Physiology 2: Renal Handling of Electrolytes Flashcards
Covers pages 38-53 in the Renal Handout.
Explain the load-dependent phenomenon known as glomerulotubular balance.
Despite fluctuations in GFR, a fairly constant fraction (~65%) of the filtered Na and Water is reabsorbed in the proximal tubule.
When might someone have an increased filtered load and increased excreted load of Na?
Hypervolemic state; secondary to higher GFR.
When might someone has a decreased filtered load and decreased excreted load of Na?
Hypovolemic state; decreased GFR.
What 2 things can stimulate the Na+-H+ exchanger?
Stimulation by Angiotensin II as well as Sympathetics.
Explain Cl-driven Na_ reabsorbtion
Since other anions are preferentially used in the proximal proximal tubual this creates an increased and favorable gradient in the distal proximal tubual for Cl to be the major Anion and help drive Na+ absorption. Also helps maintain electronutrality.
Characteristics of THIN DESCENDING limb of loop of Henle, what is it permeable to and impermeable to? Result?
- Tubular fluid entering the loop is isotonic.
- It is permeable to water
- It is IMPERMEABLE to solutes.
Therefore, water leaves and the tubular fluid OSMOLALITY INCREASES distally.
Characteristics of THIN ASCENDING limb of loop of Henle, what is it permeable to and impermeable to? Result?
- IMPERMEABLE to water
- permeable to solutes
- Passive diffusion of
- -NaCl “out”
- -Urea “in”
Results in progressively more dilute tubular fluid (decreasing osmolality).
Characteristics of THICK ASCENDING limb of loop of Henle, what is it permeable to and impermeable to? Result?
What can stimulate or inhibit absorption here?
-Impermeable to water
- *Na-K-2Cl pump
- K is recycled
- -net Na-2Cl reabsorption
Lumen “+” potential promotes reabsorption of Na+, Ca++, and Mg++ via the paracellular route.
Stimulated by ALDO and ADH
Inhibited by loop diuretics (lasix)
Na-H exchanger
Characteristics of DISTAL TUBULE, what is it permeable to and impermeable to? Result?
- Na-CL co-transporter
- NaK-ATPase
Impermeable to water - fluid becomes even more dilute
Blocked by thiazide diuretics (HCTZ)
Important in Ca++ reabsorption.
What types of diuretics (loop or distal tubule) are more efficacious and why?
Loop diuretics since there is more Na+ in the loop than in the distal tubule.
Characteristics of Collecting Ducts, what is it permeable to and impermeable to? Result?
Na and K channels present (passive movement)
NaK-ATPase
Rapid Na entry that produces a “-“ lumen potential that:
- promotes K+ secretion
- promotes Cl- reabsorption (paracellular pathway)
Stimulated by Aldosterone
Blocked by “K-sparring diuretics”
ADH sensitive region
-increases permeability to water
If you are reabsorbing Na+ what ion are you likely secreting?
K - potassium.
Aldosterone Effects in Principal Cells in Collecting Ducts:
Aldosterone:
- increased Na+ reabsorption
- increases K+ secretion
- increases Cl- reabsorption
- increases H+ secretion
Characteristics of Medullary Collecting Ducts, what is it permeable to and impermeable to? Result?
Functions parallel to the Cortical Collecting Ducts.
ALDO sensitive:
- NA/Cl reabsorption
- K/H secretion
ADH sensitive
Hypervolemia; definition, effects on secretion and other systems/factors
Increased ECBV
(-) RAAS
(+) ANP, BNP, Urodilatin
Na and water excretion increases but no change in osmolality.
Hypovolemia; definition, effects on secretion and other systems/factors
Decrease ECBV
(+) RAAS
(+) sympathetic
Na and water excretion decreases but no change in osmolality.
Hypernatremia; definition, effects on secretion and other systems/factors
Increased plasma [Na]
(+) ADH release
excretion of free water decreases and plasma osmolality decreases
Hyponatremia; definition, effects on secretion and other systems/factors
Decreased plasma [Na]
(-) ADH release
excretion of free water increases and plasma osmolality increases
Primary stimuli for aldosterone release (4), and what can suppress it:
- Angiotensin II - increases in hypovolemic states and results in release of renin
- Hyperkalemia - K+ has a direct effect on zone glomerulosa cells of the adrenal to increase aldosterone release
- Hyponatremia - weak stimulus
- ACTH (Adrenocorticotrophic hormone) - weak stimulus
- Hyperkalemia - K+ has a direct effect on zone glomerulosa cells of the adrenal to increase aldosterone release
ANP and Dopamine can suppress Aldosterone secretion.
Mechanisms of aldosterone action on the COLLECTING TUBULES (4): Net effect on Na, other effects on K+ and H+
- Increases NaK-ATPase activity
- Increases synthesis and insertion of Na+ channels
- Increases the provision of energy for active transport
- **The net effect is an increase in Na+ REABSORPTION
Increases K+ SECRETION from principal cells
Increases H+ SECRETION from intercalated cells
Effects of increased Na+ intake:
Increases urine Na+
Decreases plasma renin
Decreases aldosterone
Increases ECBV
Effects of decreased Na+ intake:
Decrease urine Na+
Increase plasma renin
Increase aldosterone
Decreases ECBV
GFR effects on Na+ excretion:
Increased GFR = increased Na excretion
Decreased GFR = decreased Na excretion
What is ANP, where does it come from and what is it a result of?
What are it’s effects?
ANP = Atrial natriuretic peptide
Released from myocytes in right atrium as a result of expansion of the vascular volume (low pressure centers).
Causes afferent arteriolar vasodilation (increased GFR but decreased FF)
Decreases peritubular capillary reabsorption
Inhibits Na+ reabsorption in collecting ducts
Inhibit ADH release, results in increased water secretion.
