Acids, Bases + Buffers Flashcards
What is an acid?
H+ donor
What is a base?
H+ acceptor
What is a strong acid?
A compound that ionises completely in solution to form hydrogen ions and a base
What is a weak acid?
Compounds that are only partially ionised in solution
What is the function of a buffer?
Resists changes in PH when small quantities of strong acid or base are added.
What is the ideal PH of blood?
7.4
Give the Henderson-Hasselbach equation.
PH = pKa + log([HCO3-]/[CO2])
How are most of the H+ ions produced in the body?
As a result of CO2 release from aerobic metabolism. CO2 rapidly reacts with water forming carbonic acid that dissociates into H+ and HCO3-
Give the equation of CO2 - H+
CO2 + H20 > H2CO3 > HCO3- + H+
Which enzyme catalyses the conversion of CO2 to H+?
Carbonic anhydrase
Which three systems work to ensure PH remains in range?
- Blood and tissue buffering
- Excretion of CO2 by lungs
- Renal excretion of H+ and regeneration of HCO3-
Name the most important buffer system of the body.
Bicarbonate
How is the bicarbonate buffer efficiency improved (think lungs and kidneys)?
- CO2 is removed by lungs
2. Bicarbonate is regenerated at the kidneys
Proteins form buffers as well. Name a protein that is part of this system.
Albumin
How do proteins work as a buffer?
The protein matrix of bone buffers large amounts of H+ ion
How is haemoglobin a buffer?
It binds to both CO2 and H+, removing these from the blood.
CO2: CO2 diffuses into red cells down their concentration gradient.. It binds with haemoglobin reversibly to form carbaminohaemoglobin or with water to form carbonic acid.
H+: CO2 in red cells combines with water to form carbonic acid. This dissociates into bicarbonate and H+ ions. H+ ions bind to reduced haemoglobin to form HHb. HCO3- ions pass back into the plasma in exchange for Cl- ions.
Which state of haemoglobin has the strongest affinity for CO2 and H+?
Deoxygenated haemoglobin
In the lungs, what mathematical relationship is between arterial partial pressure of CO2 and the alveolar ventilation?
Arterial partial pressure is inversely proportional to alveolar ventilation - i.e. if alveolar ventilation falls, PaCO2 rises.
What is alkalosis in terms of PH?
PH > 7.45
What is acidosis in terms of PH?
PH < 7.35
Name the types of alkalosis and acidosis.
Respiratory and metabolic.
What is acidaemia?
Too many hydrogen ions in plasma
What is alkalaemia?
Too few hydrogen ions in plasma
What causes respiratory acidosis?
Common: Decreased alveolar ventilation, causes decreased excretion of CO2.
Less common: Excessive production of CO2 by aerobic metabolism, can be caused by fever.
What is the PaCO2 in respiratory acidosis?
> 6kPa
What causes respiratory alkalosis?
Excessive excretion of CO2. Caused by severe asthma and pulmonary embolism
What is the PaCO2 in respiratory alkalosis?
<4.5kPa
List the causes of metabolic acidosis.
- Excess H+ production from the excessive production of organic acids as a result of anaerobic metabolism.
- Low perfusion
- Reduced ability to use oxygen as a substrate e.g. in sepsis
- Renal tubular dysfunction leads to inadequate excretion of H+
- Diabetic ketoacidosis - unable to use glucose, resulting in the production of ketone bodies which releases H+
- Crohn’s disease where excessive diarrhoea results in large amounts of bicarbonate being lost
List the causes of metabolic alkalosis.
- Excess H+ loss from prolonged vomiting
2. Excessive reabsorption of bicarbonates as a result of chloride loss through prolonged vomiting
Which type of acidosis and alkalosis has a greater effect on the body and why?
Metabolic. This is because compensation is much slower in metabolic processes than respiratory, resulting in a delayed response.
What is the anion gap?
The difference in serum concentration of cations (positive) and anions (negative).
Which ions aren’t included when considering the anion gap?
K+, PO4-, SO4-
What is the normal value of the anion gap?
Between 3-11 mEq/mol
How does the anion gap help to diagnose the cause of metabolic acidosis?
If there is a high anion gap, it can be used to see if the cause is due to excessive loss of bicarbonate or excess H+ production
