Acid-Base Balance

0.00004 mEg/L

Plasma [H+] =

-log[H+]

pH formula =

acidic, basic

• When pH is __, H+ is relatively more concentrated than OH-

• When pH is __, OH- is relatively more concentrated than H+

7.35-7.45, 6.8-8.0

Normal plasma pH: __ - __

pH sustaining life: __ - __

7.35, 7.45

• Acidemia is when Plasma pH < __

• Alkalemia is when Plasma pH > __

1, 4.5-8.5

Wider range of pH for external fluids

• Gastric pH < _

• Renal tubule/urine pH: __ - __

Buffer systems, ventilation, renal

Buffers

• __ __: First line of defense against pH disturbances

• __: Second line of defense against pH disturbances

• __ Regulation: Third line of defense against pH disturbances

H+, seconds, extracellular, intracellular

Buffer systems “soak up” and release H+

• Buffers: Molecules that reversibly bind to __

• Actions occur within __ (time)

• __ (intra/extracellular) - Bicarbonate ions, phosphate ions, ammonia

• __ (intra/extracellular) - Proteins, phosphate ions, hemoglobin

Carbonic anhydrase, H+, CO2

Only cells with high amounts of __ __ (enzyme) contribute to rapid buffering of plasma __

• As __ can easily cross cell membranes, (not H+)

CO2, H2O, H+, HCO3-, RBCs, Cl-

• CO2 + H2O reacts to form H+ + HCO3-

  • __ and __ combine to form H2CO3 via carbonic anhydrase

  • __ and __ are formed in 1:1 ratio

  • Most H+ remains in the __ whereas HCO3- is expelled to plasma (in exchange for __)

24, 40

• Normal plasma [HCO3-] = __ mEq/L

• PaCO2 = __ mmHg

HCO3-, left, lowers, higher, H+

• Plasma __ is available to buffer excess H+ ions

  • Add H+ to plasma: __ward shift

    • This __ HCO3- concentration for __ CO2 + H2O conc. (lower/higher)

    • At equilibrium, __ is still somewhat elevated but lesser magnitude

CO2, ventilation, HCO3-, H+, H+

• Changes in CO2 or H+ shift equilibrium of carbonic acid reaction

  • __ is quickly blown off via __ (general respiratory process)

  • However, __ is more concentrated than __

    • Small relative change to carbonic acid reaction

    • Change in HCO3- may NOT show up clinically compared to __ change

HCO3-, decrease, right, increase, left

Change in __ can indirectly shift reaction via buffering H+

• Gain HCO3- = __ in H+, shifts reaction to __ (left/right)

• Lose HCO3- = __ in H+, shifts reaction to __ (left/right)

Hyperventilation

Increase in CO2 being “blown off”

Low, low, high, left

Hyperventilation

• __ CO2 concentration = __ H+ concentration

• __ pH = Alkalemia

• Drives reaction to __

Hypoventilation

Increase in CO2 retained in body

increase, increase, decrease, right

Hypoventilation

• __ CO2 concentration = __ H+ concentration

• __ pH = Acidemia

• Drives reaction to __

metabolic, minutes, ventilatory

Changes in pH can correct some pH disturbances

• Major compensatory mechanism for __ acid-base disturbances

  • Rapid onset (within __)

  • CANNOT correct pH disturbances originating from __ problems

Slower, H+, HCO3-, HCO3-

Kidneys pH regulation

• __ regulation of pH (up to hours-days)

• Methods of renal pH regulation (3)

  • Secretion of __

  • reabsorption of filtered __

  • production of new __

Proximal tubule, H+, CO2, basolateral, Cl-

• __ __ reabsorbs filtered HCO3- (renal)

  • Kidneys filter HCO3- with 99% of it reabsorbed

  • HCO3- cannot cross apical membrane; joins with __ → __

  • HCO3- then transported across __ membrane via HCO3- / __ exchanger

H+, alkalosis, acidosis

• Reabsorption of HCO3- linked to __

  • __osis: If HCO3- filtration exceeds H+ secretion

  • __osis: If H+ secretion exceeds HCO3- filtration

Na+, Angiotensin, HCO3-, diuretics

• High tubule-renal [__] promotes HCO3- reabsorption

  • Increase __+ gradient and or __ II → Increase Na+/H+ exchanger activity

  • More H+ in lumen → More __ reabsorbed (crosses as CO2)

  • Most __ (meds) promote HCO3- reabsorption

HCO3-, apical, CO2, excretion, metabolic acidosis

• Carbonic anhydrase inhibitors affect renal HCO3- handling by..

  • Decrease __ available means less filtered HCO3- crossing __ (apical/basolateral) membrane

  • Less formation of __ and increased __ (reabsorption/excretion) of HCO3- via urine

  • Net outcome: __ (metabolic/respiratory) __ osis

Alpha, collecting, CO2, H+, HCO3-, chloride (Cl-)

• __-intercalated cells secrete H+ and reabsorb HCO3- 

  • Located in __ duct

  • __ enters cells and is converted to H+ and HCO3-

    • __ pumped into lumen

    • New __ reabsorbed to plasma → __ moves into cell

H+, K+

Aldosterone stimulates secretion of __ and get rid of __

(both cations)

Beta, collecting, CO2, HCO3-, chloride (Cl-), H+

• __-intercalated cells secrete HCO3- and reabsorb H+

  • Located in __ duct

  • __ enters cells and is converted to H+ and HCO3-

    • __ secreted to lumen → __ moves into cell

    • New __ reabsorbed to plasma

Phosphate, ammonia, H+, primary, high

Urinary buffers

• Once H+ is secreted to tubule lumen, it binds with __ and __ buffers

• If there were no buffers, a small amount of __ secreted would lead to dramatic drop in urine pH

• H+ secreted is against gradient via __ active transport

• Urinary buffers prevent gradient from becoming too __ (low/high)

  • Allow H+ secretion to continue