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Secondary Lymphoid Tissue

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Topic updated on 09/17/16 6:51pm

Introduction
  • Three types of secondary lymphoid tissue
    • spleen
    • lymph nodes
    • lymphoid associated tissue
  • Several important roles
    • store immune cells
    • sequester pathogens
    • increase probability of contact between divisions of the immune system
    • survey body for infection
Spleen

  • Function
    • primary defense against blood-borne pathogens
  • Anatomy
    • white pulp
      • germinal centers
        • B-cell follicles
      • periarterial lymphatic sheath (PALS)
        • location of T-cells
        • surrounds central arteriole
    • red pulp
      • fenestrated basement membrane
      • location of macrophages
      • surrounds white pulp
    • Venous drainage
      • occurs through portal circulation
      • Lymphocytes passively traffic out of leaky vessels
        • unlike other secondary lymph tissue which is an active process
  • Clinical
    • effect of asplenia
Lymph nodes
 

 

  • Perfusion
    • inflow
      • many afferent lymphatic vessels
      • drain into subcapsular sinus
    • outflow
      • 1 or more efferent lymphatic vessels
  • Function
    • zone of contact between antigen presenting cells, B-cells and T-cells
    • storage and proliferation of lymphocytes
    • primary defense against tissue-born pathogens
  • Gross anatomy
    • layers of node (in order of lymph fluid as it passes from the subcapsular sinus to the efferent lymph vessels)
      • cortex
        • contain follicles of B-cells
        • primary follicles are cell dense
        • dormant
        • secondary follicles have pale germinal center
        • active proliferation
      • paracortex
        • contains mainly T-cells
        • contains High Endothelial Vessels (HEVs)
        • allow active extravasation of lymphocytes from blood into lymph nodes
        • interactions between L-selectins on lymphocytes with addressins on HEVs
        • between cortex and medulla
        • underdeveloped in patients with DiGeorge syndrome
      • medulla
        • consists of lymphocyte and plasma cell "cords"
        • contain sinuses which drain into the efferent lymph vessels
        • houses reticular cells + macrophages
    • lymph drainage
      • right lymphatic duct
        • right arm + right half of head + right half of thorax
      • thoracic duct
        • Rest of body
Mucosal-associated lymphoid tissue 
  • Accessory lymphoid tissue in several regions in the body 
    • e.g. Peyer's patches in the GI tract, tonsils in mouth
Trafficking
  • Lymphocytes pass through secondary lymph organs daily
    • maximize potential contact with antigen 

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