Canonical Question
Renal – Anatomy
Master answer
Anatomy
- Lie in the posterior wall of the abdomen – outside peritoneum (retroperitoneal)
- Each kidney approx 150g
- Medial side of each kidney = hilum
- Renal artery and vein
- Lymphatic supply
- Nerves
- Ureter
- Kidney surrounded by tough fibrous capsule
- Kidney organized into outer cortex and inner medulla
- Nephrons = functional unit of the kidney (1 million / kidney)
- Medulla
- Organised into mutliple pyramids with the base at the corticomedullary junction and apices – the papilla – at the hilum draining into the ureters
- Renal blood flow
- ~1.25L/min (24% of cardiac output or 500ml/100g tissue/min) via renal artery
- 95% blood flow to cortex, ~5% to Medulla
- Renal artery enters through hilum it divides
- → interlobar arteries
- → arcuate arteries
- → interlobular arteries
- → afferent arterioles
- → glomerular capillaries
- → efferent arterioles
- → peritubular capillaries
- Peritubular capillaries supply blood to the renal tubules
- Juxtaglomerular capillaries have specialized vasa recta which supply the LoH and is important in renal concentration of urine
- → venous system → interlobular veins → arcuate veins → interlobar veins → renal vein
Renal Medulla
- Organised into mutliple pyramids with the base at the corticomedullary junction and apices – the papilla – at the hilum draining into the ureters
- Medullary blood flow: 1~2% of total renal blood flow
- 0.6ml/g/min in inner medulla
- 2.5ml/g/min in outer medullar
- 5ml/g/min in cortex
- 20~30% nephrons are juxtaglomerular with specialized vasa recta
- Blood from post-glomerulus, therefore decreased plasma (filtered) proportion and increased viscosity
- Decreased flow
- Factors that increase filtration fraction decrease medullary flow (e.g. angiotensin II)
- All extrinsic factors which affect afferent arterioles (humoral, neural) affect medullary blood flow similar to RBF
- Oxygen supply determined by state of oxyHb dissociation curve
- Right shift favours oxygen supply
- Renal medullary pO2 = 15mmHg (compared with 50mmHg in cortex)
- Increased O2 offloading
- Renal oxygen consumption
- Increases with sodium resorption (happens mostly in medulla)
Physiology
Oxygen Delivery
\[Oxygen \; delivery \; = \; Renal \; Blood \; flow \; \times \; CaO_2\]
CaO2 is determined by:
\[C_aO_2 \; = \; ([Hb] \; \times \; S_aO_2 \; \times \; 1.34) + (0.03 \; \times \; p_aO_2) \]
- CaO2 – Arterial oxygen content
- Hb – Haemoglobin
- SaO2 – Arterial Oxygen saturation
- paO2 – Arterial partial pressure of oxygen
Renal Blood Flow
- Determined by:
\[Renal \; Blood \; Flow \; = \; {{Renal \; arterial \; pressure \; – \; Renal \; venous \; pressure} \over {Renal \; vascular \; resistance}} \]
\[{Hagen-Poisuille \; Equation : \;} {{{\Delta pressure} \times {\pi r^4}} \over {{8} \times {viscosity} \times {length}}}\]
- Regulation:
- Renal vascular resistance maintained by interlobular arteries, afferent arterioles and efferent arterioles
- Autoregulated between 80~170mmHg
| Neural | Sympathetic | All renal vesicles richly innervated by sympathetic nerves |
| Minimal influence on GFR except in severe acute disturbances (severe haemorrhage) | ||
| Decrease blood flow due to vasoconstriction | ||
| Hormonal | Adrenaline and noradrenaline | Vasoconstrict → decrease blood flow |
| Endothelin | Vasoconstrict → decrease blood flow | |
| Angiotensin II | Constricts efferent arterioles → decrease blood flow | |
| Nitric oxide | Vasodilate → increase blood flow | |
| Prostaglandins | Vasodilate → increase blood flow |
- Starling resistors
- Increased intra-abdominal pressure will decrease blood flow in starling resistor model
- Increased intra-capsular pressure will decrease renal blood flow
Sakurai 2016
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2011B Q21 | Outline the functional anatomy, and the physiological factors, that determine oxygen delivery to the renal medulla. | historical_member | 4.00% |