L4,5 Acid Base disorders Flashcards
What is the normal range of pH for homeostasis and how does this relate to acidaemia, acidosis, alkalaemia and alkalosis
Normal range= 7.35- 7.45, with 7.4 ‘neutral’
Acidaemia = ph <7.35 and Alkalaemia =ph >7.45. This describes the state of the blood extracellular fluid pH- relative to 7.4.
Acidosis and Alkalosis are pathological processes that change pH. With severe acidosis: <7.2, severe alkalosis >7.6
What are the three processes that help to maintain blood pH.
- Buffers
- Respiratory control of ventilation
- Excretion of acid or base by kidneys
How do buffers control pH and what are the different types in the body
Buffers help to minimise changes in pH from added base or acid. This is because they are a weak acid and its conjugate base + H+ in equilibrium, so if base is added, the H+ ions can neutralise it and this pushes equilibrium to left, make more H+, or if H+ is added then equilibrium is pushed to the right to use it up to form more weak acid.
Thus the free H+ concentration are not changing much.
In the body this is mostly done by HCO3- + H+ –> H2CO3–> H2O + CO2. Bicarbonate
OR Haemoglobin H-Hb –> H+ + Hb-
Other buffers in the blood + ECF are phosphate and albumin, and long term buffers are Muscle and Liver by H+ entering cells in exchange for cation Or reacting with Calcium carbonate which is usually bound to bone matrix
What is the equation for finding pH from the bicarbonate buffer system- H-H equation.
pH= 6.74 + log (HCO3- in mmol/L / pCO2 in kPa)
convert kPa to mmol.
How does Respiratory control of ventilation affect blood pH
pCO2 produced by tissues helps to form more H+ through reaction with H2O. Ventilation helps to blow this off. So low pH (more H+) stimulates ventilation in order to decrease pCO2.
More pCO2 causes acidosis, less pCO2 causes alkalosis.
How does the kidneys help with acid base balance
It helps to reabsorb filtered bicarbonate and secretes H+ in the distal tubule and collecting duct.
