Lab 7 Immune System 2
Objectives:
Immune system
Be able to identify (based on morphology and organ location) the various cells of the immune system:
B-lymphocytes (plasma cells)
T-lymphocytes (T-helper; T-cytotoxic; Natural Killer cells)
Macrophages
Others (Dendritic cells, Neutrophil, Mast cell
Thymus
Be able to recognize the anatomical features of the thymus:
Describe pattern of blood flow within the thymus from the corticomedullary arteries through the cortex and medulla and back to the corticomedullary veins.
Define the relationship of the thymus to lymphocytes that originate in bone marrow and to lymphocytes which populate lymph nodes and unencapsulated lymphatic tissue.
GALT and MALT
Identify non-encapsulated aggregates of lymphatic tissues (e.g., Peyer's patches, palatine and nasopharyngeal tonsils) present in the mammalian body.
Correlate the function of tonsils with their location in the body.
Lymph node
Describe the architecture of a lymph node in the following terms: cortex, medulla, capsule, trabeculae, and reticular connective tissue.
Describe the flow of lymph through a lymph node from afferent lymph vessels to the efferent lymph vessel incorporating structures such as the subcapsular sinus, cortical lymph sinusoid, and medullary lymph sinusoids.
Define the lymph (lymphatic) nodule and germinal center (identify these structures on your slides).
Describe the route of recirculation of lymphocytes from blood to lymph within the lymph node.
Spleen
Describe the cellular and fibrous connective tissue elements present in the capsule and trabeculae of the spleen.
Describe the morphologic and functional differences between red and white pulp.
Identify the following vascular components of the spleen and explain the route of blood flow through the spleen:
Splenic artery
Trabecular artery
Artery (arteriole) of the white pulp
Artery of the red pulp (a.k.a. pulp arteriole)
Sheathed capillaries
Splenic (venous) sinuses or venules
Trabecular vein
Splenic vein
Slides:
#73 Bovine hyoid bone
#79 Thymus
#76 Palatine tonsil
#80 Nasopharyngeal tonsil
#74 Lymph node
#29 lymph Node - Silver stain
#75 Mesenteric node
#77 Spleen
Lymph Node - orientation to glass slide #74
Afferent lymphatic:
Lymph nodes, situated along the extensive drainage system of lymph vessels, filter the lymph before returning it to the bloodstream. Lymph nodes are the only lymphatic organs with both afferent (incoming) and efferent (outgoing) lymph vessels and sinuses. Study the general morphologic features of the lymph node on glass Slide 74 with a low power objective. One afferent lymphatic duct is found entering the capsule from the right.
Topic: Afferent Lymphatic
Blue arrows=afferent lymphatic duct; Red arrows = efferent lymphatic duct; Yellow asterisks = paracortex; Green asterisks = cortex.
Efferent lymphatic:
The node drains via an efferent lymphatic vessel that exits the hilum. This vessel may contain valves and the lymph may exhibit pale homogeneous staining.
Topic: Efferent Lymphatic
Blue arrows=afferent lymphatic duct; Red arrows = efferent lymphatic duct; Yellow asterisks = paracortex; Green asterisks = cortex
Paracortex:
Surrounded by the capsular sinus and capsule, the outer cortex contains the lymphatic nodules. Adjacent to them are areas of paracortex (or deep cortex).
Topic: Paracortex
Blue arrows=afferent lymphatic duct; Red arrows = efferent lymphatic duct; Yellow asterisks = paracortex; Green asterisks = cortex
Cortex:
Surrounded by the capsular sinus and capsule, the outer cortex contains the lymphatic nodules. Adjacent to them are areas of paracortex (or deep cortex).
Topic: Cortex
Blue arrows=afferent lymphatic duct; Red arrows = efferent lymphatic duct; Yellow asterisks = paracortex; Green asterisks = cortex
Medulla:
Most of the middle of this section consists of medulla, relatively open areas in which nodal cells and lymph intermix. The medulla, consisting of medullary sinuses adjacent to stromal medullary cords, funnels lymph toward the hilus.
Topic: Medulla
Green asterisks indicate areas of medulla; Blue arrows = a trabeculum; Red asterisk = region of the hilus.
Trabeculum:
Trabeculae of reticular connective tissue divide the cortex and carry with them extensions of the subcapsular sinus toward the medulla or hilus. Trabecular sinuses appear as spaces bordering the invaginating CT stroma.
Topic: Trabeculum
Green asterisks indicate areas of medulla; Blue arrows = a trabeculum; Red asterisk = region of the hilus.
Hilus
Locate the hilus of the node and observe any blood vessels, which both enter and leave the node in this region. The hilus contains a single efferent lymph vessel.
Topic: Hilus
Green asterisks indicate areas of medulla; Blue arrows = a trabeculum; Red asterisk = region of the hilus.
Subcapsular sinus:
The subcapsular sinus may contain various lymphatic cells in addition to open space, occupied by lymph fluid. Examine its relationship to the node's capsule and cortical lymphatic nodules.
Topic: Subcapsular sinus
Green arrows = subcapsular sinus; Yellow asterisks = cortex; Red arrows = paracortex.
Cortex:
The cortex, containing the lymphatic nodules, is divided into two areas: the outer cortex containing lymph nodules with large germinal centers and the inner paracortex, such as the areas found between deeper nodules.
Topic: Cortex
Green arrows = subcapsular sinus; Yellow asterisks = cortex; Red arrows = paracortex.
Paracortex:
The cortex, containing the lymphatic nodules, is divided into two areas: the outer cortex containing lymph nodules with large germinal centers and the inner paracortex, such as the areas found between deeper nodules.
Topic: Paracortex
Green arrows = subcapsular sinus; Yellow asterisks = cortex; Red arrows = paracortex.
Germinal center:
Within the germinal center of the cortical nodules, note the presence of mitotic lymphocytes - particularly the condensed and aligned chromatin of metaphase or anaphase cells.
Reticular cells:
In the subcapsular and medullary sinuses, note the presence of various immune cells plus reticular cells, which may be identified by an oval nucleus and delicate, elongated cytoplasm (arrows). Reticular cells can also be observed in the paracortex. The reticular cells, with their pale staining, exilic branches form a meshwork or reticulum through which lymphocytes wind their way toward the hilus. Cytoplasmic processes of the reticular cells enwrap the reticular fibers that are the primary c.t. stroma of the lymph node. Compare these areas to glass slide #29 (and next page), in which reticular fibers (collagen type III) are specifically stained.
Macrophages
The paracortex is a T-cell rich area composed of diffuse lymphatic tissue and a mix of cell types. Identify active macrophages based on vacuoles in their cytoplasm (arrows in the center of this field).
Trabeculae:
Collagenous trabeculae from the outer capsule extend inward through the cortex. The thin blue collagenous trabeculae visible in this image are presumably attached to the capsule in a different plane of section.
Medullary cords:
The medulla contains many medullary cords that provide stromal reinforcement and an attachment site for cells. The medullary cords are surrounded by pale staining medullary sinuses, which are channels for the lymph fluid. Note: Lymph flows from the afferent lymphatics→subcapsular sinus→trabecular sinus→medullary sinus→efferent lymphatics.
Topic: Medullary cords
Blue arrows are located in medullary sinuses and point to medullary cords.
Lymph node silver stain - Glass slide #29
Nodule:
This lymph node was stained with a special silver stain that reveals reticular fibers. Cells also absorb some stain, which allows the regions of the organ to be discerned even though little cellular detail is evident. Note that the nodules have few reticular fibers, located around their margins. The paracortex and medulla have a significant fibrous framework that is not evident with routine staining. Medullary cords and adjacent medullary sinuses are clearly evident in the stromal patterns.
Paracortex:
This lymph node was stained with a special silver stain that reveals reticular fibers. Cells also absorb some stain, which allows the regions of the organ to be discerned even though little cellular detail is evident. Note that the nodules have few reticular fibers, located around their margins. The paracortex and medulla have a significant fibrous framework that is not evident with routine staining. Medullary cords and adjacent medullary sinuses are clearly evident in the stromal patterns.
Medulla
This lymph node was stained with a special silver stain that reveals reticular fibers. Cells also absorb some stain, which allows the regions of the organ to be discerned even though little cellular detail is evident. Note that the nodules have few reticular fibers, located around their margins. The paracortex and medulla have a significant fibrous framework that is not evident with routine staining. Medullary cords and adjacent medullary sinuses are clearly evident in the stromal patterns.
Mesenteric Node - orientation to glass slide #75
Cortex:
Glass Slide 75 is a section of a mesenteric lymph node from a pig. Identify the cortex and medulla of the pig lymph node. All of the functional components of a lymph node are present but the node appears inverted compared to the usual mammalian lymph node such as the dog (glass slide #74). Lymph enters these nodes at the hilus and leaves at the periphery of the node. This is one of the unusual aspects of the lymphatic system in the pig.
Medulla:
Glass Slide 75 is a section of a mesenteric lymph node from a pig. Identify the cortex and medulla of the pig lymph node. All of the functional components of a lymph node are present but the node appears inverted compared to the usual mammalian lymph node such as the dog (glass slide #74). Lymph enters these nodes at the hilus and leaves at the periphery of the node. This is one of the unusual aspects of the lymphatic system in the pig.
The Spleen - glass slide #77
Capsule:
The spleen filters blood and is involved in immunologic responses to blood borne antigens. Use low power to survey the general morphologic features of the spleen on glass Slide 77. Note the capsule and trabeculae consist of a mixture of collagenous connective tissue and smooth muscle. The splenic artery and vein are visible at the top of the section.
Topic: Capsule
Blue arrows = capsule; Violet arrows = trabeculae; Red arrows = red pulp; Green asterisks = nodules (white pulp).
Trabeculum:
Trabeculae distribute the largest of the organ's substantial arteries. The amount of smooth muscle in the capsule and trabeculae varies by species. The cat spleen contains less smooth muscle and less prominent vessels than many larger species.
Topic: Trabeculum
Blue arrows = capsule; Violet arrows = trabeculae; Red arrows = red pulp; Green asterisks = nodules (white pulp).
Nodule:
Note the area of white pulp, consisting of nodules in which basophilic lymphocytes aggregate, is much smaller than the area of red pulp.
Topic: Nodule
Blue arrows = capsule; Violet arrows = trabeculae; Red arrows = red pulp; Green asterisks = nodules (white pulp).
Red pulp:
Red pulp contains a rich vascular network in which erythrocytes pool, imparting the obvious color. Erythrocytes in this section may appear either orange or red, the significance of which is unclear.
Topic: Red pulp
Blue arrows = capsule; Violet arrows = trabeculae; Red arrows = red pulp; Green asterisks = nodules (white pulp).
The Spleen - glass slide #77
Trabecular artery:
To understand the organization of the red pulp and white pulp it is necessary to understand the vasculature of the spleen. The trabeculae within the spleen distribute blood to the pulp. Recall from lecture that blood flows through the vasculature of the spleen in the following order: Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.
Also remember that reticular fibers do not stain in this triple-stained preparation. However, they are thought to play a role in directing red cell 'open' circulation in red pulp.
Topic: Trabecular artery
Red arrows = trabecular artery.
Artery white pulp:
The artery of the white pulp may branch significantly, and in larger species may also give off small nodular arterioles and capillaries within the white pulp that eventually drain into surrounding marginal sinuses. Note that in this specimen many of the 'arteries of the white' pulp are categorized as arterioles. [Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: Artery white pulp
Blue arrows = artery in longitudinal section.
Topic: Artery white pulp
Blue arrows = artery in cross section.
PALS:
White pulp is the aggregated lymphoid tissue of the spleen and is surrounded by the marginal sinuses, which are the border between the red and white pulp. Typical lymphoid nodules with many lymphocytes are located eccentrically in areas of white pulp. The lymphoid tissue associated with arteries in the white pulp is called the periarterial lymphatic sheath (PALS). The sheath may be incomplete and not fully surround the artery. Arteries of the white pulp almost all divide into smaller vessels in the marginal zone. [Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: PALS
Green asterisks = PALS; Red arrows = artery of white pulp (longitudinal).
Marginal sinuses:
[Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: Marginal sinuses
Blue arrows = sinuses containing red blood cells.
Artery Red Pulp:
Because the arteries of the red pulp are a continuation of the artery of the white pulp, they are smaller in caliber and may be no larger than a terminal arteriole. Most vasculature of the red pulp consists of capillaries and sinuses that are variable in size and empty directly in to the trabecular veins. The red pulp contains many capillaries and blood sinusoids that are bordered by cells aggregated around reticular connective tissue. These cell-lined spaces are the sites where blood cells are sufficiently retarded to allow the removal of old worn-out red cells and any foreign material present in the blood. Cells of the macrophage system are present throughout the red pulp to serve that function. [Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: Artery red pulp
Sheathed capillary:
The artery of the white pulp may branch significantly, and in larger species may also give off small nodular arterioles and capillaries within the white pulp that eventually drain into surrounding marginal sinuses. Note that in this specimen many of the 'arteries of the white' pulp are categorized as arterioles. [Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: Sheathed capillary
Blue arrows = capillary in cross section; Green circle = approximate edge of sheath surrounding the capillary.
Trabecular vein:
The trabecular veins are easily distinguished from trabecular arteries by the orientation of the smooth muscle. Veins have little smooth muscle, hence the smooth muscle visible is oriented longitudinal to the vessel - whereas arterial smooth muscle will be circumferentially-oriented around the vessel lumen. [Splenic artery→trabecular artery→artery of the white pulp→artery of the red pulp (pulp arteriole)→sheathed capillary or terminal capillary→splenic sinuses or venules→trabecular vein.]
Topic: Trabecular vein
Blue arrows = trabeculum; Red arrows = trabecular vein.
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