Acid-Base Balance Flashcards
What does pH stand for?
potential of hydrogen
determined by molar concentration of OH- and H+
What is the definition of an acid?
substance which can donate an H+ ion
What is the definition of a base?
substance which can accept an H+ ion
What happens when an acid is added to water?
Dissociates reversibly according to reaction:
HA H+ + A-
What is a conjugate base?
A-
can combine with a H+ to form HA
Why is pH important in the body?
- controls speed of body’s biochemical reactions through controlling rate of enzyme activity and electrical reactions
How does pH affect speed of body’s electrical reactions?
- synaptic function depends on IC and EC pH gradients
- synaptic activity causes local pH gradients
What is normal blood pH?
Venous - 7.35 as more CO2
Arterial - 7.45
< 7.35 = acidosis (acidaemia)
> 7.45 = alkalosis (alkalaemia)
What is the fatal pH range?
<6.8
>8.0
What happens in blood pH is outside the normal range?
Disturbance of body functions
disruption to enzyme systems and ETC in mitochondria
still compatible with life
Where do H+ ions originate from in the blood?
Normal diet is almost neutral with small acid amounts (protein diets = more acid intake)
Cellular metabolism is largest source of H+, produces large amounts of carbonic, sulphuric, phosphoric and other acids
From there H+ continually added (breakdown of foods - proteins, carbonic acid + H20 = CO2, exercise lactic acid)
How do disease states affect H+ levels?
Even more production of H+
diabetes = keto acids
How much acid is produced/intaken?
aerobic respiration -> carbonic acid (15 mol/d)
anaerobic respiration -> lactic acid (1.5mol/d)
Acid from diet - oxidation of sulfur containing amino acids -> sulfuric acid, incomplete oxidation of fatty acids -> acidic ketone bodies, hydrolysis of phosphoproteins and nucleic acids -> phosphoric acid = 60mmol/d
What mechanisms limit pH changes? How quickly do they act?
1- chemical buffer systems in blood and ICF (immediate)
2- respiratory centre in brainstem (1-3 minutes)
3- renal mechanisms (hours to days)
What is a buffer?
solution that can resist pH change upon addition of acid or base, can neutralise small amounts of acid or base maintaining stable pH
acts quickly to bind/release H+
temporary
consist of a weak acid and salt of that acid (weak base)
What are the 3 major chemical buffer systems in the body?
- bicarbonate (HCO3-) in the buffer system (ECF)
- proteins (haemoglobin and albumin) (ICF and ECF)
- phosphate (ECF)
How do acid-base disturbances affect internal K+ distribution?
Acidemia = tissues release K+ = hyperkalemia alkalemia = cells take up K+ = hypokalemia -> dangerous for the heart (essentially H+ displaces K+ from cells/blood)
What are the causes of normal gap acidosis? (TOP 2)
severe diarrhoea chronic laxative abuse villous adenoma drainage of pancreatic/biliary secretions (e.g. fistulas) NG tube losses acidifying salts administration urinary diversions