Acid Base Balance

Question 1

How do acids and bases interact differently in terms of H+ ions?

Answer 1

Acids donate hydrogen ions

Bases accept hydrogen ions

Question 2

What are conjugate acids and bases?

Answer 2

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

Question 3

What defines the pH of a solution?

Answer 3

Negative logarithm of the hydrogen ion activity

pH=-log10[H+]

Question 4

What is pKa?

Answer 4

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

Question 5

What is acid-base physiology?

Answer 5

Rate of production of H+ ions= rate of elimination

Question 6

What is tissue respiration?

Answer 6

Production of chemical energy from glucose (in form of high energy phosphate bonds)

Question 7

What occurs during incomplete metabolism of glucose?

Where does this occur?

Answer 7

Glycolysis and lactate metabolism - Produces lactate and 2H+
Occurs in skeletal muscle and erythrocytes

Question 8

How are the products of incomplete glucose metabolism dealt with?

Answer 8

Gluconeogenesis
Occurs in the liver
Lactate - pyruvate - add 6-P - glucose

Question 9

What is ketogenesis?

Outline the process

Answer 9

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+

Question 10

What is ketoacidosis?

Answer 10

Metabolic state associated with high concentrates of ketones leading to reduced blood pH. Caused by alcohol ingestion, poor food intake and stress/dehydration

Question 11

What is ureagenesis?

Answer 11

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

Question 12

What is a buffer?

Answer 12

Solution that can maintain nearly constant pH if it is diluted by small amount of stones acid or base

Question 13

What are some biological buffers?

Answer 13

Blood

Urine

Question 14

Why do we need bio buffers?

Answer 14

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

Question 15

What is the Henderson-Hasselbalch equation?

Answer 15

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

Question 16

What is the Haber-Weiss equation?

Answer 16

[H+]= k([pCO2]/[HCO3])

K=180, when [H+] in nmol/L, HCO3 in mmol/L and pCO2 in kPa

Question 17

Discuss the bicarbonate equation

Answer 17

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

Question 18

How is the Henderson-hasselbach equation applied to bicarbonate in blood?

Answer 18

pH = pKa + log[Base]/[Acid]

pH = 6.1 + log[HCO3-]/(0.025*pCO2)

Question 19

Where is excess H+ excreted?

How?

Answer 19

In the urine through renal processes

Bicarbonate is readsorbed at the glomerulus, almost 100%, and H+ us excreted against the concentration gradient

Question 20

What cells excrete H+ into urine?

Answer 20

Intercalated cells of the distal tubular cells and proximal collecting duct cells

Question 21

How much H+ is excrete in the urine?

How is the rest of the H+ acid excretion achieved?

Answer 21

~38umol/L

Buffering by phosphate achieves significant acid secretion

Question 22

Where does bicarbonate reabsorption happen?

Answer 22

85-90% in the proximal consulted tube
10-15% in the distal convoluted tube/collecting duct
4000-5000mmol/day

Question 23

What types of renal buffering exist?

Answer 23

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

Question 24

How do acidic gastric excretions occur?

Answer 24

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-

Question 25

How do alkaline gastric excretions occur?

Answer 25

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+.

Question 26

What role does haemoglobin play in H+ buffering?

Answer 26

Histidine residues in haemoglobin accept proteins and act as buffers.
Taking up the H+ produced by carbonic anhydrase action

Question 27

What role do plasma proteins play in buffering?

Answer 27

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

Question 28

What regulates respiratory rate?

Answer 28

Blood CO2 level; must remain at constant level. So rate of excretion increases if production increases, and vice verse

Question 29

What are the two types of respiratory failure?

Answer 29

Type 1; low O2 and CO2

Type 2; low O2 and high CO2

Question 30

Discuss the oxygen dissociation curve

Answer 30

Relationship between haemoglobin saturation and oxygen partial pressure; S curve
Affinity dependent on P50 value, increased p50= decreased affinity and vice versa

Question 31

What is the anion gap?

Answer 31

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

Question 32

What can the anion gap be useful for?

Answer 32

Identifies presence of metabolic acidosis
Assess severity
Differentiate between cusses

Question 33

How do organic and inorganic metabolic acidoses differ?

Answer 33

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

Question 34

What causes low Anionic gap?

Answer 34

Hypoalbuminaemia