Fluid Balance David Taylor

 When you have worked through this you should be able to explain  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) Fluid Balance

 These slides are available with all my other lectures on my website  In the text books: Chapters 25,26, 27 and 28 in Preston and Wilson (2013) Chapter 14 in Naish and Court (2014) Resources

Formation of urine and its composition

Role of the kidneys:  Remove waste products  Maintain blood volume/pressure  Electrolyte balance  Na mM, K + 5mM, Ca2+ 2mM, Cl mM  Acid-base balance  pH=7.4 Electrolyte balance

Acid-base balance

Ion channels and pumps where they relate to the kidneys Ch. 26 in Preston and Wilson (2013) Fig in Naish and Court (2014)

 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) Fluid balance regulation Fig 26.2 in Preston and Wilson (2013) Fig 14.9 in Naish and Court (2014)

 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. Urine – isomolar (more/less)

Countercurrent multiplier Ch. 27 in Preston and Wilson (2013) Fig 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 in Naish and Court (2014)

ADH system Concentration gradient 300mOsm upto 1,200mOsmol

Urea Tubule and early duct membrane impermeable to Urea Later part of collecting duct membrane permeable to Urea Urea [Urea] In duct

Local Blood Flow (kidney) Sodium reabsorption Potassium secretion Decreased renal blood flow Monitored by JGA cells Renin production Angiotensinogen Converting enzyme Angiotensin I Angiotensin II Aldosterone Vasoconstriction Chapter 20, p 243 in Preston and Wilson (2013) Chapter 11, p 556 in Naish and Court (2014)

 Aldosterone increases Na + reabsorption and K + secretion  ADH (anti-diuretic hormone) increases water reabsorption through aquaporin II  ANF decreases sodium reabsorption Hormones Chapter 20, p 244 in Preston and Wilson (2013) Chapter 11, p 556 in Naish and Court (2014)

Overview Fluid loss Blood volume Venous return Cardiac output Arterial pressure Local blood flow Blood volume Venous return Cardiac output Arterial pressure vol baro chemo kidney renin/angiotensin aldosterone ADH CNS sympathetic heart rate contractility vasoconstriction capillary pressure veins