ANHB2214 Study Guide - Final Guide: Central Artery, Follicular Dendritic Cells, Antigen
3 Jun 2018
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Lymphatic Organs:
• The thymus
o Thymus and bone marrow → primary lymphatic organs
o Produce mature B and T lymphocytes → populate secondary
lymphatic organs
o Pre-T cells migrate into thymus → divide and rearrange T cell
receptor genes → educated about what is self/foreign
o Acceptable T cells released into circulation
o Gross structure
▪ Organ with 2 lobes at base of neck
▪ Surrounded by connective tissue
▪ Septa of connective tissue divides each lobe into lobules
▪ Lobules have a central medulla surrounded by a cortex
▪ Cortex → more densely packed with small lymphocytes
o Cells of thymus
▪ T cells
• Come into medulla from blood
• Migrate to cortex and mature
▪ Macrophages → dispose killed T cells
▪ Epithelial reticular cells
• Supporting cells
• Superficially resemble reticular cells that
lymphocytes invaded
• Many different types
• Functions
o Present self-antigens to T-cells to winnow out
inappropriate T cells
o Form blood-thymus barrier
o Secrete paracrine chemical messengers to
regulate T cell development
• Some aggregate in medulla to form Hassalls
corpuscles
o Human thymus reaches maximum size before/at birth
o Continues to grow until puberty → gradually degenerates
o Fat cells replace most epithelial reticular and T cells
o Some thymic tissue remains functional into old age
o Thymus is most important very early in life
• Lymphatic tissue
o Connective tissue that has been invaded by large numbers of
lymphocytes
o Characterised by large numbers of associated lymphoid cells →
plasma cells, macrophages, reticular cells
o Connective tissue becomes lymphatic to carry out 3 functions
▪ Remove pathogens and cellular debris
▪ Produce lymphocytes
▪ Mount immune responses
o Reticular cells
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▪ Support lymphatic tissue in place of fibroblasts
▪ Synthesize reticular fibers → type III collagen
▪ Reticular cells form meshwork → other cells crowd into
spaces → attracted by proteins on cell surface
▪ Diverse to an unknown degree
▪ Originate from mesenchyme → are not phagocytic
o Lymphatic tissue can infiltrate connective tissue to various extents
• Lymphatic nodules
o Balls of lymphoid cells
o Temporary structures
o Only forms in tissues that contain B cells → activated B cells can
enter lymphatic nodule, differentiate and divide
o Creates an inner sphere → pale → germinal center → cells have
large pale nuclei
o Surrounded by a darker staining corona of small lymphocytes
o Cells of germinal centre
▪ Lymphoblasts
▪ Macrophages
▪ Reticular cells
▪ Follicular dendritic cells → present antigen cell surface to
B cells
o Function of nodules → allow an antibody response to evolve
improvements as time goes on
• Tonsils
o Palatine tonsils
▪ Either side of pharynx
▪ Stratified squamous non-keratinized epithelium dips into
lamina propria to form crypts
▪ Lamina propria packed with lymphocytes → numerous
nodules
▪ Bacteria fester in crypts, release antigens to diffuse into
lamina propria to excite lymphocytes
▪ Function → give immune system first exposure to potential
pathogens
o Pharyngeal tonsils
▪ Lie above soft palate
▪ Similar to palatine tonsils
▪ Covered in respiratory epithelium
• Lymph node
o Lymph → tissue fluid generated in CT with a blood supply
o Small amount of fluid not reabsorbed goes into lymph vessels as
lymph
o Fluid collects into superficial lymph capillaries → drains into a
network of larger vessels and eventually vena cava
o Abundance of valves keeps lymph percolating in forward direction
o Lymph drainage → potential highway for pathogens to get into
bloodstream
o Lymph nodes inserted along lymph vessels act as filters
o Function of lymph nodes
find more resources at oneclass.com
find more resources at oneclass.com
