<peir-vm>UAB-Histology-00035</peir-vm>
3. === Slide 93, Lymph node (H&E) in the hilus of the lung. These nodes help filter dust, carbon particles, and other debris that get into the lungs.===
a. Note Slide 93, Lymph node (H&E) in the innumerable macrophages filled with dark, particulate matter. Some hilus of the dark lung. These nodes help filter dust, carbon particles may not have been ingested by macrophages or may be deposited after ingestion , and rupture of other debris that get into the macrophagelungs.
bNote the innumerable macrophages filled with dark, particulate matter. The node has so many active macrophages that Some of the lymphatic tissue has dark particles may not have been greatly reduced. Note ingested by macrophages or may be deposited after ingestion and rupture of the small cortex and only scattered medullary cords, if anymacrophage.
BThe node has so many active macrophages that the lymphatic tissue has been greatly reduced. Lymph Node Details. Since you are now familiar with Note the general structure of lymph nodessmall cortex and only scattered medullary cords, study the nodes on Slides 35 and 63 in greater detailif any.
1Lymph Node Details. In slide 35 note that most Since you are now familiar with the general structure of lymph nodes, study the lymphatic nodules contain germinal centers containing small and medium-sized lymphocytes, macrophages, nodes on Slides 35 and lymphoblasts (few 63 in number)greater detail.
a<peir-vm>UAB-Histology-00093</peir-vm> ==== Slide 35, Mesenteric Lymph Nodes (H&E) ==== In slide 35 note that most of the lymphatic nodules contain germinal centers containing small and medium-sized lymphocytes, macrophages, and lymphoblasts (few in number). Small and medium-sized lymphocytes as well as macrophages are more prominent in the germinal centers than are lymphoblasts. The medium-sized lymphocytes have more euchromatin than small lymphocytes, the nucleolus is larger, and the cytoplasm is more basophilic. The macrophages may have an acidophilic, vacuolated cytoplasm and an eccentrically located nucleus. <peir-vm>UAB-Histology-00035</peir-vm> ==== Slide 63, Lymph Node ====
2. Lymphoblasts (large lymphocytes) are more easily recognized on slide 63, although fewer germinal centers are present on this slide. To identify lymphoblasts, look in the germinal centers for relatively large cells that have basophilic cytoplasm (not very distinct on our slides) and a large mostly euchromatic nucleus with one or two prominent nucleoli.
3. The germinal centers have a stroma of reticular fibers and reticular cells. Those cells, which have long almost dendritic-like protoplasmic processes, are called dendritic cells. They trap antigens in the presence of antibodies. Dendritic cells are difficult to identify so do not try to find them. Rather, identify the more typical reticular cells in the subcapsular and medullary sinuses on slide 63. Numerous macrophages can also be found in these sinuses.
4. Observe on your slides that the germinal centers are accentuated by a number of densely packed small lymphocytes that form a ring around the centers. Note that germinal centers are not usually present before birth, nor are they present in animals raised in a germ-free environment.
THYMUS<peir-vm>UAB-Histology-00063</peir-vm>
A. The thymus is unlike other lymphatic organs in two major respects: (1) its stroma consists of a framework of connecting epithelial reticular cells (cytoreticular cells) derived from endoderm. This stroma is not typical reticular connective tissue that is derived from mesoderm and characteristic of other lymphatic organs. (2) Lymphatic nodules are lacking, but the organization of the lobules into a cortex and a medulla may give the unwary student the impression that nodules are present.== Thymus ==
B. Four slides The thymus is unlike other lymphatic organs in two major respects: (1) its stroma consists of a framework of thymic tissue are to be studied. Slides 55 and 61 are connecting epithelial reticular cells (cytoreticular cells) derived from young individualsendoderm. Slide 60 This stroma is not typical reticular connective tissue that is derived from mesoderm and characteristic of other lymphatic organs. (2) Lymphatic nodules are lacking, but the organization of the lobules into a nineteen-year-old, cortex and slide 59 is an involuted thymus from a fifty-year-old person. Since medulla may give the unwary student the thymus responds to illness by undergoing stress involution, it should be realized impression that some sections might not be optimal for studying all features. Slide 55 from a ten-day old child best shows the normal features for a young thymusnodules are present.
1Four slides of thymic tissue are to be studied. Scan Slides 55 and 61 are from young individuals. Slide 60 is from a nineteen-year-old, and slide 59 is an involuted thymus from a fifty-year-old person. Since the thymus responds to illness by undergoing stress involution, it should be realized that some sections might not be optimal for studying all features. Slide 55, Thymus (Infant) (H&E) at low powerfrom a ten-day old child best shows the normal features for a young thymus.
a. Observe the thin connective tissue capsule surrounding this organ and the septa === Slide 55, Thymus (trabeculaeInfant) which project inward from the capsule. These strands of connective tissue subdivide the thymus into lobules. Blood vessels are contained within some of the larger septa.(H&E) ===
b. Note that most lobules consist of a darkly stained cortex Observe the thin connective tissue capsule surrounding this organ and a lighter-stained medulla. Reconstructions of the thymus show that the medulla is continuous septa (trabeculae) which project inward from one lobule to the next lobule within the same lobecapsule. The palely stained medulla should not be confused with germinal centers These strands of lymphatic nodules. The connective tissue subdivide the thymus lacks lymphatic nodulesinto lobules. The medulla stains lighter than the cortex because it contains more epithelial reticular cells and fewer lymphocytes than Blood vessels are contained within some of the cortex. The epithelial reticular cells are similar in appearance to primitive reticular cells of other lymphatic organs. Identify these in both cortex and medullalarger septa.
cNote that most lobules consist of a darkly stained cortex and a lighter-stained medulla. Identify Reconstructions of the acidophilic-staining thymic corpuscles (Hassall’s corpuscles) in thymus show that the medulla. These structures, unique is continuous from one lobule to the next lobule within the same lobe. The palely stained medulla should not be confused with germinal centers of lymphatic nodules. The thymus, consist of concentrically arranged lacks lymphatic nodules. The medulla stains lighter than the cortex because it contains more epithelial reticular cellsand fewer lymphocytes than are contained within the cortex. Some of the The epithelial reticular cells are similar in the center are degeneratingappearance to primitive reticular cells of other lymphatic organs. In this young thymus, the thymic corpuscles are small. Note that many are considerably larger on slide 60 Identify these in both cortex and on slide 59medulla.
dIdentify the acidophilic-staining thymic corpuscles (Hassall’s corpuscles) in the medulla. These structures, unique to the thymus, consist of concentrically arranged epithelial reticular cells. Note there are no lymphatic sinuses Some of the cells in the center are degenerating. In this young thymus but numerous , the thymic corpuscles are small blood vessels course through the organ. They Note that many are located mainly in the septa considerably larger on slide 60 and the medullaon slide 59.
eNote there are no lymphatic sinuses in the thymus but numerous small blood vessels course through the organ. They are located mainly in the septa and the medulla. In the cortex are some small, rounded clear areas about the size of a large cell.
These areas may contain palely stained macrophages, some of which have been active in engulfing other cells.
f. Study the section under high power. Distinguish between lymphocytes and epithelial reticular cells. Examine the thymic corpuscles closely. Study the macrophages. <peir-vm>UAB-Histology-00055</peir-vm> === Slide 61, Thymus (H&E) ===
2. Slide 61, Thymus, (H&E) is from a seven-year-old child. Identify as many features as possible. Observe how different this thymus appears from the section of the younger thymus previously studied on Slide 55. Slightly more connective tissue and fat are present in the seven-year-old thymus and the thymic corpuscles are larger. <peir-vm>UAB-Histology-00061</peir-vm> === Slide 60, Thymus (H&E) === Study slide 60, Thymus (H&E) from a nineteen-year-old. Note the reduced number of lobules that are widely separated by a large increase in the amount of fat. Identify the thymic corpuscles. Observe that arterioles, venules, and larger blood vessels are absent from the cortex of the lobules. The thick-walled capillaries that form the blood-thymus barrier are not readily identifiable on our slides. <peir-vm>UAB-Histology-00060</peir-vm>
3. Study slide 60=== Slide 59, Thymus (H&E) from a nineteen-year-old. Note the reduced number of lobules that are widely separated by a large increase in the amount of fat. Identify the thymic corpuscles. Observe that arterioles, venules, and larger blood vessels are absent from the cortex of the lobules. The thick-walled capillaries that form the blood-thymus barrier are not readily identifiable on our slides.===
4. Study slide 59, Thymus (H&E) from a fifty-year-old individual. Compare this involuted thymus with the sections of thymus previously studied. <peir-vm>UAB-Histology-00059</peir-vm>
TONSILS== Tonsils ==
Tonsils are defined as aggregates of lymphatic nodules associated with an epithelium. The palatine tonsils, pharyngeal tonsil and lingual tonsils form a ring of lymphatic tissue around the entrance to the throat (pharynx). This protective tonsillar ring is at the oropharyngeal isthmus. The “intestinal tonsils”, better known as aggregated nodules (Peyer’s patches) are located in the ileum of the small intestine.
A. === Palatine tonsilTonsil === ==== Slide 52, Palatine Tonsil (H&E) ====
1Observe that “one side,” the surface, is covered by stratified squamous epithelium. Scan From the surface a total of 10 to 20 deeply invaginated epithelial pockets called crypts extend into the substance of the organ. Note that the epithelium lining the crypts is continuous with the surface epithelium. Only a few crypts will be present on any one slide 52, Palatine tonsil (H&E).
a. Observe that “one On the side,” of the tonsil opposite the surface, is covered by stratified squamous epithelium. From the surface will be found a total capsule of 10 dense irregular connective tissue that serves to attach the organ to 20 deeply invaginated epithelial pockets called crypts extend into the substance wall of the organoropharynx. Note that Identify the epithelium lining capsule and the crypts is continuous with connective tissue septa that extend from it to partially subdivide the surface epithelium. Only a few crypts will be present on any organ by separating one slidecrypt from another.
b. On the side of the tonsil opposite the surface epithelium will be found a capsule of dense irregular connective tissue that serves Skeletal muscle and mucous glands occur deep to attach the organ to the wall of the oropharynx. Identify the capsule and the connective tissue septa that extend from it to partially subdivide the organ by separating one crypt from another.
cA large number of lymphatic nodules are present on this section. Skeletal muscle and mucous glands occur Many of them have germinal centers. The nodules usually lie as a single layer just beneath the epithelium surrounding each crypt. Only a loose layer of lymphatic tissue separates the nodules from the epithelium. With high power, note that deep in the crypts numerous lymphocytes have infiltrated the epithelium. In some deep areas of the crypts it is difficult to identify the type of epithelium. Observe that the capsulesurface epithelium is infiltrated by fewer lymphocytes.
d. A large number of Note that afferent lymphatic nodules vessels and lymph sinuses as seen in lymph nodes are present on this section. Many of them have germinal centers. The nodules usually lie as a single layer just beneath the epithelium surrounding each crypt. Only a loose layer of lymphatic tissue separates the nodules absent from the epithelium. With high power, note that deep in the crypts numerous lymphocytes have infiltrated the epithelium. In some deep areas of the crypts it is difficult to identify the type of epithelium. Observe that the surface epithelium is infiltrated by fewer lymphocytestonsils.
e. Note that afferent lymphatic vessels Tonsils are not divided into a cortex and lymph sinuses as seen in lymph nodes are absent from tonsilsa medulla.
fReticular connective tissue forms the stroma of the tonsil, but the reticular fibers cannot be identified without special stains. Tonsils The reticular cells are not divided into a cortex and a medullaobscured by the lymphocytes.
g. Reticular connective tissue forms the stroma of the tonsil, but the reticular fibers cannot be identified without special stains. The reticular cells are obscured by the lymphocytes.<peir-vm>UAB-Histology-00052</peir-vm>
B. === Aggregated nodules (Peyer’s patches) === Identify aggregated nodules on slide 31, 168, or 172 Ileum (H&E).
1Aggregated nodules (Peyer’s patch) consist of groups of lymphatic nodules massed together in the wall of the ileum opposite the attachment of the mesentery. Identify aggregated One Peyer’s patch may consist of ten to seventy lymphatic nodules on slide 31, 168, or 172 Ileum (H&E).
a. Aggregated The nodules (Peyer’s patch) consist of groups of lymphatic nodules massed together originate in the wall of lamina propria but they may extend into the submucosa disrupting the muscularis mucosae. Where the ileum opposite nodules project to the attachment luminal surface of the mesentery. One Peyer’s patch may consist of ten to seventy lymphatic nodulesileum, villi are absent.
b. The nodules originate in the lamina propria but they may extend into the submucosa disrupting the muscularis mucosae. Where the nodules project to the luminal surface of the ileum==== Slide 31, villi are absent.Ileum (H&E) ====<peir-vm>UAB-Histology-00031</peir-vm>
SPLEEN==== Slide 168, Ileum (H&E) ====<peir-vm>UAB-Histology-00168</peir-vm> ==== Slide 172, Ileum (H&E) ====<peir-vm>UAB-Histology-00172</peir-vm> == Spleen ==
The spleen is an organ which both forms and destroys blood cells. In the embryo the spleen is a fully hemopoietic organ generating all the kinds of blood cells. In late fetal life the spleen stops producing erythrocytes and granulocytes, but it continues to generate lymphocytes and monocytes. However, it retains full hemopoietic potentialities so that pathologically, in adulthood, the spleen may once again initiate the functions of red bone marrow. The spleen is highly active in the production of antibodies. Plasma cells are the main source of the antibodies. The spleen also serves as a specialized blood-filtering organ and it can serve for the temporary storage of platelets and erythrocytes.
=== Slide 18, Spleen (H&E) ===
A. Examine slide 18, Spleen (H&E) and identify the capsule and trabeculae
1. The capsule is covered by mesothelium. The capsule is composed of collagen, elastic and a very few smooth muscle fibers. The elastic fibers predominate in the inner half of the capsule.
2. Note that the trabeculae appear to be cut at random and that they stain similar to the capsule since they are extensions of this structure into the substance of the spleen. Trabeculae form a supporting framework.
3. The amount of elastic tissue in the trabeculae is similar to that found in the inner half of the capsule. Note that some sections of the trabeculae show trabecular arteries and veins coursing through them. Neither demonstrates an adventitia; the connective tissue of the trabecula immediately surrounds the media.
4. Identify the darkly stained lymphatic nodules (splenic nodules) of the white pulp. Identify the central arteries passing through a lymphatic nodule. Note that diffuse to dense lymphatic tissue also occurs in the white pulp mainly surrounding and following the distribution of the arterial vessels. White pulp is typical lymphatic tissue containing a stroma of reticular cells and fibers.
5. Select a particularly dense or large lymphatic nodule to identify the marginal zone at its periphery. The marginal zone is a transitional region of red pulp containing more lymphocytes and plasma cells than the pulp cords. Branches from the central artery pass into this transitional zone. It is here that T- lymphocytes leave the general circulation to take up residence in the spleen.
6. The red pulp occurs mainly as venous sinuses and the intervening pulp cords. This tissue lies between the areas of the white pulp. There is no sharp boundary between red and white pulp. The red pulp is atypical lymphatic tissue. It has reticular connective tissue infiltrated with lymphocytes and monocytes, but in addition, all other kinds of blood cells occur here as well. Especially numerous are the erythrocytes which impart a reddish coloration to the area of the red pulp in the fresh spleen. <peir-vm>UAB-Histology-00018</peir-vm> ==== Slide 19, Spleen (PASH) ==== The pulp cords consist of the tissue occupying the narrow areas between the venous sinuses. With high power, study the splenic sinuses and pulp cords. Note how much easier it is to identify the venous sinuses by using the PASH stained section of Spleen (slide 19, Spleen PASH). <peir-vm>UAB-Histology-00019</peir-vm> {{Template:Histologic}}
a. The pulp cords consist of the tissue occupying the narrow areas between the venous sinuses. With high power, study the splenic sinuses and pulp cords. Note how much easier it is to identify the venous sinuses by using the PASH stained section of Spleen (slide 19, Spleen PASH).[[Category:Histologic]]