renal regulation Flashcards
What is osmosis? What is the force involved? What is it dependent on?
Flow of water from low solute concentration to high solute concentration till equillibrium is reached. Force is osmotic/oncotic pressure & depends on number of solute particles not size
How do you calculate osmolarity?
Osmolarity (mOsm/L) = concentration x number of dissociated particles (for glucose 1 for NaCl 2)
What is the body fluid distribution in the body?
2/3 intracellular, 1/3 ECF (intesrstitial, plasma, transcellular)
What will a high water intake cause?
Increase volume of ECF and decrease osmolarity. Kidneys will produce hypoosmotic urine to lose excess water and normalize ECF.
What will dehydration cause?
Decrease volume of ECF, osmolarity increased. Kidneys produce hyperosmolar (concentrated) urine to reabsorb more water
What are methods of unregulated water loss?
Sweat, faeces, vomit, water evaporation from respiratory lining and skin
How is water reabsorbed in the kidney? Where is it reabsorbed?
Most of water reabsorbed in PCT (67%). In descending limb of loop of henle water passively reabsorbed (15%). No water reabsorbed in rest of loop. Variable amounts of water reabsorbed at collecting duct.
What is needed for water to be passively reabsorbed
equires a gradient so medullary interstitium must be hypertonic to allow water reabsorption in loop of henle and collecting duct
Where is salt reabsorbed/how in the kidney?
In PCT (67%), passively in thin ascending loop and actively reabsorbed in thick ascending loop in order to make medullary interstitium hypertonic, to allow water to be passively reabsorbed
What is the countercurrent multiplier process and what does it achieve?
Salt actively reabsorbed in thick ascedning limb so sodium falls inside and rises in medullary interstitium making it hypertonic. Water will flow out into medullary interstitium via descedning limb passively to equilibrate this.
What are vasa recta?
Series of capillaries that surround nephron
How is urea recycled?
Urea filtered through bowman’s capsule & reaches collecting duct where it moves with transporters UT-A1 & UT-A3 into the medullary interstitium. From here it can either go into vasa recta via UT-B1 or enter thin ascedning limb via UT-A2 to be recycled.
how does urea recycling affect water reabsorption?
Some of urea enters medullary interstitiuma and increases osmolarity so water passively reabsorbed. Urea excretion requires less water.
How does ADH affect urea reabsorption?
ADH increases UT-A1 & UT-A3 numbers so has role in urea reabsorption.
What is mechanism of ADH? What is it stimulated by and inhibited by?
Acts on V2 receptor (activated G protein activates protein kinase A) and signalling cascade causes secretion of aquaporin-2 channels inserted into apical membrane so water reabsorbed from collecting duct. Stimulated by increased plasma osmolarity, decreased blood pressure/volume, nausea, angiotensin II, nicotine. Inhibited by decreased plasma osmolarity, increased blood pressure/volume, ethanol, atrial natriuretic peptide (ANP)
