Producing a concentrated or Dilute Urine Flashcards
What feature differentiates juxtamedullary nephrons from cortical nephrons?
Juxtamedullary nephrons have far longer loops of henle which stretch far deeper into the medulla
What nephrons contain peritubular capillaries?
Cortical nephrons (surround all parts of the tubules)
What percent of nephrons are juxtamedullary?
15%
What does the blood from peritubular capillaries drain into?
Arcuate vein
Where does the blood go in juxtamedullary nephrons from glomerulus and efferent arterioles?
- Forms long loops which follow loop of henle (vasa recta) only some reaches the medulla
What does the vasa recta perfuse?
Loop of Henle and collecting duct that are in medulla
What is the normal osmolarity of the extracellular fluid when entering the kidney?
300 mOsm/L
What is the normal osmolarity of fluid when entering the distal convoluted tubule?
100 mOsm/L (due to reabsorption of ions)
What happens to osmolarity after the DCT?
- Further reduced in DCT and collecting ducts due to additional reabsorption of NaCl.
- In abscence of ADH CDs are impermeable to water and tubular fluid becomes even more dilute to as low as 50 mOsm/L
What does the thin descending limb transport?
Water (impermeable to salts)
What diuretic acts on the thin descending limb?
Loop diuretics (furosemide) (most powerful)
Where in the loop of henle is water uptake?
- Thin descending limb
No water can be absorbed in the thin and thick ascending limbs
What is the symporter of the thick descending limb called?
Na+/K+/2Cl-
What is the main symporter on the distal collecting tubule?
Na+/Cl-
What is the osmolarity of tubular fluid leaving the loop of henle into the DCT?
100 mOsm/L
What happens to the osmolarity of the tubular fluid in the DCT?
Falls due to continual removal of ions
What is the water reabsorbtion dependant on in the cortical section of the Collecting ducts?
ADH levels
Where is the water transported into after the cortical section of the collecting ducts?
Cortical peritubular capillaries (not vasa recta from juxtamedullary nephrons)
Where is the osmotic gradient in the medulla maintained?
Through awater absorption in the kidney cortex
What percentgae of blood flow is to the cortex?
90%
What percentage of filtered urea is reabsorbed in the PCT?
40-50% (concentration in tubular fluid rises though as it is less than that of water)
Describe urea recirculation
- High concentration of urea causes it to move out of the medullary collecting ducts into the medullary interstitial fluid
- Facilitated by specific urea transporters. One of these transporters is activated by ADH so enhancing the movement of urea out of the medullary collecting duct into the medullary interstitial fluid
- A moderate amount of this urea can move back into the tubule at the inner medullary section of the loop of Henle and so can recirculate through the tubule distal to this part of the nephron several times
- This recirculation can contribute to the concentration of urea in the distal tubular fluids in times of dehydration
- The urea recirculation also provides an additional mechanism for the formation of the hyperosmotic renal medulla
- In full hydration where waater is to be lost, then tubular flow is greater and this recirculation of urea is less marked and contributes less
What is the main osmolite in the medulla?
Urea
What is the main activator of urea transporters?
ADH
What is the normal concentration of urea in the blood?
4.5mmol
What percentage of renal blood flow is to the medulla?
5%
Does more fluid enter or leave the vasa recta?
Enter
