F: Urine Control Flashcards
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A: Kidneys MUST be able to excrete Urine either hypOosmotic or Hyperosmotic (varying osmolaLity) compared to body fluids. So this means excretion of water is regulated SEPARATELY from solute excretion
B: Since filtered solute and water are PROPORTIONALLY ReAbsorbed in the PCT –>they are NOT separated here. [Loop of Henle] is majorly where solute & water are separated
C: [ANTIdiuresis] = Occurs during State of Dehydration (common for land dwellers). Is characterized by HIGH levels of plasma ADH–>INC ReAbsorption of water & urea with production of low-volume/high-concentrate(up to 1200 mOsm/kg) and [Dark Amber urine with lots of Urea].
C2: During [ANTIdiuresis] [medullary interstitial gradient] is at MAX
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D: [Water Diuresis] = occurs during state of OVER-hydration which is NOT common in land dwellers. This can occurs with STRONG administration of hypOtonic solutions. It leads to DEC plasma ADH—> DEC ReAbsorption of water/urea and excretion [pale yellow dilute urine]
D2: [Water Diuresis] is also associated with INC [Vasa Recta blood flow] & entry of some Urea into [Collecting Duct]
—>DEC [medullary interstitium osmoLality]–>helps INC [Urine flow rate & volume]
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- Medullary HYPERosmoLality*
1. Renal Cortex is isotonic with Plasma = [300 mOsm/kg H20] = not included in Medullary HYPERosmoLality
- [Outer Medulla] has Mild HYPERosmoLality = [300-480 mOsm/kg H20]. This where “Water Shunt” occurs.
- [inner deep medulla] has STRONG HYPERosmoLality = [480-1200 mOsm/kg H20] MOSTLY due to UREA(50% of the gradient) but also to Na+ & Cl (each 25% of total gradient). Is where “Salt Trap” occurs
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A: There are 3 mechanisms that generate & regulate [Medullary HYPERosmoLality]
1) [Countercurrent Multiplier] = ESTABLISHES INITIAL osmotic gradient
2) [Urea Cycle] = STRENGHTHENS this osmotic gradient
3) [Countercurrent EXCHANGER] = MAINTAINS this Osmotic gradient
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1)A: [Countercurrent Multiplier] ESTABLISHES osmotic gradient because countercurrent flow between 2 limbs of [Loop of Henle]–>differential fluid & solute mvmnts.
ºWater moves OUT of [thin Descending] leaving salt behind.
ºsalt will then leave out of [thin ASCending] which leaves Water behind
(( This creates osmotic pressure gradient between interstitium & [descending limb]–>allows more Water to move passively OUT of [thin Descending lim]. This effect is multiplied along length of loop with fluid at bend of loop having HIGHEST OsmoLality ))
B: [THICK ASCending limb] is the diluting segment where most of the ACTIVE salt(Na/Cl/K) pumping OUT is done—>[hypOosmotic DCT] since water can’t leave at this point
C: DCT has INC Water AND NaCl ReAbsorption
D: [Upper Collecting Duct] has ACTIVE Salt ReAbsorption with passive water ReAbsorption after ADH stimulation
E: [lower collecting duct] has ACTIVE Salt ReAbsorption with passive water AND UREA ReAbsorption after ADH stimulation
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A: There are 3 mechanisms that generate & regulate [Medullary HYPERosmoLality]
1) [Countercurrent Multiplier] = ESTABLISHES INITIAL osmotic gradient
2) [Urea Cycle] = STRENGHTHENS this osmotic gradient
3) [Countercurrent EXCHANGER] = MAINTAINS this Osmotic gradient
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2) 1st:[Urea Cycle] occurs because urea is concentrated in [Upper Collecting Duct] and then passively moves out of [lower collecting duct] w/ADH stimulation.
2nd: Urea is then picked up by [ascending vasa recta] and then diffuses out into [Outer Medulla] where it diffuses back into [descending Loop of Henle]
3rd: Urea is recycled back to the [lower collecting duct] to start another [Urea Cycle]
2B: [Urea Cycle] purpose:
º strengthens [medullary osmotic gradient] to protect [Vasa Recta RBC] from crenating in a HYPERosmotic environment
º sets up gradient for urea to be excreted in low-volume urine (since only ADH allows Urea passive ReAbsorption)
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A: There are 3 mechanisms that generate & regulate [Medullary HYPERosmoLality]
1) [Countercurrent Multiplier] = ESTABLISHES INITIAL osmotic gradient
2) [Urea Cycle] = STRENGHTHENS this osmotic gradient
3) [Countercurrent EXCHANGER] = MAINTAINS this Osmotic gradient
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3) [Countercurrent EXCHANGER] Maintains Osmotic gradient because Water, [Salt & Urea] move passively into [Vasa Recta Capillary walls] within the Renal Medulla
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3B: [DEScending Vasa Recta] RECEIVES [Salt and Urea] coming in (down osmotic gradient) from the [THICK Ascending LOH]. In this recta [water] leaves the capillary down its osmotic gradient = MAINTAINS OSMOTIC GRADIENT
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3C: [Ascending Vasa Recta] RECEIVES Water coming in (down osmotic gradient) from the [Descending LOH]. In this recta [salt & urea] are actually leaving the capillary down their concentration gradient = MAINTAINS OSMOTIC GRADIENT
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A: Urea is MORE permeable in [LOWER COLLECTING DUCT] but is also somewhat permeable in the [Descending & Ascending thin Loop of Henle]
B: Concentration of Urea varies directly / NonLinearly / and passively with [Urinary flow rate]. INC [Urinary flow rate]—> INC [Lost of Urea].
C: [ADH] can also INC [NaCl ReAbsorption] in the [THICK Ascending Loop of Henle] in addition to working on water
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D: Since Medullary gradient depends on [Na/Cl/urea mvmnt], [Washing Out] the Medullary gradient occurs when any factors INC [Vasa recta blood flow] and “washes” out the [medullary interstitial gradient] —> INC urine flow. After this Dilution it takes 3 days to reestablish!
E: Requires for [Medullary HYPERosmoLality] include:
º convections of blood & urine flow
ºLong Loops of Henle
ºACTIVE Salt Pumping in [THICK Ascending LOH / DCT / CD]
ºLOH with differential permeabilities to salt and water
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A: [DESCENDING Vasa recta capillary osmolarity] is LOWER than [medulla interstitial space osmolarity] BEFORE it takes in Salt
B: [ascending vasa recta capillary osmolarity] is HIGHER than [medulla interstitial space osmolarity] because it has carried Salt from the [DESCENDING Vasa recta] —>makes it [hyperosmotic (x>300 mOsm/L)]
C: You can assess how well Kidneys dilute/concentrate urine with [Osmolar Clearance] or [Free Water Clearance]
In [Osmolar Clearance]
1. [Uosm/Posm] GREATER THAN 1= concentrated urine (occurs from ADH ANTIDiuresis)
- [Uosm/Posm] less than 1= dilute urine (occurs with water diuresis)
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You can assess how well Kidneys dilute/concentrate urine with [Osmolar Clearance] or [Free Water Clearance]
B: In [Tubular Water movement control] endogenous factors (like ADH) or EXOgenous factors (like diuretics) are used.
B2: LASIX is the MOST POTENT [exogenous diuretic] and is [K+ WASTING]
B3: Spironolactone is a less potent [exogenous diuretic] and is [K+ sparing :-)]
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A: Kidneys maintain [EXTRAcellular fluid volume] by matching the amount of [excreted NaCl] with [ingested NaCl]. If [NaCl INGESTION] exceeds excretion–>INC [EXTRAcellular fluid volume] {and vice versa}
B: Kidney response to rapid NaCl changes takes hours to days. During transition to fixing it intake and excretion of Na+ are NOT matched until new [euvolemic steady state] is reached and so a person will transiently have:
1) [Positive Na+ Balance]=NaCl INTAKE is Greater {after salty meal}–> Volume EXPANSION–> INC ECF and body weight!
or
2) [negative Na+ balance]=NaCl excretion is greater
–>volume contraction–> [DEC ECF and body weight! ]
B2: Normally alterations in Na+ balance will change VOLUME but not [actual concentration of Na+] in [EXTRAcellular fluid]
C: The major determinant of ECF osmoLality are [Na/Cl/HCO3] where as the major determinant of [ECF volume] is [ECF osmoLality].
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A: [Effective Circulating Volume] is the portion of [EXTRAcellular fluid] in vascular system EFFECTIVELY PERFUSING TISSUES. Its dependent on [volume sensor activity] in vascular system {6 diff sensors}.
A2: Normally [INC EXTRAcellular fluid Volume] —>
[INC Vascular system volume]—> [INC arterial BP and Cardiac Output] —> [INC Effective Circulating Volume]
C: There are [6 Afferent volume sensors monitoring ECV] WHEN INCREASED and are found in the:
1. Atrial [low pressure venous sensor]–> ANP –>natriuresis {occurs when right or LEFT atrial pressure INC}
- Lungs (activated from pulmonary engorgement) [low pressure venous sensor]–> DEC Sympathetics —> DEC ADH
- [Aortic Arch & Carotid Sinus Barostretchreceptors][HIGH PRESSURE ARTERIAL SENSOR] —> DEC Sympathetics —> DEC ADH
- [Afferent Arteriole Renal receptors][HIGH PRESSURE ARTERIAL SENSOR]—>stimulates JGA–>INC Renin
- Hepatic sensors ([Liver pressure] vs. [portal vein Na+ sensors]) —>DEC Sympathetics —> [INC Na+ Excretion]
- CNS Na+ sensors —> DEC Sympathetics —-> [INC Na+ Excretion]
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A: 3 Things play a big role in regulating Renin Secretion
1) [Perfusion Pressure]
2) [Sympathetic Nerve Activity]
3) [NaCl Delivery to macula Densa]
1) [Perfusion Pressure] monitored by [Afferent Arteriole Renal receptors]. If Increased too much–> DEC Renin Secretion
2) INC [Sympathetic Nerve Activity] on [beta adrenergic receptors of afferent arterioles] INCREASES Renin secretion
3) [NaCl Delivery to Macula Densa] can activate [tubuloglomerular feedback] and DEC NaCl DELIVERY—> [Macula Densa] INC renin secretion and [DEC afferent arteriole resistance]
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- Renin is secreted by [Renal JGA] when [Afferent Renal Arterioles] sense a drop in [arterial pressure]
- Renin Converts Angiotensinogen(from Liver)—>[inactive Angiotensin 1]
- [inactive Angiotensin 1] is converted to [ACTIVE ANGIOTENSIN 2] by ACE from endothelial cells in Lung & Kidney !
- [ACTIVE ANGIOTENSIN 2] is converted to [ACTIVE ANGIOTENSIN 3] by angiotensinases
- [ACTIVE ANGIOTENSIN 2]:
* DIRECTLY VASOCONSTRICTS vessels,
- [AT 2&3] Stimulate Aldosterone RELEASE from [Adrenal Cortex] under permissive action of ACTH from [ANT Pit]
- Stimulates hypothalamus to activate thirst & secrete ADH(works on Collecting Ducts)
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A: The Effect of enhancing [NaCl ReAbsorption] IS GREATEST in the PCT quantitatively. In any part of Kidney, INC Na+ ReAbsorption—>INC Water ReAbsorption if ADH is present.
B: Euvolemia = steady-state [Net ZERO Na+ balance] whenever Na+ excretion MATCHES Na+ intake! During Euvolemia the Kidneys ReAbsorb more than 99% of filtered Na+ load segmentally as follows: 67% in PCT 25% in [THICK Ascending LOH] 4% in DCT- fine control 3% in [Collecting duct]
C: In the [THICK Ascending LOH] [Na+ ReAbsorption Rate =Na+ delivery rate].
D: In the DCT & CD [Na+ ReAbsorption Rate can be stimulated by INC in Na+ load]
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A: There are 2 things NEPHRON does to Rid of Excess body water when [Effective Circulating Volume] INCREASES/EXPANSION
- Increases GFR
- Decreases PCT and CD [Na+ ReAbsorption]
**Nephron does exact OPPOSITE when [Effective Circulating Volume] decreases/contraction & it needs to conserve Water
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A: Edema [AKA Third Spacing] occurs when excess fluids accumulates in [Extracellular interstitium]. Starling forces dictate movement of fluids across capillary walls & can cause Edema. Edema fluids can be removed from body using Diuretics.
B: DEC interstitial fluid–> [DEC Effective Circulating Volume] AND [DEC Plasma Volume] WITH NO BODY WGHT CHANGE
C: edema examples:
1. Pulm. engorgement–> [Alveolar flooding]
- Pleural Effusions—> Expansion of serous fluid spaces
- Abd Ascites—> Water within abd cavity
- [Pitting ankle edema]–> [extra-vascularized ankle water]
- [Venous Vascular Engorgement (from CHF or Liver failure)]—>[Edema 3rd Spacing]
