The Role Of Ventilation In Acid-base Balance Flashcards
What does the role of ventilation in acid base balance mean?
Homeostasis of blood pH
How can ventilation be altered to maintain pH?
Excess carbon dioxide can be removed at lung by increasing ventilation to decrease hydrogen ion concentration and increase the pH.
Too little carbon dioxide levels can be fixed by reducing ventilation so that PaCO2 can rise so more hydrogen ions can form and pH can decrease.
What is the formula for pH?
pH= -log[H+]
Why is pH homeostasis so important?
pH is important to maintain the secondary, tertiary and quaternary structures in enzymes and other proteins to maintain their functions. So it maintains inter and intra chain bonding.
Changing the pH (and other factors such as temperature and pressure) can denature proteins by disrupting bonds such as ionic bonding hence impairing the function.
Explain why protein function is dependent on pH
Different enzymes function at different pH ranges depending on the environment they have been adapted to function in.
For example, pepsin displays maximum activity at low pHs (stomach acid). They have low activity as high pHs as it alters the 3D structure.
Why does arterial pH have to be tightly regulated?
Because the circulatory system supplies blood to all organs and tissues.
How is pH tightly regulated?
Due to presence of buffering systems and by regulating levels of the molecules associated with acid and base production. It resists large changes in pH.
What buffer systems exist?
Intracellular = phosphate buffer system, proteins e.g haemoglobin in RBC (Haldane’s effect - hydrogen ion binding to haemoglobin so reduced free hydrogen ion concentration) Extracellular = bicarbonate buffer system, plasma proteins like albumin
The bicarbonate buffer system has the greatest effect.
What do buffers contain?
Weak acid and conjugate base. It resists sharp changes in pH. Without a buffer, the relationship between addition of acid and pH would be linear.
Buffering systems resist small changes in pH.
Explain the bicarbonate buffer system at hypoventilation.
Hypoventilation causes accumulation of carbon dioxide which shifts the position of equilibrium to the right increasing the concentration of carbonic acid which in turn increases the concentration of hydrogen ions causing acidosis.
So this means increased concentration of carbon dioxide means increased hydrogen ion concentration. Luckily we have the buffer system which mops up the hydrogen ions. But buffer only works when small amounts of hydrogen ions are added
Explain the role the bicarbonate ion buffer system at hyperventilation
Hyperventilation causes more carbon dioxide to be removed which in turn reduces the concentration of carbonic acid and then hydrogen ions leading to alkalosis.
How do lungs contribute to acid base balance?
They regulate carbon dioxide levels.
How can signs of respiratory and metabolic distress be diagnosed and interpreted?
By ABG pH
Show the proportionality between blood pH and ratio of hydrogen carbonate ion concentration:PaCO2
pH§ [HCO3-]/PaCO2
What organs maintain blood pH homeostasis and how?
Kidneys: regulation of hydrogen carbonate ion by either reabsorbing or excreting the hydrogen carbonate ion in glomerular filtrate. The timeframe is from hours to days. So response to pH changes is slower.
Lungs: regulation of PaCO2 by ventilation. Timeframe is minutes. So response to pH changes is higher.
If either the hydrogen carbonate ion concentration or PaCO2 changes, these organs work together and can compensate for each other to maintain pH.
- What does increase in PaCO2 mean?
- What does a decrease in PaCO2 mean?
- What does an increase in hydrogen carbonate ion concentration mean?
- What does decrease in hydrogen carbonate ion concentration means?
- Decreased pH because increased carbon dioxide concentration means more hydrogen ions so think of carbon dioxide as acidic.
- Increased pH
- Increased pH- think of hydrogen carbonate ions as basic
- Decreased pH
What may excessive changes in pH be caused by?
Respiratory or metabolic dysfunction.
Can be respiratory acidosis, metabolic acidosis, respiratory alkalosis or metabolic alkalosis.
Look at slide show to figure out what is what.
Explain acidosis.
If pH of blood is below 7.35, there is acidosis.
If there’s too high carbon dioxide level (but normal hydrogen
carbonate levels), then we know it’s respiratory acidosis. But if there is too low hydrogen carbonate ion levels (but normal carbon dioxide levels), then we know it’s metabolic acidosis.
Explain alkalosis.
If the pH is greater than 7.45 then it is alkalosis.
If it is due to low carbon dioxide levels (but normal hydrogen carbonate ion levels) then it’s respiratory alkalosis. But it’s it’s due to high hydrogen carbonate ions (but normal carbon dioxide levels) then it’s metabolic alkalosis.
Explain acidosis causes, effects and compensatory mechanisms
Causes: hypercapnia (by hypoventilation), increases lactic acid and ketone bodies (diabetes), reduced kidney acid secretion (renal failure), reduced hydrogen carbonate ion reabsorption and diarrhoea (due to loss of hydrogen carbonate ion from gut).
Effects: tachypnoea, muscular weakness, headache, cardiac arrhythmia, confusion, coma, hyperkalaemia
Compensatory mechanism: Hyperventilation to reduce carbon dioxide levels, reduced hydrogen carbonate ion excretion by kidneys
Explain alkalosis causes, effects and compensatory mechanisms
Causes: hypocapnia (due to hyperventilation), vomiting leading loss of hydrogen ions in HCl, increased kidney acid secretion by diuretics, increased alkalotic agent consumption such as antacids
Effects: Bradypnoea, muscular weakness, cramps, tetany, headache, nausea, light headedeness, confusion, coma, cardiac arrhythmia, hypokalaemia
Compensatory mechanisms: hypoventilation to increase carbon dioxide levels, increases hydrogen carbonate excretion from kidneys
Explain acidosis induced hyperkalaemia
E.g when you hypoventilate:
The carbon dioxide levels go up, the hydrogen ion concentration goes up in the blood. So it’s harder to transport hydrogen ions out into the blood from cells because there’s a lower gradient. This means it’s harder to transport sodium in (as they use the same exchange protein).
This now affects the sodium-potassium pump as there’s sodium so less sodium can pumped out and less potassium can be pumped into the cell from the blood. This causes an increase in potassium ion concentration in the blood - this is hyperkalaemia.
This is bad because potassium ions have key roles in membrane potential and muscle function.
Explain alkalosis induced cerebral vasoconstriction.
Key point: carbon dioxide (via hydrogen ions) acts as a vasodilator in the blood vessels, particularly the cerebral arteries
When you hyperventilate, levels of carbon dioxide hence the levels of hydrogen ions go down. So with a lack of hydrogen ions, we get vasoconstriction of cerebral arteries, reducing blood flow to the brain.
This causes headaches, lightheadedness, confusion and seizures.
Explain anxiety causing hyperventilation
- Anxiety trigger causes panic attack
- Leads to increased ventilation (tachypnoea) without increased metabolic demand
- Leads to hyperventilation so reduced PaCO2
- Causing respiratory alkalosis
It can be treated by breathing into a bag as the air that contains the carbon dioxide will recirculate back into the person and their blood to rise the carbon dioxide levels to normal.
