Lymphoid System Flashcards

1
Q

What are the functions of the lymphoid system?

A
  1. Phagocytosis
    -macrophages
  2. Production of immunological cells
    -APCs (dendritic, macrophage, B cells)
    -B & T lymphocytes
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2
Q

Describe primary lymphoid organs.

A

produce lymphocytes
1. Bone marrow = B cells mature
2. Cloacal bursa/bursa of fabricius (birds only) = B cells mature
3. Thymus = T cells mature
lymphocytes made in bone marrow mature in bone marrow, bursa, or thymus

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3
Q

Describe secondary lymphoid organs.

A

lymphocytes migrate to secondary lymphoid organs for activation & presentation of antigen
1. Lymph nodes (not in birds)
-filter antigens before returning it to blood
2. Spleen
-filters antigens from blood
3. MALT
-local immune response
4. Tonsils

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4
Q

What are the functions of primary lymphatic organs?

A
  1. Where T & B cells originate
  2. Access by antigen is controlled by barriers
  3. Apoptotic elimination of self reactive cells
  4. Released to circulation to sites where antigens are encountered (secondary lymphoid)
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5
Q

Describe bone marrow.

A

-source of pluripotent stem cells (B & T)
-stromal cells
>release factors that aid in cell differentiation
>macrophages

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6
Q

Describe the cloacal bursa.

A

‘Bursa of fabricus’
1. Dorsal wall of cloaca
2. Function is equivalent to bone marrow in mammals (B cell differentiation)

Pseudostratified columnar
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7
Q

Describe the thymus.

A
  1. Located in mediastinum (cranial to heart)
  2. Epithelial reticulum & lymphocytes
  3. Lymphocytic stem cells migrate from bone marrow
  4. Fill spaces between reticular epithelial cells
  5. Develop into T cells which migrate to secondary lymphoid organs & MALT
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8
Q

Describe the thymus cortex.

A
  1. Stains darker = high # of lymphocytes
  2. Positive selection
    -good developing lymphocytes (thymocytes)
  3. Tingible body macrophages near medulla
    -phagocytose dead bad T cells
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9
Q

Describe the thymus medulla.

A
  1. Epithelial reticular cells
  2. Negative selection
    -bad lymphocytes (auto reactive)
    -phagocytosed by tingible body macrophages
  3. Medullary reticular epithelial cells form thymic/hassalls corpuscles
    -lg central calcified/degen cells surrounded by concentric circles of keratinized cells
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10
Q

Canine thymus picture.

A

Cortex = darker
Medulla = lighter with Hassalls corpuscles (pink circles)

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11
Q

Canine thymus medulla picture.

A
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12
Q

Describe blood vessels in thymus.

A
  1. Arteries enter via corticomedullary junction within CT septa
  2. Divide into arterioles within septa
  3. Branch into capillary network in cortex ‘cortical capillaries’
  4. Cortical capillaries = blood thymus barrier
    -continuous endothelium
    -perivascular CT
    -sheath of epithelial reticular cell processes
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13
Q

Describe thymic involution.

A
  1. Thymus active in young animals & involutes after sexual maturity
  2. Gradual depletion of lymphocytes
  3. Replacement by adipocytes
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14
Q

Describe the lymph node.

A
  1. Capsule
    -dense, irregular CT
    -trabeculae
  2. Cortex
    -subcapsular sinus
    -lymphoid follicles (B cell rich)
    -paracortex (T cell rich)
    -high endothelial blood vessels
  3. Medulla
    -medullary cords
    -medullary sinus
  4. Stroma
    -reticular cells & fibers
Circles = lymphoid follicles. Medulla = white middle. Cortex = purple
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15
Q

Describe the flow of the lymph node.

A

Afferent lymphatic vessel -> subcapsular sinus -> cortical (trabecular) sinus -> medullary sinus -> efferent lymphatic vessel

CORTEX:
-lymphoid follicles & lymphocytes
MEDULLA:
-macrophages, lymphocytes, plasma cells

Ventral = efferent lymphatic vessel
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16
Q

Describe the cortex & medulla of the lymph node.

A

Cortex:
-lymphoid follicles
-paracortex
-high endothelial blood vessels
Medulla:
-medullary cords
-lymphocytes
-macrophages
-plasma cells
>medullary sinus
—macrophages
—reticular cells

17
Q

Describe primary VS secondary lymphoid follicles.

A

Primary -> ANTIGEN -> secondary

18
Q

Describe high endothelial venules (diapedesis).

A

-in paracortex
-cuboidal
-allow extravasation of lymphocytes

19
Q

Medulla with sinus & cords (picture).

A

S = sinus
C = cords

20
Q

Close up of sinus with macrophages.

A
21
Q

Labeled lymph node picture.

A
22
Q

Describe porcine lymph nodes.

A

-backwards = central lymphoid follicles
-afferent lymphatics (V) enter though hilus (H) & follow trabeculae (t) to the central lymphatic nodules (n)
-peripheral sinus/cord (L)

23
Q

Describe hemal nodes.

A

-alongside bloodstream
-in ruminants = dark colored
-erthryocytes in sinus
-no lymphatic supply
-near spleen, kidney, lg blood vessels (ventral side of vertebrae)
-function like the spleen

24
Q

Describe hemolymph nodes.

A

-in pigs
-RBCs in sinus due to hemorrhage

1 = erythrocyte 2 = lymphocyte
25
Q

What are the functions of the spleen?

A
  1. Filter blood
    -old RBCs & WBCs
    -recover & store iron
    -macrophage of red pulp = contain RBCs & hemosiderin
  2. Sample/remove antigen from blood via phagocytosis
  3. Immune response against blood borne antigens (B & T)
  4. Hematopoiesis in fetus
  5. Store RBCs in horse, cat, dog
    -more smooth muscle & elastic in capsule = contraction & release of RBCs into blood
    -defense spleen = less smooth muscle in capsule (human & rabbit)
    -ruminants & pigs = intermediate
26
Q

Describe the splenic structure.

A

-outer capsule = dense CT with smooth muscle & elastic fiber
>gives rise to trabeculae = collagen, elastic fibers, smooth muscle
>each trabecular contain central artery or vein

Trabecular vein
27
Q

Describe white pulp VS red pulp.

A

WHITE
-central arterioles
-periarterial lymphoid sheath - PALS (T)
-follicles (B)
RED
-venous sinus (RBCs)
-reticular fiber & cells
-macrophage, lymphocyte, plasma cells
-PAMS

White pulp = purple. Red pulp = red/pink
28
Q

Describe splenic blood flow.

A

-via central artery & branches w periarterial lymphatic sheath (PALS) = white pulp
-branches = penicillary arteries
-end in blind ending capillaries w periarteriolar macrophage (PAMS) in red pulp
-capillaries drain into red pulp parenchyma & then venous sinuses in an open circulation
-capillaries drain into venous sinus = closed circulation
-sinus well developed in dogs (cats, horse, ruminant = non sinusal spleen)

29
Q

Describe MALT.

A

-GALT
-BALT
-tonsil
-ocular
-urogenital
-mammary

30
Q

BALT picture.

A

(Lymphoid tissue)

31
Q

GALT picture.

A

Light purple areas
-peyers patch
-aggregated lymphatic nodules
EX. Anti mesenteric side of ileum

32
Q

Peyers patch picture.

A
33
Q

Describe micro fold cells.

M cell = blue
A

-peyers patch are covered by a columnar layer of micro fold cells (M cells)
-specialized epithelial cells
-pinocytose GI contents & secrete content on the lymphocytes & macrophages of peyers patch

34
Q

Describe lacteals.

A

-blind ended lymph capillaries in small intestine villi

35
Q

Describe lymphatic vessels.

A

-blind ended tubes
-endothelial lining
-absorb fluid from interstitum & pass it back to blood
-inflammatory cell & antigen movement from peripheral tissue
-lymph flow in one direction = from periphery to heart
-surrounding tissue compress/expand vessel
-one way valve = prevent backflow
-anchoring fibrils = pull endothelial cells apart & fluid enters vessel

36
Q

Picture of lymphatic vessel, arteriole, venule.

A
  1. Left = lymphatic vessel with a valve
    -no erythrocytes
  2. Middle = arteriole
    -1-3 layers of circular sm muscle
  3. Right = venule
    -no sm muscle in wall
37
Q

Describe function of lymphatics.

A

-deliver lymph to lymph nodes
-drain tissue fluid through fenestrated capillaries

38
Q

Describe palatine tonsil.

White = crypt
A

-collection of lymphatic nodules present in tunica muscle of pharynx
-may/may not have crypts
-no afferent lymphatics, samples lumen
-efferent lymphatics drain tonsils
-local antibody production

Stratified squamous