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Renal physiologyRenal physiology
Dr Alison ChalmersDr Alison Chalmers
Consultant AnaesthetistConsultant Anaesthetist
Queen Victoria HospitalQueen Victoria Hospital
What you need to knowWhat you need to know
Blood flow, glomerular filtration and Blood flow, glomerular filtration and plasma clearanceplasma clearance
Tubular function and urine formationTubular function and urine formation Assessment of renal functionAssessment of renal function Regulation of fluid and electrolyte balanceRegulation of fluid and electrolyte balance Regulation of acid base balanceRegulation of acid base balance MicturitionMicturition Pathophysiology of acute renal failurePathophysiology of acute renal failure
Example questions from Example questions from SOE 1SOE 1
Buffers: what are they, how are they Buffers: what are they, how are they classified, formation of bicarbonate, classified, formation of bicarbonate, how is Hhow is H++ eliminated eliminated
Fluid balance: regulation of fluid Fluid balance: regulation of fluid balance, what happens when you infuse balance, what happens when you infuse salinesaline
Renal: renal blood flow, factors affecting Renal: renal blood flow, factors affecting GFR, autoregulation, tuberoglomerular GFR, autoregulation, tuberoglomerular feedback, measurement of GFR/RBFfeedback, measurement of GFR/RBF
Aims of this sessionAims of this session
Key facts about the kidney – function, Key facts about the kidney – function, anatomyanatomy
Renal blood flowRenal blood flow Glomerular filtration and tubular Glomerular filtration and tubular
functionfunction Regulation of body fluid volume and Regulation of body fluid volume and
electrolyte balanceelectrolyte balance Renal regulation of acid base balanceRenal regulation of acid base balance MicturitionMicturition
Key facts – function of the Key facts – function of the kidneykidney
Electrolyte and water homeostasisElectrolyte and water homeostasis Acid-base homeostasisAcid-base homeostasis Excretion of waste products and toxinsExcretion of waste products and toxins Calcium and phosphate homeostasisCalcium and phosphate homeostasis Endocrine functions – erythropoietinEndocrine functions – erythropoietin Retention of vital substances – Retention of vital substances –
glucose, proteinsglucose, proteins
Key facts - anatomyKey facts - anatomy
Renal blood flowRenal blood flow
Receives 20% cardiac Receives 20% cardiac outputoutput
Cortex > outer Cortex > outer medulla > inner medulla > inner medullamedulla
2 capillary beds in 2 capillary beds in seriesseries
RBF = RPF x 100/55RBF = RPF x 100/55 PAH clearance used to PAH clearance used to
measure RPFmeasure RPF
Regulation of renal blood Regulation of renal blood flowflow
AutoregulationAutoregulation
Renin-angiotensin Renin-angiotensin systemsystem Macula densa cellsMacula densa cells Juxtaglomerular Juxtaglomerular
complexcomplex
Glomerular filtrationGlomerular filtration
GFR = 125ml/minGFR = 125ml/min Approx 20% renal Approx 20% renal
blood flow is blood flow is filteredfiltered
GFR GFR ~ forces ~ forces favouring filtration favouring filtration – forces opposing – forces opposing filtrationfiltration
Factors affecting GFRFactors affecting GFR
Forces favouring filtrationForces favouring filtration PPGG = hydrostatic pressure in glomerular capillary = hydrostatic pressure in glomerular capillary ΠΠBB = colloid osmotic pressure in Bowman’s capsule = colloid osmotic pressure in Bowman’s capsule
Forces opposing filtrationForces opposing filtration PPBB = hydrostatic pressure in Bowman’s capsule = hydrostatic pressure in Bowman’s capsule ΠΠGG = colloid osmotic pressure in = colloid osmotic pressure in glomerular capillaryglomerular capillary
GFR GFR ~ P~ PGG – (P – (PBB + + ΠΠGG))
Molecular size – charge and sizeMolecular size – charge and size Inulin clearance used to measure GFR (or Cr cl ~ GFR)Inulin clearance used to measure GFR (or Cr cl ~ GFR)
Tubular functionTubular function
Proximal tubuleProximal tubule
Passive diffusionPassive diffusion Across membraneAcross membrane Through Through
channels/poreschannels/pores Facilitated diffusionFacilitated diffusion Active transportActive transport
Secretary Secretary processesprocesses Organic acids/basesOrganic acids/bases
Sodium reabsorptionSodium reabsorption
Passive diffusionPassive diffusion NaNa++ linked symport linked symport
and antiportand antiport NaNa++KK++ATPase into ATPase into
LISLIS
Bicarbonate reabsorptionBicarbonate reabsorption
Reabsorption Reabsorption occurs as a result occurs as a result of Hof H++ secretion into secretion into the tubular lumenthe tubular lumen
Loop of HenleLoop of Henle
Distal tubule and collecting Distal tubule and collecting ductduct
Distal tubuleDistal tubule Final reabsorption of ionsFinal reabsorption of ions
Collecting ductCollecting duct Variable permeability to water Variable permeability to water
depending on ADH presentdepending on ADH present Urea diffuses from collecting duct to aid Urea diffuses from collecting duct to aid
in the concentrating of urine under in the concentrating of urine under influence of ADHinfluence of ADH
Fluid and electrolyte Fluid and electrolyte balancebalance
Na depletion
Decrease blood volume
Decrease blood pressure
Angiotensinogen
Angiotensin I
Renin
Angiotensin II
ACE
Aldosterone
Increase BP
Na retentionIncrease blood volIncrease ADH
Decrease ANP
Renal control of acid base Renal control of acid base balancebalance
Key reaction: Key reaction: COCO22 + H + H22O O <=> H<=> H22COCO3 3 <=> H<=> H+ + + HCO+ HCO33
--
Rate of HRate of H++ secretion inversely proportional with pH secretion inversely proportional with pH Respiratory acidosisRespiratory acidosis
↑↑COCO2 2 → ↑ rate of H→ ↑ rate of H++ secretion in kidney → ↑ secretion in kidney → ↑ HCOHCO33- - reabsorption = reabsorption =
renal compensationrenal compensation Metabolic acidosisMetabolic acidosis
Change in pH detected by peripheral chemoreceptorsChange in pH detected by peripheral chemoreceptors ↑ ↑ ventilation rate – respiratory compensationventilation rate – respiratory compensation ↑ ↑ HH++ secretion in kidney → ↑ secretion in kidney → ↑ HCOHCO33
- - reabsorption – renal reabsorption – renal correctioncorrection
MicturitionMicturition
Detrusor muscle – Detrusor muscle – smooth muscle smooth muscle
2 sphincters 2 sphincters Internal – smooth Internal – smooth
musclemuscle External – skeletal External – skeletal
musclemuscle Spinal reflex with Spinal reflex with
learned voluntary learned voluntary controlcontrol
Any questions?Any questions?
SummarySummary
Key facts about the kidney – function, Key facts about the kidney – function, anatomyanatomy
Renal blood flowRenal blood flow Glomerular filtration and tubular Glomerular filtration and tubular
functionfunction Regulation of body fluid volume and Regulation of body fluid volume and
electrolyte balanceelectrolyte balance Renal regulation of acid base balanceRenal regulation of acid base balance MicturitionMicturition