Renal physiology

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Renal physiology

• Dr Alison Chalmers
• Consultant Anaesthetist
• Queen Victoria Hospital

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What you need to know

• Blood flow, glomerular filtration and plasma
  clearance
• Tubular function and urine formation
• Assessment of renal function
• Regulation of fluid and electrolyte balance
• Regulation of acid base balance
• Micturition
• Pathophysiology of acute renal failure

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Example questions from SOE 1

• Buffers what are they, how are they classified,
  formation of bicarbonate, how is H eliminated
• Fluid balance regulation of fluid balance, what
  happens when you infuse saline
• Renal renal blood flow, factors affecting GFR,
  autoregulation, tuberoglomerular feedback,
  measurement of GFR/RBF

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Aims of this session

• Key facts about the kidney function, anatomy
• Renal blood flow
• Glomerular filtration and tubular function
• Regulation of body fluid volume and electrolyte
  balance
• Renal regulation of acid base balance
• Micturition

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Key facts function of the kidney

• Electrolyte and water homeostasis
• Acid-base homeostasis
• Excretion of waste products and toxins
• Calcium and phosphate homeostasis
• Endocrine functions erythropoietin
• Retention of vital substances glucose, proteins

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Key facts - anatomy
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Renal blood flow

• Receives 20 cardiac output
• Cortex gt outer medulla gt inner medulla
• 2 capillary beds in series
• RBF RPF x 100/55
• PAH clearance used to measure RPF

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Regulation of renal blood flow

• Autoregulation
• Renin-angiotensin system
• Macula densa cells
• Juxtaglomerular complex

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Glomerular filtration

• GFR 125ml/min
• Approx 20 renal blood flow is filtered
• GFR forces favouring filtration forces
  opposing filtration

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Factors affecting GFR

• Forces favouring filtration
• PG hydrostatic pressure in glomerular capillary
• ?B colloid osmotic pressure in Bowmans capsule
• Forces opposing filtration
• PB hydrostatic pressure in Bowmans capsule
• ?G colloid osmotic pressure in glomerular
  capillary
• GFR PG (PB ?G)
• Molecular size charge and size
• Inulin clearance used to measure GFR (or Cr cl
  GFR)

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Tubular function
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Proximal tubule

• Passive diffusion
• Across membrane
• Through channels/pores
• Facilitated diffusion
• Active transport
• Secretary processes
• Organic acids/bases

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Sodium reabsorption

• Passive diffusion
• Na linked symport and antiport
• NaKATPase into LIS

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Bicarbonate reabsorption

• Reabsorption occurs as a result of H secretion
  into the tubular lumen

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Loop of Henle
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Distal tubule and collecting duct

• Distal tubule
• Final reabsorption of ions
• Collecting duct
• Variable permeability to water depending on ADH
  present
• Urea diffuses from collecting duct to aid in the
  concentrating of urine under influence of ADH

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Fluid and electrolyte balance
Angiotensinogen
Na depletion
Renin
Decrease blood volume
Angiotensin I
ACE
Increase BP
Angiotensin II
Decrease blood pressure
Na retention Increase blood vol
Aldosterone
Increase ADH Decrease ANP
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Renal control of acid base balance

• Key reaction
• CO2 H2O ltgt H2CO3 ltgt H HCO3-
• Rate of H secretion inversely proportional with
  pH
• Respiratory acidosis
• ?CO2 ? ? rate of H secretion in kidney ? ?
  HCO3- reabsorption renal compensation
• Metabolic acidosis
• Change in pH detected by peripheral
  chemoreceptors
• ? ventilation rate respiratory compensation
• ? H secretion in kidney ? ? HCO3- reabsorption
  renal correction

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Micturition

• Detrusor muscle smooth muscle
• 2 sphincters
• Internal smooth muscle
• External skeletal muscle
• Spinal reflex with learned voluntary control

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Any questions?
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Summary

• Key facts about the kidney function, anatomy
• Renal blood flow
• Glomerular filtration and tubular function
• Regulation of body fluid volume and electrolyte
  balance
• Renal regulation of acid base balance
• Micturition