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

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renal physiology

Renal physiology

Dr Alison Chalmers

Consultant Anaesthetist

Queen Victoria Hospital

what you need to know
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
example questions from soe 1
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
aims of this session
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
key facts function of the kidney
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
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

Renal blood flow
regulation of renal blood flow
Autoregulation

Renin-angiotensin system

Macula densa cells

Juxtaglomerular complex

Regulation of renal blood flow
glomerular filtration
GFR = 125ml/min

Approx 20% renal blood flow is filtered

GFR ~ forces favouring filtration – forces opposing filtration

Glomerular filtration
factors affecting gfr
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)
proximal tubule
Passive diffusion

Across membrane

Through channels/pores

Facilitated diffusion

Active transport

Secretary processes

Organic acids/bases

Proximal tubule
sodium reabsorption
Passive diffusion

Na+ linked symport and antiport

Na+K+ATPase into LIS

Sodium reabsorption
distal tubule and collecting duct
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
fluid and electrolyte balance
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

renal control of acid base balance
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
micturition
Detrusor muscle – smooth muscle

2 sphincters

Internal – smooth muscle

External – skeletal muscle

Spinal reflex with learned voluntary control

Micturition
summary
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