maturity then begins to involute

Question 39

where is the spleen located in birds?

Answer 39

located in the right coelom between the ventriculus (gizzard) and proventriculus

Question 40

describe the spleen in birds:

Answer 40

quite small, oval, triangular or elongated, does not form blood reservoir as in mammals

Question 41

most species of birds have paired thoracic ducts either side of what? what do the ducts do?

Answer 41

either side of the spine, they drain lymph from the hindlimb and abdominal vessels ad deliver it to the jugular veins at the base of the neck

Question 42

in amphibians the thymus remains functional throughout life, what can cause it to involute?

Answer 42

malnutrition/chronic stress

Question 43

what is the function of the red and white pulp in the spleen of amphibians?

Answer 43

red = erythropoiesis white = myelopoiesis

Question 44

what do amphibians have instead of lymph nodes?

Answer 44

lymph hearts (aka sacs/vesicles), smooth muscle dilations of lymphatic channels that beat independently of the heart (5-60bpm) to ensure unidirectional lymph flow to the heart

Question 45

describe the thymus in reptiles:

Answer 45

1-2 yellow/white lobes each side of the neck in lizards and chelonia, cranial to the heart in snakes, doesn't involute but weight and size decrease with age

Question 46

do reptiles have lymph nodes?

Answer 46

they lack lymph nodes but have a vast plexiform lymphatic network and large dilated reservoirs (cisternae) and lymph hearts

Question 47

do reptiles have well or under developed lymphatic trunks?

Answer 47

well-developed - jugular, subclavian, lumbar and thoracic and a saccular precardiac sinus at the base of the neck passing lymph to the venous system

Question 48

why do you have to be careful with blood samples from reptiles?

Answer 48

the lymphatic system is intimately associated with the blood, lymphdilution is a common contaminant of blood samples (e.g. low PVC)

Question 49

what haematopoietic organ do fish have additionally?

Answer 49

cephalic (cranial) kidney

Question 50

the peripheral lymph plexuses are large channels in fish that empty into the venous system in which three part?

Answer 50

cranial, middle and caudal

Question 51

do fish have lymph nodes?

Answer 51

no - they have lymph hearts