Lecture 5 - Water Balance

Question 1

Normal range for Na+ is _____mM - _____mM.

Answer 1

135mM - 145mM

Question 2

In hyper or hyponatremic states, neurological symptoms like altered mental status/confusion are NOT caused by decreased action potentials. What are they caused by?

Answer 2

They are caused by either hyper or hypo-osmosis, which cause brain cell shrinkage and swelling, respectively. Keep in mind neurological symptoms don’t start to appear in Hyponatremia until Na+ < 115mM

Question 3

Osmotic _______ Syndrome (central pontine myelinolysis) can result if Hyponatremia is corrected too fast.

Answer 3

Osmotic Demyelination Syndrome

Question 4

The minimal Urine osmole concentration is about _____mOsm/L and the Maximum is about _____mOsm/L. The minimum daily obligatory solute excretion is _____/day. From these values, we can determine the two extremes of Minimum and Maximum daily urine output. Think about the respective levels of ADH in each situation.

Answer 4

30mOsm/L

1200mOsm/L

600mOsm/day

Question 5

Remember that the Collecting duct is permeable to H2O ONLY in the presence of ____.

Answer 5

ADH

Question 6

Changes in plasma ______ stimulate or inhibit ADH secretion. The _____ receptors in the hypothalamus are highly sensitive and can detect as little as a 1% change. ADH can also be regulated by changes in _______ –> small deviations from the norm don’t really affect ADH (need at least 5-10% change), but it becomes much more sensitive to changes in severe ____-volemic states (the opposite is true in ____-volemic states). In fact, in severely volume-depleted states, it can override OSMOregulation!

Answer 6

Osmolarity

Osmoreceptors

ECF (volume)

Hypovolemic

Hypervolemic

Question 7

Increased ADH secretion can also be caused by Stress, Pain, and _______ (which hormone?)

Decreased ADH can also be caused by ____ (which hormone?) and ALCOHOL.

Answer 7

Angiotensin II

ANP

Question 8

V1 vasopressin receptors are found in the vasculature and act via ____ (which G protein coupled receptor?) to cause Ca++ influx vasoconstriction. V2 receptors are found in the ______ and act via increasing ______ to drive water reabsorption.

Answer 8

Gq

Kidneys

cAMP

Question 9

Vasopressin (ADH) antagonists are Aquaretics (“vaptans”). _____ is non-selective (blocks V1 and V2 receptors). ______ is selective for V2.

Answer 9

Conivaptan

Tolvaptan

Question 10

About 50% of Urea is reabsorbed in the _____ via ______ transport.

Answer 10

PCT

Paracellular

Question 11

Urea Recycling:

ADH stimulates urea reabsorption in the ____ ____ collecting duct by upregulating urea transporters. The urea is essentially recycled, bc it moves back into the Thin ____ _____ of the Loop of Henle, flows back to the collecting duct, and the process repeats.

Answer 11

Inner Medullary Collecting Duct

Thin Ascending Limb

Question 12

How do BUN and plasma Creatinine levels change with respect to volume depletion and/or Decreased GFR?

Answer 12

Plasma creatinine will increase ONLY when GFR decreases. Volume depletion will have no effect on plasma creatinine.

BUN will increase in BOTH scenarios. So look for an increase in the BUN : Creatinine ratio during volume depletion WITHOUT decreased GFR.

Question 13

The blood flow to the renal medulla is very low (it’s a low perfusion tissue). What does this mean for its vulnerability to ischemia/hypoxic damage?

Answer 13

It is MORE vulnerable than most tissues.