7 TOB Lymph I

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mse263
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237392
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7 TOB Lymph I
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2016-09-15 11:45:11
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TOB Exam2
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MBS TOB
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MBS TOB Exam 2
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  1. Nearly all oocytes in females are arrested in:
    prophase of Meiosis I from a few months before birth until just before or during ovulation
  2. Lymphoid tissues
    • masses of lymphocytes and associated cells required to mount an immune response
    • provide an environment that promotes immune cell-antigen interaction
  3. What are the two ways lymphoid tissue may exist?
    • 1. as discrete organs covered by either an epithelium or connective capsule
    • 2. may exist as isolated masses of cells withIN
    • various organs in close proximity to the outside world (lumen)
  4. These are the 4 lymphoid tissues we learned:
    diagnostic features: highly cellular, only a little CT, lots of cells per area, LARGE nucleus, small cytoplasm, mostly euchromatin (dark) present versus heterochromatin (light)
  5. primary lymphoid organs
    • 1. bone marrow - development of immunocompetent B-cells

    2. thymus - development of immunocompetent T-cells
  6. secondary lymphoid organs (3)
    lymph nodes, spleen, mucosa associated lymphoid tissue
  7. thymus
    • representative primary lymphoid organ where T-cells develop
  8. T lymphocyte
    cells derived from the thymus and differentiate into several sub types (cytotoxic, helper, regulatory, etc)
  9. B lymphocyte
    • type of lymphocyte is specialized to recognize foreign antigens and, once activated, to produce antibodies specific to those antigens
    • activation of B-cells requires helper T lymphocytes
    • in order to produce antibodies, activated B cells must move to connective tissues where they undergo terminal differentiation into plasma cells
  10. T-cells primary enact ________ immunity while B-cells primarily participate in _________ immunity
    • T-cell: cell-mediated immunity
    • B-cell: humoral immunity
  11. opsonization
    when antigens are marked for an immune response by molecule that enhances phagocytosis
  12. thymic epithelial cells form a ____________ that becomes infiltrated by T-cell precursors called:
    • the cytoreticulum (thymic epithelial cells) gets infiltrated by THYMOCYTES
    • cytoreticulum acts as the sole physical support for the developing T-cells
  13. What is this?
    • the thymus
    • "starry sky" appearance
    • CT capsule
    • continuous brached medulla
    • septa - CT that separates lobules
  14. thymic cortex contains epithelial cells that function to:
    • mechanically support ‘nests’ of developing thymocytes
    • produce thymic hormones that to promote T cell maturation
    • stimulate ectopic expression of “self” proteins so thymocytes learn to distinguish self from non-self
    • contribute to the formation of the blood-thymus barrier
    • the thymic cortex contains developing lymphocytes (dark pink) and macrophages (white gaps, "stars")
    • *up to 95% of thymocytes fail to become immunocompetent and die by apoptosis
    • that's why the medulla is lighter than the cortex, because fewer mature T-cells are allowed to enter there, where they can potentially be exposed to the rest of the body
  15. Is there connective tissue (from the CT capsule and running through the septa) in the thymic medulla?
    • YES only connective tissue it has
    • separated from thymus by epithelial layer
  16. What are the brown stains?
    • epithelioreticular cells
    • support the lymphocytes in the medulla & cortex
    • in the medulla they can form Hassall’s corpuscles
    • also function in the weeding out of T-cells that aren't immunocompetent
    • (white = macrophages, dark purple dots = lymphocytes)
    • in general stains: appear lighter than lymphocytes
  17. blood-thymus barrier
    • prevents foreign antigens from getting into the compartment where thymocytes are developing and becoming immunocompetent
    • composed of an inner endothelial layer and an outer epithelioreticular layer with a thick basement membrane in between that serves as a barrier for foreign material
  18. What might happen with a faulty blood-thymus barrier?
    • without the barrier a foreign protein could enter the thymus, it will be treated as derived from 'self', and all T-cells will be killed off that bind to it
    • if you later come in contact with this foreign antigen IT WON'T BE RECOGNIZED AS FOREIGN
    • thymic medulla
    • has fewer cells (appears lighter), contains numerous blood vessels, many macrophages, epithelial cells that promote expression of self-peptides, Hassall’s corpuscles, & a cortico-medullary boundary characterized by post-capillary, high endothelial venules where immunocompetent T cells exit the thymus to enter the general circulation

    • Hassall's corpuscles
    • concentric layers of epithelioreticular cells that secrete thymic stromal lymphopoietin (TSLP) which stimulates differentiation of regulatory T-cells
  19. What persists in an involuted thymus?
    • Hassall’s or thymic corpuscles
    • also has adipocytes present
  20. What is the difference between an encapsulated secondary lymphoid tissue and an unencapsulated secondary lymphoid tissue?
    • encapsulated: covered by CT
    • unencapsulated: covered by epithelium, associated w/ mucosa
  21. ALL secondary lymph organs contain BOTH nodular and diffuse lymphoid tissue
    • nodulues (follicles): B-cells & in the center a germinal center
    • diffuse: T-cells found between nodules and in the connective tissue underlying most epithelia (NO germinal centers)
  22. Why aren't all B cells daughter cells the same if they divide by mitosis?
    • affinity maturation
    • cells with the strongest affinity for antigens due to mutations will be selected over those that bind less strongly
    • selected cells must migrate to a connective tissue to fully differentiate as antibody producing plasma cells
  23. Will plasma cells (differentiated B cells) appear in nodules?
    NEVER: B cells terminally differentiate in plasma cells only in CT
  24. examples of encapsulated secondary lymphoid tissue
    • 1. lymph nodes
    • 2. spleen
    • Lymphoid Nodules (lymph nodes)
    • has a CT capsule (encapsulated)
    • filter particulate matter & promote the interaction between antigens and cells of the immune system

  25. MALT (mucosa Associated Lymphoid Tissue)
    • these encompass the UNENCAPSULATED secondary lymphoid tissue
    • 1. Peyer's Patches (gastrointestinal)
    • 2. Appendix (gastrointestinal)
    • 3. Tonsils (gastrointestinal & respiratory tract)
    • (other unencapsulated types of secondary lymph tissue = Bronchus ALT, GutALT, SALT)
  26. What 3 layers constitute a mucosa?
    • epithelial lining
    • lamina propria
    • muscularis mucosa
    • masses of nodular & diffuse lymphoid tissue lying underneath the oral or pharyngeal epithelium
    • epithelium frequently has CRYPTS (deep invaginations) which increase surface area and maximize the antigen-lymphocyte interactions
    • lymphocytes will often migrate into the epithelium and sample antigen at the surface
    • have mast cells, plasma cells and neutrophils are usually present as well as lymphatics to drain the tissue.
  27. What are the three types of tonsils?
    • 1) palatine (paired), covered by stratified squamous epithelium

    • 2) pharyngeal (single), covered by pseudostratified ciliated columnar epithelium
    • 3) lingual (multiple), covered by stratified squamous epithelium
    • (MALTs can be distinguished by their epithelial covering)
    • lingual tonsil
    • stratified squamous non-keratinizing epithelium (SSNKE)
  28. has an undulating basement membrane
    • pharyngeal tonsil - pharynx is digestive & respiratory
    • it has a pseudostratified, ciliated, columnar outer epithelial layer
    • things sticking up = cilia
    • pseudostratified
    • respiratory epithelia overlying lymphocytes --> has to be pharyngeal tonsil
    • Peyer's patch
    • nodules (with intervening diffuse lymphoid tissue) in the intestinal mucosa and/or submucosa
    • frequently found in the ileum
  29. Microfold cells (M cells)
    • cells that sample antigen; have a deep basal invagination that forms a pocket of immune cells
    • found in the epithelium overlying the Peyer's patch
    • nodules
    • (allows immune cells to get close to gut lumen)

    • weird shaped cells are M cells
    • rich in both nodular and diffuse lymphoid tissue
    • Appendix functions in
    • immune surveillance (abundant M-cells)
    • endocrine organ
    • reserve of gut flora (following loss due to diarrhea, toxic compounds)
    • MALT
    • lymphoid tissue that isn't necessarily an organ can be anywhere pathogens can access the body
    • just a clump of lymphocytes near a lumen should be a BALT or MALT indicator

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