1. Dr Alison Chalmers Consultant Anaesthetist Queen Victoria Hospital
Renal physiology
Dr Alison Chalmers
Consultant Anaesthetist
Queen Victoria Hospital

2. 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

3. 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

4. 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

5. 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

6. Key facts - anatomy

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

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

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

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

11. Tubular function

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

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

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

15. Loop of Henle

16. Distal tubule and collecting duct
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

17. 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

18. Renal control of acid base balance
Key reaction:
CO2 + H2O <=> H2CO3 <=> 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

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

20. Any questions?

21. 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