12: Physiology 8 Flashcards
What is the normal pH of the blood?
7.4
Which blood vessels have a lower pH?
Veins
more CO2
What is the normal blood concentration of bicarbonate ions?
22 - 28
sits around 25
What is the normal partial pressure of CO2 in the blood?
40 mmHg
What needs to be brought back to normal to
a) compensate for
b) correct
an acid-base imbalance?
a) pH
b) pH, [HCO3-], pCO2
What are compensation and correction of an acid-base disturbance?
Compensation - bringing pH back to normal
Correction - bringing pH, [HCO3-] and pCO2
What are the four types of acid-base imbalance?
Metabolic acidosis and alkalosis
Respiratory acidosis and alkalosis
What solutions are responsible for correcting short-term changes in pH?
Buffers
What component of blood acts as a buffer?
Hb
unoxygenated blood has a higher affinity for H+ than oxygenated blood
What happens when buffers run out?
Kidney replaces them
ph = pk + log(kidneys/lungs)
Which organs regulate blood concentration of
a) CO2
b) bicarbonate?
a) Lungs
b) Kidneys
What are the normal ranges of concs. for
a) pH
b) bicarbonate?
a) 7.35 - 7.45 (normal is 7.4)
b) 22 - 28 (normal is 25)
What general group of diseases causes CO2 retention?
Respiratory disease
CO2 retention causes an (increase / decrease) in the concentrations of which ions?
H+ (importantly)
HCO3-
shifts equilibrium to the right and causes acidosis
Can buffer solutions buffer themselves?
No
So an increase in CO2 causes both H+ and HCO3 to increase, but HCO3 doesn’t compensate
When is respiratory acidosis
a) compensated
b) uncompensated?
a) High CO2, normal pH
b) High CO2, low pH
Which system compensates for respiratory acidosis?
Renal
What drives bicarbonate reabsorption by the kidneys?
H+ secretion by the kidneys
How much bicarbonate is reabsorbed by the kidneys in metabolic acidosis?
All of it
What happens to H+ ions after they are excreted into the renal tubules to drive HCO3- reabsorption?
Excreted in urine as titratable acid and ammonium
What increases as a result of renal compensation for metabolic acidosis?
[HCO3-] reabsorption
and therefore pH increase
After the kidneys have compensated for a metabolic acidosis, how do you correct it?
Restore normal ventilation
What are some causes of respiratory alkalosis?
High altitude (conc of oxygen breathed in decreases, rate of body’s removal of CO2 stays the same –> alkalosis)
Hyperventilation
What is removed excessively in respiratory alkalosis?
CO2
What happens as a result of excessive CO2 removal in respiratory alkalosis?
H+ and HCO3- decrease
CO2 starts to increase
equilibrium shifts to the left
What system compensates for respiratory alkalosis?
Renal
What happens to H+ secretion in respiratory alkalosis?
Decreases, as no CO2 to drive it
What happens to bicarbonate reabsorption in metabolic alkalosis?
Decreases
As H+ isn’t being secreted to drive it
In uncompensated respiratory alkalosis, the urine turns ___.
alkaline
How is respiratory alkalosis corrected?
Restoration of normal breathing
What can cause metabolic acidosis?
Anything causing H+ excess not related to CO2:
Ingestion of acid
Increased metabolism of acid (anaerobic resp, uncontrolled T1DM)
Loss of bicarbonate - diarrhoea
What happens to pH in uncompensated metabolic acidosis?
pH decreases
Bicarbonate decreases
Why do bicarbonate levels decrease in uncompensated metabolic acidosis?
Used up trying to buffer for increased H+
What system compensates for metabolic acidosis?
Respiratory
What senses acidosis with a metabolic cause?
How does the respiratory system compensate for metabolic acidosis?
Peripheral chemoreceptors (carotid sinus and aorta)
Hyperventilation
How does hyperventilation compensate for metabolic acidosis?
Blows off Co2
After the resp system has compensated for metabolic acidosis, what happens to bicarbonate levels?
How does the renal system correct this?
Decrease further (equilibrium shifts to left)
Secretion of H+ as acid/ammonium
Which drives bicarbonate reabsorption
How long do the
a) respiratory
b) renal
systems take to compensate and correct for acid base imbalances?
a) Short time
b) Longer
What causes metabolic alkalosis?
Loss of H+ not related to breathing:
Vomiting - loss of HCl
Ingestion of alkali
Hypersecretion of aldosterone (because K+ and H+ filtration are PAIRED, so H+ is excreted causing an alkalosis)
What happens to pH and bicarbonate conc. in uncompensated metabolic alkalosis?
pH increases
Bicarbonate conc. increases
How does the resp system compensate for metabolic alkalosis?
Hypoventilation
retention of CO2, equilibrium shifts to the right
How does the renal system correct metabolic alkalosis?
Excess of bicarbonate is filtered
No acid generated
Excreted in urine - alkaline
