Organs of the Immune System

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Organs of the Immune System
2011-05-28 13:41:59
Organs Immune System

Organs of the Immune System
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  1. These are thin-walled vessels that drain interstitial fluid from tissues back into the venous system. They carry antigens to lymph nodes for processing and beginning of immune response.
  2. What is the function of lymph nodes?
    To allow the immune response to an antigen to begin
  3. This is the site where lymphocytes, macrophages, and other cells can contact antigen and interact with each to generate immune responses. These function to trap malignant cells.
    Lymph Nodes
  4. What is a lymph node surrounded by? What is just beneath this?
    • Fibrous Capsule
    • Subcapsular Sinuses
  5. ____________ lymphatics drain into the subcapsular sinuses; antigens reach the lymph nodes via these lymphatics.
  6. The lymph percolates down through the lymph node to the ________ of the node, where it exits.
  7. The lymph node is drained by __________ lymphatics, which leave at the hilum of the lymph node. Lymphocytes and other cells can leave the lymph node via these lymphatics as well.
  8. What are the two main functional parts of the lymph node?
    • Cortex
    • Medulla
  9. What two things are contained in the Cortex of the lymph node?
    • Follicles: predominantly B-cells (germinal centers and mantle zones)
    • Paracortical (interfollicular) Areas: predominantly T-cells
  10. What do primary follicles consist of?
    Small Lymphocytes
  11. What do secondary follicles consist of?
    • Germinal Centers
    • Surrounded by Mantle Zones
  12. Which type of follicle are immunologically active? What area within this type is the active area?
    • Secondary Follicles
    • Germinal Sites
  13. Where do memory B-cells reside in lymph nodes?
    Mantle Zones of the Secondary Follicles in the Cortex
  14. What is contained in the Medulla, or center portion, of the lymph node?
    Medullary Sinuses; there may be some lymphocytes, plasma cells, and macrophages present in the medulla
  15. In lymph nodes, the superficial cortex is predominantly a _____-cell zone; the deep cortex is more of a ____-cell zone; plasma cells are more prominent in the ____________.
    • B
    • T
    • Medulla
  16. Identify the Cap, Cortex, Medulla, and Hilum in the Lymph Node Below:
  17. Identify the Germinal Center and Mantle Zone in the secondary follicle pictured below:
    The germinal center is at bottom left and center; the darker mantle zone extends upwards and to the right of the germinal center
  18. What cell-type are revealed by the immunohistochemical stain below?
    • B-cells (brown is positive)
    • The germinal center in the middle of the follicle stains predominantly for B-cells; the dark ring surrounding the germinal center is the mantle zone, also predominantly a B-cell zone
  19. What cell-type are revealed by the immunohistochemical stain below?
    • T-cells (brown = positive)
    • Note that the center of the follicle is predominantly negative, although a few T-cells are present; the mantle zone is also predominantly negative. Not that the areas outside the follicle (bottom left and bottom right) are predominantly positive -- these are the paracortical T-cell zones
  20. Extranodal lymphoid tissue is composed of patches of lymphoid tissue located in the GI tract, lungs, and other extranodal sites. These offer immunological protection at areas that are vulnerable to potential invaders. They are also important in ______ production.
  21. In the intestine, what are the lymphoid nodules called?
    Peyer's Patches
  22. Identify the histological slide below:
    Peyer's Patches: lymphoid nodules located in the intestine
  23. What causes lymph node enlargement (lymphadenopathy)?
    • Infections
    • Drugs -- Phenytoin
    • Metastatic Malignancies
    • Systemic Diseases -- sarcoidosis, SLE
  24. If you feel an enlarged lymph node, what is the first thing to do?
    Look in the area drained by that lymph node for evidence of infection
  25. What is the picture below an example of?:
    • A reactive follicular hyperplasia: there are numerous, prominant germinal centers which vary in size and shape; some are fusing
    • This is a very common type of reactive lymph node enlargement which can occur due to many different causes
  26. All of the blood vessels of the spleen enter and leave by a __________ __________.
    Splenic Pedicule
  27. The main arterial supply to the spleen is from the ________ artery, which is a branch of the _______ trunk. A smaller amounts comes from branches of __________ arteries.
    • Splenic
    • Celiac
    • Gastric
  28. Normally the majority of blood from the spleen drains through the ________ vein, which joins with the ___________ _________ vein to form the _________ vein; a smaller amount drains to the _________ veins.
    • Splenic
    • Superior Mesenteric
    • Portal
    • Gastric
  29. The primary venous drainage of the spleen is the splenic vein, which joins the superior mesenteric vein to form the portal vein. The spleen also drains a minor amount through accessory veins which connect with a plexus of gastric and esophageal veins. If the pressure in the portal vein increases (for example, in cirrhosis of the liver), blood from the spleen is going to be shunted into the plexus of gastric and esophageal veins, which can result in what?
    Gastroesophageal Varices -- can be a source of severe hemorrhage
  30. Which organ is composed of a fibrous capsule with trabecula extending into the parenchyma? The stroma is composed of a network of fibroblast-like reticular cells.
  31. Within the spleen, the _________ artery enters at the hilum and gives off the ____________ arteries --> _________ arteries --> __________ arteries.
    • Splenic
    • Trabecular
    • Central
    • Penicilliary
  32. The parenchyma of the spleen is divided into white pulp and red pulp. What does the white pulp consist of?
    • Lymphoid Zone
    • Surrounds Central Arteries
    • Periarteriolar Lymphoid Sheath (PALS): T-cells
    • Follicles & Marginal Zones: B-cells
  33. The parenchyma of the spleen is divided into white pulp and red pulp. What does the red pulp consist of?
    Network of splenic cords (which are lined by macrophages) and vascular sinuses
  34. The arteries of the spleen eventually drain into the red pulp. Most of the blood drains directly into ________________ (closed circulation); a smaller amount drains into an open network of _____________ (open circulation). These together make up the red pulp.
    • Splenic Venous Sinusoids
    • Splenic Cords
  35. Identify the structure below:
  36. Identify the structure below:
    What do the asterisks indicate?
    • Spleen
    • Arteries, which are surrounded by the periarteriolar lymphoid sheath which primarily consists of T-cells
    • LN indicates follicles, which primarily contain B-cells
    • R indicates red pulp
  37. What area of the spleen is shown below?
    White Pulp
  38. Identify the area of the spleen below:
    Red Pulp
  39. What are the functions of the spleen?
    • Major site of protection against blood-born pathogens
    • Site of antibody production
    • Screens and eliminates senescent or defective RBCs
    • Stores platelets and some granulocytes
  40. These are small nuclear fragments left behind when red cells lose their nucleus. We all produce some RBCs with these, but they are normally removed by the spleen. Therefore, their presence is a sign of what?
    • Howell-Jolly Bodies
    • Lack of splenic function
  41. Identify the small dark structures within the RBCs below. What are these a morphologic sign of?
    • Howell-Jolly Bodies
    • They are the morphologic sign on a blood smear of lack of splenic function
  42. The spleen removes excess ________ ________ from young RBCs.
    Membrane Lipids
  43. RBCs must pass through a narrow slit to enter vascular sinuses from splenic cords. What does this require?
  44. Hypersplenism is characterized by splenic enlargement with sequestration of WBCs, RBCs, and platelets. What is this usually due to?
    Passive Splenic Congestion
  45. Hyposplenism is usually due to surgical splenectomy, autosplenectomy in sickle cells disease, and congenital aplasia. What does this put a patient at an increased risk for?
    Severe Bacterial Sepsis
  46. What are the four main causes of Splenomegaly?
    • Congestive Spenomegaly
    • Reactive Splenomegaly
    • Infiltrative Disease -- Gaucher Disease, others
    • Malignancies -- hematologic, non-hematologic
  47. This cause of splenomegaly is characterized by a backup of venous blood flow through the splenic vein. Causes include cirrhosis of the liver, right heart failure, thrombosis of the portal or splenic veins; this may be associated with hemorrhage from gastroesophageal varices.
    This also may occur in chronic hemolytic anemias: hereditary spherocytosis, thalassemia, others.
    Congestive Splenomegaly
  48. What infection-types are associated with Reactive Splenomegaly?
    • Viral: EBV and others
    • Parasitic: Malaria and others
    • Bacterial, fungal, and mycobacterial
  49. What are the three causes of Reactive Splenomegaly?
    • Infections
    • Chronic Inflammatory Disorders
    • Hemolytic Anemias
  50. This syndrome is the triad of rheumatoid arthritis, splenomegaly, and neutropenia; it is often associated with a lymphoproliferative disorder composed of large granular lymphocytes (LGLs).
    What type of splenomegaly is this associated with?
    • Felty Syndrome
    • Reactive Splenomegaly
  51. What are the most common type of neoplasms in the spleen?
    Hematologic Neoplasms: Hodgkin and Non-Hodgkin Lymphomas, Myeloproliferative Neoplasms, Hairy Cell Leukemia
  52. Primary splenic neoplasms are rare; usually they are vascular tumors. What two types of benign; what kind are malignant?
    • Hemangiomas & Lymphangiomas
    • Hemangiosarcomas
  53. What are the Hematologic Neoplasms?
    • Hodgkin & non-Hodgkin Lymphomas
    • Myeloproliferative Neoplasms: CML, P. vera; primary myelofibrosis
    • Hairy Cell Leukemia
  54. This organ is located in the superior mediastinum. It is bilobed and irregularly pyramidal. It is derived predominantly from the 3rd pair of pharyngeal pouches plus or minus 4th pouches. This organ atrophies after puberty --> there are only a few small islands of epithelial cells in older adults
  55. The thymus and the parathyroid glands are both derived from what?
    The Pharyngeal Pouches
  56. Identify the organ below:
  57. This organ is the site of T-cell selection and maturation. In the absence of this organ, there will be no functional T-cells, which basically results in no functional immune system.
  58. This is an epithelial organ. It is composed of two fused lobes, surrounded by a fibrous capsule. The fibrous bands divide it into lobules. It predominantly consists of epithelial cells and immature T-cells.
    It is divided into a cortex and medulla; the medulla contains Hassall's Corpuscles (islands of squamous cells). The most immature T-cells are located in superficial cortex; T-cells move down the medulla as they mature
  59. Where are the most immature T-cells found in the Thymus?
    In the superficial cortex; T-cells move down into the medulla as they mature
  60. Identify the histological section below:
    • Thymus: divided into lobules
    • The outer, darker areas are the cortex; the inner, paler areas are the medulla
  61. Identify the histological section below:
    • Thymus: Cortex
    • The capsule (outer portion) is at the bottom
    • The cortex is composed of immature cortical T-cells (the smaller nuclei with slightly darker chromatin) and thymic epithelial cells (the larger cells with larger nuclei, open chromatin, and distinct nucleoli)
  62. Identify the histological section below:
    • Thymus: Medulla
    • Recognized by the presence of Hassall's Corpuscles: the round to oval islands of squamous cells
  63. The earliest cortical thymocytes express NEITHER the CD4 or the CD8 antigen. Then, as they move down into the deeper cortex they express BOTH the CD4 and the CD8 antigen; what happens as they enter the medulla?
    They must choose to express EITHER the CD4 or the CD8 antigen
  64. This congenital syndrome is related to a deletion of part of the long arm of chromosome 22 at band 11.2. It is related to abnormalities of the 3rd and 4th pharyngeal pouches -- which gives rise to the thymus and parathyroid glands. The absence or hypoplasia of the thymus results in an immunodeficiency related to deficient T-cell function; the patients are predisposed to infections, particularly by species of Candida fungi. The absence or hypoplasia of the parathyroid glands results in hypoparathyroidism and hypocalcemia.
    There are variable congenital cardiac abnormalities, mild facial dysmorphism.
    DiGeorge Syndrome
  65. What is the confirmatory test for DiGeorge Syndrome?
    FISH looking for deletion of chromosome 22q11.2
  66. This syndrome is linked to abnormalities of the gene producing the WAS protein. It is X-linked recessive, and is linked to a hypoplastic thymus, recurrent infections, and thrombocytopenia with small platelets.
    Wiskott-Aldrich Syndrome
  67. This syndome is due to a mutation in the ATM gene, which basically acts as a tumor suppressor gene. It has an autosomal recessive inheritance. Patients with this have cerebellar ataxia and immunodeficiency
  68. This is characterized by the presence of lymphoid follicles with germinal centers in the thymus: lymphoid follicles are not normally found in the thymus; thymus size is often normal. This is often associated with autoimmune diseases -- especially myasthenia gravis: muscle weakness due to antibody against the acetylcholine receptor on muscle cells
    Thymic Follicular Hyperplasia
  69. These are tumors of thymic epithelial cells -- they are the most common tumor of the thymus. There are three variants: encapsulated; invasive but cytologically benign, and thymic carcinomas -- cytologically malignant. Which type are most common?
    • Thymomas
    • Encapsulated
  70. What are the three types of neoplasms of the Thymus?
    • Thymomas
    • Hematologic Neoplasms: T lymphoblastic leukemia/lymphoma; B-cell Lymphomas
    • Germ Cell Tumors: rare
  71. Identify the phenomenon below:
    Thymoma -- consists predominantly of spindle cells
  72. Identify the phenomenon below:
    Thymoma -- mixture of spindle cells and immature T-cells
  73. What are thymomas often associated with?
    Autoimmune Diseases: myasthenia gravis; pure red cell aplasia; graves' disease; others
  74. What is the most common hematologic malignancy involving the thymus? In what population is this most commonly seen in? What do patients present with?
    • T Lymphoblastic Leukemia/Lymphoma
    • Adolescent Males
    • Large Mediastinal Mass -- may have respiratory compromise, pleural effusions
  75. This is an uncommon neoplasm of the thymus. It is derived from thymic B-cells, and is a histologic variant of diffuse large B-cell lymphoma. This typically occurs in young women.
    Primary Mediastinal Large B-Cell Lymphoma