Renal Lec 5 Flashcards
sources of water gain (input)
- ingested liquid
- water from oxidation of food
sources of water loss (output) (6)
- skin
- respiratory airways
- sweat
- GI tract
- urinary tract
- menstrual flow
water moves via diffusion across water channels called
aquaporins
percentage of water reabsorbed in proximal tubules
67%
aquaporins in proximal tubule cells are
always open
water reabsorption is dependent on
Na+ reabsorption
the driving force for water reabsorption is
the osmotic gradient set up by Na+
cortical collecting duct
collecting duct in the cortex
medullary collecting duct
collecting duct in the medulla
cells in cortical and medullary collecting ducts are
under physiological control
hormone that controls water reabsorption (2 names)
-vasopressin/ antidiuretic hormone (ADH)
vasopressin/ADH regulate
a specific type of aquaporin
vasopressin/ADH act on (location)
cells of the collecting cuts
percentage of water reabsorbed in loop of henle
15%
percentage of water reabsorbed in distal tubule
0%
percentage of water reabsorbed in large distal tubule and collecting duct
8 to 17%
mechanism of water reabsorption in proximal tubule (via)
passive via AQP-1
mechanism of water reabsorption in loop of henle- descending thin limb only (via)
passive via AQP-1
mechanism of water reabsorption in large distal tubule and collecting duct (via)
passive via AQP-2, AQP-3, AQP-4
water reabsorption in PCT (summary)
- Na+ movement from tubular lumen to epithelial cells then into interstitial fluid via Na+/K+ ATPase
- local osmolarity of tubular lemn decrease
- local osmolarity of interstitial fluid increase
- water enters interstitial fluid through gap junctions and through epithelial cells via osmosis
- bulk flow of water into peritubular capillaries
ascending limb of loop of henle is impermeable to
water
water reabsorption in loop of henle (on which limb?)
descending thin limb
salt reabsorption in loop of henle (on which limb?)
ascending thick limb
loop of henle structure
- single tubule
- two sides closely juxtaposed
- fluid streams in opposite direction
- different transport capabilities on each side of tubule
structure-function relationship
a relationship between the structure of a biological entity and the functions (and sometimes the mechanisms) carried out by that entity
countercurrent mechanism system is a mechanism
that expends energy to create a concentration gradient.
loop of henle descending limb (osmolarity of interstitial fluid)
isotonic to tubule
loop of henle descending limb (osmolarity of tubule lumen increases as…because…)
loop descends because tubule is permeable to water and water diffuses out into the interstitial fluid
loop of henle ascending limb (osmolarity of interstitial fluid)
hypertonic to tubule
loop of henle ascending limb (osmolarity of tubule lumen decreases as…because…)
loop ascendes because tubule is impermeable to water and salt is actively transported into interstitial fluid/out of tubule
gradient difference between interstitial space and ascending limb is
200 mOsm
counter current multiplier
multiplication of gradient down the length of the loop of Henle
long loop of henle =
high osmotic gradient= better water retention
osmolarity in distal tubule is … because
low (80 mOSm) because permeable only to salt so salt moves out to the interstitial fluid
cortical collecting duct becomes
isosmotic with interstitial fluid (300 mOsm/L)
cortical collecting duct is permeable to both.. so
salt and water so salt and water are reabsorbed
ADH works on cortcial collecting duct to
reabsorb more water
the osmolarity gradient created by loop of henle
helps draw water out into interstitial space from medullary collecting tubule
in medullary collecting duct, osmolarity is
increasing (1400 mOsm/L)
fluid flow in vasa recta is
opposite to the flow in the loop of henle
vasa recta is permeable to
both water and salt, ions,urea
descending vasa recta picks up
salt and osmolarity increases
ascending vasa recta picks up
water and osmolarity decreases
vasa recta prevents
salt from being carried away and therefor maintains the gradient
blood flow in vasa recta serve as
counter-current exchnager
blood flow in medulla is … so
low so it prevents solute loss
vasa recta does not create
medullary hyperosmolarity
urea in the tubule (summary)
-100% filtrated
-50% reabsorbed in the proximal tubule
-50% secreted back
-100% enters the distal tubule
-30% enters reabsorbed from cortical collecting duct
-55% reabsorbed from inner medullary collecting duct (due to ADH action)
-Only 5% diffuses out to vasa recta and another 50%
secreted back into tubule
- 15% of the original amount is excreted (much less than the
filtered amount)
minimal uptake of urea by vasa recta and recycling urea in the interstitial space
helps in maintaining high osmolarity in the medulla
Why is there a need for concentrated urine?
-kidneys save water by producing hyperosmotic urine
Mechanisms used to maintain the hyperosmotic environment of the medulla:
- Counter-current anatomy and opposing fluid flow through the
Loop of Henle of the juxta medullary nephrons - reabsorption of NaCl in ascending limb
- impermeability of ascending limb to water
- trapping of urea in medulla
- hairpin loops of vasa recta maintains the hyperosmotic
interstitium in medulla
