Acid Base Balance Flashcards
Plasma HCO3 us how much more concentrated then plasma H+
600,000 times (H+ bound to Hb)
How is the relationship between CO2, HCO3 and H+ expressed
CO2 + H20 <—-> H+ + HCO3
Shifts according to law of mass action
Increase CO2 shifts the equation which direction
To right creating one H and one HCO3
Adding H causes equation to shift to what direction
Right
HCO3 acts as buffer resulting in
Increase CO2 + increased H20 <— increased H+ + decreased HCO3
How does ventilation compensate for pH disturbances
Peripheral and central chemoreceptors sense changes in plasma PCO2 and or H+ and signal to respiratory CC to adjust ventilation
What can correct disturbances in acid-base balance as well as cause them
Ventilation
Acidosis causes what kind of ventilation
Hypoventilation - right shift
Decrease plasma CO2
Alkaline state causes what type of ventilation
Hyperventilation- left shift
Increase CO2
What is direct mechanism of kidneys to handle pH disturbances
Altering rates of excretion or reabsorption of H+
- if alkalosis reabsorb H+
- if acidosis secrete H+ for excretion
How do kidneys indirectly handle pH disturbances
Changing rate at which HCO3 buffer is reabsorbed or excreted
- if acidosis buffer excess H+
- is alkaline decrease buffers
During acidosis what do kidneys generally do
Excess H+ is buffered by ammonia within tubule cells or enter lumen and buffered by phosphate
Is not filtered, enters tubule via secretion only
H+
Secretes H+ and reabsorb HCO3
Proximal tubule
First mechanism of secretion of H and reabsorption of HCO3
- Na-H exchanger secretes H
- H in filtrate combines with filtered HCO3 to form CO2
- H+ is secreted again to repeat
- HCO3 is reabsorbed with Na
Secondary mechanism of H+ secretion and HCO3 reabsorption
- Glutamine is metabolized to ammonium and HCO3 2. NH4 is secreted and excreted with H+
What controls acid excretion
Distal nephron, initial portion of collecting duct plays role in fine regulation of acid-base balance
when do type A intercalated cells in collecting duct function
during acidosis
when do type B intercalated cells in collecting duct function
during alkalosis
what do type A cells do
function to increase H+ secretion and HCO3 reabsorption
- usually accompanied by increase in K+ reabsorption (can cause hyperkalemia)
what do type B cells do
function to increase H+ reabsorption and HCO3 secretion (excreted so less buffer)
- usually accompanied by increased K+ secretion (may cause hypokalemia)
what transports H+ on intercalated cells
H+ trasnporters and H-K ATPase
what trasnports HCO3 on intercalated cells
HCO3/Cl exchanger
what are the differences between transporters on type a and type b
Type A has H+ trasnporters on apical and HCO3 on basolateral
Type B has the opposite
what is the range buffers function in
7.38-7.42
what are acid-base disturbances classified by
direction of pH change (acidosis or alkolosis) and by the underlying cause (respiratory or metabolic)
by the time an acid-base disturbance causes a change in plasma pH what has occurred
body’s buffers are ineffective leaving respiratory and renal compensation to alleviate change
4 types of acid/base disturbances
- respiratory acidosis
- respiratory alkalosis
- metabolic acidosis
- metabolic alkalosis
what must respiratory induced changes in pH be resolved by
renal mechanisms (excrete H+, reabsorb HCO3)
respiratory acidosis
occurs when alveolar hypoventilation results in CO2 retention and elevated plasma CO2
what are possible causes of respiratory acidosis
pulmonary fibrosis, asthma attack, drugs, emphysema, muscular dystrophy
respiratory alkalosis
much less common, result of hyperventilation in absence of increased metabolic CO2 production
causes of respiratory alkalosis
excessive artificial respiration, anxiety induced hyperventilation
what will raise plasma CO2 levels
rebreathing exhaled CO2
what does renal system do to compensate for respiratory alkalosis
HCO3 excretion and H+ reabsorption
metabolic acidosis
occurs when dietary and/or metabolic input of H+ exceeds H+ excretion
- lactic acid, or ketoacidosis
- can also occur from excessive HCO3 loss (diarrhea)
How is metabolic acidosis resolved
rarely seen, resolved by respiratory (increased ventilation) and slow renal compensation (HCO3 reabsorbed, H+ excreted)
metabolic alkalosis
excessive vomiting of acidic stomach contents or excessive ingestion of bicarbonate containing antacids
what is metabolic alkalosis resolved by
rapidly resolved by decrease in ventilation but can cause hypoxia
renal: HCO3 excreted, H+ reabsorbed
