Part Tres--Electrolyte Balance & Acid/Base Buffer Flashcards
___% of total body K+ is intracellular (recall the role of the Na+-K+-ATPase)……Normal plasma [K+] = __ mEq/L:
98%…4 mEq/L
What can high [K+] do to resting membrane potential and therefore excitability of the cell?
high [K+] = lower resting membrane potential = increased excitability
How do we NOT DIE after eating a banana? (2 ways :))
- RAPID uptake of K+ into the cells (aldosterone, insulin, eli) 2.Slower renal excretion
‘Obligatory’ reabsorption of approx 90% of the filtered load of K+ in the ________ and the ___________.
proximal tubule….thick ascending limb
How is the physiologic regulation of renal K+ excretion primarily achieved?
By SECRETING into the LATE distal and collecting tubules (OPPOSITE mechanism from Salt and Water)
How do I find FL (filtered load)?
GFR x Amount of Substance in body
Since K+ is secreted late in the game what are the three transporters used? Also, what is driving the charge difference?
- Na+/K+ pump (BL membrane) 2.K+ channels (L membrane) 3. K+/Cl- cotransporters (L membrane)….Na+ reabsorption at this stage is promoting a negative environment (thus promoting K+ secretion)
What do we do when we have K+ depletion? (name some transporters for me)
- Energy dependent K+/H+ antiporter (L membrane) 2.K+ selective channels (BL membrane)
What does a hypertonic extracellular environment result in K+ levels in the blood?
HyperKalemia
What does cell lysis do to plasma levels of K+?
HyperKalemia (exercise-induced muscle breakdown)
What is the relationship between ECF [H+] and Plasma [K+]?
Parallel…increase in ECF [H+] = increase in plasma [K+]…vis versa
Metabolic acidosis due to ________ (HCl, H2SO4) increases plasma K+ to a much greater extent than a similar acidosis produced by __________ (lactic acid, keto acids)
inorganic acids….vs…..organic acids
How does respiratory acidosis/alkylosis affect plasma [K+]?
little to no effect :)
What are the two ways the body works to secrete a high [K+] ECF?
Increase Na+/K+ action on the distal nephron cells 2.increase aldosterone secretion (also increases Na+/K+ action AND increases luminal K+ permeability
What does increased tubular flow do to K+ secretion?
increases secretion (1.c/o low tubular fluid [K+] 2.more Na+ reabsorption and more Na+/K+ activity)
What can loop diuretics do to plasma [K+]?
can cause HypoKalemia (1.less reabsorption 2.more secretion (Na+/K+ pumps goin crazy!)
What are the three ways the body combats hypoCalcemia?? how does the kidney connect to the G.I. tract here?
1.Kidney (more to come) 2.G.I. absorption (renal Vit-D activation!!) 3.bone resorption
Which part of the kidney does PTH target? What are the 2 outcomes? Which membrane?
PTH acts on the distal tubule…1) Ca2+ ATPase (BL) 2)Na+-Ca2+ exchanger(BL)
How is the problem of hyperPhosphatemia solved during bone resorption? WHERE does this happen?? Which transporter is involved???
PTH inhibits Renal HPO42- reabsorption….PROXIMAL TUBULE….the Na+/HPO42- cotransporter on the L membrane is BLOCKED! thus we’ll pee it on out
H+ balance: note that concentrations are expressed in _____ Eq “Normal” pH range: ____ - ____ Survival limits: ____ - ____.
7.37 - 7.42…….6.80 - 8.00
What are the two sources for H+ accumulation? What is the release for both?
1.Volatile- oxidative metabolism…2. Fixed-AA metabolism
What are the two main ways fixed metabolism causes a build up of acid?
1.exercise (lactic acid) 2. DM
How do we get rid of volatile acid?
respiration
Which is more prevalent volatile or fixed acid?
Volitile is 5,000x more prevalent in the body
What are the three lines of defense against fixed acid accumulation in the body?
1.Physiochemical Buffering (H2PO4, HCO3) 2.Respiratory compensation 3.Renal compensation
What does the pK represent?
the point of greatest buffering capasity
Do our buffer systems work intra or extracellularly?
BOTH!
Which buffer system is most important? WHY!?
bicarb!! cause it’s regulated by the lungs and the kidneys
Why doesn’t H2CO3 last very long in the body?
Carbonic Anhydrase is very active and converts h2co3 to h2o and co2 very quickly!
What is the pK for hco3? why is this relevant?
6.1..for the HH eq
What is the HH eq for evaluating the bicarb buffer system?
pH = 6.1 + log ([24mmol/L hco3])/([1.2 mmol/L co2])===a pH of 7.4
What is the MAGIC RATIO for maintaining pH balance in our bodies??
20 base : 1 acid (in our eq 24:1.2)
Where is co2 converted to H+ and HCO3? What happens to the H+? What happens to the HCO3?
in the RBC…the H+ attaches to Hemoglobin…the HCO3 diffuses out via the CHLORIDE SHIFT!
What is the Chloride shift? Is this the same in the lungs as in the body?
when HCO3 diffuses out of the RBC with an exchange of a Cl-…no they are opposite in the lungs and the body tissue (so in lungs we are picking up HCO3)
What is the relationship between plasma [H+]/pCO2 and alveolar ventilation?
increase in plasma [H+] and or arterial pCO2/ = increase in ventilation
What are the 4 steps to fix pH after infusion of a 12mmol/L HCl I.V.?!?!
1.Physicochemical Buffering 2.Respiration to eliminate the increased CO2 made 3.MORE respiration to keep eliminating CO2 (gets us CLOSE to 20b : 1a) 4.RENAL compensation
How do the kidneys contribute to fix the pH of our 12mmol/L HCl infusion? (2 ways)
- make new HCO3 (get it back to 24mEq/L) 2. Excrete the excess H+
More than ___% of filtered HCO3- is reabsorbed in the ________.
99%….PROXIMAL tubule
Reabsorptive process ‘______’ since HCO3- transport proteins not present on the luminal membrane…SO how is it done??
‘indirect’….by taking in CO2 and H2O, then using Carbonic Anhydrase to make HCO3 (H+ then peed out)
Which two cell types make HCO3?
Proximal Tubule Cells & RBCs
During the WACK reabsorption of HCO3 process…..H+ secreted into the lumen, combines with ______ HCO3- forming CO2 and H2O.
filtered
For every __ mEq of filtered HCO3- converted, __ mEq is added to the ECF – “indirect” reabsorption.
1 mEq… 1 mEq
What two things regulate HCO3 reabsorption?
- arterial blood pCO2 2.Na+ reabsorption
Where does the renal generation of NEW bicarb happen?
distal nephron
Generation of NEW HCO3- dependent on the availability of _______ to accept secreted H+. What’s a possible downside to this?
urinary buffers (HPO42-)..these are limited (filtered load relatively low)
HCO3- can also be generated from ________ metabolism in the proximal tubule….Then: Co-generated ________ ion secreted into the tubular lumen.
glutamine…..ammonium
What happens to the ammonium ion in the NEW bicarb story?
it gets reabsorbed in the thick ascending limb
Interstitial NH4/NH3 diffuses across ______ cells into the lumen and interacts with secreted H+.
intercalated
Metabolic _______ increases glutamine metabolism and thus HCO3 synthesis/NH3 availability.
acidosis
HCO3 synthesis also regulated by ________.
Aldosterone
OVERVIEW: what three important processes is aldosterone involved in?
HCO3 reabsorption, NaCl reabsorption, K+ secretion/excretion
Acidemia: blood pH < ____
7.35
Alkalemia: blood pH > ____
7.45
What causes the shift in pH during a Respiratory acid/base disturbance?
changes in plasma pCO2
What causes the pH shift during metabolic acid/base disturbances?
changes in plasma HCO3
What is an example of each of the four acid/base disturbances?
Respiratory acidosis: hypoventilation……Respiratory alkalosis: hyperventilation……Metabolic acidosis: diabetes mellitus……Metabolic alkalosis: chronic vomiting
Renal compensation for a pH change due to a primary respiratory change in _____.
pCO2
Respiratory disturbances involve relatively _____ renal compensatory responses.
slow
What do I look for during Metabolic Acidosis? Which system compensates for this situation?
Is the HCO3- < 24 mEq/L?????…the respiratory sys will compensate!
What do I look for during Respiratory acidosis? Which system compensates for this situation?
Is the pCO2 > 40mmHg??????….the renal system compensates!
What do we use the anion gap to find? Whats the normal range?
finds the underlying cause of the metabolic acidosis…Anion gap = [Na+] - ([Cl-] + [HCO3-])….8-16 mEq/L
With diabetic ketoacidosis or lactic acidosis, what happens to the anion gap?
INCREASES
With HCl-induced acidosis & diarrhea, what happens with anion gap?
NOTHING :) (just decreased HCO3)
