Gross anatomy



Blood supply

Every minute, 20% of the cardiac output (∼ 1200 mL in the average adult) is pumped through the kidneys!

The left renal vein passes between the abdominal aorta and the superior mesenteric artery; compression by these arteries can result in varicocele in men and lower abdominal pain in women.

Microscopic anatomy


Renal corpuscle

Glomerular filtration barrier

  • Definition: a membrane consisting of 3 layers that allows selective filtration of blood plasma components based on their size and charge
  • Function
Layer Description Clinical relevance Function
Size barrier Charge barrier
Fenestrated glomerular capillary endothelium
  • Molecules (> 100–50 nm)
  • Negatively charged glycoproteins (e.g., with heparan sulfate on the BM) prevent entry of negatively charged molecules (e.g., albumin)
Glomerular basement membrane
  • Molecules (> 70 nm)


  • Foot processes that surround the capillaries and leave filtration slits (slit diaphragms)
  • In contact with the endothelium of glomerular capillaries
  • Anionic glycoproteins
  • Molecules (> 50–60 nm)

The glomerular filtration barrier ensures that large and/or negatively charged molecules from the blood are unlikely to filter through and into the Bowman capsule!

Renal tubules



Microscopy Function
Proximal convoluted tubule Renal cortex
  • Each segment has a distinct epithelial lining and function
    • Receives the ultrafiltrate from the renal corpuscle
    • Transports and concentrates the ultrafiltrate
    • Forms urine via reabsorption, secretion, excretion of substances
    • For details see the learning card “Physiology of the kidney
Loop of Henle Thin descending loop of Henle Renal medulla
Thick ascending loop of Henle
  • Wider diameter than the descending segment
  • Epithelium with variable short brush border and tight junctions (impermeable to water)
Distal convoluted tubule Renal cortex
Connecting tubule and collecting duct Renal cortex and renal medulla

Juxtaglomerular complex

  • Definition: specialized structure that is located between the distal convoluted tubule and the afferent arteriole of the nephron
  • Parts
    • Extramesangial cells
    • Juxtaglomerular cells: modified smooth muscle cells located in the afferent arterioles
      • Function: synthesis of renin
    • Macula densa: composed of tall cuboid cells in the distal convoluted tubule
      • Monitors the NaCl concentration within the lumen of the DCT
        • Hypoosmolar urine triggers the release of reninvasoconstriction of the efferent arteriole → increase in GFR
        • Hyperosmolar urine triggers the release of adenosinevasoconstriction of the afferent arteriole → decrease in GFR


Elevated EPO levels induce an increased hematocrit and improved oxygen-carrying capacity! Athletes may train in high elevation (hypoxia-induced EPO synthesis) or conduct EPO doping to increase their RBC count.

Patients with chronic kidney disease may develop renal anemia due to deficient EPO synthesis.


The ureteropelvic junction canalizes last and is the most common site of obstruction.

Impaired renal function during fetal development results in oligohydramnios. The subsequent compression of the fetus causes characteristic abnormalities referred to as Potter sequence.

If the inferior poles of both kidneys fuse during fetal development, they form a horseshoe kidney and become trapped underneath the inferior mesenteric artery.

Clinical significance