Renal Control of Acid-Base Balance Flashcards
what are some of the metabolic acid sources
Glucose and Fat produce give rise to HCO3- and H+
-eliminated primarily by lungs and is changeable
Glucose anerobicly gives rise to Lactate and H+
Cysteine to H+ and sulfate
Phosphoprotein to H+ and phospate
-these three eliminated by kidneys and is normally a fixed amount
what are the four body buffers and what are their pK values
HCO3-/H2CO3, bicarbonate
-pK is 6.1
Hb-/HHb hemoglobin
-pK is 7.3
HPO4/H2PO4, phosphate
-6.8
Pr/HPr, plasma proteins
-pK is 6.7
all are instantaneous rates of reaction
what are the 4 organs and their mechanisms and rate for body buffer systems
Lungs:
- regulates retention or elimination of CO2 and therfore H2CO3 concentration
- Minutes to hours rate
Ionic shifts:
- Exchange of intracellular potassium and sodium for hydrogen
- 2-4 hours
Kidneys:
- Bicarbonate reabsorbtion and regeneration, ammonia formation, phosphate buffering
- hours to days
Bone:
- exchanges of calcium, phosphate, and release of carbonate
- hours to days
what is the pK of a buffer
it is the pH at which this buffer, acting as an H+ sponge has sopped up half of the H+ it can hold
-middle of the sigmoidal curve
How does the buffering of Extracellular Hydrogen Ion affect potassium
also known as the Ionic shifts,
the cell has a high intracellular level of K+ therefore it will exchange K+ for H+ in the extracellular fluid
if it is acidema, low pH in the ECF, the cell will exchange the H+ for the K+ decreasing the H+ in the ECF, increasing the pH and increasing the K+ in the ECF
if it is alkalemia, the cell lets go of H+ into the ECF and picks up K+ from the ECF, pH decreases and ECF K+ concentration decreases but increases ICF K+ concentration
How does the buffering of hydrogen ion by the plasma proteins and hemoglobin work
CO2 dissolves into the red blood cell and converted to HCO3- and H+
H+ will bind to HHb to absorb the H+ and act as the buffer
the HCO3- will exchange with Cl- and be left in the ECF
what is the Henderson-Hasselbalch equation
pH= 6.1 + log ([HCO3-]/(0.03 x pCO2))
HCO3- is controlled by kidneys, slow with large capacity
pCO2 is controlled by lungs, fast with limited capacity
what happens when you increase rate of ventilation vs decrease rate of ventilation
increase rate means there is less pCO2 and the pH increases
decrease rate means there is more pCO2 and more H+ meaning lower pH
but can only hyperventilate or hold breath for so long
what is the direction of water flow in the countercurrent exchange
moves from high concentration of water to low concentration
in nephron the flow is downward while the osmotic pressure differences are sucking the water sideways
solute concentration always starts slightly higher on the ascending side than on the descending side but will quickly eqiulibrates
the continuous extraction of water from the downward side makes the flow at the tip comparatively sluggish
at top of cortex it is isotonic
at medulla it is hypertonic
what are some factors regulating increased H+ secretion/HCO3- reabsorption by the nephron
Primary:
- Decrease in plasma HCO3- concentration (decrease pH)
- increase in partial pressure of arterial carbon dioxide
Secondary: not directly for maintaining acid-base
- Increase in filtered load of HCO3- (Proximal tubule)
- Decrease in ECF volume (proximal tubule)
- increase in angiotensin II (proximal tubule)
- increase in aldosterone (collecting duct)
- Hypokalemia (proximal tubule)
what are some factors regulating decreased H+ secretion/HCO3- reabsorption by nephron
Primary:
- Increased plasma HCO3- concentration (increase pH)
- Decrease in partial pressure of arterial carbon dioxide
Secondary:
- Decrease in filtered load of HCO3- (proximal tubule)
- Increase in ECF volume (proximal tubule)
- Decrease in aldosterone (collecting duct)
- hyperkalemia (proximal tubule)
how does the phosphate buffering of secreted hydrogen ions work
in the tubular cells they take up CO2 from the ECF and convert to HCO3- and H+ via carbonic anhydrase
then H+ is exchanged with Na+ to the tubular lumen and the HPO4- will bind with H+ (make urine acidic)
HCO3- still in the tubular cell will get sent back into the ECF making the body less acidic (increase pH)
Production, transport, excretion and excretion of ammonia by the Nephron for generation of New bicarbonate
from glutamine, it is converted into NH4 and the carbon is made into 2HCO3- in the tubular cell of the proximal tubule
the NH4+ is sent into the tubular lumen
new 2 HCO3- is sent into the blood and the H+ is sent into the tubular lumen
NH4 is transported via Na/K/2Cl in place of K until it reaches the Collecting duct in where it gets stuck in the ion trap and excreted out in the urine
Overall, new bicarbonate was created during urinary acidification when H+ was buffered by NH3, and phosphate while the bicarbonate was reabsorbed
what is the function of the alpha and beta intercalated cells in the collecting ducts
alpha will secrete H+ via K+/H+ transporter (absorb K+) and ATPase
-will also reabsorb HCO3- as CO2 from Tubular luumen and convert to HCO3- via the carbonic anhydrase
the Beta intercalated cell will reabsorb H+ and secret HCO3-
- does this by taking in CO2 from the interstital fluid and convert to HcO3- and H+ via carbonic anhydrase
- pumps H+ back into the interstitium
- uses Cl- to exchange with HCO3- back into the tubular fluid
what is the Net Acid Excretion equation?
NAE = [(Unh4+ x V) +(Uta+ x V) - (Uhco3 x V)]
TA = Titrable acids which are salts of primarily phosphate but other constitutents of urine such as creatine.
-accounts for 1/3 of NAE
Ammonium (NH4+) synthesis and secretion is responsible for 2/3 of NAE
-not apart of TA because of the high pK of ammonium (7.4), and can be easily made
