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Renal physiology Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital.

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Presentation on theme: "Renal physiology Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital."— Presentation transcript:

1 Renal physiology Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital

2 What you need to know Blood flow, glomerular filtration and plasma clearance Blood flow, glomerular filtration and plasma clearance Tubular function and urine formation Tubular function and urine formation Assessment of renal function Assessment of renal function Regulation of fluid and electrolyte balance Regulation of fluid and electrolyte balance Regulation of acid base balance Regulation of acid base balance Micturition Micturition Pathophysiology of acute renal failure Pathophysiology of acute renal failure

3 Example questions from SOE 1 Buffers: what are they, how are they classified, formation of bicarbonate, how is H + eliminated 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 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 Renal: renal blood flow, factors affecting GFR, autoregulation, tuberoglomerular feedback, measurement of GFR/RBF

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

5 Key facts – function of the kidney Electrolyte and water homeostasis Electrolyte and water homeostasis Acid-base homeostasis Acid-base homeostasis Excretion of waste products and toxins Excretion of waste products and toxins Calcium and phosphate homeostasis Calcium and phosphate homeostasis Endocrine functions – erythropoietin Endocrine functions – erythropoietin Retention of vital substances – glucose, proteins Retention of vital substances – glucose, proteins

6 Key facts - anatomy

7 Renal blood flow Receives 20% cardiac output Receives 20% cardiac output Cortex > outer medulla > inner medulla Cortex > outer medulla > inner medulla 2 capillary beds in series 2 capillary beds in series RBF = RPF x 100/55 RBF = RPF x 100/55 PAH clearance used to measure RPF PAH clearance used to measure RPF

8 Regulation of renal blood flow Autoregulation Autoregulation Renin-angiotensin system Renin-angiotensin system Macula densa cells Juxtaglomerular complex

9 Glomerular filtration GFR = 125ml/min GFR = 125ml/min Approx 20% renal blood flow is filtered Approx 20% renal blood flow is filtered GFR ~ forces favouring filtration – forces opposing filtration GFR ~ forces favouring filtration – forces opposing filtration

10 Factors affecting GFR Forces favouring filtration Forces favouring filtration P G = hydrostatic pressure in glomerular capillary P G = hydrostatic pressure in glomerular capillary Π B = colloid osmotic pressure in Bowman’s capsule Π B = colloid osmotic pressure in Bowman’s capsule Forces opposing filtration Forces opposing filtration P B = hydrostatic pressure in Bowman’s capsule P B = hydrostatic pressure in Bowman’s capsule Π G = colloid osmotic pressure in glomerular capillary Π G = colloid osmotic pressure in glomerular capillary GFR ~ P G – (P B + Π G ) GFR ~ P G – (P B + Π G ) Molecular size – charge and size Molecular size – charge and size Inulin clearance used to measure GFR (or Cr cl ~ GFR) Inulin clearance used to measure GFR (or Cr cl ~ GFR)

11 Tubular function

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

13 Sodium reabsorption Passive diffusion Passive diffusion Na + linked symport and antiport Na + linked symport and antiport Na + K + ATPase into LIS Na + K + ATPase into LIS

14 Bicarbonate reabsorption Reabsorption occurs as a result of H + secretion into the tubular lumen Reabsorption occurs as a result of H + secretion into the tubular lumen

15 Loop of Henle

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

17 Fluid and electrolyte balance Na depletion Decrease blood volume Decrease blood pressure Angiotensinogen Angiotensin I Renin Angiotensin II ACE Aldosterone Increase BP Na retention Increase blood vol Increase ADH Decrease ANP

18 Renal control of acid base balance Key reaction: Key reaction: CO 2 + H 2 O H 2 CO 3 H + + HCO 3 - CO 2 + H 2 O H 2 CO 3 H + + HCO 3 - Rate of H + secretion inversely proportional with pH Rate of H + secretion inversely proportional with pH Respiratory acidosis Respiratory acidosis ↑CO 2 → ↑ rate of H + secretion in kidney → ↑ HCO 3 - reabsorption = renal compensation ↑CO 2 → ↑ rate of H + secretion in kidney → ↑ HCO 3 - reabsorption = renal compensation Metabolic acidosis Metabolic acidosis Change in pH detected by peripheral chemoreceptors Change in pH detected by peripheral chemoreceptors ↑ ventilation rate – respiratory compensation ↑ ventilation rate – respiratory compensation ↑ H + secretion in kidney → ↑ HCO 3 - reabsorption – renal correction ↑ H + secretion in kidney → ↑ HCO 3 - reabsorption – renal correction

19 Micturition Detrusor muscle – smooth muscle Detrusor muscle – smooth muscle 2 sphincters 2 sphincters Internal – smooth muscle External – skeletal muscle Spinal reflex with learned voluntary control Spinal reflex with learned voluntary control

20 Any questions?

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


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