TY  - CHAP
M1  - Book, Section
TI  - Connective Tissue
A1  - Mescher, Anthony L.
PY  - 2021
T2  - Junqueira's Basic Histology Text and Atlas, 16e
AB  - Connective  Tissue  SUMMARY  OF  KEY  POINTSConnective  tissue  is  specialized  to  physically  support  and  connect  other  tissues  and  maintain  the  water  required  for  metabolite  diffusion  to  and  from  cells.Connective  tissues  all  consist  primarily  of  extracellular  material  rather  than  cells.Within  most  organs  connective  tissue  proper  forms  the  supportive  stroma,  which  supports  the  organ’s  unique  functional  components  or  parenchyma.The  ECM  of  connective  tissue  proper  usually  consists  of  both  large  protein  fibers  and  nonfibrous  areas  of  unstained  ground  substance  rich  in  various  GAGs  and  water.All  adult  connective  tissues  are  derived  from  an  embryonic  form  of  connective  tissue  called  mesenchyme,  which  contains  uniformly  undifferentiated  cells  scattered  in  a  gel-like  matrix.Cells  of  Connective  TissueFibroblasts  (fibrocytes),  the  major  cells  of  connective  tissue  proper,  are  elongated,  irregularly  shaped  cells  with  oval  nuclei  that  synthesize  and  secrete  most  components  of  the  ECM.Adipocytes  (fat  cells)  are  very  large  cells  specialized  for  storage  of  triglycerides;  they  predominate  in  a  specialized  form  of  connective  tissue  called  adipose  tissue.Macrophages  are  short-lived  cells  that  differentiate  in  connective  tissue  from  precursor  cells  called  monocytes  circulating  in  the  blood;  they  function  in  ECM  turnover,  phagocytosis  of  dead  cells  and  debris,  and  antigen  presentation  to  lymphocytes.Mast  cells  also  originate  from  blood  cell  precursors  and  are  filled  with  granules  for  the  release  of  various  vasoactive  agents  and  other  substances  during  inflammatory  and  allergic  reactions.Plasma  cells  are  short-lived  cells  that  differentiate  from  B  lymphocytes  and  are  specialized  for  the  abundant  secretion  of  specific  antibodies  (immunoglobulins).Besides  macrophages  and  plasma  cells,  other  leukocytes  normally  wander  through  all  types  of  connective  tissue  proper,  providing  surveillance  against  bacterial  invaders  and  stimulating  tissue  repair.Fibers  of  Connective  TissueThe  most  important  and  abundant  fibers  of  connective  tissue  are  composed  of  the  protein  collagen,  of  which  there  are  some  20  related  types.Synthesis  of  collagen  by  fibroblasts  and  certain  other  cells  involves  posttranslational  modifications  in  the  RER,  notably  hydroxylation  of  the  numerous  prolines  and  lysines,  and  formation  of  helical  trimeric  subunits  of  procollagen.Upon  exocytosis,  the  nonhelical  ends  of  the  procollagen  subunits  are  removed,  forming  trimeric  collagen  molecules  that  aggregate  and  become  covalently  bound  together  in  large  collagen  fibrils.The  highly  regular  assembly  of  collagens  in  the  fibrils  produces  a  characteristic  pattern  of  crossbanding  visible  ultrastructurally  along  the  fibrils  of  some  collagen  types.Fibrils  of  type  I  collagen  are  bundled  together  by  other  forms  of  nonfibrillar,  linking  collagens  to  produce  large  collagen  bundles.Collagen  fibrils  are  degraded  by  collagenase  enzymes  classified  as  MMPs,  produced  primarily  by  macrophages.Type  III  collagen  produces  a  network  of  delicate  reticular  fibers,  which  stain  very  dark  with  silver  stains  and  are  abundant  in  immune  and  lymphoid  tissues.Elastic  fibers,  or  sheets  called  elastic  lamellae,  are  composed  of  the  proteins  elastin  and  fibrillin,  which  exist  in  a  stretchable  conformation  that  provides  elastic  properties  to  connective  tissues  rich  in  this  material.Ground  SubstanceGround  substance  is  the  watery,  largely  unstained  extracellular  material  that  is  more  abundant  than  fibers  in  some  types  of  connective  tissue  proper.Ground  substance  is  rich  in  hydrated  GAGs,  proteoglycans,  and  multiadhesive  glycoproteins.The  major  types  of  GAGs  are  hyaluronan  (hyaluronic  acid),  which  is  a  very  long  polymer  of  the  disaccharide  glucosamine-glucuronate,  and  various  ...
SN  - 
PB  - McGraw Hill
CY  - New York, NY
Y2  - 2024/04/19
UR  - accessmedicine.mhmedical.com/content.aspx?aid=1184199621
ER  -