lecture 17- (T3) Urine Concentration and dilution Flashcards
what are the major functions of the kidneys
regulation of extracellular osmolality, including water loss and conservation
what happens when there is a large excess of water in the body
kidneys can excrete as much as 20 liters per day with a concentration as low as 50 mOsm/L
what is avidly reabsorbed in the ascending thick limb of henle
sodium. potassium and chloride
is the ascending thick limb of henle permeable to water?
NOOOOO
what is osmolarity at the early distal tubular segment of the ascending thick limb of henle
100 mOsm/L
is the ascending thick limb of henle affected by ADH
NOOO
what happens to urine output when ADH is present
it decreases
what are attributes of the late distal convoluted tubule
addition reabsorption of sodium chloride
impermeable to water in absence of ADH
osmolarity reaches 50 mOsm/L
what is the maximum urine concentration of the kidneys
1200 mOsm/L
what are the requirements for forming concentrated urine
presence of ADH
high osmolarity of renal medullary interstitial tubule (establishes osmotic gradient necessary for water reabsorption to occur)
what is the normal obligatory urine volume
0.5 L/Day
what is the tubular osmolarity of the proximal tubule
300 mOsm/L
where is about 65% of filtered electrolytes reabsorbed
proximal tubule
is the descending loop of henle permeable to water?
YESSS
what is the osmolarity of the descending loop of henle when ADH is high
1200
what does the thin ascending loop of henle reabsorb
sodium chloride
urea also diffuses into ascending limb (comes from urea absorbed into interstitial from collecting ducts)
what is the osmolarity in the thick ascending loop of henle
100 mOsm./L
what does the osmolarity of fluid in the late distal tubule and cortical collecting duct dependent on
ADH
what is the concentration gradient limited to in the countercurrent multiplier system
200 mOsm/L because of paracellular diffusion of ions back into tubule
what parts of the kidney are impermeable to urea
ascending loop of henle and distal cortical collecting tubule
what happens when ADH increases and cortical collection tubule
water is reabsorbed form cortical collecting tubule
urea is not very permeant here and becomes more concentrated in the tubule
what happens when ADH increases and medullary collecting duct
more water is reabsorbed from medullary collecting duct, resulting in higher concentration of urea
higher concentration of urine results in diffusion of urea out of duct into interstitial fluid
facilitated by UT-A1 and UT-A3 (ADH activated) transporters
how is the high concentration of urea in the tubular fluid and the urin maintained even though urea is being reabsorbed
simultaneous movement of water and urea out of the inner medullary collecting ducts
what does vasa recta do
prevents medullary hyperosmolarity from being dissipated
what is the role of osmoreceptor-ADH feedback mechanism
controls extracellular fluid sodium concentration and osmolarity
where are int magnocelular neurons that form ADH found
supraoptic and paraventricular nuclei
where are osmoreceptor cells found
vicinity of the AV3V region (anterior region of third ventricle)
define isotonic volume depletion
osmolarity remains the same but volume decreases
define isovolemic osmotic increase:
volume remains the same but osmolarity increases
