TY  - CHAP
M1  - Book, Section
TI  - The Urinary System
A1  - Mescher, Anthony L.
Y1  - 2021
N1  - 
T2  - Junqueira's Basic Histology Text and Atlas, 16e
AB  - The  Urinary  System  SUMMARY  OF  KEY  POINTSKidneyEach  kidney  has  a  thick  outer  cortex,  surrounding  a  medulla  that  is  divided  into  8-12  renal  pyramids;  each  pyramid  and  its  associated  cortical  tissue  comprises  a  renal  lobe.The  apical  papilla  of  each  renal  pyramid  inserts  into  a  minor  calyx,  a  subdivision  of  two  or  three  major  calyces  extending  from  the  renal  pelvis.The  ureter  carries  urine  from  the  renal  pelvis  and  exits  the  renal  hilum,  where  the  renal  artery  and  vein  are  also  located.Renal  VasculatureRenal  arteries  branch  to  form  smaller  arteries  between  the  renal  lobes,  with  interlobular  arteries  entering  the  cortex  to  form  the  microvasculature;  venous  branches  parallel  the  arterial  supply.In  the  cortex,  afferent  arterioles  enter  capillary  clusters  called  glomeruli,  which  are  drained  by  efferent  arterioles,  instead  of  venules,  an  arrangement  that  allows  higher  hydrostatic  pressure  in  the  capillaries.The  efferent  arterioles  from  cortical  glomeruli  branch  diffusely  as  peritubular  capillaries,  while  those  from  juxtamedullary  glomeruli  branch  as  long  microvascular  loops  called  vasa  recta  in  the  medulla.NephronsFunctional  units  of  the  kidney  are  the  nephrons,  numbering  about  1.25  million,  each  with  a  renal  corpuscle  and  a  long  renal  tubule,  and  a  system  of  collecting  ducts.The  renal  corpuscle  has  a  simple  squamous  parietal  layer  of  the  glomerular  (Bowman)  capsule,  continuous  with  the  proximal  tubule,  and  a  specialized  visceral  layer  of  podocytes  surrounding  the  glomerular  capillaries.Podocytes  extend  large  primary  processes  that  curve  around  a  capillary  and  extend  short,  interdigitating  secondary  processes  or  pedicels,  between  which  are  narrow  spaces  called  slit  pores.The  elevated  pressure  in  the  capillaries  forces  water  and  small  solutes  of  blood  plasma  through  the  glomerular  filter  into  the  capsular  (or  urinary)  space  inside  the  glomerular  capsule.In  each  glomerulus  the  filter  has  three  parts:  the  finely  fenestrated  capillary  endothelium;  the  thick  (330  nm)  fused  basal  laminae  of  type  IV  collagen  and  other  proteins  produced  by  the  endothelial  cells  and  podocytes;  and  the  slit  pores  between  the  pedicels,  covered  by  thin  filtration  slit  diaphragms.From  the  renal  corpuscle,  filtrate  enters  the  long  nephron  tubule  that  extends  through  both  the  cortex  and  medulla,  with  epithelial  cells  for  both  reabsorption  and  secretion  of  substances  into  the  filtrate.The  first  tubular  part,  the  PCT,  is  mainly  cortical,  has  simple  cuboidal  cells  with  long  microvilli  in  the  lumen,  abundant  mitochondria,  and  large,  interdigitating  basolateral  folds.In  the  PCT,  all  glucose  and  other  organic  nutrients,  all  small  proteins  and  peptides  (which  are  degraded  to  amino  acids),  and  much  water  and  electrolytes  are  reabsorbed  from  the  filtrate  and  transferred  to  the  peritubular  capillaries.From  the  PCT  filtrate  flows  into  the  loop  of  Henle,  located  in  the  medulla,  which  has  squamous  thin  descending  and  ascending  limbs;  the  latter  extends  as  a  TAL  back  into  the  cortex.In  the  cortex,  the  TAL  (also  known  as  the  distal  straight  tubule)  contacts  the  arterioles  at  the  vascular  pole  of  its  parent  renal  corpuscle  and  there  thickens  focally  as  the  macula  densa.Tall  epithelial  cells  of  the  macula  densa  and  specialized  smooth  muscle  cells  in  the  adjacent  afferent  arteriole  called  juxtaglomerular  cells,  which  secrete  renin,  comprise  a  JGA  that  is  an  important  regulator  of  blood  pressure.Beyond  the  macula  densa,  ...
SN  - 
PB  - McGraw Hill
CY  - New York, NY
Y2  - 2024/04/23
UR  - accessmedicine.mhmedical.com/content.aspx?aid=1184201521
ER  -