Lymphatic System

Question 1

Gut Associated Lymphatic Tissue (GALT)

Answer 1

• Large, relatively permanent lymphatic nodules found in CT of gastrointestinal tract
• One region where B lymphocytes develop immunocompetency
• E.g. Peyer’s Patches of ileum

Question 2

Epithelial Reticular Cells

Answer 2

• “CT” cells of thymus of epithelial origin
• Cells have long processes attached to one another by desmosomes to form 3D scaffolding to support thymic cells
• Large, round-to-oval, pale-staining nuclei
• Differentiate into keratin producing cells that form Hassalls corpuscles

Question 3

T Lymphocyte

Answer 3

• Cells responsible for cell-mediated immunity
• Become immunocompetent in thymus
• Occupy T cell domains of secondary lymphoid organs and tissues
• When exposed to antigens, differentiate into cytotoxic, helper or supresser T cells

Question 4

B Lymphocyte

Answer 4

• Cells responsible for antibody-mediated immunity
• Become immunocompetent in bursal equivalent areas (liver and GALT)
• Occupy B cell domains in secondary lymphoid organs and tissues
• Differentiate into plasma cells when exposed to antigen; begin producing antibodies to target antigen for destruction by macrophages

Question 5

Blood-Thymic Barrier

Answer 5

• Function: prevents entry of antigens into thymus; required for development of T lymphocyte immunocompetency
• Components:
  
  • Endothelium of capillary (continuous zonula occludens)
  • Endothelial basement membrane
  • Perivascular CT sheath (contains fibroblasts, macrophages)
  • Epithelial reticular basement membrane
  • Epithelial reticular cell sheath

Question 6

White Pulp

Answer 6

• Lymphoid tissue of spleen that screens blood for antigens
• Consists of aggregations of lymphocytes (stains deeply basophilic) structured around a central artery
• Appears white in fresh preparations

Question 7

Red Pulp

Answer 7

• Consists predominantly of packed erythrocytes
  
  • Stains acidophilic and appears red in fresh preparation
• Functions as reservoir of erythrocytes
• Macrophages phagocytose damaged erythrocytes:
  
  • Iron recycled as ferritin or hemosiderin
  • Hemoglobin converted to bilirubin

Question 8

Periarterial Lymphatic Sheath

Answer 8

• Cylinder of lymphoid cells located closest to and surrounding central artery of the white pulp
• T-cell domain

Question 9

Peyer’s Patches

Answer 9

• Numerous lymphatic nodules located in CT on one side of ileum