Acid-Base balance
Importance
the presence of H+ can alter the machinery inside of cells
the concentration of H+ changes the activity of most cells
The hydrogen atom vs hydrogen ion
the atom has 1 proton, 1 electron
the hydrogen ion only has 1 proton since it lost the e-
acid and bases
bases
acid
releases H+ and increases the solution's H+ concentration
accepts H+ and decrease the solution's H+ concentration (solution is more basic/alkaline)
pH scale
measures the amount of H+ in solution (on logarithmic scale)
more H+ means more acidic and lower pH
less H+ means more basic and higher pH
pH 7 is neutral
above 7 is basic
below 7 is acidic
when body fluids above 7.4 (normal blood pH), person has alkalosis
when body fluids below 7.4 (normal blood pH), person has acidosis
source of acid in the body
volatile acid
nonvolatile acid
comes from carbonic acid in the respiratory system
known as volatile because carbonic acid is reconverted to CO2 and H2O, removed from lungs, causing no net increase of free H+
comes from the stomach
known as nonvolatile because the acids cannot be removed by lungs and are a constant source of free H+
Regulation of H+
buffers
respiratory system
kidneys
binds reversibly to free H+ to ,minimize pH change until the lungs or kidneys can remove the free H+
they are the first line of defense, but they do not alter pH or remove H+
regulates volatile acids
slow response to control nonvolatile acids
X + H+ ⇌ XH
intracellular buffers
phosphates
intracellular proteins
hemoglobin
extracellular buffers
bicarbonate
can reversibly bind to H+ to to stabilize the acidity
can bind to CO2 to reduce potential acidity in case it combines with H2O to form carbonic acid
ensure that CO2 levels are constant, meaning a constant pH of the blood
how this function is performed
CO2 regulation is detected by the central and peripheral chemoreceptors
BOTH these receptors will detect change and cause increased ventilation
ventilation causes more CO2 to be removed and return blood CO2 levels to normal
excreting the H+ coming from non-volatile acids
try to reabsorb all bicarbonate ions filtered at the glomerulus
creation of new bicarbonate ions that get absorbed into the circulation
the H+ are secreted into the filtrate in the proximal tubule by the Na+/H+ exchanger
the H+ are also secreted in the late distal tubule and collecting duct by a H+/ATP pump
the reabsorption of bicarbonate ions at the glomerulus is done at the proximal tubule
the bicarbonate must first be converted to CO2 before getting reabsorbed by tubule cells
The CO2 then combines with H2O and using carbonic anhydrase, bicarbonate and H+ is made
bicarbonate ions leave the tubule cells by simple diffusion and are reabsorbed into circulation
H+ is secreted into the lumen by the Na+/H+ exchanger
for every 1 bicarbonate ion reabsorbed, there is 1 H+ secreted
active transport
secretes only 5% of H+ ions
the pump is found on the luminal side of tubule cells, secreting 1 H+ for 1 ATP used
these H+ come from CO2 combining into water in the tubule cells, forming bicarbonate and H+
this CO2 came from the cell itself or the interstitial fluid
makes urine extremely acidic
when 1 H+ is secreted, a new bicarbonate is absorbed into circulation
bicarbonate first becomes carbonic acid which dissociates into H2O and CO2
when more H+ is excreted than bicarbonate, there is net loss of acid, causing increase in pH
when bicarbonate excretion is greater than H+ secreted, there is net base loss, causing decrease in pH
the body balances this by excretion of H+ and reabsorption of bicarbonate to balance the buffer
acidosis is caused by
too much acid (H+) in body
too little bicarbonate
alkalosis is caused by
too much bicarbonate (HCO3-)
too little acid (H+)
types of acidosis
types of alkalosis
respiratory alkalosis
metabolic alkalosis
respiratory acidosis
metabolic acidosis
caused by decreased ventilation
increased partial pressure of CO2 (PCO2)
caused by damage to the breathing center in the brain stem, being unable to removeCO2 from blood
acidosis is reversed by buffers in blood and excretion of H+ by kidneys
caused by increased ventilation
decreased PCO2
caused by stress/emotionally induced hyperventilation or high altitudes causing low PO2 levels in blood stimulating hyperventilation
can be compensated by excretion of bicarbonate by the kidneys
hyperventilation causes this by increased removal of CO2
caused by decreased in extracellular bicarbonate ions
causes
kidney failure, causing inability to excrete acid or reabsorb bicarbonate into the filtrate
formation of excess metabolic acids
ingestion of acids through aspirin and methyl alcohol
loss of bicarbonate in diarrhea (most common cause of metabolic acidosis)
caused by buildup of bicarbonate or loss of H+ from the body
most commonly caused by loss of HCl from stomach through vomiting
can also be caused by ingestion of alkaline drugs such as sodium bicarbonate for ulcers