Renal Regulation of Water and Acid-Base Balance Flashcards
What is the relationship between osmotic pressure and the number of solute particles?
proportional
What is osmolarity?
concentration x number of dissociated particles (Osm/L, mOsm/L)
Where is the majority of body fluid found?
2/3 in the intracellular fluid
Where is the 1/3 of extracellular fluid found?
1/4 intravascular (plasma)
3/4 extravascular (95% - interstitial fluid, 5% - transcellular fluid)
What are the different forms of unregulated water loss?
- sweat
- feces
- vomit
- water evaporation from respiratory lining and skin
What are the different forms of regulated water loss?
renal regulation (urine production)
What are the 2 different forms of renal regulation?
positive and negative water balance
What is positive water balance?
- high water intake
- increased ECF volume
- reduced Na+ concentration
- reduced osmolarity
- hypoosmotic urine production
- osmolarity normalises
What is the first compartment of the body where new fluid is put?
ECF
What is negative water balance?
- low water intake
- reduced ECF volume
- increased [Na+]
- increased osmolarity
- hyperosmotic urine production
- thirst induced
- osmolarity normalizes
Where is the majority (67%) of water reabsorbed?
the DCT
What is absorbed in the ascending limb of the loop of Henle?
- Thin: passive NaCl
- Thick: active NaCl
no water
What is absorbed in the descending limb of the loop of Henle?
- passive water
-
Why is water reabsorbed first in the loop of Henle?
- since water is reabsorbed through the passive process of osmosis, a gradient is required
- the medullary interstitium needs to be hyperosmotic for water reabsorption to occur from LoH and CD
What process causes the gradient in the medullary interstitium?
countercurrent multiplication
What transports urea from the collecting duct to the medullary interstitial?
UT-A1, UT-A3
What are the 2 possible locations for urea to go to once in the medullary interstitial?
- the descending loop of Henle
- the Vasa-Recta
What transporters allows for the movement of urea into the Vasa Recta?
UT-B1
What transporters allows for the movement of urea into descending LoH?
UT-A2
What is the purpose fo urea recycling?
to increase the interstitial osmolarity
- causes urine concentration
- urea excretion needs less water (high concentrations can be excreted)
How is vasopressin involved in urea recycling?
boosts UT-A1 and UT-A3 numbers
What is the main function of ADH/vasopressin?
promote water reabsorption from the collecting duct
Where is ADH produced?
- hypothalamus
- neurons in the supraoptic and paraventricular nuclei
Where is ADH stored?
the posterior pituitary gland
What detects fluctuation in plasma osmolarity?
osmoreceptors in the hypothalamus
What factors stimulate ADH production and release?
- increased plasma osmolarity
- hypovolemia (reduced BP)
- nausea
- angiotensin II
- nicotine
What factors inhibit ADH production and release?
- low plasma osmolarity
- hypervolemia (increased BP)
- ethanol
- ANP,BNP
What detects changes in BP?
baroreceptors to the hypothalamus
What is required in order for baroreceptors to detect BP changes?
5-10% change
What receptor binds ADH?
V2 receptor
What happens when ADH binds to a V2 receptor?
- activates the G protein mediated signalling cascade
- activating protein kinase A
- increasing the secretion of Aquaporin 2 channels that are transporters of water on apical membrane
What happens in diuresis?
increased dilute urine secretion (low/no ADH)
What is absorbed/excreted in the collecting duct during diuresis?
- NaCl reabsorbed
- water reabsorption in the inner medulla (even with absent ADH)
What is the type of fluid that enters the LoH?
Isosmotic
What is the type of fluid that enters the DCT?
Hypoosmotic
What is reabsorbed in the DCT during diuresis?
- active NaCl
- water channels closed in DCT
What is the type of fluid that exits the CD?
hypoosmotic
How is sodium reabsorbed in the collecting duct?
- Na+/K+/ATPase Pump
- sodium channels
What is antidiuresis?
- concentrated urine in low volume excretion
- high ADH
How does ADH increase salt reabsorption in the thick ascending limb?
increased number/action of the Na+/K+/2Cl- symporter
How does ADH increase salt reabsorption in the DCT?
increased number/action of the Na+/Cl- symporter
How does ADH increase salt reabsorption in the CD?
increased Na+ channels
What is reabsorbed in the DCT during antidiuresis?
- active NaCl
- water through AQP2
What is reabsorbed in the CD during antidiuresis?
- water reabsorbed increases as passing into the medulla
What are some examples of ADH related clinical disorders?
- central diabetes insipidus
- syndrome of inapropriate ADH secretion (SIADH)
- Nephrogenic Diabetes Insipidus
What is the cause of central diabetes insipidus?
decreased/negligent production/release of ADH
What are the clinical features of central diabetes insipidus?
- polyuria
- polydipsia
What is the treatment given for central diabetes insipidus?
external ADH
What is the cause of SIADH?
increased production and release of ADH
What are the clinical features of SIADH?
- hyperosmolar urine
- hypervolemia
- hyponatremia
What is the treatment given for SIADH?
Non-peptide inhibitor of ADH receptor
- (conivaptan and tolvaptan)
What mechanisms neutralise excess metabolic acids?
- bicarbonate buffering mechanism
What is the role of kidneys?
- secretion and excretion of H+
- reabsorption of HCO3-
- production of new HCO3-
How much of bicarbonate ions are reabsorbed in the PCT?
80%
How much of bicarbonate ions are reabsorbed in the ascending LoH?
10%
What mechanisms neutralise excess metabolic acids?
- bicarbonate buffering mechanism
- phosphate buffering system
How much of bicarbonate ions are reabsorbed in the CD?
4%
How is bicarbonate reabsorbed in the PCT?
- CO2 from the tubule enters the cell
- reacts with water to form HCO3-
- Na/HCO3- symporter into the blood
Where are intercalated cells found?
- DCT
- CD
What is the role of the alpha-intercalated cells?
- HCO3- reabsorption
- H+ secretion
What is the role of the beta-intercalated cells?
- HCO3- secretion
- H+ reabsorption
What happens in the alpha-intercalated cell?
- H+ back into tubule via H+ATPase and H+/K+ ATPase
- HCO3- into blood by Cl-/HCO3- antiporter
What happens in the beta-intercalated cell?
- HCO3- into tubule by Cl-/HCO3- antiporter
- H+ ATPase pump for H+ into the blood
Where are new bicarbonate ions produced
PCT
How is new bicarbonate produced?
- glutamine into 2 ammonia and one divalent ion
- 2 HCO3- ions that are reabsorbed
What happens if ammonia reaches the blood and eventually back to the liver?
- ammonia = one urea and one H+
- then uses up another HCO3- for neutralisation
How do you prevent ammonia from reentering the blood stream and reaching the liver?
- Na+/H+ antiporter (NH4+ replacing H+)
- Ammonium gas that binds with a H+ to produce ammonia that is excreted
What happens to the excess proton when HCO3- is produced (from CO2 in the tubule) in the DCT and CD?
it is neutralised by phosphate in the tubule
What are the characteristics of metabolic acidosis?
- low [HCO3-]
- low pH
What are the characteristics of metabolic alkalosis?
- high [HCO3-]
- high pH
What is the compensatory response to metabolic acidosis?
- increased ventilation
- increased [HCO3-] reabsorption and production
What is the compensatory response to metabolic alkalosis?
- hypoventilation
- increased [HCO3-] excretion
What are the characteristics of respiratory acidosis?
- high Pco2
- low pH
What is the compensatory response to respiratory acidosis?
acute
- intracellular buffering
chronic
- increase [HCO3-] reabsorption and production
What are the characteristics of respiratory alkalosis?
- low Pco2
- high pH
What is the compensatory response to respiratory alkalosis?
acute
- intracellular buffering
chronic (more carbonic acid production)
- increase [HCO3-] excretion and reduced [HCO3-] production
