Acid Base Balance Flashcards
How is carbon dioxide transported in the body?
10% dissolved in plasma
30% Carbaminohaemoglobin
60% Bicarbonate
What is carbaminohaemoglobin? How does it work?
The binding of carbon dioxide to haemoglobin
- CO2 binds to the globin portion (rather than haem group that oxygen does)
- reduced Hb (deoxygenated blood) has a greater affinity for CO2 than oxygenated Hb
- The unloading of O2 into the tissues enables the picking up of carbon dioxide
- At the alveolus the bond becomes weak thus enabling the release of CO2 into the alveoli
What is the reaction between CO2 and Bicarbonate?
Co2 + H20 = H2CO3 = HCO3- + H+
CA = Carbonic Anhydrase
CO2 combines with with H20 to form Carbonic Acid. This reaction is slow but is accelerated in RBCs due to Carbonic Anhydrase. Carbonic acid is then ionised to HCO3- and H+
Why does CO2 react with Bicarbonate?
CO2 is more soluble than O2 -> reacts chemically with water
What the reason for the reaction between Bicarbonate and CO2 to take place?
Maintain acid base balance where CO2 is a major part of the system controlling blood pH
Where do the bicarbonate and CO2 reactions take place?
In the plasma and in the RBCs
Slower reaction in the plasma because there is no CA enzyme present
How is the H+ bi product removed to maintain acid base balance?
H+ binds with haemoglobin to form Haemoglobinic acid
Hb + H+ = HHb
How are the number of bicarbonate ions regulated in the body?
Bicarbonate ions diffuse from the red blood cells into the plasma
-To maintain electrical neutrality within the red blood cell, chloride ions diffuse into the cell (Chloride Shift)
What does a CO2 dissociation curve display?
- Increase in the partial pressure of carbon dioxide is associated with increase in the blood carbon dioxide content
- Correlation between the greater the saturation of haemoglobin with Oxygen (In arterial blood 98% O2 saturation has only 5.3KPa CO2), the lower the saturation of haemoglobin with Carbon Dioxide (In venous blood 75% O2 saturation has 6.0KPa CO2)
What are the normal ranges for blood pH?
H+ ions - 40nanoMol
HCO3- ions - 23milliMol
Hydrogen ions are far more important with acid base balance than Bicarbonate
How do hydrogen ions interfere with blood pH?
Amount of H+ ions can range from 35.5 to 44.7 nmol/L which can cause the pH to change between 7.35 and 7.45
Extracellular pH = 7.4
Intracellular pH = 6.8-7.2
Where in the body are there differing levels of pH?
Gastric secretions have a very acidic pH of 1.1
Pancreatic secretions have an alkali pH of 8.8
What is the Henderson-Hasselbach equation?
CO2 + H20 = H2CO3 = HCO3- + H+
Dependent on all parameters
How is the pH calulated?
pH = pK + log(Base / Acid)
pK = dissociation of the acid
What causes acid base imbalances?
Hypoventilation (not breathing out effectively)
- increase in CO2 levels which will cause an increase in hydrogen ions which in turn will decrease pH
- known as respiratory acidosis
