LYMPHOID ORGANS

• IMMUNE SYSTEM 

  • provides defense or immunity against infectious agents ranging from viruses to multicellular parasites
  • innate immunity and adaptive immunity
• Innate Immunity

  • preexisting nonspecific defenses

  1. Physical barriers

  2. Chemical defenses

  3. Various secretory substances

  4. Phagocytes
• Adaptive immunity

  •  Specific
  • acquired gradually by exposure to microorganisms, is more specific, slower to respond
  • Humoral response (Ab)  and cellular response (cytotoxic) 
  • APCs
  • Memory cells
  • CD8
• Antigen

  • molecule that is recognized by cells of the adaptive immune system and typically elicits a response from these cells

  • Epitopes → antigenic determinants
• Antibodies

  • a glycoprotein of the immunoglobulin family that interacts specifically with an antigenic determinant
  • secreted by plasma cells
  • IgG (most abundant)
  • IgD, IgG, IgA, IgE, IgM

  
• Antibodies

  A) Monomer

  B) Pentamer

  C) Dimer

  D) Trimer

  E) Monomer

  F) Monomer

  G) phagocytosis

  H) first

  I) mucosae

  J) B

  K) cell

  L) parasitic

  M) worms

  N) allergies

  
• Antibody

  • able to bind specifically and NEUTRALIZE certain viral particles and bacterial toxins, AGGLUTINATE many bacterial cells, and PRECIPITATE most soluble antigens
  • Binding of Fc portion promotes:
  • Complement activation
  • Opsonization
  • NK cell activation
• Binding

  A) Neutralization

  B) Agglutination

  C) Precipitationn

  
• Exposed Fc portion

  A) Complement fixation

  B) Opsonization

  C) Activation of NK cells

  
• CELLS OF ADAPTIVE IMMUNITY

  •  Antigen-Presenting Cells
  •  Lymphocytes

  
• LYMPHOID ORGANS

  • groups of cells, tissues, and organs that monitor body surfaces and internal fluid compartments and react to the presence of potentially harmful substances.
  • Lymphocytes are the definitive cell type
• Primary lymphoid organs

  • Thymus
  • Bone marrow
• Secondary lymphoid organs

  • Lymph nodes
  • Spleen
  • Diffuse lymphoid tissue

  
• Thymus

  •  primary or central lymphoid organ in which T

  cells are produced

  • bilobed structure in the mediastinum 
  • main function: induction of central tolerance
  •  originates from the embryo's third pair of pharyngeal pouches
  • Involution

  
• Cortex (Thymus)

  • outer portion of the parenchyma 
  • darkly basophilic 
  • contains an extensive population of T lymphoblasts (or thymocytes)

  
• name it

  A) desmosome

  B) thymic epithelial cell

  C) Lymphocyte

  
• Medulla (Thymus)

  • inner portion of the parenchyma 
  • contains mostly large lymphocytes
  • Thymic or Hassall's corpuscles

  
• Epithelioreticular cells (Thymus)

  • provide a framework for the developing T cells
  • 6 types
• Type I

  • function as a barrier that isolates developing T cells from the connective tissue of the organ
• Type II

  • express MHC I and MHC Il molecules, which are involved in thymic cell education 
• Type III

  • functional barrier; possess MHC I and MHC Il molecules
• Type IV

  • with type Ill cells, they create the barrier at the corticomedullary junction 
• Type V

  • provide the cellular framework of the medulla and to compartmentalize groups of lymphocytes
• Type Vl

  -  form the most characteristic feature of the thymic medulla, the thymic (Hassall's) corpuscles
• Blood-Thymus Barrier

  •  protects developing lymphocytes in the thymus from exposure to antigens.
  • capillary endothelium and its basal lamina
  • Perivascular connective tissue space occupied by macrophages
  • type I epithelioreticular cells with their basal lamina.
  • non afferent

  
• name it

  A) apoptosis

  B) survive

  C) medulla

  
• name it

  A) apoptosis

  B) survive

  C) maturation

  D) 2%

  E) CD4

  F) CD8

  G) Helper T lymphocyte

  H) Cytotoxic T lymphocyte

  
• Diffuse Lymphatic Tissue

  • mucosa-associated lymphatic tissue (MALT)
  • Lymphatic nodules
  • Tonsils
  • Peyer patches
  • Vermiform appendix
• Lymphatic nodules

  • discrete concentrations of lymphocytes contained in a meshwork of reticular cells. 
  • primary nodule - lymphatic nodule consisting chiefly of small lymphocytes
  • secondary nodule - has the following features:
  • Germinal center
  • Mantle zone or corona
• Germinal center

  • Contains large immature lymphocytes (lymphoblasts and plasmablasts
  • a morphologic indication of lymphatic tissue response to antigen
• Tonsils

  • large, irregular masses of lymphoid tissue in the mucosa of the posterior oral cavity and nasopharynx where their cells encounter antigens entering the mouth and nose
  • tonsillar crypts - deep invaginations in which the epithelial lining is densely infiltrated with lymphocytes and other leukocytes
  • PALATINE
  • LINGUAL
  • PARYNGEAL
• Palatine

  • stratified squamous epithelium
• Lingual

  • covered by stratified squamous epithelium; lack distinct capsules
• pharyngeal tonsils

  • pseudostratified ciliated columnar epithelium, and has a thin underlying capsule, lacks crypts

  A) Pharyngeal tonsil

  B) Palatine tonsil

  C) Lingual tonsil

  
• Tonsil

  A) Tonsillar crypts

  B) lymphatic nodules

  
• Peyer patches

  • located in the ileum 
  • consist of numerous aggregations of lymphatic nodules containing T and B lymphocytes

  
• Vermiform appendix

  • a short, small diameter projection from the cecum
  • Lamina propria is heavily infiltrated with lymphocytes and contains numeric lymphatic nodules

  
• Appendix

  
• Lymph node

  • bean-shaped, encapsulated structures distributed throughout the body along the lymphatic vessels
  •  nodes constitute a series of in-line filters of lymph that defend against the spread of microorganisms and tumor cells
  • Provide enclosed environments that facilitate production of plasma cells secreting non-IgA antibodies.

  
• Lymph node

  • Two types of lymphatic vessels serve the lymph node:
  • Afferent lymphatic vessels - convey lymph toward the node and enter it at various points on the convex surface of the capsule.
  • Efferent lymphatic vessels - convey lymph away from the node and leave at the hilum