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Microanatomy > Lymphatic System > Flashcards

Lymphatic System Flashcards

1
Q

Lymphoreticular System

A

To protect the body against pathogenic organisms and their products and to help in the removal and disposal of cells undergoing natural or induced degenerations

Phagocytosis: Macrophages
Production of immunologically competent cells: Antigen presenting cells (dendritic cells, Macrophage, B cell); B and T lymphocytes

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2
Q

Mononuclear Phagocytic System

A 
Fixed Macrophages (within tissues): sinusoids of liver, sinusoids of spleen, sinusoids of lymph node, reticulum of bone marrow
Free macrophages (monocytes): Blood, lung, serous cavities
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3
Q

Antigen Presenting Cells (APCs)

A

Cells that get exposed to an antigen (cancer, virus, toxin, etc)
Cells that capture, process, and present protein fragments from extracellular antigens (on MHC II)
Binds to antigen and then through cytokin processes, presents to T-cell– then mounts an immune response
Dendritic cells, Macrophages, B-cells

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4
Q

Lymphatic System: Primary Organs

A

Generate lymphocytes form progenitor cells
Bone Marrow (B lymphocytes)
Cloacal Bursa
Thymus (T lymphocytes): cortex and medulla

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5
Q

Lymphatic System: Secondary Organs

A

Sites of lymphocyte activation/differentiation in context of immune response
Lymph nodes
Spleen
Mucosal Associated Lymphoid Tissue

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6
Q

B and T Lymphocytes

A

In Bone marrow, Lymphoid stem cell leaves to Thymus where T cell differentiation takes place. (then populate secondary organs and can further differentiate in immune response) Helper/suppressor/effector, Natural Killer etc

In bone marrow, lymphoid stem cell stays and B cell differentiation takes place. (populate secondary organs and can further differentiate in immune response) Memory cell, plasma cell

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7
Q

Primary Lymphatic Organs

A

Where lymphoid stem cells originate from
Where T and B cells originate and their unique features are established
Access by antigen is strictly controlled (barriers): if primary lymphoid organs become exposed to antigens, process of positive selection would not occur properly
Apoptotic elimination of self-reactive cells
Released to circulation to sites where antigen encountered (secondary lymphoid)

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8
Q

Bone Marrow

A

Source of pluripotent stem cells (lymphoid line): B and T cells
B cells mature in bone marrow
T cells migrate to thymus
A background of stromal cells exist also: release factors aiding cell differentiation and macrophages for ion storage, antigen presentation etc.

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9
Q

Cloacal Bursa

A

In Birds
Dorsal wall of the cloaca
Functionally equivalent to mammalian bone marrow for B cell differentiation
Surface mucosa of bursal fold covered by pseudostratified columnar epithelium
3 lymphoid nodules, dark corices, light medulla
Lymphocytes emigrating through surface epithelium

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10
Q

Thymus

A

T cell differentiation
Located in mediastinum just cranial to heart
Composed of epithelial reticulum and lumphocytes
Lymphocytic stem cells migrate from bone marrow
Fill spaces between reticular epithelial cells of the developing organ
Develop into T cells
Thin connective tissue capsule, sends in septae. These divide the organ into partially separated lobules. Dark cortex, light medulla-which is continuous between adjacent lobules, despite island appearance

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11
Q

Thymic Cortex

A

Stains much darker than thymic medulla due to greater number of lymphocytes present
Area of positive selection (Good lymphocytes)
Tingible body macrophages- frequent near the medulla: Phagocytose and eliminate dead T cells

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12
Q

Positive Selection

A

During T lymphocyte development
Need to demonstrate that it has certain receptor (MHC II complex). This determines if down the line T cell binds to antigen presenting cell
If it can bind, it passes and moves to medulla of thymus
If not it dies by apoptosis

Lymphocytes pass positive selection by encountering Thymic epithelial cells. They traverse through the cortex and bump into many of these cells and possible and if they bind to any they pass the selection test
Thymic reticular cells present in medulla and cortex

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13
Q

Thymic Medulla

A

Also contains epithelial reticular cells
Area of negative selection (bad lymphocytes-autoreactive): tingible body macrophages
Some medullary reticular epithelial cells form thymic corpuscles or Hassall’s copuscles

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14
Q

Thymic epithelial reticular cells

A

Present as much of own DNA as possible on cell surface. So T cells bump into a lot and is exposed to a lot of self DNA

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15
Q

Negative Selection

A

Dont want T lymphocytes to be too sensitive to binding own antigens
If it binds too strongly to self antigen, it will fail and have to die

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16
Q

Hassall’s Corpuscles

A

Large central calcified or degenerated cells surrounded by concentric circles of keratinized cells

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17
Q

Blood Vessels in Thymus: Blood Supply

A

Arteries enter via the corticomedullary junction within the connective tissue septa
Divide into arterioles within the septa
Branch into a capillary network in the cortes

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18
Q

Blood Vessels in Thymus: Cortical Capillaries

A

Blood thymus barrier:
continuous endothelium
perivascular connective tissue
sheath of epithelial reticular cell processes: decrease antigen access to thymus, limits interference with positive T cell selection

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19
Q

Educated T cells

A

After passing positive and negative selection
Leave the thymus through the postcapillary venules at the coricomedullary junction
Enter blood, settle in T cell areas of secondary lymphatic tissue

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20
Q

Thymic Involution

A

Thymus is active in young animals, involutes after sexual maturity
Gradual depletion of lymphocytes
Replacement by adipocytes

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21
Q

Secondary lymphatic organs

A

Where lymphocytes are stores, mature and become activated

Lymph nodes, spleen, mucosal-associated lymphoid organs

22
Q

Lymph nodes

A 
Filter antigens from lymph before returning it to bloodstream
Capsule
Cortex
Medulla
Hilus
23
Q

Lymph Node: Cortex

A

Primary and secondary follicles (B cell rich)
Paracortical tissue (T cell rich)
High endothelial blood vessels
Subcapsular Sinus

24
Q

Lymph Node: Medulla

A

Medullary cords

Medullary Sinus

25
Q

Lymph Node: Hilus

A

Slight indentation- arteries enter, and efferent lymphatics and veins leave

26
Q

Lymph Node: Structure

A

Capsule-dense, irregular connective tissue (ruminants have smooth muscle cells too)
Trabecula extend from capsule into cortex and medulla: structural support, contain blood vessels and nerves. Surrounded by sinuses
Lymph node stroma- reticular cells and fibers that support lymphocytes, macrophages, and plasma cells

27
Q

Lymph vessels and sinuses

A

Afferent lymph vessels enter the lymph node at several places along the capsule-enter through cortex
Open into the subscapsular sinus
Afferent and efferent lymph vessels have valves- one way flow of lymph
cortical sinuses from subcapsular sinus, follow trabeculae to form medullary sinuses: open network of channels, converge toward the hilus, open into efferent lymph vessels- all lymph leaves node this way

28
Q

Blood Vessels

A

Major arteries enter at hilus: branch and supply medullary cords and cortex (Deep cortex: postcapullary venules-lines by cuboidal endothelium- high endothelial venules: only lymphcytes can extravasate via HEV) or supply traveculae- supply connective tissue and capsule

Smaller vessels enter capsule at various sites
Veins leave at hilus

29
Q

Primary and secondary lymphoid follicles

A

When stimulated by antigen, they change histologic morphology from primary to secondary lymphoid follicles. (this is reversible)
Follicle: site of antigen presentation and B cell differentiation

30
Q

Microanatomy of the secondary follicle

A

Germinal center is subdivided into basilar dark zone and apical light zone
Marginal zone

31
Q

Cellular movement in lymph node

A

Lymphocytes and DCs enter lymph nodes by different routes
Most lymphocytes migrating to lymph nodes enter from the peripheral blood
Most DCs enter lymph nodes through the afferent lymphatics

32
Q

Hemal Nodes

A

Run alongside (not connected) the bloodstream
Seen predominately in ruminants- dark color
Rich content of erythrocytes within sinuses
No lymphatic supply
Near the spleen, the kidney and large blood vessels along the ventral side of the vertebrae
Functions are probably like those of the spleen

33
Q

Hemolymph nodes

A

In pigs

Probably only a lymph node that contains RBCs in its sinuses as a result of hemorrhage in its tributary field

34
Q

Spleen: Filters Blood

A

Filters blood (phagocytize them)
Senescent (old) RBCs and WBCs
Recovers and stores iron
Macrophages of red pulp commonly contain portions of RBCs and hemosiderin
Samples and removes antigens from blood
Mounts immune responses against blood-borne antigens- B and T cells
Hematopoiesis in fetus, sometimes in adult

35
Q

Spleen: Stores RBCs and PLTs

A

Stores RBCs and PLTs
mainly in horses, dogs, and cattle
Smooth muscle is a prominent feature of capsule and trabeculae in these species
Splenic contraction increases systemic hematocrit
Cats do not have storage type spleen

36
Q

Splenic Structure

A

Outer capsule is dense connective tissue with underlying smooth muscle
Capsule gives rise to: trabeculae-collagen, elastic fibers, smooth muscle cells
Each trabecula contains a central artery or vein
White and Red pulp

37
Q

Splenic Blood flow

A 
In at central artery
Branches to form penicillary arteries
End in sheathed capillaries (CT and macrophages)- no endothelial cells, end blindly (do not connect to anything)
Blood enters space in parenchyma
Then to sinus system
Sinuses become larger and larger
Splenic vein
Hepatic portal vein
Called an open circulation system since the parenchyma is not a true blood vessel
38
Q

White Pulp

A

Central arterioles
Periarterial lymphoid sheaths -PALS (t)
Follicles (b)

Parenchyma:
B cells- lymphoid follicles, will have germinal centers in young animals
T cells- located around central arterioles ~sheath, periarteriolar lymphoid sheath (PALS)

39
Q

Red pulp

A 
Sinusoids
1. Parenchyma (functional tissue):
macrophages of sheathed capillaries
Other macrophages and blood cells that will eventually enter the venous sinuses
2. Venus sinuses (dog, rat, human)
Compose the rest of the red pulp
Long endothelial cells-contractile
Basement membrane- discontinuous (blood cells easily enter from parenchyma to venous sinus)

Long endothelial cells delimit venous sinus (leaky and will ooze out to red pulp). Parenchyma composed of macrophages and blood cells

40
Q

Mucosal Associated Lymphoid Tissue

A 
Gut associated lymphoid tissue (GALT)
Bronchial associated lymphoid tissue (BALT)
Tonsil
Ocular
Urogenital
Mammary
41
Q

Secondary lymphatic tissue

A

Strategic location at sites of antigen entry
Antigen-presenting cells induce immune response
Single or aggregations of lymphoid nodules
Augment mechanical and chemical barriers of surface mucosal epithelium

42
Q

Gut associated lymphoid tissue (GALT)

A 
Includes: 
Solitary and aggregated lymphatic nodules
Intraepithelial lymphocytes
Subepithelial lymphocytes
Plasma cells
Macrophages
43
Q

Aggregated lymphatic nodules

A

In GALT
Peyer’s patches
Small intestin-ileum
Ileal peyer’s patch may involute with age, may function differently to smaller patches
Smaller aggregated nodules in small-intestine, colon and rectum persist into adulthood

44
Q

Lacteals

A

Blind-ended lymphatic capillaries within intestinal villi of the small intestine
Micelles from the chyme are absorbed, converted by the cell to chylomicrons- these enter the lacteals to become part of the chyle
Smooth muscles in the villi contract the villous up and down pumping the lacteal to force the chyle into the one-way lymphatic vessels of the submucosa

45
Q

Lymphatic nodules and diffuse lymphatic tissues

A

lots of lymphatic tissue because it comes across stuff a lot

The mucosa and submucosa contain diffuse lymphatic tissue and large lymphatic nodules with germinal centers

46
Q

Peyer’s Patches

A

Microscopically: aggregation of lymphatic nodules in the lamina propria and submucosa of the distal jejunum/ileum
B cells migrate there from bone marrow (as some level of B cell maturation occurs here, often considered as a primary lymphatic organ)

Same central light and peripheral dark zones as typical lymphoid nodules
Overlain by simple columnar (M-cells; microfold cells)
Bursa of fabricius in chicken considered its equivalent hence the suggestion of its role in B cell development

Anti-mesenteric side of ileum contain GALT
Peyer’s Patch domes are covered by a simple columnar layer of microfold cells

47
Q

M cells

A

Close proximity to luminar surface
Specialized epithelial cells
Pinocytose GI contents and secrete content on the lymphocytes and macrophages of the peyer’s patch

48
Q

Tonsils

A 
Aggregated lymphatic nodules in pharynx
-Adjacent to lumen of host organ- sample luminal content
-No afferent lymphatic vessels
Local production of antibodies occurs
-important in immune response

squamous epithelium
collection of lymphatic nodules present in tunica mucosa of pharynx
May or may not have crypts
Efferent lymphatics drain tonsils (into lymphoids)

49
Q

Lymphatics drain tissue fluid

A

Frank-starling
Inbalances between hydrostatic and osmotic pressure will result in 10% of fluid being unabsorbed back to blood circulation
the 10% ends up in interstitium and then lymph
lymph willhave antigens etc

50
Q

Lymphatic vessels

A

Blind-ending tubes lined by endothelial cells
Absorb fluid from interstitium, pass it back into blood stream
Inflammatory cell and antigen movement from peripheral tissue to nearest local lymph node for recognition and response
Anchoring fibrils pull endothelial cells apart, fluid enters vessel
Lymphatics deliver lymph to lymph nodes- regional monitoring centers for immune response
Lymph flows in one direction from periphery to heart
surrounding tissues compress or expand vessel
one way valve prevents backflow

Microanatomy (21 decks)

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