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Kidney anatomy

Overview

  • High up on posterior abdominal wall
  • At best, only lower poles can be palpated in normal individual
  • Oblique lie – long axis parallel to lateral border of Psoas Major
    • NB: Long axis slopes downwards and laterally
  • Well back in paravertebral gutter such that the Hilum face somewhat forwards as well as medially
  • In the erect position, lies opposite the first 3 Lumbar Vertebrae

  • Normal dimensions: 12 x 6 x 3 cm, Weight 130-150g
  • Hilum of Right Kidney just below and Hilum of Left Kidney just above the Transpyloric Plane, 5cm from midline
  • Upper pole of Left Kidney overlies 11th Rib
  • Upper pole of Right Kidney overlies 12th Rib
  • Renal Pelvis emerges from the Hilum behind the vessels to pass down as the Ureter
  • Perinephric fat lies outside the Renal Capsule
  • Renal Fascia (of Gerota) surrounds the Perinephric Fat
    • Condensation of the areolar tissue between the Parietal Peritoneum and Posterior Abdominal Wall
    • Restrains the extension of a Perinephric Abscess
    • Ascends as a dome over the upper pole of the Kidney and Suprarenal
      • Fascial septum separates the two organs
    • At the lateral renal border, the anterior and posterior layers fuse
    • At the hilum, the fascia is attached to the Renal vessels and the Ureter
    • Pus in perinephric space and injections into it do not usually track downwards
      • Increasing pressure may force the fascia to rupture and allow such contents to flow downwards retroperitoneally towards the pelvis

Relations

  • Posterior:

    • Diaphragm
      • Upper poles lies on fibres from the Lateral and Medial Arcuate Ligaments
      • Small triangular part of the Costodiaphragmatic Recess of the pleura lies behind the diaphragm
    • Quadratus Lumborum
    • Psoas Major (overlap medially)
    • Transversus Abdominis (overlap laterally)
      • Convexity of lateral border of Kidney lies on its aponeurosis origin
    • Subcostal Artery and Subcostal Vein
    • Subcostal Nerve
      • Subcostal vessels and Nerve emerge beneath the Lateral Arcuate Ligament
    • Iliohypogastric Nerve
    • Ilioinguinal Nerve
      • These nerves emerge from the lateral border of the Psoas Major

  • Anterior:

    • Suprarenal Glands
      • Overlap a small part of their anterior surfaces
    • Peritoneum of the Hepatorenal Pouch on the right (part of the Greater Sac)
    • Peritoneum of the Lesser Sac (Part of the Stomach Bed) on the left medially
    • Peritoneum of the Greater Sac on the left laterally (between the Kidney and the Spleen) with the Splenorenal ligament passing forwards between these areas
    • Hepatic Flexure on the Right
    • Splenic Flexure on the Left
      • These colonic segments separate the kidneys from peritoneum
    • Coils of Jejunum (with intervening peritoneum)
    • Right Colic Artery (ascending branches) – between the peritoneum and kidney
    • Left Colic Artery (ascending branches) – between peritoneum and kidney

  • NB: Pancreas makes contact with the surface of the Left Kidney

  • Renal Pelvis

    • Funnel-shaped commencement of the Ureter
    • Normally the most posterior of the three main structures in the Hilum
    • Capacity of the average pelvis: < 5mls

Blood Supply and Segments

  • Renal Arteries
    • Blood flow in excess of 1L per minute
    • Leave Abdominal Aorta at right angles
    • Lie behind the Pancreas and Renal Veins
    • At the hilum, each artery typically gives an anterior and posterior division
  • Renal Segments
    • Each kidney has 5 segments
    • Posterior division of Renal Artery – supplies posterior segment
    • Anterior division of Renal Artery – supplies apical, upper, middle and lower segments
    • No collateral circulation between segments
    • Abnormal or aberrant renal arteries, e.g. a vessel running from Aorta to the Lower Pole, are actually segmental vessels with an unusual origin (persistence of a foetal vessel)
      • Not usually accompanied by veins

  • Renal Veins
    • Formed from 5 or 6 vessels that unite at the Hilum
    • Veins from renal segments communicate with one another (unlike the arteries)

Lymph Drainage

  • Drain to Para-Aortic Nodes at the level of origin of the Renal Arteries (L2)

Nerve Supply

  • Derived from both parts of the autonomic nervous system
  • Sympathetic innervation:
    • Sympathetic Preganglionic cells in the spinal cord from T12 to L1 segments
    • Send Preganglionic fibres to the thoracic and lumbar Splanchnic Nerves
    • Synapse in the Coeliac and Renal Ganglia
    • Vasomotor
    • Afferent fibres
      • Includes those subserving pain
      • Accompany sympathetic nerves
    • Pathway for pain of renal colic ⇒ Coeliac Plexus ⇒ Splanchnic Nerves ⇒ Sympathetic Trunk (via White Rami Communicantes to T12 to L1 spinal nerves) ⇒ Spinal Cord by the Posterior Nerve Roots
    • Possible that some afferents run with vagal fibres which could explain the nausea and vomiting that accompany renal pain

Structure

  • Cortex
    • Lies beneath the capsule
    • Extends towards the Pelvis as the Renal Columns
    • Lies between a number of darker and triangular striated areas, the Pyramids of the Medulla
  • Apices of several pyramids open into a Renal Papilla
    • Each Papilla opens into a Minor Calyx
  • Minor Calyces unite to form 2 or 3 Major Calyces which open into the Renal Pelvis
  • Functional unit: Nephron
    • 1 million in each kidney
  • Nephron
    • Consists of a Glomerulus and a Tubule system
    • Glomerulus
      • Tuft of capillaries
      • Supplied by Afferent Arteriole and leaves as an Efferent Arteriole
        • Efferent Arteriole breaks up into Peritubular Capillaries surrounding the Proximal and Distal Convoluted Tubules
      • Surrounded by very thin epithelial cells (Podocytes)
      • Complex projects into Bowman’s Capsule
        • Epithelium covering capillaries is continuous with those forming the boundary of Bowman’s capsule which is in turn continuous with the epithelium of the Tubule system
    • Proximal Convoluted Tubule
      • Adjacent to Bowman’s Capsule
    • Loop of Henle ⇒ Distal Convoluted Tubule ⇒ Collecting Tubule ⇒ Collecting Duct ⇒ Collecting Ducts unite and the largest open at the tip of a Renal Papilla in a Minor Calyx
    • Glomeruli and Convoluted Tubules are in the Cortex
    • Loops of Henle and Collecting Tubules and Ducts are in the Medulla
    • Cells in the Arteriolar system and the Distal Convoluted Tubule constitute the Juxtaglomerular Apparatus – secretes Renin
  • Renal Pelvis:
    • Transitional epithelium
    • Smooth muscle in its wall
    • Specialized muscle cells in the walls of the Minor Calyces act as ‘pacemakers’ that initiate contractile waves which pass down the Ureter

Development

  • Three separate excretory organs appear in vertebrate evolution: Pronephros, Mesonephros, and Metanephros

  • Pronephros and Mesonephros – consist of excretory tubules arranged segmentally and empty into the same duct

  • Metanephros – mass of tubules having no segmental arrangement and drains into a new duct that develops specifically for the purpose (the Ureter)

  • Pronephros

    • Evanescent (quickly disappearing)
    • Duct persists
    • Mesonephric Tubules develop and open into the Pronephric Duct a.k.a. Mesonephric (Wolffian) Duct
    • Caudal to the Mesonephros, the intermediate cell mass gives rise to a million new tubules forming the Metanephros

  • Metanephros

    • Induces a bud, the Ureter, to grow from the caudal end of the Mesonephric Duct
    • Ureter bud separates from the Mesonephric Duct
      • The Mesonephric Duct forms part of the Bladder, the Vas Deferens, and associated structures
      • Ureter bud grows and divides into Calyces of the Pelvis (Major and Minor) and Collecting Tubules of the Medullary Pyramids
      • Into these, the Distal Convoluted Tubules of the Mesonephros come to drain

  • Foetal and neonatal kidney have lobulated appearance – reflects the way the Metanephric tissue overlies Tubular budding from the Calyces

  • Definitive Kidney (Metanephros) develops in the Pelvis and is supplied by the Internal Iliac Artery

  • Subsequently migrates to adult position gaining successively new arteries of supply from the Common Iliac and then the Aorta

    • Older vessels degenerate as new vessels appear

  • Hilum initially anterior but the kidney rotates 90° medially

Anomalies

  • Persistence of foetal lobulation
    • No significance
  • Persistence of one of the foetal arteries
    • Common (30% of individuals)
    • Esp. Vessel from the Aorta to the lower pole
  • Horseshoe Kidney
    • Fusion of the lower poles of the Kidneys
    • 1 in 800
    • Ureters pass anterior to the isthmus of the kidney substance
    • Inferior Mesenteric Artery also passes anterior to isthmus
      • Limits ascent of horseshoe
  • Polycystic Disease
    • 1 in 500
    • Both kidneys riddled with cysts
    • Hereditary
    • May be associated with cysts in the Liver, Pancreas and Lungs
  • Renal Agenesis
    • Only one kidney
    • 1 in 500
    • This must be excluded before considering Nephrectomy

Surgical Approach Lumbar Approach - Renal Fascia and Peri-Renal fat incised to expose kidney - Upper pole freed leaving the Suprarenal Gland within its own compartment of the fascia - Overlying peritoneum pushed away forwards and medially - Renal vessels then exposed, ligated and divided - Artery divided before the vein - Ureter transected

  • Diseased Right Kidney may adhere to Colon, Duodenum, Inferior Vena Cava or Suprarenal Gland
  • Diseased Left Kidney may adhere to the Colon, Spleen, Pancreas or Suprarenal Gland
  • Right Renal Vein only 2.5cm long – thus, Inferior Vena Cava very close to the operation area

Percutaneous Renal Biopsy

  • Lower pole entered by an approach 2.5cm below the 12th rib
  • Needle only advanced when patient is holding their breath so that the kidney is not torn by respiratory movement.

Transplantation

  • Donor kidney placed retroperitoneally in the Iliac Fossa with the Hilum parallel to the External Iliac Vessels
  • Renal Artery anastomosed to the Internal or External Iliac Artery
  • Renal Vein anastomosed to the External Iliac Vein
  • Ureter implanted into the bladder

Graph View

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