Fluid balance

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Transcript Fluid balance

Fluid Balance
David Taylor
[email protected]
http://www.liv.ac.uk/~dcmt
Fluid Balance
 When you have worked through this you should be able to
explain
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Electrolyte balance
Ion channels and pumps where they relate to the kidneys
Fluid balance regulation
Urine – isomolar (more/less)
Countercurrent multiplier
RAAS and ADH system
Acid-base balance
Hormonal regulation (Angiotensin II, ADH, ANP, Aldosterone)
Resources
 These slides are available with all my other lectures on
my website http://www.liv.ac.uk/~dcmt
 In the text books:
Chapters 25,26, 27 and 28 in Preston and Wilson (2013)
Chapter 14 in Naish and Court (2014)
Formation of urine and its
composition
Electrolyte balance
Role of the kidneys:
 Remove waste products
 Maintain blood volume/pressure
 Electrolyte balance
 Na+ 142 mM, K+ 5mM, Ca2+ 2mM, Cl- 105 mM
 Acid-base balance
 pH=7.4
Acid-base balance
Ion channels and pumps where they
relate to the kidneys
Ch. 26 in Preston and Wilson (2013)
Fig. 14.9 in Naish and Court (2014)
Fluid balance regulation
 Two thirds of the filtered water (and almost all
sodium and chloride) is reabsorbed in the proximal
convoluted tubule
 Sodium is rescued by the Na/K ATPase
 Some of the water is reabsorbed through paracellular
pathways
 And some is reabsorbed through transcellular
pathways (Aquaporin I)
Fig 26.2 in Preston and Wilson (2013)
Fig 14.9
in Naish and Court (2014)
Urine – isomolar (more/less)
 The key thing to remember is that the fluid leaving
the proximal convoluted tubule is almost iso-osmotic
with capillary fluid
 But is no longer contains glucose (unless the pump
was saturated by high concentrations), or amino acids
 Fine tuning of electrolyte concentration occurs in the
loop of Henlé.
Countercurrent multiplier
Ch. 27 in Preston and Wilson (2013)
Fig 14.15 in Naish and Court (2014)
Countercurrent multiplier
Permeable to water,
Impermeable to NaCl
Permeable to NaCl
Impermeable to water
Ch. 27 in Preston and Wilson (2013)
Fig 14.15 in Naish and Court (2014)
ADH system
Concentration gradient
300mOsm upto 1,200mOsmol
Urea
Tubule and
early duct
membrane
impermeable
to Urea
[Urea]
In duct
Urea
Later part of
collecting duct
membrane
permeable to
Urea
Local Blood Flow (kidney)
Decreased renal blood flow
Monitored by JGA cells
Renin production
Angiotensinogen
Angiotensin I
Converting enzyme
Angiotensin II
Sodium reabsorption
Aldosterone
Potassium secretion
Vasoconstriction
Chapter 20, p 243 in Preston and Wilson (2013)
Chapter 11, p 556 in Naish and Court (2014)
Hormones
 Aldosterone increases Na+ reabsorption and K+
secretion
 ADH (anti-diuretic hormone) increases water
reabsorption through aquaporin II
 ANF decreases sodium reabsorption
Chapter 20, p 244 in Preston and Wilson (2013)
Chapter 11, p 556 in Naish and Court (2014)
Overview
ADH
Fluid loss
Arterial pressure
Blood volume
Venous return
heart rate
vol
sympathetic
contractility
vasoconstriction
Cardiac output
baro
Arterial pressure
chemo
CNS
Cardiac output
Venous return
veins
capillary
pressure
Blood volume
Local blood flow
kidney
renin/angiotensin
aldosterone