Last updated: January 31, 2023

Summarytoggle arrow icon

The kidneys are paired retroperitoneal organs located on either side of the vertebral column extending between the 12th thoracic and the 3rd lumbar vertebral levels. They play an important role in the excretion of waste products, the regulation of extracellular fluid volume and osmolality, the maintenance of acid-base balance, hormone synthesis (e.g., erythropoietin), and gluconeogenesis. The kidneys receive their blood supply from the paired renal arteries and drain into the paired renal veins. The lymphatics drain into the paraaortic lymph nodes. The left renal vein passes between the abdominal aorta and the superior mesenteric artery. The kidneys receive sympathetic innervation via the sympathetic trunk and parasympathetic innervation via the vagus nerve. Anatomically, the kidneys are composed of the renal capsule, renal cortex, renal medulla, renal sinus, and renal hilum. The nephron is the functional unit of the kidney, and it is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of the glomerulus and the Bowman capsule, which are separated by the glomerular filtration barrier (GFB). The GFB, which is composed of the fenestrated glomerular capillary endothelium, the glomerular basement membrane, and the podocyte layer, is responsible for filtering blood plasma. The filtrate passes through the renal tubule, which is divided into the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct. In the renal tubule, urine is formed from the filtrate via reabsorption, secretion, and excretion of substances. The kidneys originate embryologically from the mesoderm.

Gross anatomytoggle arrow icon


Internal macrostructure

The kidneys receive 20–25% of the cardiac output. Despite this, the medulla is relatively hypoxic and vulnerable to ischemic damage.

Surrounding structures

Each kidney is encapsulated by layers of fascia and fat. These layers comprise (from the outside to the inside):

Vasculature, lymphatics, and innervation

Sympathetic innervation
Parasympathetic innervation
  • None [2][3]

The left renal vein drains blood from the left kidney, the left suprarenal vein, and the left gonadal vein.

Blood Arrives through the Afferent arteriole and blood Exits through the Efferent arterioles.

Microscopic anatomytoggle arrow icon


Renal corpuscle

Layers of the glomerular filtration barrier
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 GBM) prevent the entry of negatively charged molecules (e.g., albumin).
Glomerular basement membrane (GBM)
  • Molecules > 70 nm


  • Molecules > 50–60 nm

The glomerular filtration barrier ensures that large and/or negatively charged molecules in the blood cannot pass into the Bowman capsule.

Renal tubules

Overview of the renal tubules


Microscopy Function
Proximal convoluted tubule (PCT)
  • Each segment has a distinct epithelial lining and function
  • Receive the ultrafiltrate from the renal corpuscle
  • Transport and concentrates the ultrafiltrate
  • Form urine via reabsorption, secretion, and excretion of substances
  • See ”Physiology of the kidney.”
Loop of Henle Thin descending loop of Henle
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
Connecting tubule and collecting duct

Juxtaglomerular complex

Functiontoggle arrow icon

Embryologytoggle arrow icon


Stages [5]

  1. Pronephros: the first embryonic excretory organ (rudimentary in human embryos)
    • Arises in the cervical region of the embryo during the 3rd4th week of embryonic development
    • Migrates caudally to connect with the pronephric duct
    • Composed of nephrotomes and nephric tubules temporary excretory function
    • Degenerates with the development of the mesonephros
  2. Mesonephros: the second embryonic excretory organ, developing caudally to the pronephros and degenerating with the development of the metanephros
  3. Metanephros: the third embryonic excretory organ, developing caudally to the mesonephros and persisting as the permanent kidney

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

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

Referencestoggle arrow icon

  1. Layton AT. Recent advances in renal hypoxia: insights from bench experiments and computer simulations. American Journal of Physiology. 2016.
  2. $Neural Control of Renal Function.
  3. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences ; 2016
  4. Denic A, Lieske JC, Chakkera HA, Poggio ED, Alexander MP, Singh P, Kremers WK, Lerman LO, Rule AD. The Substantial Loss of Nephrons in Healthy Human Kidneys with Aging. J Am Soc Nephrol. 2017; 28 (1): p.313-320.doi: 10.1681/ASN.2016020154 . | Open in Read by QxMD
  5. Jain S. Kidney Development and Related Anomalies. Elsevier ; 2014: p. 2701-2715
  6. Feher JJ. Quantitative Human Physiology. Academic Press ; 2017
  7. Kurklinsky AK, Rooke TW. Nutcracker phenomenon and nutcracker syndrome.. Mayo Clinic proceedings. 2010; 85 (6): p.552-9.doi: 10.4065/mcp.2009.0586 . | Open in Read by QxMD
  8. Vaziri ND. Mechanism of erythropoietin-induced hypertension.. Am J Kidney Dis. 1999; 33 (5): p.821-8.doi: 10.1016/s0272-6386(99)70413-0 . | Open in Read by QxMD

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