Week 14 - Renal/LE Flashcards
What are the components of internal K balance?
Of external K balance?
internal: intracellular vs extracellular pools
external: intake vs excretion
What things can increase K shifting into the cell?
How is this accomplished?
- insulin and B2 agonists
- increases the activity of the Na/K ATPase
What are the ways to affect internal K balance?
- insulin and B2 agonists bring K into the cell
2. acid/base status, where acidemia kicks K out (and alkalemia sucks K in)
Where does regulation of external K balance mainly occur?
in the kidney
Where can you lose K to, externally?
- kidney
- GI tract
- skin
Describe the proximal tubule’s overall role in K balance.
it participates in a significant amount of K reabsorption, but is not a site for major regulation
Describe the TAL’s overall role in K balance.
it participates in a significant amount of K reabsorption, but is not a site for major regulation
Describe the distal neprhon’s overall role in K balance.
- it secretes K variably, depending upon a lot of factors including the size load
- it is a major site for K regulation
Where does K secretion occur?
How?
- the principal cells of the late distal tubule and collecting duct
- K channel in the apical membrane
What maintains the high intracellular K concentration in the principal cells?
the Na/K ATPase
Of the 3, where is K concentration the highest:
tubular lumen, inside the principal cell, or ECF?
inside the principal cell (thanks to the Na/K ATPase)
What is the negative lumen potential in the principal cell generated by?
ENaC
What is the net movement of K in the principal cells?
What things allow for that?
- K secretion via K channels
- electrochemical gradient made by ENaC and the Na/K ATPase
What can lower the drive for K secretion?
- intercellular K concentration decreases
- lumen K concentration increases
- lumen potential becomes less negative
What is one of the most important regulators of K secretion?
aldosterone
What are the methods in which aldosterone affects K secretion?
- aldosterone increases the activity of the Na/K ATPase, increasing intracellular K
- increase the number of ENaC channels, causing increased reabsorption of Na, leading to an increase in the negative lumen potential
- increases the number of K channels in the apical membrane of the principal cell
Why does tubular fluid flow rate have a large effect on K secretion?
- if low/no blood flow, the K equilibrates and K secretion stops
- if fast flow, the secreted K is swept away and the gradient remains strong, promoting K secretion
What things increase K secretion?
- aldosterone
- increased dietary K
- increased Na delivery
- increased flow rate
- loop diuretics
- thiazide diuretics
- alkalosis
What things decrease K secretion?
- decreased dietary K
- decreased flow rate
- K-sparing diuretics
- acidosis
In regards to ADH, what happens when there is excess free water?
this means that serum osmolarity is low, inhibiting ADH release, causing the kidney to produce dilute urine and dump free water (and vice versa for low free water)
Where is the primary target for ADH action in the kidney?
the principal cell of the collecting duct
Describe the principal cell when there is no ADH, theoretically.
collecting duct will be impermeable to water
Describe the principal cell when there is ADH.
ADH stimulates V2 receptors to insert acquaporin2 channels into the apical membrane, making the collecting duct permeable to water
Is ADH an all-or-none phenomenon?
no, the more ADH is around the higher the water permeability will be (in varying degrees)
How does ADH help to make a concentrated urine?
- causes aquaporin 2 insertion in principal cells (saving free water from being lost in urine)
- stimulates NKCC2 in TAL (takes more stuff out of the urine into the medulla, makes hyperosmolar inner medulla)
- increases reabsorption of urea from the collecting duct into inner medulla (makes hyperosmolar inner medulla)
Why is Na primarily regulated?
for ECF volume
Why is free water primarily regulated?
for osmolarity (or Na concentration)
What is the kidney’s role in acid/base balance?
- bicarb reabsorption
2. acid excretion/new bicarb production
What processes are involved in acid excretion/new bicarb production?
- titratable acids
- ammonium generation
Where does bicarbonate reabsorption occur?
How?
- in the proximal tubule (indirect process)
1. Na/H antiporter secretes H into lumen (+ by ang II), which associates with bicarb to make carbonic acid
2. carbonic anhydrase makes CO2 and water, pulling more H into the reaction by removing the acid
3. CO2 and water move into the cell
4. a different carbonic anhydrase pushes them back into carbonic anhydrase, which immediately dissociates into bicarb and H
5. bicarb pumped out of basolateral membrane where it diffuses into the blood stream
6. H is recycled back to the lumen via Na/H antiporter to bind with another bicarb
What is the NET in bicarb reabsorption?
- movement of bicarb from the lumen to the bloodstream
- no NET acid excretion
- no generation of new bicarb
What structure can reclaim essentially all of the filtered bicarb?
the proximal tubule
What stimulates the activity of the Na/H antiporter in the proximal tubule?
In the collecting duct?
- PT: angiotensin II
- CD: aldosterone
What processes result in net acid excretion?
Where does each occur?
- titratable acids, in the proximal tubule
- ammonium generation, in the proximal tubule
Describe the process of titratable acids.
- carbonic anhydrase makes carbonic acid from water and CO2 in the proximal tubule cells
- carbonic acid immediately dissociates into H and bicarb
- H ions are pumped into the lumen via the Na/H antiporter
- the H in the lumen is buffered by the phosphate that was previously filtered
- the bicarb made uses the bicarb/Na symporter to enter the blood, acting as a buffer there
Which process is more important- titratable acids or ammonium generation?
Why?
Ammonium generation, because it is an inducible process where more ammonium can be generated if more acid needs excreted. The phosphate is limited in amount to what was filtered
Describe the process of ammonium generation.
- glutamine is broken down into ammonium and a-ketoglutarate in proximal tubule cells
- a-ketoglutarate is converted to bicarb, which is pumped into the blood
- ammonium is pumped into the tubular lumen (the Na/H antiporter doubles as a Na/NH4 antiporter)
- pH converts ammonium to ammonia in the tubular fluid
Describe the process of ammonium excretion.
- water and CO2 make carbonic acid using carbonic anhydrase
- carbonic acid dissociates into H and bicarb
- bicarb is transported into the blood
- H pumped out via the H-ATPase
- ammonia combines with H to make ammonium, which is excreted
Where does ammonium generation occur?
Ammonium excretion?
- generation: mostly in the proximal tubule
- excretion: in the intercalated cells of the collecting duct
What simulates the H-ATPase activity?
What process is that transporter important for?
- aldosterone
- ammonium excretion
What is the normal fractional excretion of K?
10-20%
Why do thiazide and loop diuretics cause K wasting?
they inhibit the Na reabsorption upstream of the collecting duct, causing high Na delivery to the collecting duct, which drives further K secretion by the principal cells
What are the pH limits compatible with life?
6.8 to 7.8
What is the net effect of ammonium generation/excretion?
- excretion of acid in urine
- generation of new bicarb to replenish what was consumed buffering metabolic acids in the ECF
Why can hyperaldosteronism be associated with metabolic alkalosis?
Aldosterone stimulates the activity of the H ATPase in the distal collecting duct. This pushes more new bicarb into the bloodstream.
What is likely your K state if you have acidosis?
hyperkalemia (with acidosis, cells buffer about half of H+ by taking it into the cells – push K+ into ECF for electroneutrality)
if low on total K (urinary/GI losses) and in acidosis, will have artificially normal K in ECF but when acidosis is corrected and take up K again – reveals low K
What is likely your K state if you have alkalosis?
hypokalemia (alkalosis makes you reduce H secretion, so dump more K to keep the charge balance)
What defines respiratory acidosis?
a PaCO2 over 45 mmHg
What defines respiratory alkalosis?
a PaCO2 under 35 mmHg
What defines metabolic acidosis?
bicarb concentration less than 22 mEq/L
What defines metabolic alkalosis?
bicarb concentration greater than 28 mEq/L
What can cause metabolic acidosis?
What is usually present?
- excess production of acids (ketones, lactic acid, chronic renal failure)
- ingestion of fixed acids (methanol, ethylene glycol, aspirin)
- loss of bicarb (GI fluid loss from diarrhea, renal tubule acidosis)
-compensatory respiratory alkalosis: reduces arterial PCO2 and increases the pH towards normal
How do you resolve metabolic acidosis without treatment?
- increased renal generation of new bicarb
- increased H excretion via NH3 production
- titratable acid excretion
Metabolic acidosis: H? Bicarb? Arterial PCO2? Compensation?
- increased H concentration
- decreased bicarb concentration
- decreased arterial PCO2
- hyperventilation (secondary respiratory alkalosis)
Metabolic alkalosis: H? Bicarb? Arterial PCO2? Compensation?
- decreased H concentration
- increased bicarb concentration
- increased arterial PCO2
- hypoventilation (secondary respiratory acidosis)
Respiratory acidosis: H? Bicarb? Arterial PCO2? Compensation?
- increased H concentration
- increased bicarb
- increased arterial PCO2
- increased H excretion and increased bicarb generation (renal)
Respiratory alkalosis: H? Bicarb? Arterial PCO2? Compensation?
- decreased H concentration
- decreased bicarb
- decreased arterial PCO2
- decreased H excretion and decreased bicarb generation (renal)
How do you calculate the anion gap?
Na - (Cl + bicarb)
What is the normal anion gap?
What does that reflect?
- between 8-16 mEq/L
- the concentration of unmeasured anions like protein, phosphate, sulfate, and citrate
When metabolic acidosis is caused by a loss of bicarb, what happens to the anion gap?
there is an increase of Cl (hyperchloremic metabolic acidosis) rather than the addition of other unmeasured anions, and the anion gap is normal (b/c ECF is electroneutral at all times in regards to measured anions)
What are the most common causes of metabolic acidosis with an increased anion gap?
(MULEPAK) Methanol ingestion Uremia Lactic acidosis Ethylene glycol ingestion Paraldehyde ingestion Aspirin overdose Ketoacidosis
What are the most common causes of metabolic acidosis without an increased anion gap?
(Could Really DeHydrate) Carbonic anhydrase inhibitors Renal tubular acidosis Diarrhea Hyperalimentation (IV feeding)
What are the most common causes of metabolic alkalosis?
- loss of gastric H from vomiting (excess bicarb in blood)
- contraction alkalosis, a net gain of bicarb by the renal system (bicarb retention occurs as a side effect of low effective circulating volume)
How can low effective circulating volume cause bicarb retention?
- low GFR, reducing the bicarb filtered load
- avid proximal tubular reabsorption regardless of filtered load
What usually accompanies metabolic alkalosis?
compensatory respiratory acidosis, where arterial PCO2 increases to try to decrease the pH back to normal
How can you correct metabolic alkalosis without treatment?
- increased renal excretion of bicarb
- reduced rates of acid excretion
- reduced rates of bicarb retention
What physiologically causes respiratory acidosis?
inadequate alveolar ventilation that results in CO2 retention
What can things can cause respiratory acidosis?
- neuromuscular disorders
- airway obstruction
- narcotics that suppress breathing
What happens in chronic respiratory acidosis?
the renal system normalizes the pH by excreting more acid and producing more bicarb, which is added to the ECF
What are sensible losses?
water loss that we can measure
What are insensible losses?
water loss that you cannot measure
What physiologically causes respiratory alkalosis?
excessive alveolar ventilation, resulting in greater CO2 loss than production
What can cause respiratory alkalosis?
- high altitude (hypoxemia)
- pulmonary embolism (hypoxemia)
- psychogenic hyperventilation
What happens in chronic respiratory alkalosis?
the renal system normalizes the pH by excreting less acid and producing less “new” bicarb
What does ‘compensation’ refer to?
responses that normalize plasma pH
If both alkalosis and acidosis are present and the pH is acidic, what do you consider the primary disorder?
the acidosis (although both are present)
Explain the effects of excessive aspirin ingestion.
- aspirin uncouples os/phos, causing a primary metabolic lactic acidosis
- directly affects the respiratory centers in the meduall, causing the central chemoreceptors to be more sensitive to arterial PCO2 levels, which cause primary respiratory alkalosis
What does furosamide do?
Where does it act?
How does it work?
K status?
- inhibits the NKCC2
- the loop of Henle (TAL)
- decreases the electrochemical gradient, reducing Na, Ca, and Mg reabsorption
- K wasting, because lower electrochemical gradient by the time it gets to the collecting duct
What are the K wasting diuretics?
loop and thiazide