title: [Intrarenal smooth muscle: histology of a complex urodymamic machine].
abstract: OBJECTIVE
  To know better the microscopic arrangement of the bundles of smooth muscle in the human renal parenchyma, their distribution and anatomical relationships, trying to make a reconstruction of this muscular system.
  
  
  METHODS
  Five adult human kidneys and one fetal kidney were processed "in toto" with cross sections every 300μm. In the histological sections we identify the smooth muscle fibers trying to determine its insertion, course and anatomical relationship with other structures of the kidney tissue.
  
  
  RESULTS
  There are bundles of smooth muscle fibers of variable thickness parallel to the edges of the medullary pyramids, bundles that surrounding the medulla in a spiral course, and bundles that accompany arcuate vessels, the latter being the most abundant and easy to identify. These groups of muscle fibers do not have a precise or constant insertion site, their periodicity is not homogeneous and they are not a direct extension of the muscle of the renal pelvis, although some bundles are in contact with it. There are also unusual and inconstant small muscle fibers no associated to vessels in the interstitium of the cortex and, exceptionally, in the medulla.
  
  
  CONCLUSIONS
  There is a complex microscopic system of smooth muscle fibers that partially surround the renal medulla and are related to renal pelvic muscles without a direct continuity with them. Although this small muscular system is under-recognized, could be very important in urodynamics.
authors: Grupo PRYT, Departamento de Patología, Facultad de Medicina, Universidad de Antioquia, Medellín, Colombia. lfarias@kidneypathology.com
authors: L F
authors: LF
authors: Arias
authors: N
authors: N
authors: Ortiz-Arango
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007668:Kidney / Q000033:anatomy & histology* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009130:Muscle, Smooth / Q000033:anatomy & histology* / Q000502:physiology; D014563:Urodynamics; D055815:Young Adult