Acid Base Balance Flashcards
How do acids and bases interact differently in terms of H+ ions?
Acids donate hydrogen ions
Bases accept hydrogen ions
What are conjugate acids and bases?
Species formed by removal or reception of a proton respectively
E.g. Ammonium ion is conjugate base of ammonia and hydrogen carbonate ion is conjugate acid of carbonic acid
What defines the pH of a solution?
Negative logarithm of the hydrogen ion activity
pH=-log10[H+]
What is pKa?
Negative logarithm of the ionisation constant of an acid.
pH at which a buffer exists in equal proportions with its acid and conjugate base.
<7 for acid
>7 for a base
What is acid-base physiology?
Rate of production of H+ ions= rate of elimination
What is tissue respiration?
Production of chemical energy from glucose (in form of high energy phosphate bonds)
What occurs during incomplete metabolism of glucose?
Where does this occur?
Glycolysis and lactate metabolism - Produces lactate and 2H+
Occurs in skeletal muscle and erythrocytes
How are the products of incomplete glucose metabolism dealt with?
Gluconeogenesis
Occurs in the liver
Lactate - pyruvate - add 6-P - glucose
What is ketogenesis?
Outline the process
Incomplete metabolism of triglycerides
Liberation of free fatty acids (FFA) from triglycerides produces H+. The FFAs are then further metabolised, in the liver, to produce ketones and more H+
What is ketoacidosis?
Metabolic state associated with high concentrates of ketones leading to reduced blood pH. Caused by alcohol ingestion, poor food intake and stress/dehydration
What is ureagenesis?
Metabolism of neutral amino acids to form urea (via pyruvate), requires ammonium ion
Metabolism of sulphurous amino acids, e.g. Methionine, to form urea
Metabolism of acidic amino acids, e.g. Aspartate, to form urea
What is a buffer?
Solution that can maintain nearly constant pH if it is diluted by small amount of stones acid or base
What are some biological buffers?
Blood
Urine
Why do we need bio buffers?
Daily excretion of H+ is 40-80mmol/day
Intermediate metabolism accounts for H* turnover of 2500-3000mmol/day
Buffers compensate for disturbances in the above
What is the Henderson-Hasselbalch equation?
pH=pKa + log [base]/[acid]
In physiology the [acid] is carbonic acid and is not measured as a concentration but by its liner relationship with dissolved CO2
What is the Haber-Weiss equation?
[H+]= k([pCO2]/[HCO3])
K=180, when [H+] in nmol/L, HCO3 in mmol/L and pCO2 in kPa
Discuss the bicarbonate equation
CO2 + H20 – H2CO3 – H+ + HCO3-
When CO2 dissolves in blood it becomes an acid
The more CO2 the more carbonic acid and the more H+ released
Blood pH doe ends not on amount of CO2 or HCO3-, but the ratio of the two 20:1 HCO3:CO2
How is the Henderson-hasselbach equation applied to bicarbonate in blood?
pH = pKa + log[Base]/[Acid]
pH = 6.1 + log[HCO3-]/(0.025*pCO2)
Where is excess H+ excreted?
How?
In the urine through renal processes
Bicarbonate is readsorbed at the glomerulus, almost 100%, and H+ us excreted against the concentration gradient
What cells excrete H+ into urine?
Intercalated cells of the distal tubular cells and proximal collecting duct cells
How much H+ is excrete in the urine?
How is the rest of the H+ acid excretion achieved?
~38umol/L
Buffering by phosphate achieves significant acid secretion
Where does bicarbonate reabsorption happen?
85-90% in the proximal consulted tube
10-15% in the distal convoluted tube/collecting duct
4000-5000mmol/day
What types of renal buffering exist?
Type 1: monohydrogen and dihydrogen phosphates form buffer pair with 6.8 pKa. Levels too low in plasma and more important in renal filtrate for urine buffer
Type 2: ammonium pKa is 100x lower then [H+] so almost all ammonia in body is NH4+ ion
How do acidic gastric excretions occur?
CO2 from interstitial fluid and H20 converted to HCO3- by carbonic anhydrase. H+ excreted into stomach by H+/K+ pump. HCO3- swapped into lumen for Cl-
How do alkaline gastric excretions occur?
CO2 from interstitial fluid and H20 converted to HCO3- by carbonic anhydrase. HCO3- excreted into pancreas or intestine swapped for Cl-. Cl- recycled back into lumen. H+ swapped for Na+ into interstitial fluid . Na+ swapped back out for K+.
What role does haemoglobin play in H+ buffering?
Histidine residues in haemoglobin accept proteins and act as buffers.
Taking up the H+ produced by carbonic anhydrase action
What role do plasma proteins play in buffering?
Proteins contains weakly acidic and basic groups due to amino acid composition
Albumin is predominant plasma protein and is the main protein buffer
Intracellular proteins can also act as buffers
Bone proteins play a major role in acid-base
What regulates respiratory rate?
Blood CO2 level; must remain at constant level. So rate of excretion increases if production increases, and vice verse
What are the two types of respiratory failure?
Type 1; low O2 and CO2
Type 2; low O2 and high CO2
Discuss the oxygen dissociation curve
Relationship between haemoglobin saturation and oxygen partial pressure; S curve
Affinity dependent on P50 value, increased p50= decreased affinity and vice versa
What is the anion gap?
Positive anions(sodium and potassium) - negative anion (chloride and carbonate). Normal range=6-16
Gap is made up mainly mad up of negatively charged proteins
What can the anion gap be useful for?
Identifies presence of metabolic acidosis
Assess severity
Differentiate between cusses
How do organic and inorganic metabolic acidoses differ?
Inorganic: infused Cl- replaces HCO3- and Anionic gap is normal
Organic: HCO3- replaced by acidic anion which is not usually measured and the Anionic gap increases
What causes low Anionic gap?
Hypoalbuminaemia
