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Functional  divisions  of  the  renal  tubule  
 
Nephron  structure  (1-­‐2  x  106  per  kidney)  
 
 
 
 
 
 
 
 
 
 
 
 
 
Representative  glomerulus  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Proximal  convoluted  tubule  
• Reabsorb  the  majority  of  solutes  back  
into  the  systemic  circulation  
• Long  fringe  of  processes  (brush  
border)  gives  each  cell  a  large  surface  
area  to  absorb  solutes  from  the  
tubular  lumen  
• Full  Mitochondria  because  they  do  so  
much  absorbing  and  secreting  
• Little  capacity  for  anaerobic  
respiration  
• Concentration  gradient  of  sodium  
drives  most  processes  at  the  apical  
membrane  
 
 
 
 

Loop  of  Henle  
• The  epithelial  cells  are  thin  and  flattened  (the  wall  thickness  is  only  1-­‐
2um)  
• Compared  to  the  cells  of  the  proximal  tubule,  these  cells  have  few  
mitochondria  
• Divided  into  two  structures  
o The  thin  descending  limb  turns  and  ascends  towards  the  cortex  
finally  merging  with  the  thick  segment    
o The  cells  in  the  thick  segment  are  cuboidal  with  extensive  
invaginations  of  the  basolateral  membrane  
o Like  the  cells  of  the  proximal  tubule,  they  are  rich  in  mitochondria  
due  to  their  major  role  in  active  transport  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Distal  convoluted  tubule  
• Involved  in  sodium  and  chloride  transport  as  well  as  calcium  and  
magnesium  transport  
• Do  not  have  the  brush  border  that  the  proximal  tubules  have  
• Are  smaller  (in  diameter)  than  Proximal  tubules  

Collecting  duct  
• Filtrate  turned  into  pro-­‐urine  and  then  urine  
• Salt  transport  and  the  concentration  of  urine  
• Acid  base  balance  
• Pass  through  the  cortex  and  medulla  to  the  renal  pelvis  
• 2  important  types  of  cells  in  the  epithelium  
o Principal  cell  
§ Main  cell  in  the  collecting  duct  
§ Involved  in  salt  absorption  as  well  as  water  absorption  
§ Epithelial  sodium  channel  (ENaC):  Sensitive  to  aldosterone  
§ Aquaporin:  Under  vasopressin  (ADH)  regulation  
o Intercalated  cell  
§ Between  lots  of  principal  cells  
§ Acid  base  regulation  
§ Alpha  intercalated  cell  involved  with  excreting  H+  into  the  
tubular  lumen,  there  to  get  rid  of  an  acid  load  into  the  urine  
§ Beta  intercalated  cells  secrete  bicarbonate  into  the  urine  



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