Regulation Of Body Fluid Osmolality: Regulation Of Water Balance Flashcards
How does the LoH act as a countercurrent multiplier
By producing a hypertonic medulla by pooling NaCl in the interstitium, it favors a movement of water out of the CD under the regulation of ADH
The ThALoH maintains what gradient between the Tf and the interstitium
A 200 mOsmol gradient
The fluid leaving the TDLoH is what?
Hypertonic
Tubular fluid entering the descending limb from the PCT is what
Isotonic (around 300 mOsmol)
Before the vertical osmotic gradient is established, the medullary IF concentration is what
300 mOsmol, just like the rest of the body
The ThALoH pumps NaCl into the IF until when? Then what does this gradient cause
The IF is 200 mOsm/L more concentrated than the TF in this limb
This gradient causes water to be REBS from the TDLoH since water follows salt.
Passive movement of water from the TDLoH continues until when
The osmolarities of the TF and If are equal
What is the osmotic equilibrium of the LoH’s and IF
The ThALoH is 200 mOsm/L and the IF and TDLoH are 400 mOsm/L
The IF always achieves equilibrium with what, ensuring a concentration gradient ranging from 300 to 1200 mOsm/L
The TDLoH
What is the role of the vasa recta?
blood supply to the medulla
Removes the water and solute that is continuously added to the medullary intersitium
What does an increase or decrease in vasa recta BF mean
Increase - dissipates the medullary gradient (medullary washout)
Decreased - reduces the ability to concentrate the urine
What parts of the nephron are impermeable to Urea REBS
The ThALoH, the DCT, ands the cortical CD
What transporter allows urea to be transported across the apical membrane to be REBS and re enter at the LoH
UT - A1
UT - A3
What teo things overall created the IF osmotic gradient?
AQP within the TDLoH which allows water to be REBS into the IF
The anatomy of the LoH and CD which allows for progressively increasing osmolality
What are the two neurons that synthesize ADH in the brain
The supraoptic and paraventricular nuclei of the hypothalamus
Where is ADH released from
The posterior lobe
Generally, what is activated first, ADH or thirst?
ADH
What is used to actively transport Na across the basolateral membrane into the IF
Na/K Pump
ADH effects what AQP on which cells
AQP - 2 on principal cells
What is the role os Aldosterone in the intercalated cells
Increasing H secretion by the intercalated cells by stimulating the H/ATPase
What channels does Aldosterone work on
ENaC channels (moving Na into the cell from the TF)
The CDC are _____ to water at all times
Permeable
The permeability of the MCD is determined by what
ADH/AQP - 2
What happens in regards to ADH if you are overhydrated or dehydrated
Overhydrated - ADH inhibited
Dehydrated - ADH activated
An adequately hydrated person has a plasma osmol of what
275 - 295
Define Central Diabetes Insipidus
An inability to produce or release ADH from the posterior pituitary usually caused by a head injury
DCT can not REBS water so a large volume of dilute urine is created (polyuria) while the plasma becomes increasingly hyperosmotic leading to hypernatremic dehydration
Restricting water intake in a patient with central DI can cause what
Sever dehydration
What is the Tx for Central DI
Administration of desmopressin which acts selectively on V2 receptors to increase water permeability in the late DCT and CD
Define Nephrogenic DI
A failure of the kidneys to respond to ADH
Elevated levels of ADH in the renal tubule, but no more AQP-2 made
This means increased diuresis and dehydration
Adding an antidiuretic like furosemide can greatly compromise the urine concentrating ability
Define SIADH
Excessive release of ADH and thus excessive water REBS
Causes cells to swell and the body to hold onto electrolyte free water which causes hyponatremic dehydration
Dilution of urine is dependent on what
The ThALoH to REBS more solutes without water
And the CD to not REBS as much H2O (less ADH)
So, what happens in excess water/decreased NaCl intake
Increased H20 intake = increased NKCC/decreased ADH & AQP - 2 = increased diuresis = hyposomotic urine and hyperosmotic plasma
So, what happens in decreased water intake or excess salt intake
Decreased water = increased ADH & AQP-2 = decreased diuresis = hyperosmotic urine/hypoosmotic plasma
What is the most abundant electrolyte disturbance in hospitalized patients
Hyponatremia
What causes hyponatremia
Too much ADH caused by pain, nausea, decreased arterial volume, exercise
What causes hypernatremia
Inadequate free water intake and impaired thirst as well a volume depletion
What is considered polyuria and what causes it
> 2.5L/day
DB, DI, excess caffeine/alcohol, SSA
What is considered oliguria and what causes it
300 - 500 ml/day
Dehydration, blood loss, cardiogenic shock,
What is considered anuria and what causes it
<50ml/day
Kidney failure, obstruction
What are the 4 things that can cause polyuria
- Increased water intake
- Increased GFR (hyperthyroidisim/fever/hypermetabolic states)
- Increased outputs of solutes (thus more output of water)
- Inability of the kidneys to REBS water in the DCT
Define water diuresis and hat causes it
Increased water excretion without corresponding increase in salt excretion
Primarily caused by increased intake of water/polydipsia, DI
What is solute diuresis and what causes it
Increased water excretion concurrent with increased salt excretion
Caused by significant increases in salt in TF, aka hyperglycemia, high protein diet
A positive water clearance means what
Excess water is being excreted by the kidneys
This means decreased ADH/AQP - 2 and increased NKCC2
What does a negative water clearance mean
Excess solutes are removed from the blood by the kidneys and water is being conserved
This means increased ADH/AQP - 2
If urine osmol is greater than plasma osmol, what has happened
Free water clearance will be negative, indicating water conservation
What occurs in DI
High urinary output Low levels of ADH Hypernatremia Dehydrated Lose too much fluid Excessive thirst
What occurs in SIADH
Low urinary output High levels of ADH Hyponatremia Overhydrated Retain too much fluid Excessive thirst
What is normal plasma osmol
285 - 295
Is there too much or too little aldos. In SIADH? Why?
Too little
Because SIADH causes the body to create way too much ADH, the body holds onto free water. This increases the ECFV, causing the SNS to not stimulate the RAAS complex and thus not secrete aldos. This diminished aldos secretion causes the body to not absorb NaCl, leading to hyponatremia and concentrated urine.
In SIADH, there is increased ECFV. What 4 things does this cause to happen?
Reduced plasma osmol
Hyponatremia
Diminished aldos
Elevated GFR
What do the principal cells do when acted on my aldos. And what does this mean physiologically
REBS NaCl, and secrete K
This means with that with increased aldos, there is hypokalemia
