Flashcards in Tubular Transport II Deck (38):
Water loss from body
sweat, respiration, feces, urine, vomit
Water gain to body
The amount of water that leaves the body affects the
ECF Volume is a reflection of the
Body Na content
ECF volume is sensed by
arterial and cardiac baroreceptors
Low/High ECF volume triggers
Ang II, aldosterone, SNS/ANP
Low/High ECF volume leads to the
excretion or retention of Na
Plasma osmolality is a reflection of the
body water content of body fluid
HIgh/Low Plasma osmolality is sensed by
High/Low Plasma osmolality leads to the
excretion of H2O or intake of H2O (thirst)
A problem with total body water manifests as
plasma osmolality alteration [Na]
problems with total body Na content manifest as
ECF volume alteration
excretion of large amounts of urine (hypoosmolar)
excretion of small amount of urine (hyperosmolar)
Normal plasma osmolality is
ADH release is triggered by
atrial or arterial baroreceptors
ADH is released from the __________ due to signals from __________
posterior pituitary; hypothalamic osmoreceptors
Osmoreceptors in the hypothalamus sense change sin
Low plasma osmolality -->
reduced ADH --> decreased reabsorption of H2O in the collecting duct
When plasma osmolality is <280 , ADH is
High plasma osmolality -->
increased ADH --> increased reabsorption of water (AQP-2)
binds to vasopressin-2 (V2) receptor on principal cells --> increased cAMP --> increased AQP-2 --> H2O reabsorption
What 2 things are necessary to concentrate urine?
ADH and permeable distal tubule and collecting duct AND hypertonic medullary gradient
What establishes the hypertonic medullary gradient?
thick ascending limb reabsorption of solutes (NaCl and urea)
arrangement of loop of Henle and the collecting duct, creates a gradient as the loop dips deeper into the medulla
Dilution of urine requires 2 things
reabsorption of solutes (W/O H2O) in the thick ascending limb AND low levels of ADH
Concentration of urine step-wise
isoosmolar (300) filtrate in descending limb loses H2O to become hyperosmolar (600), NaCl is lost in the thin ascending limb and Na-K-Cl reabsorbs solute in the thick ascending limb to create a hypoosmolar filtrate (150), NaCl is reabsorbed in the distal tubule and collecting duct (W/O H2O loss) concentrating the urine to 50mOsm
Concentrating the urine step-wise
isoosmolar (300) filtrate in descending limb loses H2O to become hyperosmolar (600), NaCl is lost in the thin ascending limb and Na-K-Cl reabsorbs solute in the thick ascending limb to create a hypoosmolar filtrate (150), in the presence of ADH H2O can rapidly move down it's concentration gradient in the distal tubule and collecting duct until it equilibrates with its surrounding (1200mOsm)
What happens if the NaCl reabsorption out of the thick limb is impaired?
hypertonic gradient cannot be established and concentrating the urine cannot take place
Role of Urea in medulla osmolality
In conditions of severe dehydration, ADH phosphorylates urea transporters (UT-A1) in the thick ascending limb and allows for the resorption of Urea. Contributing to the maximal ability to concentrate the urine.
How would a high protein diet effect the ability to concentrate urine?
High protein, high urea in filtrate, higher medullary interstitial, greater ability to concentrate urine.
How would consuming large amounts of water contribute to the ability to concentrate urine?
Large amounts of water, large amounts of flow in vase recta, "washing-out" of solutes in hypertonic medulla --> decreased ability to concentrate urine
Why isn't the maximum medullary osmolarity 1200 during diuresis?
Low ADH --> less urea in interstitial, and large volume flow through the vasa recta "washes-out" hypertonic medulla
If vasa recta blood flow is decreased, what will happen to the concentrating ability of the kidney?
decreased blood flow, decreased ATP and O2 for Na reabsorption, decreased osmolality of interstium, DECREASED ability to concentrate urine
Comparison of urine osmolality to plasma osmolality tells you if you are concentrating or diluting the urine
hypoosmolar: Uosm < Posm (dilute urine)
isoosmolar: Uosm = Posm
Hyperosmolar: Uosm > Posm (concentrating urine)
Free water clearance
(+) Ch2o added to urine to make it dilute
(-) Ch2o retained to make urine concentrated
Negative water clearance is called
TcH2O (tubular conservation of H2O)