Acid base balance Flashcards
what artery is usually used for a blood test
radial artery
Why is acid base important
Physiologically threat
- Enzyme function eg coagulation
- Electrolyte regulation - hydrogen and potassium ions
- Drug ionization eg local anaesthetics
Diagnotic guide
- Establish diagnosis and to monitor during therapy
Acid base balance composed of acid production and acid elimination
what are the 2 ways acid is produced
respiratory - carbonic from CO2
metabolic - organic such as lactate or amino and inrognaic like sulphuric and phosphorus
acidic and alkaline secretions are produced in normal GI physiology from where
gastric - hydrogen ion
pancreatic - bicarbonate
how is acid removed from the body
respiratory - ventilation removes CO2
metabolic - inorganic excreted via the kidneys unchanged
organic undergo liver metabolism before being excreted
formular for pH
-log to the base 10 multiplied by the hydrogen conc
what is plasma pH
7.4
what is stomach pH
2
the acid base homeostasis aims to keep pH constant - what are the 3 main systems for regulation of this
how quick are all these processes
- Buffers - immediate seconds to minutes
- Respiratory - rapid minutes to hours
- Renal ( metabolic) - slow hours to days - plus minor from liver contribution
Respiratory and/or metabolic dominant under normal conditions - other systems provide compensation
what is the most important extracellular buffer for maintaing acid-base balance in the blood
carbonic acid-bicarbonate buffer - dissolved Co2 and bicarbonate ion are at eq
other mentions are protein albumin ( histidine - donor of positive charges in case of alkalosis and and negative charges in acidosis) and phosphates
the Henderson hasselbalch equation can be written as
pH = pKa + Log [HCO3-] / [H2CO3]
because or rapid reaction resulting from carbonic anhydrase, PCO2 can be substituted for [H2CO3]
how does the respiratory system regulate acid-base homeostasis
central chemoreceptors detect rise or fall in Pco2 which is kept between 5.1-5.5 kPa
acts on medulla via the CSF pH to stimulate ventilation to increase to get rid of CO2
what is hyperventilation
Hyperventilation is rapid or deep breathing, usually caused by anxiety or panic. This overbreathing, as it is sometimes called, may actually leave you feeling breathless. When you breathe, you inhale oxygen and exhale carbon dioxide.
high volume but low PaCO2
how does the renal system monitor acid base homeostasis
The kidneys have two main ways to maintain acid-base balance - their cells reabsorb bicarbonate HCO3− from the urine back to the blood and they secrete hydrogen H+ ions into the urine. By adjusting the amounts reabsorbed and secreted, they balance the bloodstream’s pH.
what is respiratory acidosis indicated by
raised carbon dioxide
what is metabolic acidosis indicated by
dropped bicarbonate
what is respiratory alkalosis indicated by
dropped carbon dioxide due to hyperventilation
what is metabolic alkalosis indicated by
raised bicarbonate and severe vomiting
compensation and respiratory failure should be looked for with all
final urien acidity is determined by what cells in the DCT
intercalated cells
what other ion via contransport - transports bicarbonate into the blood in PCT
sodium
Bicarbonate is the marker of metabolic disturbance but not the cause
So if excess acid is made - conc of bicarbonate is going to full to restore eq
Fall is marker not cause
what is the anion gap
A measure to help identify the cause of metabolic acidosis as benign a disturbance of
Organic acid raised anion gap
Or inorganic acid which is normal anion gap
AG = [Na + K] - [Cl + HCO3 ]
total cations must equal anions
the anion gap is usually albumin
this gap increased with metabolic acidosis due to ketoacids
how does the body compensate during acidosis
respiratory compensation : primary metabolic acidosis increase hydrogen concentration this acts on peripheral chemoreceptors (aortic and carotid bodies) conducted to the medulla to increase Vmin
opposite changes are seen in compensation fro alkalosis
metabolic compensation : primary respiratory acidosis ( increase CO2) leads to kidney retaining additional bicarbonate and excreting more protons
3 rules fro determine acid-base anylsis
Acidosis or alkalosis - pH value
Respiratory or metabolic - biacroabte- metabolic or co2- repsiroatyr
Compensated or not
Compensation attempts to return Ph to normal with change in the box opposite to primary abnormality
Egh primary problem of respiratory acidosis - so CO2 high - compensation comes from increasing bicarbonate
How does acetazolamide help
Acetazolamide belongs to a class of drugs known as carbonic anhydrase inhibitors. It works by decreasing the production of fluid inside the eye. It is also used to decrease a buildup of body fluids (edema) caused by heart failure or certain medications.
hydrogen ion retention so less bicarbonate produced
