Renal regulation of water and acid-base balance Flashcards
How do you calculate osmolarity?
Concentration x No. of Dissociated Particles
size of molecule doesn’t matter
What is osmotic pressure directly proportional to?
No. of Solute Particles
What are the units for osmolarity?
Osm/L or mOsm/L
Calculate the osmolarity for 100mmol/L of glucose
Osmolarity = 100 x 1 particle = 100 mOsm/L
Calculate the osmolarity for 100mmol/L of NaCl
Osmolarity = 100 x 2 particles (Na+, Cl-) = 200 mOsm/L
Osmolarity
Osmoles per 1L of solvent
Osmolality
number of solute particles in 1 kg of solvent
Can be measured
Body fluid distribution
1/3 - Extracellular fluid
1/4 - intravascular (plasma)
3/4 - extravascular
95% interstitial fluid
5% transcellular fluid
2/3 - Intracellular fluid
What are some examples of unregulated water loss?
Sweat, released for temp homeostasis
Faeces, to allow easy excretion
Vomit,
Water evaporation from resp lining and skin
What is an example of regulated water loss?
Renal urine production
Explain how renal regulated water loss works for a positive water balance
Positive water balance = too much water in blood, decreased osmolarity -> hypoosmotic urine production
Explain how renal regulated water loss works for a negative water balance
Negative water balance = too little water in blood, increased osmolarity -> hyperosmotic urine production
Explain how countercurrent multiplication in the loop of henle works?
Water passively diffuses out of descending limb. Ions are actively pumped out of ascending limb. This leads to even more water passively diffusing out of descending limb. The remaining fluid is even higher in concentration, so more ions are actively pumped, until the highest concentration of medulla (1200 mOsm) is reached - at the base of loop of henle. Top of loop of henle is less concentrated as ions are actively pumped out from the bottom of the ascending loop first.
Explain how urea recycling works
Urea is freely filtered in the PCT. Urea passively enters the descending loop of henle via the UT-A2 transporter. Urea cannot leave the ascending loop nor DCT. In the collecting duct, ADH stimulates UT-A1 and UT-A3 transporters to bind to cell membrane, allowing urea to leave the collecting duct. The remaining urea re-enters the descending loop of henle (hence recycling), or enters blood supply via UTB-1 (vasa recta)
Why is it beneficial for vasopressin to stimulate urea reabsorption in the collecting duct?
Urea recycling requires less water than urea remaining in the urine - net positive effect and blood water levels
Role of NaCl and urea in the interstitium
Responsible for generating a hyperosmotic medullary interstitium
Where is vasopressin produced?
Supraoptic and Paraventricular Nuclei of Hypothalamus
How much change in blood volume is required for the hypothalamus to be alerted, and through what receptor does this occur?
5-10% plasma osmolarity, through baroreceptors
What are examples of stimulatory stimuli for ADH production and release?
Increased plasma osmolarity, decreased blood pressure, hypovolemia, nausea, ang II, nicotine
What are examples of inhibitory stimuli for ADH production and release?
Decreased plasma osmolarity, increased blood volume, hypervolemia, ethanol, Atrial Natiuretic Peptide
Explain the mechanism of action of ADH
ADH binds to V2 receptor on collecting duct (attached to G protein). G protein activates adenyl cyclase converts ATP to cAMP, leading to protein kinase A upregulating expression of aquaporin 2. Attach both to apical cell membrane for more water reabsorption
Explain how NaCl reabsorption occurs in the thick ascending loop of henle
Na+.K+.2Cl- Symporter moves all of these ions from lumen into cell.
Na+/K+ ATPase pump moves sodium into blood.
K+.Cl- Symporter moves these ions into blood
Explain how NaCl reabsorption occurs in the distal convoluted tubule
Na+.Cl- Symporter moves these ions from lumen into cell. Na+/K+ATPase pump moves sodium into blood. K+.Cl- Symporter moves ions into blood. (ONLY DIFFERENCE is Na+.Cl- Symporter)
Main function of ADH aka AVP
promotes water reabsorption form the collecting duct
